KOMPENDIUM
KAJIAN LINGKUNGAN DAN
PEMBANGUNAN
PHYTO-REMEDIATION
Hg
Dikoleksi oleh:
Novie A.S. dan Soemarno
PDKLP-PPSUB Mei 2012
FITOREMEDIASI
Phytoremediation (from Ancient Greek φυτο (phyto), meaning "plant",
and Latin remedium, meaning "restoring balance") describes the
treatment of environmental problems (bioremediation) through the use
of plants that mitigate the environmental problem without the need to
excavate the contaminant material and dispose of it elsewhere.
Phytoremediation consists of mitigating pollutant concentrations in
contaminated soils, water, or air, with plants able to contain, degrade, or
eliminate metals, pesticides, solvents, explosives, crude oil and its
derivatives, and various other contaminants from the media that contain
them.
Application
Phytoremediation may be applied wherever the soil or static water environment has become
polluted or is suffering ongoing chronic pollution. Examples where phytoremediation has
been used successfully include the restoration of abandoned metal-mine workings, reducing
the impact of sites where polychlorinated biphenyls have been dumped during manufacture
and mitigation of on-going coal mine discharges.
Phytoremediation refers to the natural ability of certain plants called hyperaccumulators to
bioaccumulate, degrade,or render harmless contaminants in soils, water, or air.
Contaminants such as metals, pesticides, solvents, explosives, and crude oil and its
derivatives, have been mitigated in phytoremediation projects worldwide. Many plants such
as mustard plants, alpine pennycress, hemp, and pigweed have proven to be successful at
hyperaccumulating contaminants at toxic waste sites.
Phytoremediation is considered a clean, cost-effective and non-environmentally disruptive
technology, as opposed to mechanical cleanup methods such as soil excavation or pumping
polluted groundwater. Over the past 20 years, this technology has become increasingly
popular and has been employed at sites with soils contaminated with lead, uranium, and
arsenic. However, one major disadvantage of phytoremediation is that it requires a long-term
commitment, as the process is dependent on plant growth, tolerance to toxicity, and
bioaccumulation capacity.
Sumber: http://en.wikipedia.org/wiki/Phytoremediation …. Diunduh 7/5/2012
KEUNTUNGAN DAN KETERBATASAN
FITOREMEDIASI
KEUNTUNGAN
1.
2.
3.
4.
the cost of the phytoremediation is lower than that of traditional processes
both in situ and ex situ
the plants can be easily monitored
the possibility of the recovery and re-use of valuable metals (by companies
specializing in “phyto mining”)
it is potentially the least harmful method because it uses naturally occurring
organisms and preserves the environment in a more natural state.
KETERBATASAN
1.
2.
3.
4.
5.
Phytoremediation is limited to the surface area and depth occupied by the
roots.
Slow growth and low biomass require a long-term commitment with plantbased systems of remediation,
It is not possible to completely prevent the leaching of contaminants into
the groundwater (without the complete removal of the contaminated
ground, which in itself does not resolve the problem of contamination)
The survival of the plants is affected by the toxicity of the contaminated
land and the general condition of the soil.
Bio-accumulation of contaminants, especially metals, into the plants which
then pass into the food chain, from primary level consumers upwards or
requires the safe disposal of the affected plant material.
Sumber: …. Diunduh 7/5/2012
BERBAGAI PROSES FITOREMEDIASI
A range of processes mediated by plants or algae are useful in treating environmental
problems:
1.
2.
3.
4.
5.
6.
Phytoextraction — uptake and concentration of substances from the environment
into the plant biomass.
Phytostabilization — reducing the mobility of substances in the environment, for
example, by limiting the leaching of substances from the soil.
Phytotransformation — chemical modification of environmental substances as a
direct result of plant metabolism, often resulting in their inactivation, degradation
(phytodegradation), or immobilization (phytostabilization).
Phytostimulation — enhancement of soil microbial activity for the degradation of
contaminants, typically by organisms that associate with roots. This process is also
known as rhizosphere degradation. Phytostimulation can also involve aquatic
plants supporting active populations of microbial degraders, as in the stimulation
of atrazine degradation by hornwort.
Phytovolatilization — removal of substances from soil or water with release into
the air, sometimes as a result of phytotransformation to more volatile and/or less
polluting substances.
Rhizofiltration — filtering water through a mass of roots to remove toxic
substances or excess nutrients. The pollutants remain absorbed in or adsorbed to
the roots.
Sumber: …. Diunduh 7/5/2012
. Phytoextraction
Phytoextraction (or phytoaccumulation) uses plants or algae to remove contaminants
from soils, sediments or water into harvestable plant biomass (organisms that take
larger-than-normal amounts of contaminants from the soil are called
hyperaccumulators). Phytoextraction has been growing rapidly in popularity
worldwide for the last twenty years or so. In general, this process has been tried more
often for extracting heavy metals than for organics. At the time of disposal,
contaminants are typically concentrated in the much smaller volume of the plant
matter than in the initially contaminated soil or sediment. 'Mining with plants', or
phytomining, is also being experimented with.
The plants absorb contaminants through the root system and store them in the root
biomass and/or transport them up into the stems and/or leaves. A living plant may
continue to absorb contaminants until it is harvested. After harvest, a lower level of
the contaminant will remain in the soil, so the growth/harvest cycle must usually be
repeated through several crops to achieve a significant cleanup. After the process, the
cleaned soil can support other vegetation.
Advantages: The main advantage of phytoextraction is environmental friendliness.
Traditional methods that are used for cleaning up heavy metal-contaminated soil
disrupt soil structure and reduce soil productivity, whereas phytoextraction can clean
up the soil without causing any kind of harm to soil quality. Another benefit of
phytoextraction is that it is less expensive than any other clean-up process.
Disadvantages: As this process is controlled by plants, it takes more time than
anthropogenic soil clean-up methods.
Two versions of phytoextraction:
natural hyper-accumulation, where plants naturally take up the contaminants in soil
unassisted, and
induced or assisted hyper-accumulation, in which a conditioning fluid containing a
chelator or another agent is added to soil to increase metal solubility or mobilization
so that the plants can absorb them more easily. In many cases natural
hyperaccumulators are metallophyte plants that can tolerate and incorporate high
levels of toxic metals.
Examples of phytoextraction (see also 'Table of hyperaccumulators'):
Arsenic, using the Sunflower (Helianthus annuus), or the Chinese Brake fern (Pteris
vittata), a hyperaccumulator. Chinese Brake fern stores arsenic in its leaves.
Cadmium, using Willow (Salix viminalis): In 1999, one research experiment performed
by Maria Greger and Tommy Landberg suggested Willow (Salix viminlais) has a
significant potential as a phytoextractor of Cadmium (Cd), Zinc (Zn), and Copper (Cu),
as willow has some specific characteristics like high transport capacity of heavy metals
Sumber:of ….
Diunduhproduction;
7/5/2012 can be used also for
from root to shoot and huge amount
biomass
. Phytostabilization
Phytostabilization focuses on long-term stabilization and containment of the
pollutant. Example, the plant's presence can reduce wind erosion; or the
plant's roots can prevent water erosion, immobilize the pollutants by
adsorption or accumulation, and provide a zone around the roots where the
pollutant can precipitate and stabilize. Unlike phytoextraction,
phytostabilization focuses mainly on sequestering pollutants in soil near the
roots but not in plant tissues. Pollutants become less bioavailable, and
livestock, wildlife, and human exposure is reduced. An example application
of this sort is using a vegetative cap to stabilize and contain mine tailings
Sumber: …. Diunduh 7/5/2012
. Phytotransformation
In the case of organic pollutants, such as pesticides, explosives, solvents, industrial
chemicals, and other xenobiotic substances, certain plants, such as Cannas, render
these substances non-toxic by their metabolism. In other cases, microorganisms living
in association with plant roots may metabolize these substances in soil or water. These
complex and recalcitrant compounds cannot be broken down to basic molecules
(water, carbon-dioxide, etc.) by plant molecules, and, hence, the term
phytotransformation represents a change in chemical structure without complete
breakdown of the compound. The term "Green Liver Model" is used to describe
phytotransformation, as plants behave analogously to the human liver when dealing
with these xenobiotic compounds (foreign compound/pollutant).[7] After uptake of the
xenobiotics, plant enzymes increase the polarity of the xenobiotics by adding
functional groups such as hydroxyl groups (-OH).
This is known as Phase I metabolism, similar to the way that the human liver increases
the polarity of drugs and foreign compounds (Drug Metabolism). Whereas in the
human liver enzymes such as Cytochrome P450s are responsible for the initial
reactions, in plants enzymes such as nitroreductases carry out the same role.
In the second stage of phytotransformation, known as Phase II metabolism, plant
biomolecules such as glucose and amino acids are added to the polarized xenobiotic to
further increase the polarity (known as conjugation). This is again similar to the
processes occurring in the human liver where glucuronidation (addition of glucose
molecules by the UGT (e.g. UGT1A1) class of enzymes) and glutathione addition
reactions occur on reactive centres of the xenobiotic.
Phase I and II reactions serve to increase the polarity and reduce the toxicity of the
compounds, although many exceptions to the rule are seen. The increased polarity
also allows for easy transport of the xenobiotic along aqueous channels.
In the final stage of phytotransformation (Phase III metabolism), a
sequestration[disambiguation needed ] of the xenobiotic occurs within the plant. The
xenobiotics polymerize in a lignin-like manner and develop a complex structure that is
sequestered in the plant. This ensures that the xenobiotic is safely stored, and does
not affect the functioning of the plant. However, preliminary studies have shown that
these plants can be toxic to small animals (such as snails), and, hence, plants involved
in phytotransformation may need to be maintained in a closed enclosure.
Hence, the plants reduce toxicity (with exceptions) and sequester the xenobiotics in
phytotransformation. Trinitrotoluene phytotransformation has been extensively
researched and a transformation pathway has been proposed
Sumber: …. Diunduh 7/5/2012
. Hyperaccumulators and biotic interactions
A plant is said to be a hyperaccumulator if it can concentrate the pollutants in a
minimum percentage which varies according to the pollutant involved (for example:
more than 1000 mg/kg of dry weight for nickel, copper, cobalt, chromium or lead; or
more than 10,000 mg/kg for zinc or manganese).[10] This capacity for accumulation is
due to hypertolerance, or phytotolerance: the result of adaptative evolution from the
plants to hostile environments through many generations. A number of interactions
may be affected by metal hyperaccumulation, including protection, interferences with
neighbour plants of different species, mutualism (including mycorrhizae, pollen and
seed dispersal), commensalism, and biofilm.
Hyperaccumulators and contaminants : Al, Ag, As, Be, Cr, Cu, Mn, Hg, Mo, naphthalene, Pb, Pd, Pt, Se,
Zn – accumulation rates.
Contaminant
Accumulation
rates (in mg/kg Latin name
dry weight)
Al-Aluminium
A-
Agrostis
castellana
Hg-Mercury
A-
Bacopa monnieri
Hg-Mercury
xxx
Brassica napus
Hg-Mercury
xxx
Eichhornia
crassipes
Hg-Mercury
H-
Hydrilla verticillata
Hg-Mercury
1000
Pistia stratiotes
Hg-Mercury
xxx
Salix spp.
English name
HHyperaccumul
ator or ANotes
Accumulator PPrecipitator TTolerant
Sources
Highland Bent
Grass
As(A), Mn(A),
Pb(A), Zn(A)
[1]
Origin
Portugal.
Origin India.
Cd(H), Cr(H),
Aquatic emergent
Cu(H), Hg(A), Pb(A)
species.
Rapeseed plant Ag, Cr, Pb, Se, Zn Phytoextraction
Cd(H), Cr(A),
Pantropical/Subtro
Cu(A), Pb(H),
pical, 'the
Water Hyacinth
Zn(A)Also Cs, Sr,
troublesome
[21]
U, and
weed'.
pesticides.[22]
Hydrilla
Cd(H), Cr(A), Pb(H)
xxx
35 records of
Water lettuce
Cd(T), Cr(H), Cu(T)
plants
Ag, Cr, Se,
Petroleum
hydrocarbures,
Organic solvents,
Phytoextraction.
MTBE, TCE and byPerchlorate
[7]
Osier spp.
products; Cd, Pb,
(wetland
U, Zn (S.
halophytes)
viminalix);[8]
Potassium
ferrocyanide (S.
babylonica L.)[9]
Smooth Water
Hyssop
[1][17]
[6][7]
[1]
[1]
[1][3][31][36]
[7]
Sumber: http://en.wikipedia.org/wiki/Phytoremediation,_Hyperaccumulators …. Diunduh 7/5/2012
. Phytoscreening
As plants are able to translocate and accumulate particular types of contaminants,
plants can be used as biosensors of subsurface contamination, thereby allowing
investigators to quickly delineate contaminant plumes.[11][12] Chlorinated solvents, such
as trichloroethylene, have been observed in tree trunks at concentrations related to
groundwater concentrations.[13] To ease field implementation of phytoscreening,
standard methods have been developed to extract a section of the tree trunk for later
laboratory analysis, often by using an increment borer.[14] Phytoscreening may lead to
more optimized site investigations and reduce contaminated site cleanup costs.
Sumber: http://en.wikipedia.org/wiki/Phytoremediation …. Diunduh 7/5/2012
Phytoremediation plants
Phytoremediation process and principles diagram. (French)
Plants used for Phytoremediation in sustainable bioremediation
treatment—cleanup—restoration projects to contain, degrade, or eliminate
transient pollution—waste and/or on-site pollution—toxins
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Rhizofiltration
Rhizofiltration is a form of bioremediation that involves filtering water through a mass
of roots to remove toxic substances or excess nutrients.
Rhizofiltration is a type of phytoremediation, which refers to the approach of using
hydroponically cultivated plant roots to remediate contaminated water through
absorption, concentration, and precipitation of pollutants.It also filters through water
and dirt.
The contaminated water is either collected from a waste site and brought to the
plants, or the plants are planted in the contaminated area, where the roots then take
up the water and the contaminants dissolved in it. Many plant species naturally uptake
heavy metals and excess nutrients for a variety of reasons: sequestration, drought
resistance, disposal by leaf abscission, interference with other plants, and defense
against pathogens and herbivores.[1] Some of these species are better than others and
can accumulate extraordinary amounts of these contaminants. Identification of such
plant species has led environmental researchers to realize the potential for using these
plants for remediation of contaminated soil and wastewater.
. Process
This process is very similar to phytoextraction in that it removes contaminants by
trapping them into harvestable plant biomass. Both phytoextraction and rhizofiltration
follow the same basic path to remediation. First, plants are put in contact with the
contamination. They absorb contaminants through their root systems and store them
in root biomass and/or transport them up into the stems and/or leaves. The plants
continue to absorb contaminants until they are harvested. The plants are then
replaced to continue the growth/harvest cycle until satisfactory levels of contaminant
are achieved. Both processes are also aimed more toward concentrating and
precipitating heavy metals than organic contaminants. The major difference between
rhizofiltration and phytoextraction is that rhizofiltration is used for treatment in
aquatic environments, while phytoextraction deals with soil remediation.
Sumber: http://en.wikipedia.org/wiki/Rhizofiltration …. Diunduh 7/5/2012
RHIZOFILTRASI
. Applications
Weeping Willows
Rhizofiltration may be applicable to the treatment of surface water and groundwater,
industrial and residential effluents, downwashes from power lines, storm waters, acid
mine drainage, agricultural runoffs, diluted sludges, and radionuclide-contaminated
solutions. Plants suitable for rhizofiltration applications can efficiently remove toxic
metals from a solution using rapid-growth root systems. Various terrestrial plant
species have been found to effectively remove toxic metals such as Cu2+, Cd2+, Cr6+,
Ni2+, Pb2+, and Zn2+ from aqueous solutions.[2] It was also found that low level
radioactive contaminants can successfully be removed from liquid streams.[3] A system
to achieve this can consist of a “feeder layer” of soil suspended above a contaminated
stream through which plants grow, extending the bulk of their roots into the water. The
feeder layer allows the plants to receive fertilizer without contaminating the stream,
while simultaneously removing heavy metals from the water. [4] Trees have also been
applied to remediation. Trees are the lowest cost plant type. They can grow on land of
marginal quality and have long life-spans. This results in little or no maintenance costs.
The most commonly used are willows and poplars, which can grow 6 - 8’ per year and
have a high flood tolerance. For deep contamination, hybrid poplars with roots
extending 30 feet deep have been used. Their roots penetrate microscopic scale pores
in the soil matrix and can cycle 100 L of water per day per tree. These trees act almost
like a pump and treat remediation system.[5]
Sumber: http://en.wikipedia.org/wiki/Rhizofiltration …. Diunduh 7/5/2012
RHIZOFILTRASI
. Cost
Sunflowers used for rhizofiltration
Rhizofiltration is cost-effective for large volumes of water having low concentrations of
contaminants that are subjected to stringent standards.[6] It is relatively inexpensive,
yet potentially more effective than comparable technologies. The removal of
radionuclides from water using sunflowers was estimated to cost between $2 and $6
per thousand gallons of water treated, including waste disposal and capital costs.[7]
[edit] Advantages
Rhizofiltration is a treatment method that may be conducted in situ, with plants being
grown directly in the contaminated water body. This allows for a relatively inexpensive
procedure with low capital costs. Operation costs are also low but depend on the type
of contaminant. This treatment method is also aesthetically pleasing and results in a
decrease of water infiltration and leaching of contaminants.[5] After harvesting, the
crop may be converted to biofuel briquette, a substitute for fossil fuel.[8]
[edit] Disadvantages
This treatment method has its limits. Any contaminant that is below the rooting depth
will not be extracted. The plants used may not be able to grow in highly contaminated
areas. Most importantly, it can take years to reach regulatory levels. This results in
long-term maintenance. Also, most contaminated sites are polluted with many
different kinds of contaminants. There can be a combination of metals and organics, in
which treatment through rhizofiltration will not suffice.[5] Plants grown on polluted
water and soils become a potential threat to human and animal health, and therefore,
careful attention must be paid to the harvesting process and only non-fodder crop
should be chosen for the rhizofiltration remediation method.
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BIO-RETENSI
. Bioretention is the process in which contaminants and sedimentation are removed
from stormwater runoff. Stormwater is collected into the treatment area which
consists of a grass buffer strip, sand bed, ponding area, organic layer or mulch layer,
planting soil, and plants. Runoff passes first over or through a sand bed, which slows
the runoff's velocity, distributes it evenly along the length of the ponding area, which
consists of a surface organic layer and/or groundcover and the underlying planting soil.
The ponding area is graded, its center depressed. Water is ponded to a depth of 15 cm
(5.9 in) and gradually infiltrates the bioretention area or is evapotranspired. The
bioretention area is graded to divert excess runoff away from itself. Stored water in the
bioretention area planting soil exfiltrates over a period of days into the underlying soils
A bioretention cell, also called a rain garden, in the United States. It is designed to treat
polluted stormwater runoff from an adjacent parking lot. Plants are in winter
dormancy.
Sumber: http://en.wikipedia.org/wiki/Bioretention …. Diunduh 7/5/2012
Merkuri (Hg)
. Toxicity and safety
See also: Mercury poisoning and Mercury cycle
Mercury and most of its compounds are extremely toxic and must be
handled with care; in cases of spills involving mercury (such as from certain
thermometers or fluorescent light bulbs), specific cleaning procedures are
used to avoid exposure and contain the spill.[77] Protocols call for physically
merging smaller droplets on hard surfaces, combining them into a single
larger pool for easier removal with an eyedropper, or for gently pushing the
spill into a disposable container. Vacuum cleaners and brooms cause greater
dispersal of the mercury and should not be used. Afterwards, fine sulfur,
zinc, or some other powder that readily forms an amalgam (alloy) with
mercury at ordinary temperatures is sprinkled over the area before itself
being collected and properly disposed of. Cleaning porous surfaces and
clothing is not effective at removing all traces of mercury and it is therefore
advised to discard these kinds of items should they be exposed to a mercury
spill.
Mercury can be inhaled and absorbed through the skin and mucous
membranes, so containers of mercury are securely sealed to avoid spills and
evaporation. Heating of mercury, or of compounds of mercury that may
decompose when heated, is always carried out with adequate ventilation in
order to avoid exposure to mercury vapor. The most toxic forms of mercury
are its organic compounds, such as dimethylmercury and methylmercury.
Inorganic compounds, such as cinnabar are also highly toxic by ingestion or
inhalation.[78] Mercury can cause both chronic and acute poisoning.
Sumber: http://en.wikipedia.org/wiki/Mercury_%28element%29 …. Diunduh 7/5/2012
Merkuri (Hg):
Pelepasan ke Lingkungan
. Preindustrial deposition rates of mercury from the atmosphere may be about 4 ng /(1
L of ice deposit). Although that can be considered a natural level of exposure, regional
or global sources have significant effects. Volcanic eruptions can increase the
atmospheric source by 4–6 times.[79]
Natural sources, such as volcanoes, are responsible for approximately half of
atmospheric mercury emissions. The human-generated half can be divided into the
following estimated percentages:[80][81][82]
65% from stationary combustion, of which coal-fired power plants are the largest
aggregate source (40% of U.S. mercury emissions in 1999). This includes power plants
fueled with gas where the mercury has not been removed. Emissions from coal
combustion are between one and two orders of magnitude higher than emissions from
oil combustion, depending on the country.[80]
11% from gold production. The three largest point sources for mercury emissions in
the U.S. are the three largest gold mines. Hydrogeochemical release of mercury from
gold-mine tailings has been accounted as a significant source of atmospheric mercury
in eastern Canada.[83]
6.8% from non-ferrous metal production, typically smelters.
6.4% from cement production.
3.0% from waste disposal, including municipal and hazardous waste, crematoria, and
sewage sludge incineration.
3.0% from caustic soda production.
1.4% from pig iron and steel production.
1.1% from mercury production, mainly for batteries.
2.0% from other sources.
The above percentages are estimates of the global human-caused mercury emissions
in 2000, excluding biomass burning, an important source in some regions.[80]
Current atmospheric mercury contamination in outdoor urban air is (0.01–0.02 µg/m3)
indoor concentrations are significantly elevated over outdoor concentrations, in the
range 0.0065–0.523 µg/m3 (average 0.069 µg/m3).[84]
Mercury also enters into the environment through the improper disposal (e.g., land
filling, incineration) of certain products. Products containing mercury include: auto
parts, batteries, fluorescent bulbs, medical products, thermometers, and
thermostats.[85] Due to health concerns (see below), toxics use reduction efforts are
cutting back or eliminating mercury in such products. For example, the amount of
mercury sold in thermostats in the United States decreased from 14.5 tons in 2004 to
3.9 tons in 2007.[86] Most thermometers now use pigmented alcohol instead of
mercury, and galinstan alloy thermometers are also an option. Mercury thermometers
are Sumber:
still occasionally
used in the medical field because they are
more accurate
http://en.wikipedia.org/wiki/Mercury_%28element%29
…. Diunduh
7/5/2012 than
Merkuri (Hg)
. Chemistry
See also: Category:Mercury compounds
Mercury exists in two main oxidation states, I and II. Higher oxidation states are
unimportant, but have been detected, e.g., mercury(IV) fluoride (HgF4) but only under
extraordinary conditions.[29]
[edit] Compounds of mercury(I)
Different from its lighter neighbors, cadmium and zinc, mercury forms simple stable
compounds with metal-metal bonds. The mercury(I) compounds are diamagnetic and
feature the dimeric cation, Hg2+
2. Stable derivatives include the chloride and nitrate. Treatment of Hg(I) compounds
complexation with strong ligands such as sulfide, cyanide, etc. induces
disproportionation to Hg2+ and elemental mercury.[30] Mercury(I) chloride, a colorless
solid also known as calomel, is really the compound with the formula Hg2Cl2, with the
connectivity Cl-Hg-Hg-Cl. It is a standard in electrochemistry. It reacts with chlorine to
give mercuric chloride, which resists further oxidation.
Indicative of its tendency to bond to itself, mercury forms mercury polycations, which
consist of linear chains of mercury centers, capped with a positive charge. One
example is Hg32+(AsF6–)2.[31]
[edit] Compounds of mercury(II)
Mercury(II) is the most common oxidation state and is the main one in nature as well.
All four mercuric halides are known. The form tetrahedral complexes with other
ligands but the halides adopt linear coordination geometry, somewhat like Ag+ does.
Best known is mercury(II) chloride, an easily sublimating white solid. HgCl2 forms
coordination complexes that are typically tetrahedral, e.g. HgCl42–.
Mercury(II) oxide, the main oxide of mercury, arises when the metal is exposed to air
for long periods at elevated temperatures. It reverts to the elements upon heating
near 400 °C, as was demonstrated by Priestly in an early synthesis of pure oxygen.[7]
Hydroxides of mercury are poorly characterized, as they are for its neighbors gold and
silver.
Being a soft metal, mercury forms very stable derivatives with the heavier chalcogens.
Preeminent is mercury(II) sulfide, HgS, which occurs in nature as the ore cinnabar and
is the brilliant pigment vermillion. Like ZnS, HgS crystallizes in two forms, the reddish
cubic form and the black zinc blende form.[5] Mercury(II) selenide (HgSe) and
mercury(II) telluride (HgTe) are also known, these as well as various derivatives, e.g.
mercury cadmium telluride and mercury zinc telluride being semiconductors useful as
infrared detector materials.[32]
Mercury(II) salts form a variety of complex derivatives with ammonia. These include
+
Millon's
basehttp://en.wikipedia.org/wiki/Mercury_%28element%29
(Hg2N+), the one-dimensional polymer (salts of….
HgNH
and "fusible
Sumber:
Diunduh
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2 )n),
Merkuri (Hg)
. Properties
[edit] Physical properties
A pound coin (density ~7.6 g/cm3) floats in mercury due to the combination of the
buoyant force and surface tension.
Mercury is a heavy, silvery-white metal. As compared to other metals, it is a poor
conductor of heat, but a fair conductor of electricity.[5] Mercury has an exceptionally
low melting temperature for a d-block metal. A complete explanation of this fact
requires a deep excursion into quantum physics, but it can be summarized as follows:
mercury has a unique electronic configuration where electrons fill up all the available
1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d and 6s subshells. As such configuration
strongly resists removal of an electron, mercury behaves similarly to noble gas
elements, which form weak bonds and thus easily melting solids. The stability of the 6s
shell is due to the presence of a filled 4f shell. An f shell poorly screens the nuclear
charge that increases the attractive Coulomb interaction of the 6s shell and the
nucleus (see lanthanide contraction). The absence of a filled inner f shell is the reason
for the somewhat higher melting temperature of cadmium and zinc, although both
these metals still melt easily and, in addition, have unusually low boiling points. Metals
such as gold have atoms with one less 6s electron than mercury. Those electrons are
more easily removed and are shared between the gold atoms forming relatively strong
metallic bonds.[3][6]
[edit] Chemical properties
Mercury does not react with most acids, such as dilute sulfuric acid, although oxidizing
acids such as concentrated sulfuric acid and nitric acid or aqua regia dissolve it to give
sulfate, nitrate, and chloride salts. Like silver, mercury reacts with atmospheric
hydrogen sulfide. Mercury even reacts with solid sulfur flakes, which are used in
mercury spill kits to absorb mercury vapors (spill kits also use activated carbon and
powdered zinc).[7]
Sumber: http://en.wikipedia.org/wiki/Mercury_%28element%29 …. Diunduh 7/5/2012
FITOREMEDIASI Merkuri (Hg)
Mercury is an element
Mercury (Hg) is a silvery metallic liquid as toom temperature. Nautral sources of Hg
occur from outgassing of the earth's crust through volcanoes and evaporation from the
ocean. It can be found in familiar items such as lightbulbs, batteries, thermometers,
pesticides, paint and some dental fillings (amalgams). It is also sometimes used as a
catalyst in chemical reactions or in gold extraction procedures. In nature, mercury
exists in several forms: 1) as ionic salts in either the mercurous (I) or mercuric (II)
states, 2) as an organometallic compound such as methyl mercury, or 3) as elemental
mercury Hg(0) in either liquid or vapor phase.
Mercury in the Environment
Mercury is believed to be transported throughout the environment by two
cycles. On a global scale, Hg(0) vapor circulates through the earth's atmosphere from
land sources to the oceans (3). Researchers believe that the global amount of Hg has
increased by a factor of 2-5 since the advent of industry (3). This amounts to a total
estimate of approximately 10,000 tons of mercury being released worldwide into the
environment from both man-made and natural sources. The second cycle occurs on a
local scale and involves methylation of atmospheric mercury, which is deposited into
bodies of water, by methanogenic bacteria to form methyl mercury. This compound is
somewhat soluble in water and is taken up by organisms and concentrations are
"biomagnified" in animals such as fish, which are higher up in the food chain (3).
Sumber: http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/homepage.html …. Diunduh
7/5/2012
FITOREMEDIASI Merkuri (Hg)
. The Problem: Mercury is toxic to many organisms
Because many animals, including humans, can potentially feed on contaminated
fish, shellfish, or sea mammals, contamination poses an immediate health threat.
Mercury is toxic to humans
During the 1950's the first major mercury posioning epidemic occurred in Minamata
Bay in Kyushu, Japan. Residents had cons
umed methyl mercury-contaminated fish and shellfish. The source of contamination
was effluent from a chemical manufacturing company, Chisso, which specialized in the
production of acetylaldehyde. Mercury was used as a catalyst in the production
process and waste was released into Minamata Bay. Many families who suffered
posioning were associated with the local fishing industry. Victims experienced ataxia
(loss of precise control of movement), visual problems, loss of hearing and mental
confusion. They became prone
to shouting and violent behavior which often lead to coma (1). An estimated 1,435
people have died because of this contamination (4). Additional epidemics occurred
not long afterward in Niigata, Japan due to contaminated seafood (1) and in Iraq due
to consumption of seed grain that had been treated with a mercury-containing
fungicide (2). The largest concern, however, is that low levels of mercury exposure is
particularly harmful to the fetus. Infants born to mothers who have been exposed to
mercury contamination while or before becoming pregnant have shown a high
incidence of mental retardation, ataxia, seizure, sensory disturbance, visual problems,
and hearing impairment (1).
Sumber: http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/homepage.html …. Diunduh
7/5/2012
FITOREMEDIASI Merkuri (Hg)
Mercury is toxic to most plants
Plants that are exposed to mercury accumulate the metal, however
drastic decreases in growth are usually observed. Plants exposed to ionic
mercury through the root exhibit reduced growth of shoots and roots. They
also accumulate mercury in the root with slow movement to the
shoot. Tree leaves can trap atmospheric mercury. It is thought that
inorganic mercury may cause changes in root tip cell membrane integrity
while methyl mercury may affect organelle metabolism processes that
eventually interrup cell membrane integrity
Sumber: http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/homepage.html …. Diunduh
7/5/2012
FITOREMEDIASI Merkuri (Hg)
. A solution: Removing methyl mercury from water and soil Phytoremediation Technologies
Phytoremediation or remedying a contaminated site using plants, is a
relatively new area of research. Mercury-resistant bacteria have been
reported to produce enzymes that catalyze two reactions: 1)
organomercurial lyase - which removes methyl groups from mercury to
create ionic mercury, and 2) mercuric ion reductase which converts ionic
mercury to volatile elemental mercury. Plants engineered to express these
genes could have potential for relatively inexpensive clean-up of mercury
contaminated sites. Additionally, many sites that are contaminated with
various metals are also contaminated with mercury which may be the most
toxic metal and is limiting to growth. Volatilization of elemental mercury
would allow mercury to diffuse out of the plant and into the atmosphere at
diffuse and non-toxic concentrations (15).
. Phytoremediation Technologies
-Solutions(sumber:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationt
echnologies.html )
Mercury pollution poses an immediate threat not only to human health, but also to
other plants, microorganisms and animals in the environment. Methanogenic bacteria
convert ionic and/or elemental mercury to methyl mercury, which is highly
toxic. Other bacteria have been reported to produce enzymes that remove methyl
groups from mercury and reduce ionic mercury to less toxic elemental mercury Hg
(0). Elemental Hg (0) is highly volatile and is readily converted from liquid to vaporphase. These bacteria could be used to volatilize Hg (0), however this process is
slow. The genes involved in bacterial conversion of methyl mercury to ionic mercury
Hg+, to elemental mercury vapor Hg(0) are all a part of a mercury-responsive bacterial
operon. When a bacterium is exposed to mercury, the gene products of the operon
are expressed. These include a mercury responsive regulatory protein, transport
proteins that bind and transport mercury into the cell, organomercuric lyase, which
catalyzes
the removal of the methyl group of methyl mercury converting it into
ionic
Sumber:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/homepage.html
…. Diunduh
mercury Hg+ (merB), and mercuric ion
reductase which catalyzes the conversion of
7/5/2012
FITOREMEDIASI Merkuri (Hg)
Rugh, C., Dayton Wilde, H., Stack, N., Thompson, D.M., Summers A.O., and Meagher, R.B.,
(1996) Mercuric ion reduction and resistance in transgenic Arabidopsis thaliana plants expressing
a modified bacterial merA gene. Proc. Natl. Acad. Sci. 93:3182-3187.
The enzyme, mercuric ion reductase, encoded by the gene merA, reduces ionic
mercury (Hg+) to the less toxic volatile Hg(0) using NADPH reducing
equivalents. Because the merA gene was found to be very G+C rich (~67%) and was
suited for expression only in a bacterial system, early attempts to express this gene in
plant systems were unsuccessful.
Rugh et al. replaced codons 287-336, which constituted 9% of the coding region to
contain a sequence of DNA that had codon usage that was more suited to expression
in plant systems. Transgenic Arabidopsis thaliana plants containing this modified
merApe9 expressed the gene product mercuric ion reductase. Additionally, merApe9
seeds germinated and grew into seedlings on agar plates containing 50 micromolar
HgCl2 while control plants did not.
Mercury vapor analysis showed that transgenic merApe9 plants
volatilized significant amounts (~50 ng Hg(0)/mg tissue of mercury
vapor.
Finally, Northern blots of total mRNA from transgenic plants
confirmed merApe9 gene expression. These data suggest that the
potential for plants that volatilize Hg are viable.
Sumber:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationtechnologies.html ….
Diunduh 7/5/2012
FITOREMEDIASI Merkuri (Hg)
Rugh, C., Senecoff, J., Meagher, R., and Merkle, S. (1998) Development of
transgenic yellow poplar for mercury phytoremediation. Nature
Biotechnology. 16:925-928.
. Transgenic Arabidopsis plants expressing the merA9 gene construct converted ionic
Hg+ to volatile Hg(0). Expression of this type of system in a high biomass plant with
potential environmental application, such as yellow poplar (Liriodendron tulipifera)
may provide a means for phytovolatilization of mercury pollution. The merA9
sequence was further modified to contain an additional 9% of the coding sequence
fragment of DNA with plant-like codon usage. This further modified merA18 sequence
was transformed using particle bombardment of yellow poplar proembryonic
masses. Transgenic plantlets grew on agar plates containing 25microM and 50microM
HgCl2, whereas control plants did not. Additionally significant Hg (0) volatilization was
observed by transgenic lines. The demonstrated ability of genetically engineered
yellow poplar to grow on increased concentrations of ionic Hg+ may demonstrate the
potential for phytovolitazion methods of mercury remediation. However, this research
is still in its infancy and future experiments may include growing transgenic poplar
plants on mercury-contaminated soils.
Sumber:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationtechnologies.html ….
FITOREMEDIASI Merkuri (Hg)
Bizily, S., Rugh, C., Summers, A., Meagher, R. (1999) Phytoremediation of
methylmercury pollution: merB expression in Arabidopsis thaliana confers resistance
to organomercurials. Proc. Natl. Acad. Sci. 96:6808-6813.
Mercury deposited into bodies of water is typically converted to methyl-mercury by
methanogenic bacteria. Other mercury-resistant bacteria eliminate methyl mercury by
producing an enzyme, organomercurial lyase encoded by the gene merB. Because
most mercury-contaminated water contains methyl mercury, there would be a benefit
to producing a model system in which merB was expressed.
Bizily et al., report that transformants of Arabidopsis with merB grow on higher
concentrations of methyl mercury-like compounds than control plants. The merB
gene that was isolated from mercury-resistant bacteria was modified using PCR
techniques to contain flanking regions containing consensus plant sequences and
restriction sites.
The new merB gene was transformed into Arabidopsis thaliana by Agrobacterium
tumefaciens-mediated transformation. Transgenic merB plants grew on agar
plates containing phenylmercuric acetate or methylmercuric chloride while control
plants and transgenic merA plants did not. Additional western blot studies
confirmed the expression of significant amounts of the merB gene product,
organomercruial lyase.
Results suggest that merB was successfully transformed and expressed in
Arabidopsis thaliana plants as well as conferring resistance to organomercurials.
Sumber:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationtechnologies.html ….
Diunduh 7/5/2012
FITOREMEDIASI Merkuri (Hg)
Bizily, S., Rugh, C., Meagher, R. (2000) Phytodetoxification of hazardous
organomercurials by genetically engineered plants. Nature Biotechnology. 18:213217.
Methylmercury is found in wetlands and aquatic sediments worldwide. Both ionic
mercury and methylmercury are absorbed in the gastrointestinal tract of animals, but
methylmercury is retained much longer in the body and is, therefore, is carried up
through the food chain more efficiently. Plants engineered with both the merA and
merB genes should be able to extract methylmercury from contaminated
environments and transpire Hg(0) into the atmosphere.
Because Hg(0) resides in the atmosphere for approximately two years, transpired
Hg(0) will be diluted to much lower concentrations before being redeposited into
terrestrial waters and sediments rather than being concentrated in one
area. Additionally the amount of Hg(0) emitted from sites undergoing
phytovolitalization can be regulated and will most likely be small in comparison to the
concentrations of Hg(0) already in the atmosphere.
Arabidopsis thaliana plants that had been separately transformed to contain
constructs that express merA and merB, respectively, were crossed. F2
generation plants were analyzed for expression of both the merA and merB
gene products in the same plant. Plantlets containing merA or merA and
merB grew on concentrations of methylmercury-like compounds (mainly
CH3HgCl) up to 5 micromolar. Only plants expressing the gene products of
both merA and merB grew on concentrations of 10 micromolar methyl
mercury.
Mercury vapor analysis showed significant Hg(0) volatilization emitted from
merA/merB plants and western blots confirmed the expression of the gene
products of merA and merB. These results demonstrate that transgenic plants
efficiently phytovolatilize methylmercury.
Sumber:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationtechnologies.html ….
Diunduh 7/5/2012
FITOREMEDIASI Merkuri (Hg)
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Wantanabe, Chiho, Satoh, Hiroshi. (1996) Evolution of our understanding of methylmercury as a
health threat. Environmental Health Perspectives Supplements. 104(2):367.
Wheeler, M. (1996) Measuring Mercury. Environmental Health Perspectives.
104(8): http://ephnet1.nih.gov/docs/1996/104-8/focus.html.
Boening, D. (2000) Ecological effectws, transport, and fate of mercury: a general
review. Chemosphere. 40:1335-1351.
Greimel, H. (2001) Poisoning victims of Japan's mercury bay may be double previous
estimates. http://www.enn.com/news/wire-stories/2001/10112001/ap-45234.asp
Mercury Chemical Backgrounder. http://www.nsc.org/library/chemical/Mercury.htm
Mercury, chemical element: The Columbia Encyclopedia, Sixth
Edition. (2001). http://www.bartelby.com/65/me/mercury/html
Chemical Properties of Mercury. http://pasture.ecn.purdue.edu/~mercury/src/props.htm
Toxic Mercury Rains on U.S. Midwest. (1999) http://www.uwsp.edu/geo/courses/geog100/ENSMercury.htm
UGA Genetics - Richard B. Meagher. http://www.genetics.uga.edu/faculty/bio-Meagher.html
Phytoremediation Research Lab, Michigan State University. Department of Crop and Soil
Sciences. http://www.css.msu.edu/phytoremediation/c_rugh.html
Applied PhytoGenetics Inc. Apgen's phytoremediation technologies. http://www.applied
phytogenetics.com/apgen/technology.htm
Rugh, C., Wilde, H.D., Stack, N., Thompson, D., Summers, A., and Meagher, R. (1996) Mercuric
ion reduction and resistance in transgenic Arabidopsis thaliana plants expressing a modified
bacterial merA gene. Proc. Natl. Acad. Sci. 93:3182-3187.
Rugh, C., Senecoff, J., Meagher, R., and Merkle, S. (1998) Development of transgenic yellow
poplar for mercury phytoremediation. Nature Biotechnology. 16:925-928.
Bizily, S., Rugh, C., Summers, A., and Meagher, R. (1999) Phytoremediation of methylmercury
pollution: merB expression in Arabidopsis thaliana confers resistance to organomercurials. Proc.
Natl. Acad. Sci. 96:6808-6813.
Bizily, S., Rugh, C., Meagher, R. (2000) Phytodetoxification of hazardous organomercurials by
genetically engineered plants. Nature Biotechnology. 18:213-217.
Sumber:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationtechnologies.html ….
Diunduh 7/5/2012
FITOREMEDIASI Merkuri (Hg)
. Phytoremediation of Mercury and Organomercurials in Chloroplast Transgenic Plants:
Enhanced Root Uptake, Translocation to Shoots, and Volatilization
Hussein S. Hussein,† Oscar N. Ruiz,‡§ Norman Terry,† and Henry Daniell
Environ Sci Technol. 2007 December 15; 41(24): 8439–8446.
. Transgenic tobacco plants engineered with bacterial merA and merB genes via the
chloroplast genome were investigated to study the uptake, translocation of different
forms of mercury (Hg) from roots to shoots, and their volatilization. Untransformed
plants, regardless of the form of Hg supplied, reached a saturation point at 200 µM of
phenylmercuric acetate (PMA) or HgCl2, accumulating Hg concentrations up to 500 µg
g−1 with significant reduction in growth. In contrast, chloroplast transgenic lines
continued to grow well with Hg concentrations in root tissues up to 2000 µg g−1.
Chloroplast transgenic lines accumulated both the organic and inorganic Hg forms to
levels surpassing the concentrations found in the soil. The organic-Hg form was
absorbed and translocated more efficiently than the inorganic-Hg form in transgenic
lines, whereas no such difference was observed in untransformed plants. Chloroplasttransgenic lines showed about 100-fold increase in the efficiency of Hg accumulation in
shoots compared to untransformed plants. This is the first report of such high levels of
Hg accumulation in green leaves or tissues. Transgenic plants attained a maximum rate
of elemental-Hg volatilization in two days when supplied with PMA and in three days
when supplied with inorganic-Hg, attaining complete volatilization within a week. The
combined expression of merAB via the chloroplast genome enhanced conversion of
Hg2+ into Hg,0 conferred tolerance by rapid volatilization and increased uptake of
different forms of mercury, surpassing the concentrations found in the soil. These
investigations provide novel insights for improvement of plant tolerance and
detoxification of mercury.
Sumber: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2590779/…. Diunduh 7/5/2012
FITOREMEDIASI Merkuri (Hg)
Differential mercury volatilization by tobacco organs expressing a
modified bacterial merA gene.
He YK, Sun JG, Feng XZ, Czakó M, Márton L.
Cell Res. 2001 Sep;11(3):231-6.
. Mercury pollution is a major environmental problem accompanying industrial
activities. Most of the mercury released ends up and retained in the soil as complexes
of the toxic ionic mercury (Hg2+), which then can be converted by microbes into the
even more toxic methylmercury which tends to bioaccumulate. Mercury detoxification
of the soil can also occur by microbes converting the ionic mercury into the least toxic
metallic mercury (Hg0) form, which then evaporates. The remediation potential of
transgenic plants carrying the MerA gene from E. coli encoding mercuric ion reductase
could be evaluated. A modified version of the gene, optimized for plant codon
preferences (merApe9, Rugh et al. 1996), was introduced into tobacco by
Agrobacterium-mediated leaf disk transformation. Transgenic seeds were resistant to
HgCl2 at 50 microM, and some of them (10-20% ) could germinate on media containing
as much as 350 microM HgCl2, while the control plants were fully inhibited or died on
50 microM HgCl2. The rate of elemental mercury evolution from Hg2+ (added as
HgCl2) was 5-8 times higher for transgenic plants than the control. Mercury
volatilization by isolated organs standardized for fresh weight was higher (up to 5
times) in the roots than in shoots or the leaves. The data suggest that it is the root
system of the transgenic plants that volatilizes most of the reduced mercury (Hg0). It
also suggests that much of the mercury need not enter the vascular system to be
transported to the leaves for volatilization. Transgenic plants with the merApe9 gene
may be used to mercury detoxification for environmental improvement in mercurycontaminated regions more efficiently than it had been predicted based on data on
volatilization of whole plants via the upper parts only (Rugh et al. 1996).
Sumber: http://www.ncbi.nlm.nih.gov/pubmed/11642409…. Diunduh 7/5/2012
FITOREMEDIASI Merkuri (Hg)
. Plant Biotechnol J. 2011 Jun;9(5):609-17. doi: 10.1111/j.1467-7652.2011.00616.x.
Epub 2011 Apr 24.
Metallothionein expression in chloroplasts enhances mercury accumulation and
phytoremediation capability.
Ruiz ON, Alvarez D, Torres C, Roman L, Daniell H.
. Genetic engineering to enhance mercury phytoremediation has been accomplished
by expression of the merAB genes that protects the cell by converting Hg[II] into Hg[0]
which volatilizes from the cell. A drawback of this approach is that toxic Hg is released
back into the environment. A better phytoremediation strategy would be to
accumulate mercury inside plants for subsequent retrieval. We report here the
development of a transplastomic approach to express the mouse metallothionein gene
(mt1) and accumulate mercury in high concentrations within plant cells. Real-time PCR
analysis showed that up to 1284 copies of the mt1 gene were found per cell when
compared with 1326 copies of the 16S rrn gene, thereby attaining homoplasmy. Past
studies in chloroplast transformation used qualitative Southern blots to evaluate
indirectly transgene copy number, whereas we used real-time PCR for the first time to
establish homoplasmy and estimate transgene copy number and transcript levels. The
mt1 transcript levels were very high with 183,000 copies per ng of RNA or 41% the
abundance of the 16S rrn transcripts. The transplastomic lines were resistant up to 20
μm mercury and maintained high chlorophyll content and biomass. Although the
transgenic plants accumulated high concentrations of mercury in all tissues, leaves
accumulated up to 106 ng, indicating active phytoremediation and translocation of
mercury. Such accumulation of mercury in plant tissues facilitates proper disposal or
recycling. This study reports, for the first time, the use of metallothioneins in plants for
mercury phytoremediation. Chloroplast genetic engineering approach is useful to
express metal-scavenging proteins for phytoremediation.
Sumber: http://www.ncbi.nlm.nih.gov/pubmed/21518240…. Diunduh 7/5/2012
J. Ind Microbiol Biotechnol. 2005 Dec;32(11-12):502-13. Epub 2005 Jul 2.
Strategies for the engineered phytoremediation of toxic element pollution: mercury and
arsenic.
Meagher RB, Heaton AC.
Plants have many natural properties that make them ideally suited to clean up polluted
soil, water, and air, in a process called phytoremediation. We are in the early stages of
testing genetic engineering-based phytoremediation strategies for elemental
pollutants like mercury and arsenic using the model plant Arabidopsis. The long-term
goal is to develop and test vigorous, field-adapted plant species that can prevent
elemental pollutants from entering the food-chain by extracting them to aboveground
tissues, where they can be managed. To achieve this goal for arsenic and mercury, and
pave the way for the remediation of other challenging elemental pollutants like lead or
radionucleides, research and development on native hyperaccumulators and
engineered model plants needs to proceed in at least eight focus areas: (1) Plant
tolerance to toxic elementals is essential if plant roots are to penetrate and extract
pollutants efficiently from heterogeneous contaminated soils. Only the roots of
mercury- and arsenic-tolerant plants efficiently contact substrates heavily
contaminated with these elements. (2) Plants alter their rhizosphere by secreting
various enzymes and small molecules, and by adjusting pH in order to enhance
extraction of both essential nutrients and toxic elements. Acidification favors greater
mobility and uptake of mercury and arsenic. (3) Short distance transport systems for
nutrients in roots and root hairs requires numerous endogenous transporters. It is
likely that root plasma membrane transporters for iron, copper, zinc, and phosphate
take up ionic mercuric ions and arsenate. (4) The electrochemical state and chemical
speciation of elemental pollutants can enhance their mobility from roots up to shoots.
Initial data suggest that elemental and ionic mercury and the oxyanion arsenate will be
the most mobile species of these two toxic elements. (5) The long-distance transport
of nutrients requires efficient xylem loading in roots, movement through the xylem up
to leaves, and efficient xylem unloading aboveground. These systems can be enhanced
for the movement of arsenic and mercury. (6) Aboveground control over the
electrochemical state and chemical speciation of elemental pollutants will maximize
their storage in leaves, stems, and vascular tissues. Our research suggests ionic Hg(II)
and arsenite will be the best chemical species to trap aboveground. (7) Chemical sinks
can increase the storage capacity for essential nutrients like iron, zinc, copper, sulfate,
Sumber: …. Diunduh 7/5/2012
and phosphate. Organic acids and thiol-rich chelators are among the important
Environ Sci Pollut Res Int. 2009 Mar;16(2):162-75. Epub 2008 Dec 6.
Implications of metal accumulation mechanisms to phytoremediation.
Memon AR, Schröder P.
. BACKGROUND, AIM, AND SCOPE:
Trace elements (heavy metals and metalloids) are important environmental pollutants, and many of
them are toxic even at very low concentrations. Pollution of the biosphere with trace elements has
accelerated dramatically since the Industrial Revolution. Primary sources are the burning of fossil fuels,
mining and smelting of metalliferous ores, municipal wastes, agrochemicals, and sewage. In addition,
natural mineral deposits containing particularly large quantities of heavy metals are found in many
regions. These areas often support characteristic plant species thriving in metal-enriched
environments. Whereas many species avoid the uptake of heavy metals from these soils, some of
them can accumulate significantly high concentrations of toxic metals, to levels which by far exceed
the soil levels. The natural phenomenon of heavy metal tolerance has enhanced the interest of plant
ecologists, plant physiologists, and plant biologists to investigate the physiology and genetics of metal
tolerance in specialized hyperaccumulator plants such as Arabidopsis halleri and Thlaspi caerulescens.
In this review, we describe recent advances in understanding the genetic and molecular basis of metal
tolerance in plants with special reference to transcriptomics of heavy metal accumulator plants and
the identification of functional genes implied in tolerance and detoxification.
RESULTS:
Plants are susceptible to heavy metal toxicity and respond to avoid detrimental effects in a variety of
different ways. The toxic dose depends on the type of ion, ion concentration, plant species, and stage
of plant growth. Tolerance to metals is based on multiple mechanisms such as cell wall binding, active
transport of ions into the vacuole, and formation of complexes with organic acids or peptides. One of
the most important mechanisms for metal detoxification in plants appears to be chelation of metals by
low-molecular-weight proteins such as metallothioneins and peptide ligands, the phytochelatins. For
example, glutathione (GSH), a precursor of phytochelatin synthesis, plays a key role not only in metal
detoxification but also in protecting plant cells from other environmental stresses including intrinsic
oxidative stress reactions. In the last decade, tremendous developments in molecular biology and
success of genomics have highly encouraged studies in molecular genetics, mainly transcriptomics, to
identify functional genes implied in metal tolerance in plants, largely belonging to the metal
homeostasis network.
DISCUSSION:
Analyzing the genetics of metal accumulation in these accumulator plants has been greatly enhanced
through the wealth of tools and the resources developed for the study of the model plant Arabidopsis
thaliana such as transcript profiling platforms, protein and metabolite profiling, tools depending on
RNA interference (RNAi), and collections of insertion line mutants. To understand the genetics of metal
accumulation and adaptation, the vast arsenal of resources developed in A. thaliana could be extended
to one of its closest relatives that display the highest level of adaptation to high metal environments
such as A. halleri and T. caerulescens.
CONCLUSIONS:
This review paper deals with the mechanisms of heavy metal accumulation and tolerance in plants.
Detailed information has been provided for metal transporters, metal chelation, and oxidative stress in
metal-tolerant plants. Advances in phytoremediation technologies and the importance of metal
accumulator plants and strategies for exploring these immense and valuable genetic and biological
resources for phytoremediation are discussed.
RECOMMENDATIONS AND PERSPECTIVES:
A number of species within the Brassicaceae
have7/5/2012
been identified as metal accumulators. To
Sumber: ….family
Diunduh
understand fully the genetics of metal accumulation, the vast genetic resources developed in A.
. Environ Sci Pollut Res Int. 2009 Mar;16(2):162-75. Epub 2008 Dec 6.
Implications of metal accumulation mechanisms to phytoremediation.
Memon AR, Schröder P.
. BACKGROUND, AIM, AND SCOPE:
Trace elements (heavy metals and metalloids) are important environmental pollutants, and many of
them are toxic even at very low concentrations. Pollution of the biosphere with trace elements has
accelerated dramatically since the Industrial Revolution. Primary sources are the burning of fossil
fuels, mining and smelting of metalliferous ores, municipal wastes, agrochemicals, and sewage. In
addition, natural mineral deposits containing particularly large quantities of heavy metals are found in
many regions. These areas often support characteristic plant species thriving in metal-enriched
environments. Whereas many species avoid the uptake of heavy metals from these soils, some of
them can accumulate significantly high concentrations of toxic metals, to levels which by far exceed
the soil levels. The natural phenomenon of heavy metal tolerance has enhanced the interest of plant
ecologists, plant physiologists, and plant biologists to investigate the physiology and genetics of metal
tolerance in specialized hyperaccumulator plants such as Arabidopsis halleri and Thlaspi caerulescens.
In this review, we describe recent advances in understanding the genetic and molecular basis of metal
tolerance in plants with special reference to transcriptomics of heavy metal accumulator plants and
the identification of functional genes implied in tolerance and detoxification.
RESULTS:
Plants are susceptible to heavy metal toxicity and respond to avoid detrimental effects in a variety of
different ways. The toxic dose depends on the type of ion, ion concentration, plant species, and stage
of plant growth. Tolerance to metals is based on multiple mechanisms such as cell wall binding, active
transport of ions into the vacuole, and formation of complexes with organic acids or peptides. One of
the most important mechanisms for metal detoxification in plants appears to be chelation of metals
by low-molecular-weight proteins such as metallothioneins and peptide ligands, the phytochelatins.
For example, glutathione (GSH), a precursor of phytochelatin synthesis, plays a key role not only in
metal detoxification but also in protecting plant cells from other environmental stresses including
intrinsic oxidative stress reactions. In the last decade, tremendous developments in molecular biology
and success of genomics have highly encouraged studies in molecular genetics, mainly
transcriptomics, to identify functional genes implied in metal tolerance in plants, largely belonging to
the metal homeostasis network.
DISCUSSION:
Analyzing the genetics of metal accumulation in these accumulator plants has been greatly enhanced
through the wealth of tools and the resources developed for the study of the model plant Arabidopsis
thaliana such as transcript profiling platforms, protein and metabolite profiling, tools depending on
RNA interference (RNAi), and collections of insertion line mutants. To understand the genetics of
metal accumulation and adaptation, the vast arsenal of resources developed in A. thaliana could be
extended to one of its closest relatives that display the highest level of adaptation to high metal
environments such as A. halleri and T. caerulescens.
CONCLUSIONS:
This review paper deals with the mechanisms of heavy metal accumulation and tolerance in plants.
Detailed information has been provided for metal transporters, metal chelation, and oxidative stress
in metal-tolerant plants. Advances in phytoremediation technologies and the importance of metal
accumulator plants and strategies for exploring these immense and valuable genetic and biological
resources for phytoremediation are discussed.
RECOMMENDATIONS AND PERSPECTIVES:
Sumber: http://www.ncbi.nlm.nih.gov/pubmed/19067014
…. Diunduh 7/5/2012.
A number of species within the Brassicaceae family have been identified as metal accumulators. To
. Ying Yong Sheng Tai Xue Bao. 2003 Apr;14(4):632-6.
[Phytochelatin and its function in heavy metal tolerance of higher plants].
[Article in Chinese]
Wu F, Zhang G.
. The biosynthesis pathway of phytochelatins (PC) and its function in heavy metal
tolerance of higher plants were summarized in this paper. The toxic heavy metal
accumulation in soil would deteriorates crop growth and yield components, and
threaten the agro-products security. There were significantly differences in the
accumulation and tolerance to heavy metals among plant species and genotypes. The
formation of PC in response to the stress caused by heavy metals was one of the truly
adaptive responses occurred commonly in higher plants. In the heavy metal tolerant
genotypes, there was a much higher accumulation of PC than the non-tolerant lines.
Glutathione (GSH) was the substrate for the synthesis of PC, which chelated the
metals. The inactive toxic metal ions of metal--PC chelatins were subsequently
transported from cytosol to vacuole before they could poison the enzymes of lifesupporting metabolic routes, and transiently stored in vacuole to reduce the heavy
metal concentration in cytosol, thus, heavy metal detoxification was attained. The
break through of genetic mechanism and bio-chemical pathway of PC synthesis
induced by heavy metals would depend on the further study on molecular biology in
this field. The isolation of Cd-sensitive cad1 and cad2 mutants of Arabidopsis thaliana,
that was deficient in PC, demonstrted the importance of PC for heavy metal tolerance.
The effect of PC on food security and on phytoremediation of soil and water
contaminated by heavy metals was also discussed in this paper.
Sumber: http://www.ncbi.nlm.nih.gov/pubmed/12920919 …. Diunduh 7/5/2012
Gene. 1996 Nov 7;179(1):21-30.
Heavy metal detoxification in higher plants--a review.
Zenk MH.
. A set of heavy-metal-complexing peptides was isolated from plants and plant
suspension cultures. The structure of these peptides was established as (gammaglutamic acid-cysteine)n-glycine (n = 2-11) [(gamma-Glu-Cys)n-Gly]. These peptides
appear upon induction of plants with metals of the transition and main groups (Ib-Va, Z
= 29-83) of the periodic table of elements. These peptides, called phytochelatins (PC),
are induced in all autotrophic plants so far analyzed, as well as in select fungi. Some
species of the order Fabales and the family Poaceae synthesize aberrant PC that
contain, at their C-terminal end, either beta-alanine, serine or glutamic acid. For this
group of peptides the name iso-PC is proposed. The biosynthesis of PC proceeds by
metal activation of a constitutive enzyme that uses glutathione (GSH) as a substrate;
this enzyme is a gamma-glutamylcysteine dipeptidyl transpeptidase which was given
the trivial name PC synthase. It catalyzes the following reaction: gamma-Glu-Cys-Gly +
(gamma-Glu-Cys)n-Gly-->(gamma-Glu-Cys)n+1-Gly + Gly. The plant vacuole is the
transient storage compartment for these peptides. They probably dissociate, and the
metal-free peptide is subsequently degraded. Sequestration of heavy metals by PC
confers protection for heavy-metal-sensitive enzymes. The isolation of a Cd(2+)sensitive cadl mutant of Arabidopsis thaliana, that is deficient in PC synthase,
demonstrates conclusively the importance of PC for heavy metal tolerance. In spite of
the fact that nucleic acid sequences and proteins are found in higher plants that have
distant homology to animal metallothioneins, there is absolutely no experimental
evidence that these "plant metallothioneins' are involved in the detoxification of heavy
metals. PC synthase will be an interesting target for biotechnological modification of
heavy metal tolerance in higher plants.
Sumber: http://www.ncbi.nlm.nih.gov/pubmed/8955625 …. Diunduh 7/5/2012
. J Trace Elem Med Biol. 2005;18(4):339-53.
Molecular mechanisms of heavy metal hyperaccumulation and phytoremediation.
Yang X, Feng Y, He Z, Stoffella PJ.
A relatively small group of hyperaccumulator plants is capable of sequestering heavy
metals in their shoot tissues at high concentrations. In recent years, major scientific
progress has been made in understanding the physiological mechanisms of metal
uptake and transport in these plants. However, relatively little is known about the
molecular bases of hyperaccumulation. In this paper, current progresses on
understanding cellular/molecular mechanisms of metal tolerance/hyperaccumulation
by plants are reviewed. The major processes involved in hyperaccumulation of trace
metals from the soil to the shoots by hyperaccumulators include: (a) bioactivation of
metals in the rhizosphere through root-microbe interaction; (b) enhanced uptake by
metal transporters in the plasma membranes; (c) detoxification of metals by
distributing to the apoplasts like binding to cell walls and chelation of metals in the
cytoplasm with various ligands, such as phytochelatins, metallothioneins, metalbinding proteins; (d) sequestration of metals into the vacuole by tonoplast-located
transporters. The growing application of molecular-genetic technologies led to the well
understanding of mechanisms of heavy metal tolerance/accumulation in plants, and
subsequently many transgenic plants with increased resistance and uptake of heavy
metals were developed for the purpose of phytoremediation. Once the rate-limiting
steps for uptake, translocation, and detoxification of metals in hyperaccumulating
plants are identified, more informed construction of transgenic plants would result in
improved applicability of the phytoremediation technology.
Sumber: http://www.ncbi.nlm.nih.gov/pubmed/16028496 …. Diunduh 7/5/2012
Crit Rev Biotechnol. 2010 Mar;30(1):23-30.
Understanding molecular mechanisms for improving phytoremediation of heavy metalcontaminated soils.
Hong-Bo S, Li-Ye C, Cheng-Jiang R, Hua L, Dong-Gang G, Wei-Xiang L.
Heavy metal pollution of soil is a significant environmental problem with a negative
potential impact on human health and agriculture. Rhizosphere, as an important
interface of soil and plants, plays a significant role in phytoremediation of
contaminated soil by heavy metals, in which, microbial populations are known to affect
heavy metal mobility and availability to the plant through release of chelating agents,
acidification, phosphate solubilization and redox changes, and therefore, have
potential to enhance phytoremediation processes. Phytoremediation strategies with
appropriate heavy metal-adapted rhizobacteria or mycorrhizas have received more and
more attention. In addition, some plants possess a range of potential mechanisms that
may be involved in the detoxification of heavy metals, and they manage to survive
under metal stresses. High tolerance to heavy metal toxicity could rely either on
reduced uptake or increased plant internal sequestration, which is manifested by an
interaction between a genotype and its environment.A coordinated network of
molecular processes provides plants with multiple metal-detoxifying mechanisms and
repair capabilities. The growing application of molecular genetic technologies has led
to an increased understanding of mechanisms of heavy metal tolerance/accumulation
in plants and, subsequently, many transgenic plants with increased heavy metal
resistance, as well as increased uptake of heavy metals, have been developed for the
purpose of phytoremediation. This article reviews advantages, possible mechanisms,
current status and future direction of phytoremediation for heavy-metal-contaminated
soils.
Sumber: http://www.ncbi.nlm.nih.gov/pubmed/19821782 …. Diunduh 7/5/2012
Environ Sci Pollut Res Int. 2003;10(5):335-40.
Heavy metals in plants and phytoremediation.
Cheng S.
GOAL, SCOPE AND BACKGROUND:
In some cases, soil, water and food are heavily polluted by heavy metals in China. To
use plants to remediate heavy metal pollution would be an effective technique in
pollution control. The accumulation of heavy metals in plants and the role of plants in
removing pollutants should be understood in order to implement phytoremediation,
which makes use of plants to extract, transfer and stabilize heavy metals from soil and
water.
METHODS:
The information has been compiled from Chinese publications stemming mostly from
the last decade, to show the research results on heavy metals in plants and the role of
plants in controlling heavy metal pollution, and to provide a general outlook of
phytoremediation in China. Related references from scientific journals and university
journals are searched and summarized in sections concerning the accumulation of
heavy metals in plants, plants for heavy metal purification and phytoremediation
techniques.
RESULTS AND DISCUSSION:
Plants can take up heavy metals by their roots, or even via their stems and leaves, and
accumulate them in their organs. Plants take up elements selectively. Accumulation
and distribution of heavy metals in the plant depends on the plant species, element
species, chemical and bioavailiability, redox, pH, cation exchange capacity, dissolved
oxygen, temperature and secretion of roots. Plants are employed in the
decontamination of heavy metals from polluted water and have demonstrated high
performances in treating mineral tailing water and industrial effluents. The purification
capacity of heavy metals by plants are affected by several factors, such as the
concentration of the heavy metals, species of elements, plant species, exposure
duration, temperature and pH.
CONCLUSIONS:
Phytoremediation, which makes use of vegetation to remove, detoxify, or stabilize
persistent pollutants, is a green and environmentally-friendly tool for cleaning polluted
Sumber: http://www.ncbi.nlm.nih.gov/pubmed/14535650 …. Diunduh 7/5/2012.
soil and water. The advantage of high biomass productive and easy disposal makes
. Phytoremediation of Mercury-Contaminated Mine Tailings by Induced Plant-Mercury
Accumulation
a1c1
Fabio N. Moreno , Chris W. N. Anderson a1, Robert B. Stewart a1 and Brett H. Robinson
Environmental Practice (2004), 6 : pp 165-175
In most contaminated soils and mine tailings, mercury (Hg) is not readily available for
plant uptake. A strategy for inducing Hg mobilization in soils to increase accumulation
potential in plants was investigated to enhance Hg phytoremediation. Accumulation of
Hg in the nickel hyperaccumulator Berkheya coddii, the salt-tolerant Atriplex
canescens, and the nonaccumulators Brassica juncea and Lupinus sp. was studied by
pot trials containing mine tailings treated with either soluble Hg or sulfur-containing
ligands. Accumulation of Hg in shoots of B. coddii and A. canescens after addition of
soluble Hg was lower than 10 mg/kg dry weight. The addition of ammonium
thiosulfate (NH4S2O3) to tailings mobilized Hg in substrates, as indicated by the
elevated Hg concentrations in leachates from the pots of both species. Ammonium
thiosulfate caused a significant increase in the Hg concentration in shoots of B. juncea.
Conversely, Hg translocation to Lupinus sp. shoots was significantly reduced in the
presence of this ligand. Mass balance calculations revealed a significant fraction of Hg
was lost from the system. This unaccounted-for Hg may indicate Hg volatilization. The
results suggest that there is potential for induced plant Hg accumulation for
phytoremediation of Hg-contaminated sites. Issues of Hg leaching and volatilization,
however, need to be addressed before this technology can be implemented in the
field.
Sumber:
http://journals.cambridge.org/action/displayAbstract;jsessionid=1E7D249F1167541C9ABFF5DBF479E2F9.jo
urnals?fromPage=online&aid=348969 …. Diunduh 7/5/2012
Effect of Selective Pressure and Genetically Engineered Microorganism (GEM) Densities on
Mercury Resistance (mer) Operon Transfer in Elbe River and Estuarine Sediments
Björg V. Pauling a1, Niels Kroer a2 and Irene Wagner-Döbler
Environmental Practice (2004), 6 : pp 176-190
Bacterial reduction of mercury ions to elemental mercury by the mer operon-encoded
microbial resistance mechanism has recently been shown to be a promising approach
in the bio-remediation of mercury-contaminated wastewater. Mercury resistance is
widespread among environmental bacteria and several isolates have proven to be
adaptable catalyzers for mercury reduction in bioreactors. To accomplish high, stable,
and predictable performance, however, the genetically engineered microorganism
(GEM) Pseudomonas putida KT2442::mer73 has been constructed, which constitutively
expresses the mercury resistance operon at a high level, is nonpathogenic, and does
not contain plasmids. To assess the safety of this GEM in an open environmental
application, gene transfer was investigated in stream and estuarine microcosms
containing sediments from the Elbe River and Roskilde Fjord, Denmark. In P. putida
KT2442::mer73, the merTPAB genes have been stably integrated into the chromosome
to reduce the chance of horizontal transfer. Consequently gene transfer to an isogenic
recipient strain, P. putida KT2442::Tc, could not be detected, although parameters such
as recipient cell density, cell shock, continuous addition of cells, or application of
mercury selective pressure were adjusted with respect to increasing the probability of
gene exchange. On the basis of these experiments, the strain P. putida KT2442::mer73
can be regarded as safe.
Sumber:
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=348969&next=true&jid=ENP&
volumeId=6&issueId=02 …. Diunduh 7/5/2012
. Mercury Behavior in a Tropical Environment: The Case of Small-Scale Gold Mining in
Poconé, Brazil
a1c1
Lazaro J. Oliveira
, Lars D. Hylander a2 and Edinaldo de Castro e Silva.
Environmental Practice (2004), 6 : pp 121-134
. An estimated 50 tons of mercury (Hg) have been emitted by gold miners in the Bento
Gomes river basin, in the municipality of Poconé, Brazil, since the 1980s. Since the midl990s, the state agency for environmental protection, FEMA (Fundação Estadual do
Meio Ambiente de Mato Grosso), has enforced regulations to reduce Hg emissions to
air and water and has also implemented an environmental assessment program. The
objectives of this study were to evaluate efforts to reduce emissions of Hg to air and
water from nine improved amalgamation centers, and to assess the pollution level in
sediment at 25 sites around Poconé. In spite of the fact that retorts were used, results
showed large emissions of Hg when burning amalgam, resulting in Hg air
concentrations above the limit for occupational air (50 μg/m3) at all centers except
one. Keeping washing water in closed systems and dumping residues in specially
prepared sites reduced Hg emissions to watercourses. The average Hg concentration of
fine sediments (<74 μm) in the Bento Gomes river basin was 104 ng Hg/g dry weight,
three to four times higher than the background level; large amounts of Hgcontaminated sediments are re-suspended during the rainy season. In conclusion,
present emissions to local watercourses have been efficiently reduced, but the use of
retorts in improved amalgamation centers has not adequately reduced Hg emissions to
air, which is why the use of Hg remains an occupational and environmental problem.
Sumber:
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=348961&fulltextType=RA&fileI
d=S1466046604000237 …. Diunduh 7/5/2012
. Bioaccumulation Factors for Mercury in Stream Fish
George R. Southworth a1c1, Mark J. Peterson a1 and
Mary Anna Bogle.
Environmental Practice (2004), 6 : pp 135-143
. The bioaccumulation of methylmercury in fish is a complex process affected by many
site-specific environmental factors. The US Environmental Protection Agency (USEPA)
recently recommended changing the basis for expressing the ambient water quality
criterion for mercury from an aqueous concentration to a measure of the
methylmercury concentration in fish. This change would make the regulation of
mercury in surface waters a site-specific exercise in which fish-based bioaccumulation
factors (BAF; the ratio of mercury concentration in fish to the concentration of mercury
in water) are used to calculate aqueous concentration limits for total mercury. These
limits would then be used to allocate mercury loading among various point and
nonpoint sources and guide regulatory actions. In order for this approach to succeed, it
is critical that the site-specific BAFs and methylmercury:total mercury conversion
factors be independent of aqueous total mercury concentration (HgT). We investigated
this relationship by measuring aqueous methylmercury and HgTs and mercury in fish in
ecologically similar warm-water streams in the southeastern United States.
Bioaccumulation factors based on HgT in water were found to decrease with increasing
HgT, primarily as a consequence of the reduction in the ratio of aqueous
methylmercury to total mercury with increasing HgT. Methylmercury-based BAFs did
not vary as a function of HgT. The implication of this relationship is that site-specific
determination of aqueous HgT limits at contaminated sites may use BAFs that would be
underestimates of the appropriate BAFs to describe mercury bioaccumulation in the
system after mercury inputs have been reduced. In such cases, regulatory limits set
using site-specific BAFs might not achieve their intended purpose of reducing mercury
contamination in fish to acceptable concentrations.
Sumber:
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=348961&next=true&jid=ENP&
volumeId=6&issueId=02 …. Diunduh 7/5/2012
Thermal Desorption for Mercury Removal from Sediments Sampled from the
Adriatic Sea
Daniele Benotti a1c1, Massimo Delfini a1, Mauro Ferrini a1, Floriana La Marca a1,
Paolo Massacci a1, Luigi Piga a1 and Paolo Colosimo
Environmental Practice (2004), 6 : pp 144-156
. Overall sampling of the sediments in the Adriatic Sea at the mouth of the Isonzo
(Soça) River in Italy has permitted updating of the extent and level of mercury
contamination. The lsonzo River transports mercury-bearing residues from the ldrija
mine (Slovenia); that area is contaminated due to the mining of cinnabar (HgS). The
mercury mine started operations in the 15th century and was finally shut down in the
1980s because of the decreased demand for mercury. An attempt was made to remove
mercury from the contaminated sediments by thermal desorption, with the aim of
ascertaining whether low temperature and short residence time could be suitable
parameters for sediment cleanup if future needs should so require. To date, no studies
have been done on the health of the Italian population living in the Gulf of Trieste
area; hence there is no known correlation between the anomalous mercury content of
the sediments and symptoms attributable to the ingestion of even small quantities of
mercury. Desorption times of about 20 to 30 minutes, at temperatures ranging from
325° C to 350° C, yielded residues with a mercury content below the limit imposed by
Italian regulations for contaminated soils and sediments (5 ppm). The air and the
mercury vapors driven off during roasting were treated before being released to the
atmosphere.
Sumber:
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=348963&next=true&jid=ENP&
volumeId=6&issueId=02 …. Diunduh 7/5/2012
. Phytoremediation of Mercury-Contaminated Mine Tailings by Induced Plant-Mercury
Accumulation
a1c1
Fabio N. Moreno , Chris W. N. Anderson a1, Robert B. Stewart a1 and Brett H. Robinson
Environmental Practice (2004), 6 : pp 165-175
In most contaminated soils and mine tailings, mercury (Hg) is not readily available for
plant uptake. A strategy for inducing Hg mobilization in soils to increase accumulation
potential in plants was investigated to enhance Hg phytoremediation. Accumulation of
Hg in the nickel hyperaccumulator Berkheya coddii, the salt-tolerant Atriplex
canescens, and the nonaccumulators Brassica juncea and Lupinus sp. was studied by
pot trials containing mine tailings treated with either soluble Hg or sulfur-containing
ligands. Accumulation of Hg in shoots of B. coddii and A. canescens after addition of
soluble Hg was lower than 10 mg/kg dry weight. The addition of ammonium
thiosulfate (NH4S2O3) to tailings mobilized Hg in substrates, as indicated by the
elevated Hg concentrations in leachates from the pots of both species. Ammonium
thiosulfate caused a significant increase in the Hg concentration in shoots of B. juncea.
Conversely, Hg translocation to Lupinus sp. shoots was significantly reduced in the
presence of this ligand. Mass balance calculations revealed a significant fraction of Hg
was lost from the system. This unaccounted-for Hg may indicate Hg volatilization. The
results suggest that there is potential for induced plant Hg accumulation for
phytoremediation of Hg-contaminated sites. Issues of Hg leaching and volatilization,
however, need to be addressed before this technology can be implemented in the
field.
Sumber:
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=348969&fulltextType=RA&fileI
d=S1466046604000274 …. Diunduh 7/5/2012
Phytoremediation of mercury using Eichhornia crassipes (Mart.) Solms
Upma Narang, Renu Bhardwaj, S.K. Garg, A.K. Thukral
International Journal of Environment and Waste Management 2011 Vol. 8, No.1/2 pp. 92 – 105.
Roots of Eichhornia crassipes were found to accumulate maximum content
of mercury (92.21 μg g−1 dry wt) in the roots of plants treated with 1000 μg
l−1 concentration of mercuric acetate on 14th day of treatment. The
bioconcentration factor (BCF) was found to be highest for lowest mercury
concentrations (1 μg l−1) in the medium. The uptake of mercury follows dual
pattern of ion uptake. Type-1 mechanism operates at mercury
concentrations up to 100 μg l−1, which is carrier-mediated and follows
Michaelis–Menten kinetics. Type-2 mechanism occurs at concentrations up
to 1000 μg l−1.
Sumber: http://www.inderscience.com/search/index.php?action=record&rec_id=40967 …. Diunduh
8/5/2012
. International Journal of Chemical Engineering
Volume 2011 (2011), 31 pages
A Review on Heavy Metals (As, Pb, and Hg) Uptake by Plants through Phytoremediation
Bieby Voijant Tangahu, Siti Rozaimah Sheikh Abdullah, Hassan Basri, Mushrifah Idris, Nurina
Anuar, and Muhammad Mukhlisin
. Heavy metals are among the most important sorts of contaminant in the
environment. Several methods already used to clean up the environment from these
kinds of contaminants, but most of them are costly and difficult to get optimum
results. Currently, phytoremediation is an effective and affordable technological
solution used to extract or remove inactive metals and metal pollutants from
contaminated soil and water. This technology is environmental friendly and potentially
cost effective. This paper aims to compile some information about heavy metals of
arsenic, lead, and mercury (As, Pb, and Hg) sources, effects and their treatment. It also
reviews deeply about phytoremediation technology, including the heavy metal uptake
mechanisms and several research studies associated about the topics. Additionally, it
describes several sources and the effects of As, Pb, and Hg on the environment, the
advantages of this kind of technology for reducing them, and also heavy metal uptake
mechanisms in phytoremediation technology as well as the factors affecting the uptake
mechanisms. Some recommended plants which are commonly used in
phytoremediation and their capability to reduce the contaminant are also reported.
Sumber: http://www.hindawi.com/journals/ijce/2011/939161/abs/ …. Diunduh 8/5/2012
Phytofiltration of mercury-contaminated water: Volatilisation and plant-accumulation
aspects
Fabio N. Moreno, Christopher W.N. Anderson, Robert B. Stewart, Brett H. Robinson.
Environmental and Experimental Botany
Volume 62, Issue 1, January 2008, Pages 78–85
. Phytofiltration may be a cost-effective approach for treating Hg-contaminated
wastewater. We investigated the removal of Hg from solutions by Indian mustard
[Brassica juncea (L.) Czern.] grown in hydroponic conditions with solutions containing
Hg concentrations from 0 to 10 mg/L. Plants were enclosed in gastight volatilisation
chambers to assess the effect of Hg concentrations on plant transpiration,
accumulation and volatilisation. We also determined the speciation and site of origin
of volatilised Hg. Solution Hg concentrations of 5 and 10 mg/L detrimentally affected
transpiration. Roots concentrated Hg 100–270 times (on a dry weight basis) above
initial solution concentrations. The plants translocated little Hg to the shoots, which
accounted for just 0.7–2% of the total Hg in the plants. Volatilisation from planted
vessels increased linearly as a function of Hg concentrations in solutions. Most Hg
volatilisation occurred from the roots. Volatilised Hg was predominantly in the Hg(0)
vapour form. Volatilisation was dependant on root uptake and absorption of Hg from
the ambient solution. Production of Hg(0) vapour in the solutions may result from the
activity of root-associated algae and Hg-resistant bacteria. Phytofiltration effectively
removed up to 95% of Hg from the contaminated solutions by both volatilisation and
plant accumulation. However, Hg(0) vapours released from living roots may have
unforeseen environmental effects.
Sumber: http://www.sciencedirect.com/science/article/pii/S009884720700113X …. Diunduh 8/5/2012
. Mercury volatilisation and phytoextraction from base-metal mine tailings
Fabio N. Moreno, Chris W.N. Anderson, Robert B. Stewart , Brett H. Robinson.
Environmental Pollution
Volume 136, Issue 2, July 2005, Pages 341–352
. Experiments were carried out in plant growth chambers and in the field to investigate
plant-mercury accumulation and volatilisation in the presence of thiosulphate (S2O3)containing solutions. Brassica juncea (Indian mustard) plants grown in Hgcontaminated Tui mine tailings (New Zealand) were enclosed in gastight volatilisation
chambers to investigate the effect of ammonium thiosulphate ([NH4]2S2O3) on the
plant-Hg volatilisation process. Application of (NH4)2S2O3 to substrates increased up to
6 times the Hg concentration in shoots and roots of B. juncea relative to controls.
Volatilisation rates were significantly higher in plants irrigated only with water (control)
when compared to plants treated with (NH4)2S2O3. Volatilisation from barren pots
(without plants) indicated that Hg in tailings is subject to biological and photochemical
reactions. Addition of sodium thiosulphate (Na2S2O3) at 5 g/kg of substrate to B. juncea
plants grown at the Tui mine site confirmed the plant growth chambers studies
showing the effectiveness of thio-solutions at enhancing shoot Hg concentrations.
Mercury extraction from the field plots yielded a maximum value of 25 g/ha. Mass
balance studies revealed that volatilisation is a dominant pathway for Hg removal from
the Tui mine site. A preliminary assessment of the risks of volatilisation indicated that
enhanced Hg emissions by plants would not harm the local population and the
regional environment.
Sumber: http://www.sciencedirect.com/science/article/pii/S0269749105000035 …. Diunduh 8/5/2012
Kennedy, C. D. and Gonsalves, F. A. N. 1987.
J. exp. Bot. 38: 800–817.
The action of divalent zinc, cadmium, mercury, copper and lead on the trans-root potential
and H+ efflux of excised roots.
The action of Zn2+, Cd2+, Hg2+, Cu2+ and Pb2+ ions on the trans-root potential and H+
efflux of young excised maize roots has been studied. Micro-electrode implantations
into root epidermal cells confirmed the root outer membranes as the major
contributor in the trans-root potential changes. The effects of these ions on H+ efflux
were studied over a period of time in a continuous flow cell apparatus, adequate
controls allowing for transient interference due to divalent cations at the pH probe.
The addition of Zn2+, 5 to 100 μmol dm−3, to the solution bathing the roots reduces H+
efflux and depolarizes the trans-root potential. However, in the presence of Mg2+, 0·1
or 1·0 mmol dm−3, not only is this depolarization inhibited, but hyperpolarization is
observed instead. Cd2+ affects trans-root potential and H+ efflux at a much slower rate
than Zn2+, suggesting a lower membrane permeability. Without Mg2+, Cd2+
hyperpolarizes the trans-root potential, but this is better sustained in its presence.
Hyperpolarization did not occur with Hg2+, Cu2+ or Pb2+ whether or not Mg2+ was
present Hg2+ and to a lesser extent Cu2+ are potent depolarizers of the trans-root
potential and strongly inhibit H+ efflux.
The maximum rates of depolarization observed in the absence of Mg2+ increase in the
order Cd ≈ PCMBS ≪.lt; Zn ≈ Cu < Hg. This is similar to the relative maximum rates of
H+ inhibition, Pb ≈ Cd ≪.lt; Zn < Cu < Hg, suggesting considerable differences in mode
of action and/or membrane permeability. The lower membrane permeability of the
sulphydryl reagent PCMBS apparently prevents ready access to the site(s) of action
available to Hg2+.
The reductions in trans-root potential and H+ gradients induced by this range of cations
would be detrimental to the acquisition of nutrients using these gradients as an energy
source. In contrast, Zn2+, , in the presence of adequate Mg2+, could be beneficial to
nutrient uptake by maintaining a higher membrane potential than would occur in its
absence.
Sumber: http://jxb.oxfordjournals.org/content/38/5/800.abstract?sid=90319c95-0a26-45b1-9299a9e8e7d25f62…. Diunduh 8/5/2012
. Cellular damage induced by cadmium and mercury in Medicago sativa
Cristina Ortega-Villasante, Rubén Rellán-Álvarez , Francisca F. Del Campo, Ramón O.
Carpena-Ruiz and Luis E. Hernández
J. Exp. Bot. (August 2005) 56 (418): 2239-2251.
. Alfalfa (Medicago sativa) plantlets were exposed to Cd or Hg to study the kinetics of
diverse stress indexes. In the so-called beaker-size hydroponic system, plantlets were
grown in 30 μM of Cd or Hg for 7 d. Oxidative stress took place and increased over
time, a linear response being observed with Cd but not with Hg. To improve the
sensitivity of the stress assays used, a micro-assay system, in which seedlings were
exposed for 24 h, was developed. Phytotoxicity of metals, quantified as growth
inhibition, was observed well before there was any change in the non-protein thiol
tissue concentration. When measured with conventional techniques, oxidative stress
indexes did not show significant variation. To trace early and small plant responses to
Cd and Hg, a microscopic analysis with novel fluorescent dyes, which had not yet been
exploited to any significant extent for use in plants, was conducted. These fluorescent
probes, which allowed minute cellular responses to 0, 3, 10, and 30 μM of both metals
to be visualized in the roots of the alfalfa seedlings, were: (i) 2′,7′-dichlorofluorescin
diacetate that labels peroxides; (ii) monochlorobimane that stains reduced
glutathione/homoglutathione (GSH/hGSH); and (iii) propidium iodide that marks nuclei
of dead cells. Oxidative stress and cell death increased after exposure for 6–24 h to Cd
and Hg, but labelling of GSH/hGSH decreased acutely. This diminution might be the
result of direct interaction of GSH/hGSH with both Cd and Hg, as inferred from an in
vitro conjugation assay. Therefore, both Cd and Hg not only compromised severely the
cellular redox homeostasis, but also caused cell necrosis. In plants treated with 1 mM
L-buthionine sulphoximine, a potent inhibitor of GSH/hGSH synthesis, only the
oxidative stress symptoms appeared, indicating that the depletion of the GSH/hGSH
pool was not sufficient to promote cell death, and that other phytotoxic mechanisms
might be involved.
Sumber: http://jxb.oxfordjournals.org/content/56/418/2239.abstract?sid=90319c95-0a26-45b1-9299a9e8e7d25f62…. Diunduh 8/5/2012
. Silver ions disrupt K+ homeostasis and cellular integrity in intact barley (Hordeum vulgare
L.) roots
Devrim Coskun, Dev T. Britto, Yuel-Kai Jean, Lasse M. Schulze, Alexander Becker and
Herbert J. Kronzucker
J. Exp. Bot. (2012) 63 (1): 151-162.
. The heavy metals silver, gold, and mercury can strongly inhibit aquaporin-mediated
water flow across plant cell membranes, but critical examinations of their side effects
are rare. Here, the short-lived radiotracer 42K is used to demonstrate that these metals,
especially silver, profoundly change potassium homeostasis in roots of intact barley
(Hordeum vulgare L.) plants, by altering unidirectional K+ fluxes. Doses as low as 5 μM
AgNO3 rapidly reduced K+ influx to 5% that of controls, and brought about pronounced
and immediate increases in K+ efflux, while higher doses of Au3+ and Hg2+ were
required to produce similar responses. Reduced influx and enhanced efflux of K+
resulted in a net loss of >40% of root tissue K+ during a 15 min application of 500 μM
AgNO3, comprising the entire cytosolic potassium pool and about a third of the
vacuolar pool. Silver also brought about major losses of UV-absorbing compounds,
total electrolytes, and NH4+. Co-application, with silver, of the channel blockers Cs+,
TEA+, or Ca2+, did not affect the enhanced efflux, ruling out the involvement of
outwardly rectifying ion channels. Taken together with an examination of propidium
iodide staining under confocal microscopy, the results indicate that silver ions affect K+
homeostasis by directly inhibiting K+ influx at lower concentrations, and indirectly
inhibiting K+ influx and enhancing K+ efflux, via membrane destruction, at higher
concentrations. Ni2+, Cd2+, and Pb2+, three heavy metals not generally known to affect
aquaporins, did not enhance K+ efflux or cause propidium iodide incorporation. The
study reveals strong and previously unknown effects of major aquaporin inhibitors and
recommends caution in their application.
Sumber: http://jxb.oxfordjournals.org/content/63/1/151.abstract?sid=90319c95-0a26-45b1-9299a9e8e7d25f62…. Diunduh 8/5/2012
. Plasma membrane of Beta vulgaris storage root shows high water channel activity
regulated by cytoplasmic pH and a dual range of calcium concentrations
Karina Alleva , Christa M. Niemietz, Moira Sutka , Christophe Maurel , Mario Parisi ,
Stephen D. Tyerman , and Gabriela Amodeo
J. Exp. Bot. (February 2006) 57 (3): 609-621.
. Plasma membrane vesicles isolated by two-phase partitioning from the storage root
of Beta vulgaris show atypically high water permeability that is equivalent only to
those reported for active aquaporins in tonoplast or animal red cells (Pf=542 μm s−1).
The values were determined from the shrinking kinetics measured by stopped-flow
light scattering. This high Pf was only partially inhibited by mercury (HgCl2) but showed
low activation energy (Ea) consistent with water permeation through water channels.
To study short-term regulation of water transport that could be the result of channel
gating, the effects of pH, divalent cations, and protection against dephosphorylation
were tested. The high Pf observed at pH 8.3 was dramatically reduced by medium
acidification. Moreover, intra-vesicular acidification (corresponding to the cytoplasmic
face of the membrane) shut down the aquaporins. De-phosphorylation was discounted
as a regulatory mechanism in this preparation. On the other hand, among divalent
cations, only calcium showed a clear effect on aquaporin activity, with two distinct
ranges of sensitivity to free Ca2+ concentration (pCa 8 and pCa 4). Since the normal
cytoplasmic free Ca2+ sits between these ranges it allows for the possibility of changes
in Ca2+ to finely up- or down-regulate water channel activity. The calcium effect is
predominantly on the cytoplasmic face, and inhibition corresponds to an increase in
the activation energy for water transport. In conclusion, these findings establish both
cytoplasmic pH and Ca2+ as important regulatory factors involved in aquaporin gating.
Sumber: http://jxb.oxfordjournals.org/content/57/3/609.abstract?sid=90319c95-0a26-45b1-9299a9e8e7d25f62…. Diunduh 8/5/2012
Radial hydraulic conductivity along developing onion roots
David E. Barrowclough , Carol A. Peterson , and Ernst Steudle
J. Exp. Bot. (2000) 51 (344): 547-557.
Although most studies have shown that water uptake varies along the length of a
developing root, there is no consistent correlation of this pattern with root anatomy. In
the present study, water movement into three zones of onion roots was measured by a
series of mini‐potometers. Uptake was least in the youngest zone (mean hydraulic
conductivity, Lpr=1.5× 10−7±0.34×10−7 m MPa−1s−1; ±SE, n=10 roots) in which the
endodermis had developed only Casparian bands and the exodermis was immature.
Uptake was significantly greater in the middle zone (Lpr=2.4× 10−7±0.43×10−7 m MPa−1
s−1; ±SE, n=10 roots) which had a mature exodermis with both Casparian bands and
suberin lamellae, and continued at this level in the oldest zone in which the
endodermis had also developed suberin lamellae (Lpr=2.8×10−7±0.30× 10−7 m MPa−1
s−1; ±SE, n=10 roots). Measurements of the hydraulic conductivities of individual cells
(Lp) in the outer cortex using a cell pressure probe indicated that this parameter was
uniform in all three zones tested (Lp=1.3×10−6±0.01×10−6 m MPa−1 s−1; ±SE, n=60 cells).
Lp of the youngest zone was lowered by mercuric chloride treatment, indicating the
involvement of mercury‐sensitive water channels (aquaporins). Water flow in the older
two root zones measured by mini‐potometers was also inhibited by mercuric chloride,
despite the demonstrated impermeability of their exodermal layers to this substance.
Thus, water channels in the epidermis and/or exodermis of the older regions were
especially significant for water flow. The results of this and previous studies are
discussed in terms of two models. The first, which describes maize root with an
immature exodermis, is the ‘uniform resistance model’ where hydraulic resistances are
evenly distributed across the root cylinder. The second, which describes the onion root
with a mature exodermis, is the ‘non‐uniform resistance model’ where resistances can
be variable and are concentrated in a certain layer(s) on the radial path.
Sumber: http://jxb.oxfordjournals.org/content/51/344/547.abstract?sid=90319c95-0a26-45b1-9299a9e8e7d25f62…. Diunduh 8/5/2012
Plant responses to abiotic stresses: heavy metal‐induced oxidative stress and protection
by mycorrhization
Andres Schützendübel and Andrea Polle
J. Exp. Bot. (2002) 53 (372): 1351-1365.
. The aim of this review is to assess the mode of action and role of antioxidants as protection from
heavy metal stress in roots, mycorrhizal fungi and mycorrhizae. Based on their chemical and physical
properties three different molecular mechanisms of heavy metal toxicity can be distinguished: (a)
production of reactive oxygen species by autoxidation and Fenton reaction; this reaction is typical for
transition metals such as iron or copper, (b) blocking of essential functional groups in biomolecules,
this reaction has mainly been reported for non‐redox‐reactive heavy metals such as cadmium and
mercury, (c) displacement of essential metal ions from biomolecules; the latter reaction occurs with
different kinds of heavy metals. Transition metals cause oxidative injury in plant tissue, but a
literature survey did not provide evidence that this stress could be alleviated by increased levels of
antioxidative systems. The reason may be that transition metals initiate hydroxyl radical production,
which can not be controlled by antioxidants. Exposure of plants to non‐redox reactive metals also
resulted in oxidative stress as indicated by lipid peroxidation, H2O2 accumulation, and an oxidative
burst. Cadmium and some other metals caused a transient depletion of GSH and an inhibition of
antioxidative enzymes, especially of glutathione reductase. Assessment of antioxidative capacities by
metabolic modelling suggested that the reported diminution of antioxidants was sufficient to cause
H2O2 accumulation. The depletion of GSH is apparently a critical step in cadmium sensitivity since
plants with improved capacities for GSH synthesis displayed higher Cd tolerance. Available data
suggest that cadmium, when not detoxified rapidly enough, may trigger, via the disturbance of the
redox control of the cell, a sequence of reactions leading to growth inhibition, stimulation of
secondary metabolism, lignification, and finally cell death. This view is in contrast to the idea that
cadmium results in unspecific necrosis. Plants in certain mycorrhizal associations are less sensitive to
cadmium stress than non‐mycorrhizal plants. Data about antioxidative systems in mycorrhizal fungi in
pure culture and in symbiosis are scarce. The present results indicate that mycorrhization stimulated
the phenolic defence system in the Paxillus–Pinus mycorrhizal symbiosis. Cadmium‐induced changes
in mycorrhizal roots were absent or smaller than those in non‐mycorrhizal roots. These observations
suggest that although changes in rhizospheric conditions were perceived by the root part of the
symbiosis, the typical Cd‐induced stress responses of phenolics were buffered. It is not known
whether mycorrhization protected roots from Cd‐induced injury by preventing access of cadmium to
sensitive extra‐ or intracellular sites, or by excreted or intrinsic metal‐chelators, or by other defence
systems. It is possible that mycorrhizal fungi provide protection via GSH since higher concentrations
of this thiol were found in pure cultures of the fungi than in bare roots. The development of
stress‐tolerant plant‐mycorrhizal associations may be a promising new strategy for phytoremediation
and soil amelioration measures.
Sumber: http://jxb.oxfordjournals.org/content/53/372/1351.abstract?sid=90319c95-0a26-45b1-9299a9e8e7d25f62…. Diunduh 8/5/2012
Relationships of root conductivity and aquaporin gene expression in Pisum sativum:
diurnal patterns and the response to HgCl2 and ABA
Philip C. Beaudette, Michael Chlup, Janet Yee and R. J. Neil Emery.
J. Exp. Bot. (2007) 58 (6): 1291-1300.
Experiments were undertaken to test how aquaporins (AQPs) facilitate the uptake of
water by roots of Pisum sativum. Changes in PsPIP2-1 gene expression and root
hydraulic conductivity (Lpr) were measured in response to the time of day as well as
treatment of the roots with a compound that reduced Lpr [i.e. mercuric chloride
(HgCl2)] and one that was intended to increase Lpr [abscisic acid (ABA)].
. There was a diurnal rhythm in PsPIP2-1 expression in lateral roots that
was strongly correlated with diurnal changes in Lpr. Taproots also
displayed a rhythm in PsPIP2-1 expression, but this was offset from that of
Lpr. This suggested that changes in Lpr were mediated by changes in
PsPIP2-1 mRNA transcript abundance. Reduction of Lpr by HgCl2 treatment
was accompanied by an increase in PsPIP2-1 expression, implying that
PsPIP2-1 expression may have increased to compensate for AQPs blocked
by mercury.
ABA usually increased Lpr, but changes in PsPIP2-1 were variable
and the direction of the response was strongly dependent on the
dose of ABA that was applied.
Overall, the coincident rhythms in Lpr and PIP2 expression and
response to AQP blockage are consistent with the hypothesis that
Lpr changes are mediated, at least in part, by changes in PsPIP2-1
expression.
Inconsistencies with ABA data may have been due to more
complex interactions of ABA with AQP channels.
Sumber: http://jxb.oxfordjournals.org/content/58/6/1291.abstract?sid=90319c95-0a26-45b1-9299a9e8e7d25f62 …. Diunduh 8/5/2012
. Environmental relevance of heavy metal-substituted chlorophylls using the example of
water plants
Hendrik Küpper, Frithjof Küpper and Martin Spiller
J. Exp. Bot. (1996) 47 (2): 259-266.
. Following experiments which studied the substitution of the central ion of isolated
chlorophylls by heavy metal ions in vitro, in vivo experiments with submersed water
plants were carried out. It was discovered that the substitution of the central atom of
chlorophyll, magnesium, by heavy metals (mercury, copper, cadmium, nickel, zinc,
lead) in vivo is an important damage mechanism in stressed plants. This substitution
prevents photosynthetic light-harvesting in the affected chlorophyll molecules,
resulting in a breakdown of photosynthesis. The reaction varies with light intensity. In
low light irradiance all the central atoms of the chlorophylls are accessible to heavy
metals, with heavy metal chlorophylls being formed, some of which are much more
stable towards irradiance than Mg-chlorophyll. Consequently, plants remain green
even when they are dead. In high light, however, almost all chlorophyll decays,
showing that under such conditions most of the chlorophylls are inaccessible to heavy
metal ions.
Sumber: http://jxb.oxfordjournals.org/content/47/2/259.abstract?sid=8b94415c-95a0-42d8-8b5a283b72a48f10…. Diunduh 8/5/2012
. Water channels in Chara corallina
Kerstin Schütz and Stephen D. Tyerman
J. Exp. Bot. (1997) 48 (8): 1511-1518.
. Water relations parameters ofChara
corallina inter-nodes were measured
using the single cell pressure probe.
The effect of mercurials, which are
recognized as non-specific water channel
inhibitors, was examined.
. HgCl2 concentrations greater than 5 mmol m−3 were found to inhibit hydraulic
conductivity {Lp) close to 90%, whereas pCMPS was found to have no effect on Lp. The
activation energy of water flow was increased significantly from 21.0 kJ mol−1 to 45.6 kJ
mol−1, following the application of HgCl2.
These results are in accordance with evidence for Hg2+sensitive water channels in the
plasma membrane of charophytes (Henzler and Steudle, 1995; Tazawa et al., 1996).
The metabolic effects must, however, be considered in view of the rapid inhibition of
respiration and the depolarization of the membrane potential with HgCl2
concentrations lower than those found to affect Lp. It was possible to measure
simultaneously water relations and membrane PD, in order to examine the
contribution of potassium channels to Lp. Cells were induced into a K+ permeable
state.
The K+ channels, assumed to be open, were subsequently blocked by various blockers.
No significant difference in Lp was found for any of these treatments. Finally, the
permeability of C. corallina membranes to ethanol was examined.
HgCl2 was found to cause a decrease in reflection coefficient, coinciding with a
decrease in Lp, but there was no change in the ethanol permeability coefficient. This
has been interpreted in terms of both the frictional model and composite model of
non-electrolyte membrane transport.
Sumber: http://jxb.oxfordjournals.org/content/48/8/1511.abstract?sid=8b94415c-95a0-42d8-8b5a283b72a48f10…. Diunduh 8/5/2012
Phytoremediation of mercury-contaminated mine wastes : a thesis presented in partial fulfilment of the
requirements for the degree of Doctor of Philosophy in Soil Science, Massey University, Palmerston North
Morena, Fábio Netto
http://hdl.handle.net/10179/1746
Date: 2004.
Mercury (Hg) is a toxic heavy metal that is concentrated in organisms. Injudicious use of Hg and its
compounds have resulted in widespread soil contamination.
This study investigates the potential use of plants for the remediation of Hg-contaminated mine wastes.
Plants can remove soil Hg via phytoextraction and phytovolatilisation. I investigated both of these strategies
by focusing on a methodology for Hg analyses in plants and soils with a view to the determination of
volatile Hg emitted from plants. Secondly, I determined the feasibility of Hg phytoextraction and
phytovolatilisation from contaminated mine wastes. An accurate method for the analysis of Hg in air, plant
and various soil fractions was a key component of this study. I developed a hydride-generation atomic
absorption spectroscopy method for total Hg analyses in digest and liquid matrices of the aforementioned
samples. Quality assurance was ensured by comparing results with those of an external certified laboratory.
The maximum discrepancy was 15 %. To measure plant Hg-volatilisation, a method that captures Hg-vapour
in solution for subsequent analyses was developed. Initially this system was used to trap Hg vapours
released from the root system of Brassica juncea plants grown in hydroponic solutions. A subsequent study
improved the Hg trapping system, allowing the capture of volatile Hg from both roots and shoots. Mercury
recoveries from the whole plant system (traps + plant + solutions) averaged 90 % using this experimental
apparatus. In most contaminated substrates, plant Hg uptake is insignificant, possibly due to the low
bioavailability of Hg. This represents an obstacle for effective remediation using phytoextraction.
Geochemical studies were carried out in Hg-contaminated substrates to examine the potential of chemical
agents to induce Hg solubility and subsequent plant uptake. These studies utilised Hg-contaminated mine
tailings collected from three locations: the Tui base-metal mine, in the North Island of New Zealand, the
Gold Mountain mine, in North-Central China and, the Serra Pelada artisanal mine site, in Northern Brazil.
The results demonstrated that Hg solubility in all tested substrates is increased in the presence of sulphurcontaining chemical ligands. The effectiveness of these ligands was influenced by site-specific geochemistry.
Plants species were able to accumulate up to 60 mg/kg of Hg in shoot tissues upon addition of sulphurcontaining ligands to Tui and Gold Mountain substrates. The degree of plant-Hg accumulation was shown to
be dependant on plant species and on the thioligand-induced soluble Hg fraction. Shoot Hg transport was
inhibited for Gold Mountain substrate amended with 1.25g/kg of humic acid. The maximum Hg extraction
yield for B. juncea plants growing in Tui field sites averaged 25 g per hectare following application of sodium
thiosulphate. Volatilisation of Hg vapour from barren substrates occurred as a result of biotic
(microorganisms) and abiotic (chemical and photochemical reduction) processes. The presence of B. juncea
plants in substrates enhanced the volatilisation process up to 23 fold.
Phytovolatilisation was the dominant pathway responsible for between 75 to 99.5 % of the total Hg
removed from substrates. It was concluded that Hg removal from contaminated mine wastes can be
accomplished by both thioligand-induced phytoextraction and phytovolatilisation. There are risks of
groundwater contamination by Hg species mobilised after application of thioligands to substrates.
Estimated Hg (0) emissions from plant-based operations at contaminated sites ranged between 1.5 to 3.6 kg
of Hg/ha per year. Due to extensive atmospheric dilution, Hg emissions from small-scale phytoremediation
operations would not cause serious harm to the local population or the regional environment.
Phytoremediation combined with gold-phytoextraction can help to mitigate Hg-pollution in artisanal mine
sites in the developing world.
. Accumulation of Mercury in Selected Plant Species Grown in Soils Contaminated With
Different Mercury Compounds
Yi Su , Fengxiang Han, and Safwan Shiyab
The 11th International Conference on Environmental Remediation and Radioactive Waste Management
(ICEM2007) . September 2–6, 2007 , Bruges, Belgium
The objective of our research is to screen and search for suitable plant species for phytoremediation
of mercury-contaminated soil. Currently our effort is specifically focused on mercury removal from
the U.S. Department of Energy (DOE) sites, where mercury contamination is a major concern. In order
to cost effectively implement mercury remediation efforts, it is necessary now to obtain an improved
understanding of biological means of removing mercury and mercury compounds
Phytoremediation is a technology that uses various plants to degrade, extract, contain, or immobilize
contaminants from soil and water. In particular, phytoextraction is the uptake of contaminants by
plant roots and translocation within the plants to shoots or leaves. Contaminants are generally
removed by harvesting the plants. We have investigated phytoextraction of mercury from
contaminated soil by using some of the known metal-accumulating plants since no natural plant
species with mercury hyperaccumulating properties has yet been identified. Different natural plant
species have been studied for mercury uptake, accumulation, toxicity and overall mercury removal
efficiency. Various mercury compounds, such as HgS, HgCl2, and Hg(NO3)2, were used as contaminant
sources. Different types of soil were examined and chosen for phytoremediation experiments. We
have applied microscopy and diffuse reflectance spectrometry as well as conventional analytical
chemistry to monitor the phytoremediation processes of mercury uptake, translocation and
accumulation, and the physiological impact of mercury contaminants on selected plant species. Our
results indicate that certain plant species, such as beard grass (Polypogon monospeliensis),
accumulated a very limited amount of mercury in the shoots (<65 mg/kg), even though root mercury
accumulation is significant (maximum 2298 mg/kg). Consequently, this plant species may not be
suitable for mercury phytoremediation. Other plant species, such as Indian mustard (Brassica juncea),
a well-studied metal accumulator, exhibited severe chlorosis symptoms during some experiments.
Among all the plant species studied, Chinese brake fern (Pteris vittata) accumulated significant
amount of mercury in both roots and shoots and hence may be considered as a potential candidate
for mercury phytoextraction. During one experiment, Chinese brake ferns accumulated 540 mg/kg
and 1469 mg/kg in shoots after 18 days of growing in soils treated with 500 parts-per-million (ppm)
and 1000 ppm HgCl2 powder, respectively; no visual stress symptoms were observed. We also studied
mercury phytoremediation using aged soils that contained HgS, HgCl2, or Hg(NO3)2. We have found
that up to hundreds of ppm mercury can be accumulated in the roots of Indian mustard plants grown
with soil contaminated by mercury sulfide; HgS is assumed to be the most stable and also the
predominant mercury form in floodplain soils. We have also started to investigate different mercury
uptake mechanisms, such as root uptake of soil contaminant and foliar mercury accumulation from
ambient air. We have observed mercury translocation from roots to shoot for Chinese fern and two
Indian mustard varieties.
Sumber:
http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=ASMECP002007043390001001000001&i
dtype=cvips&gifs=yes&ref=no…. Diunduh 8/5/2012
Mercury Detoxification with Transgenic Plants and Other Biotechnological Breakthroughs
for Phytoremediation
Clayton L. Rugh
In Vitro Cellular & Developmental Biology. Plant
Vol. 37, No. 3 (May - Jun., 2001), pp. 321-325
. Phytoremediation, or the use of plants for removal and detoxification of
environmental pollutants, has garnered great attention in recent years. This
heightened interest is both scientifically, due the fascinating processes utilized by
plants for tolerance and removal of harmful compounds, and commercially, as plants
represent a more environmentally compatible and less expensive method of site
remediation compared to standard approaches. The majority of phytoremediation
studies have been with naturally occurring plant species after empirical discovery of
their exceptional abilities for such applications. This has led to a growing body of
literature and wider acceptance for plants in many aspects of environmental
rehabilitation. However, this has occurred with little understanding of their basic
biological mechanisms of action or investigation of alternative strategies for enhancing
the capabilities of these extraordinary plants. Better understanding of plant physiology,
biochemistry and molecular biology in response to specific contaminants is critical for
optimization and advancement of phytoremediation. By applying the tools of
biotechnology, the potential for plants as an aggressive method of environmental
decontamination may be realized. This paper will serve as an introduction to the first
Symposium assembled exclusively to review the use of molecular genetic and
biotechnological methods for improvement of plants for phytoremediation. After a
brief review of the other invited speakers' works (with more extensive papers
following), the pioneering work using bacterial genes expressed in plants for removal
of mercurial compounds will be surveyed.
Sumber:
http://www.jstor.org/discover/10.2307/4293468?uid=3738224&uid=2129&uid=2&uid=70&uid=4&sid=561
50158803…. Diunduh 8/5/2012
. Journal of Soil Contamination . Volume 7, Issue 4, 1998. pages 497-509
Phytoremediation of Mercury- and Methylmercury-Polluted Soils Using Genetically
Engineered Plants
Andrew C. P. Heatona, Clayton L. Rughb, Nian-jie Wangb & Richard B. Meagherb
Inorganic mercury in contaminated soils and sediments is relatively immobile, though
biological and chemical processes can transform it to more toxic and bioavailable
methylmercury. Methylmercury is neurotoxic to vertebrates and is biomagnified in
animal tissues as it is passed from prey to predator. Traditional remediation strategies
for mercury contaminated soils are expensive and site-destructive. As an alternative
we propose the use of transgenic aquatic, salt marsh, and upland plants to remove
available inorganic mercury and methylmercury from contaminated soils and
sediments. Plants engineered with a modified bacterial mercuric reductase gene,
merA, are capable of converting Hg(II) taken up by roots to the much less toxic Hg(0),
which is volatilized from the plant. Plants engineered to express the bacterial organomercurial lyase gene, merB, are capable of converting methylmercury taken up by
plant roots into sulfhydryl-bound Hg(II). Plants expressing both genes are capable of
converting ionic mercury and methylmercury to volatile Hg(0) which is released into an
enormous global atmospheric Hg(0) pool. To assess the phytoremediation capability of
plants containing the merA gene, a variety of assays were carried out with the model
plants Arabidopsis thaliana, and tobacco (Nicotiana tabacum).
Sumber: http://www.tandfonline.com/doi/abs/10.1080/10588339891334384…. Diunduh 8/5/2012
. Mercury in Plants from Fields Surrounding a Contaminated Channel of Ria de Aveiro,
Portugal
E. Pereiraa, C. Valeb, C. F. Tavaresa, M. Válegaa & A. C. Duarte
Soil and Sediment Contamination: An International Journal . Vol. 14, Issue 6, 2005. p. 571577.
. Samples of plants and soil were collected in March and June 1995 at 12 sites in fields
surrounding the Estarreja Channel (Ria de Aveiro), where the mercury-rich effluent of a
chlor-alkali plant has been discharged since the 1950s. Mercury concentrations in soil
ranged from 0.64 to 182 μ g g−1. The highest values were attributed to soil
contaminated with sediments dredged from the Estarreja Channel. Plant roots
contained between 0.03 and 3.2 μ g g−1 of total mercury, and there is evidence that
root systems uptake mercury from the soil. The linear relationship between mercury
concentrations in the roots of Holcus lanatus and in soil over a wide range of mercury
concentrations suggests that mercury uptake depends on the element's concentration
in the soil. The ratio root:soil concentrations for the analyzed plants varied between
0.003 and 0.199, indicating varying mercury uptake by the root systems. Levels of
mercury in the aerial parts of plants showed no clear relationship with the values
found in soil or in roots, presumably being influenced mostly by the atmospheric
deposition of airborne particles or absorption of atmospheric mercury.
Sumber: http://www.tandfonline.com/doi/abs/10.1080/15320380500263774…. Diunduh 8/5/2012
Bioaccessibility of Mercury in Soils
Mark O. Barnetta & Ralph R. Turnera
Soil and Sediment Contamination: An International Journal . Vol. 10, Issue 3, 2001
p. 301-316
. The initial risk assessment for the East Fork Poplar Creek (EFPC) floodplain in Oak
Ridge, Tennessee, a superfund site heavily contaminated with mercury, was based on a
reference dose for mercuric chloride. Mercuric chloride, however, is a soluble mercury
compound not expected to be present in the floodplain, which is frequently saturated
with water. Previous investigations had suggested mercury in the EFPC floodplain was
less soluble and therefore potentially less bioavailable than mercuric chloride, possibly
making the results of the risk assessment unduly conservative. A bioaccessibility study,
designed to measure the amount of mercury available for absorption in a child's
digestive tract (the most critical risk pathway endpoint), was performed on 20 soils
from the EFPC floodplain. The average bioac-cessible mercury for the 20 soils was
5.3%, compared with 100% of the mercuric chloride subjected to the same conditions.
The alteration of the procedure to more closely mimic conditions in the digestive tract
did not significantly change the results. Therefore, the use of a reference dose for
mercuric chloride at EFPC, and potentially at other mercury-contaminated sites,
without incorporating a corresponding bioavailability adjustment factor may
overestimate the risk posed by the site.
Sumber: http://www.tandfonline.com/doi/abs/10.1080/20015891109275…. Diunduh 8/5/2012
Screening and Thermal Desorption for Remediation of a Sediment Polluted by the Mercury
of a Chlor-Alkaly Plant
Andrea Manni, Paolo Massacci, Luigi Piga & Silvia Serranti
Soil and Sediment Contamination: An International Journal. Vol. 13, Issue 4, 2004
p. 391-404
Thermal desorption tests were performed on samples taken from a mercury polluted
sediment (133 mg/kg) in the vicinity of a chlor-alkali plant that has been operating
over a long period using mercury cathodes.
After characterization of
the sediment, by means
of TGA/DTA, SEM, XRD
and chemical analysis,
the material was
screened into various
size-fractions. Chemical
analysis showed that
only the finest sizefractions had a mercury
content above the
regulatory limit (5
mg/kg) established for
areas destined for
industrial installations.
Thermal desorption tests were applied on the finest size-sediment fractions at
furnace temperatures between 300°C and 400°C and solids residence times between
3 minutes and 120 minutes.
After 3 minutes at 400°C, the treated sediment residue had a mercury content below
the regulatory limit.
The short solid residence time and the low desorption temperature required to meet
the treatment standards would permit the use of a continuous thermal desorption
treatment process in a rotatory dryer, providing that the values of residence times
obtained by the lab-scale plant are suitable for a larger scale plant.
Sumber: http://www.tandfonline.com/doi/abs/10.1080/10588330490466003…. Diunduh 8/5/2012
Mercury translocation in and evaporation from soil. III. quantification of evaporation of
mercury from podzolized soil profiles treated with Hg Cl
K. Schlüter, H. M. Seip & J. Alstad. Journal of Soil Contamination . Vol. 5, Issue 2, 1996 .
pages 121-139.
Mercury evaporation from undisturbed iron‐humus podzol lysimeters was measured
over 3 months after treatment with HgCl2 spiked with radioactive 203Hg.
The relative evaporation rate
from HgCl2 treated soils followed
the sum of two exponential
functions. Because evaporation
asymptotically approaches zero
with time, the integral of the fit
curve represents the evaporative
loss in percent of atmospheric
deposition. For the soil
investigated, about 5% of
atmospheric Hg deposition was
reemitted into the atmosphere.
It is hypothesized that mercury
evaporation can decrease the
leaching of mercury in and from
soil significantly; this effect is
probably increasing with
decreasing rain acidity or soil
acidity.
Mercury deposited as soluble
salt remains susceptible to
reemission to air for 300 d after
incorporation into the soil
matrix.
Indications are found that Hg evaporation from soils in geological background areas
predominantly derives from recent atmospheric Hg deposition and not from geological
sources.
Sumber: http://www.tandfonline.com/doi/abs/10.1080/15320389609383518…. Diunduh 8/5/2012
Mercury translocation in and evaporation from soil. I. soil lysimeter experiments with
203Hg‐radiolabeled compounds
K. Schlüter, J. Alstad & H. M. Seip
Journal of Soil Contamination . Vol. 4, Issue 4, 1995 . pages 327-353
Due to a considerable increase of anthropogenic mercury emissions, the mercury load
of many soils has risen significantly, for instance in northern Europe. Understanding
the fate of mercury in soils is a prerequisite for assessing the effects of ecotoxicological
concern.
. This paper presents a method for
obtaining qualitative and quantitative
information about mercury
translocation in and evaporation from
soil. Soil lysimeters were treated with
203Hg‐labeled HgCl and CH HgCl and
2
3
irrigated with artificial rain.
It was demonstrated that the leaching of
Hg can be detected by measuring the
relative y‐activity throughout the soil
profile by means of Na(TI)I detectors.
Furthermore, the set‐up was designed
to allow detection of Hg volatilization
from soil by using traps of iodized
charcoal, followed by a potassium
peroxodisulfate solution and measuring
the γ‐activity. The amount of radioactive
Hg in soil leachate was measured by a
Na(Tl)I well‐type detector after
upconcentration.
The determination of monomethyl 203Hg was been performed by extraction
procedures that isolate the methyl mercury compounds.
The amount of 203Hg retained in the soil profile and the real depth of leaching were
determined by stratifying the soil profile at the end of the experiment and measuring
the y‐activity.
With control of all pathways of Hg, the experimental design allows performance of a
mass balance analysis.
Sumber: http://www.tandfonline.com/doi/abs/10.1080/15320389509383504 …. Diunduh 8/5/2012
Mercury translocation in and evaporation from soil. I. soil lysimeter experiments with
203Hg‐radiolabeled compounds
K. Schlüter, J. Alstad & H. M. Seip
. Journal of Soil Contamination . Vol. 4, Issue 4, 1995 . pages 327-353
Due to a considerable increase of anthropogenic mercury emissions, the mercury load
of many soils has risen significantly, for instance in northern Europe. Understanding
the fate of mercury in soils is a prerequisite for assessing the effects of ecotoxicological
concern.
This paper presents a method for
obtaining qualitative and quantitative
information about mercury translocation
in and evaporation from soil. Soil
lysimeters were treated with
203Hg‐labeled HgCl and CH HgCl and
2
3
irrigated with artificial rain. It was
demonstrated that the leaching of Hg can
be detected by measuring the relative
y‐activity throughout the soil profile by
means of Na(TI)I detectors. Furthermore,
the set‐up was designed to allow
detection of Hg volatilization from soil by
using traps of iodized charcoal, followed
by a potassium peroxodisulfate solution
and measuring the γ‐activity. The amount
of radioactive Hg in soil leachate was
measured by a Na(Tl)I well‐type detector
after upconcentration. The
determination of monomethyl 203Hg was
been performed by extraction
procedures that isolate the methyl
mercury compounds.
The amount of 203Hg retained in the soil profile and the real depth of leaching were
determined by stratifying the soil profile at the end of the experiment and measuring
the y‐activity. With control of all pathways of Hg, the experimental design allows
performance of a mass balance analysis.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/15320389509383504?prevSearch=mercury&searchHistoryK
ey= …. Diunduh 8/5/2012
ADSORPTION/DESORPTION AND FATE OF MERCURY (II) BY TYPICAL BLACK SOIL AND RED
SOIL IN CHINA
Jia Liu, Jiulan Dai, Renqing Wang, Fasheng Li, Xiaoming Du & Wenxing Wang
Soil and Sediment Contamination: An International Journal. Vol. 19, Issue 5, 2010 . pages
587-601.
Rapid industrial development in the old northeastern industrial region of China
resulted in Hg pollution.
A series of batch experiments
were conducted to assess the
adsorption/ desorption and
transfer of Hg (II) within typical
black soil in this region and
typical red soil in south China as
a comparison: both are typical
soils in China.
It was found that both soils had
high affinity for Hg (II) and the
absorbed amount was more than
95% of the added.
Hg (II) adsorption isotherms
were well fitted with the
Langmuir and Freundlich
equations. The affinity of Hg (II)
for black soil was three times
higher than that of red soil.
Results demonstrated that soil organic matter had an important role in Hg (II)
adsorption. Fifty-three and twenty-eight percent of the maximum sorption amount for
Hg (II) was contributed by organic matter for black soil and red soil, respectively.
Kinetic studies showed that Hg adsorption on both soils was characterized by a
biphasic pattern, with a fast step followed by a slow step. Black soil completed 90% of
total Hg (II) adsorption in 34 min and reached equilibrium in 321 min, compared to 91
min and 630 min on red soil, respectively.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/15320383.2010.499925?prevSearch=mercury&searchHistor
yKey= …. Diunduh 8/5/2012
The influence of pH and chloride on the retention of cadmium, lead, mercury, and zinc by
soils
David G. Lumsdon, Leslie J. Evans & Kim A. Bolton
. Journal of Soil Contamination. Vol. 4, Issue 2, 1995. pages 137-150
The extent of contamination of soils by toxic heavy metals not only depends on the
rate of loading of the metal but also on the nature of the adsorbing surfaces, the
degree of alkalinity or acidity of the soil and the presence of aqueous complexant
ligands.
This work reports on the role of pH on the retention of Cd, Hg, Pb and Zn
by two soils and on the influence of the chloride, Cl‐, ion on the chemical
speciation and retention of the four metals. Batch adsorption
experiments were conducted from pH 3 to 7 in the presence of either 0.1
M LiCl or LiClO4.
The results of the study showed that high concentrations of Cl‐ ions can greatly
decrease the retention of Hg and have an increasingly lesser effect on Cd, Pb and Zn
retention. The effect of the Cl‐ons was directly related to the metal‐Cl formation
constants.
The results of computer modeling of Cd and Hg retention by goethite and humic acid
fractions indicated the relative importance of aqueous vs. surface complexation on
metal retention. For organic surfaces, which do not form ternary surface complexes,
the presence of aqueous complexant ligands should always decrease the adsorption of
the metal. For mineral surfaces, which do form ternary surface complexes, there may
be increased or decreased metal retention depending on the formation constant of the
aqueous metal‐ligand species, the intrinsic complexation constants for the various
binary and ternary complexes of the metal and the concentration of the complexant
ligand. Thus for Hg, which forms very strong aqueous species with Cl‐ ions, reduced
adsorption on goethite was predicted in the presence of 0.1 M LiCl, while enhanced
adsorption was predicted for Cd and Pb. The results suggest caution in the disposal of
Cl‐containing wastes onto metal‐contaminated soils. The deleterious effects of Cl‐ ion
addition would be greatest for soils with relatively high organic matter contents and
low contents of hydrous ferric oxides.
Sumber: http://www.tandfonline.com/doi/abs/10.1080/15320389509383488 …. Diunduh 8/5/2012
Brassicaceae (Cruciferae) Family, Plant Biotechnology, and Phytoremediation
Constantine E. Palmer, Suzanne Warwick & Wilf Keller.
International Journal of Phytoremediation . Vol. 3, Issue 3, 2001 . pages 245-287
. Plants represent a natural environmentally safe way to clean or remediate
contaminated sites. Members of the Brassicaceae or Cruciferae plant family have a key
role in phytoremediation technology. Many wild crucifer species are known to
hyperaccumulate heavy metals and possess genes for resistance or tolerance to the
toxic effects of a wide range of metals.
Metal uptake, sensitivity, and sequestration have been studied extensively in
Arabidopsis thaliana, and a number of heavy metal-sensitive and ion-accumulating
mutants have been identified. This species is a likely source of genes for
phytoremediation. Within the Brassicaceae, Brassica and other crop species are likely
candidates for phytoremediation.
There is a wealth of information on the agronomics of the economically important
members and biomass production can be extensive. Many of these species are well
adapted to a range of environmental conditions. Some species are tolerant to high
levels of heavy metals, and there is the potential to select superior genotypes for
phytoremediation. They are well suited to genetic manipulation and in vitro culture
techniques and are attractive candidates for the introduction of genes aimed at
phytoremediation.
Biotechnology and molecular biology are valuable tools for studies of
metal accumulation and tolerance in hyperaccumulating species and for
the transfer of relevant genes into crucifer species suitable for
phytoremediation.
The purpose of this article is to review the potential use of both wild
and cultivated members of the Brassicaceae in phytoremediation.
Sumber: http://www.tandfonline.com/doi/abs/10.1080/15226510108500059 …. Diunduh 8/5/2012
TRANSGENIC PLANTS FOR PHYTOREMEDIATION
Elena Maestri & Nelson Marmiroli
International Journal of Phytoremediation . Vol. 13, Supplement 1, 2011 .pages 264-279
Phytoremediation is a green, sustainable and promising solution to problems of
environmental contamination. It entails the use of plants for uptake, sequestration,
detoxification or volatilization of inorganic and organic pollutants from soils, water,
sediments and possibly air. Phytoremediation was born from the observation that
plants possessed physiological properties useful for environmental remediation. This
was shortly followed by the application of breeding techniques and artificial selection
to genetically improve some of the more promising and interesting species. Now, after
nearly 20 years of research, transgenic plants for phytoremediation have been
produced, but none have reached commercial existence.
Three main approaches have been developed:
(1) transformation with genes from other organisms (mammals, bacteria,
etc.); (2) transformation with genes from other plant species; and (3)
overexpression of genes from the same plant species.
Many encouraging results have been reported, even
though in some instances results have been contrary to
expectations.
This review will illustrate the main examples with a critical
discussion of what we have learnt from them.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/15226514.2011.568549?prevSearch=mercury%2Bphytorem
ediation&searchHistoryKey= …. Diunduh 8/5/2012
International Journal of Phytoremediation . Vol. 12, Issue 6, 2010. pages 586-598
Growth Response and Tissue Accumulation Trends of Herbaceous Wetland Plant Species
Exposed to Elevated Aqueous Mercury Levels
Jonathan M. Willis, Robert P. Gambrell & Mark W. Hester
The impacts of elevated aqueous mercury levels (0, 2, and 4 ppm) on the growth
status and mercury tissue concentrations of Eleocharis parvula, Saururus cernuus,
Juncus effuses, Typha latifolia, and Panicum hemitomon were determined.
Both short-term (net CO2 assimilation) and long-term (biomass) indicators of
plant growth status suggest that Eleocharis parvula, Saururus cernuus, and
Juncus effuses were relatively unimpacted by elevated mercury levels, whereas
Typha latifolia and Panicum hemitomon were somewhat impacted at elevated
mercury levels.
Eleocharis parvula, Panicum hemitomon, and Typha latifolia generally had the
greatest overall belowground tissue concentrations of mercury (2 ppm
treatment: 7.21, 7.32, and 9.64 ppm respectively; 4 ppm treatment: 16.23,
18.23, and 13.98 ppm, respectively) and aboveground tissue concentrations of
mercury (2 ppm treatment: 0.01, 0.04, 0.02; 4 ppm treatment: 0.26; 0.11; 0.17
ppm, respectively).
However, the species investigated in this study demonstrated lower levels of
mercury accumulation into tissues when compared with similar investigations
of other aquatic plants, suggesting that the above species are not optimal for
phytoremediation efforts.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/15226510903390460?prevSearch=mercury%2Bphytoremedi
ation&searchHistoryKey= …. Diunduh 8/5/2012
. International Journal of Environmental Studies . Vol. 64, Issue 2, 2007 pages 189-194
Accumulation of mercury by the aquatic plant Lemna minor
Rachel Isaksson, Steven J. Balogh & Michael A. Farris
. We hypothesized that Lemna minor (Lemnaceae) would
sequester mercury occurring at environmentally relevant
concentrations in aquatic systems.
Lake water was collected from Cedar Lake, Minnesota, USA and added to 18
experimental containers placed in an environmental chamber set to replicate summer
growth conditions. Different amounts of mercury (Hg2+) were added to 12
experimental containers, resulting in final aquatic mercury concentrations of 1.7 ng/L
Hg (control), 112 ng/L Hg (low Hg treatment), and 270 ng/L Hg (high Hg treatment).
Nutrients and two grams of L. minor were added to 700 mL of lake water in each
container. Plant mercury concentrations were assayed before and after the 14‐day
experiment. Total mercury was determined by cold vapor atomic fluorescent
spectrometry with single gold trap amalgamation.
Mean plant tissue mercury concentrations were significantly
higher in both treatments than in the control containers (p <
0.0001).
The concentration of mercury in the plant material was
positively correlated with the concentration of the mercury in
the water.
The ability of L. minor to sequester mercury within its biomass
makes it a potential candidate for use in phytoremediation in
waters with realistic levels of mercury contamination.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/00207230701238556?prevSearch=mercury%2Bphytoremedi
ation&searchHistoryKey= …. Diunduh 8/5/2012
International Journal of Phytoremediation
Volume 10, Issue 2, 2008
Heavy Metal Pollution in Aquatic Ecosystems and its Phytoremediation using Wetland
Plants: An ecosustainable approach
PreviewView full textDownload full textFree access
DOI:10.1080/15226510801913918Prabhat Kumar Raia
pages 133-160
.
. This review addresses the global problem of heavymetal pollution originating from increased
industrialization and urbanization and its amelioration by using wetland plants both in a microcosm as
well as natural/field condition. Heavymetal contamination in aquatic ecosystems due to discharge of
industrial effluents may pose a serious threat to human health. Alkaline precipitation, ion exchange
columns, electrochemical removal, filtration, and membrane technologies are the currently available
technologies for heavy metal removal. These conventional technologies are not economical and may
produce adverse impacts on aquatic ecosystems. Phytoremediation of metals is a cost-effective
“green” technology based on the use of specially selected metal-accumulating plants to remove toxic
metals from soils and water. Wetland plants are important tools for heavy metal removal. The Ramsar
convention, one of the earlier modern global conservation treaties, was adopted at Ramsar, Iran, in
1971 and became effective in 1975. This convention emphasized the wise use of wetlands and their
resources. This review mentions salient features of wetland ecosystems, their vegetation component,
and the pros and cons involved in heavy metal removal. Wetland plants are preferred over other bioagents due to their low cost, frequent abundance in aquatic ecosystems, and easy handling. The
extensive rhizosphere of wetland plants provides an enriched culture zone for the microbes involved
in degradation. The wetland sediment zone provides reducing conditions that are conducive to the
metal removal pathway. Constructed wetlands proved to be effective for the abatement of
heavymetal pollution from acid mine drainage; landfill leachate; thermal power; and municipal,
agricultural, refinery, and chlor-alkali effluent. the physicochemical properties of wetlands provide
many positive attributes for remediating heavy metals. Typha, Phragmites, Eichhornia, Azolla, Lemna,
and other aquatic macrophytes are some of the potent wetland plants for heavy metal removal.
Biomass disposal problem and seasonal growth of aquatic macrophytes are some limitations in the
transfer of phytoremediation technology from the laboratory to the field. However, the disposed
biomass of macrophytes may be used for various fruitful applications. An ecosustainable model has
been developed through the author's various works, which may ameliorate some of the limitations.
The creation of more areas for phytoremediation may also aid in wetlands conservation. Genetic
engineering and biodiversity prospecting of endangered wetland plants are important future
prospects in this regard.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/15226510801913918?prevSearch=mercury%2Bphytoremedi
ation&searchHistoryKey= …. Diunduh 8/5/2012
. International Journal of Phytoremediation
Volume 10, Issue 6, 2008
Phytoextraction and Accumulation of Mercury in Three Plant Species: Indian Mustard
(Brassica Juncea), Beard Grass (Polypogon monospeliensis), and Chinese Brake Fern (Pteris
vittata)
PreviewBuy now
DOI:10.1080/15226510802115091Yi Sua, Fengxiang X. Hanb, Jian Chenb, B. B. Maruthi
Sridharc & David L. Montsa
pages 547-560
. The objective of this research was to screen and search for suitable plant species to
phytoextract mercury-contaminated soil. Our effort focused on using some of the
known metal-accumulating wild-type plants since no natural plant species with
mercury-hyperaccumulat ing properties has yet been identified. Three plant species
were evaluated for their uptake efficiency for mercury: Indian mustard (Brassica
juncea), beard grass (Polypogon monospeliensis), and Chinese brake fern (Pteris
vittata). Four sets of experiments were conducted to evaluate the phytoremediation
potential of these three plant species: a pot study with potting mix where mercury was
provided daily as HgCl2 solution; experiments with freshly mercury-spiked soil; and a
study with aged soils contaminated with different mercury sources (HgCl2, Hg(NO3)2,
and HgS). Homemade sunlit chambers were also used to study foliar uptake of Hg from
ambient air. Among the three plant species, Chinese brake fern showed the least stress
symptoms resulting from mercury exposure and had the highest mercury
accumulation. Our results indicate that Chinese brake fern may be a potential
candidate for mercury phytoextraction. We found that mercury contamination is
biologically available for plant uptake and accumulation, even if the original and
predominating mercury form is HgS, and also after multiple phytoremediation cycles.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/15226510802115091?prevSearch=mercury%2Bphytoremedi
. International Journal of Phytoremediation
Volume 10, Issue 5, 2008
Technical Note: Phytoremediation of Hg and Cd from Industrial Effluents using an Aquatic
Free Floating Macrophyte Azolla Pinnata
PreviewView full textDownload full textFree access
DOI:10.1080/15226510802100606Prabhat Kumar Raia
pages 430-439
. The level of heavy metal pollution in Singrauli, an industrial region in India, was
assessed and the phytoremediation capacity of a small water fern, Azolla pinnata R.Br
(Azollaceae), was observed to purify waters polluted by two heavy metals, i.e., mercury
(Hg) and cadmium (Cd) under a microcosm condition. Azolla pinnata is endemic to
India and is an abundant and easy-growing free-floating water fern usually found in the
rice fields, polluted ponds, and reservoirs of India. The fern was grown in 24 40-L
aquariums containing Hg2+ and Cd2+ ions each in concentrations of 0.5, 1.0, and 3.0
mgL−1 during the course of this study. The study revealed an inhibition of Azolla
pinnata growth by 27.0–33.9% with the highest in the presence of Hg (II) ions at 0.5
mgL−1 in comparison to the control. After 13 days of the experiment, metal contents in
the solution were decreased up to 70–94%. In the tissues of Azolla pinnata, the
concentration of selected heavy metals during investigation was recorded between
310 and 740 mgKg−1 dry mass, with the highest level found for Cd (II) treatment at 3.0
mgL−1 containing a metal solution.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/15226510802100606?prevSearch=mercury%2Bphytoremedi
. International Journal of Phytoremediation
Volume 11, Issue 8, 2009
VETIVER GRASS, VETIVERIA ZIZANIOIDES: A CHOICE PLANT FOR PHYTOREMEDIATION OF
HEAVY METALS AND ORGANIC WASTES
PreviewBuy now
DOI:10.1080/15226510902787302Luu Thai Danha, Paul Truongb, Raffaella Mammucaria,
Tam Trana & Neil Fostera
pages 664-691
. Glasshouse and field studies showed that Vetiver grass can produce high biomass
(>100t/tha−1 year−1) and highly tolerate extreme climatic variation such as prolonged
drought, flood, submergence and temperatures (−15°–55°C), soils high in acidity and
alkalinity (pH 3.3–9.5), high levels of Al (85% saturation percentage), Mn (578 mg kg−1),
soil salinity (ECse 47.5 dS m−1), sodicity (ESP 48%), and a wide range of heavy metals
(As, Cd, Cr, Cu, Hg, Ni, Pb, Se, and Zn). Vetiver can accumulate heavy metals,
particularly lead (shoot 0.4% and root 1%) and zinc (shoot and root 1%). The majority
of heavy metals are accumulated in roots thus suitable for phytostabilization, and for
phytoextraction with addition of chelating agents. Vetiver can also absorb and
promote biodegradation of organic wastes (2,4,6-trinitroluene, phenol, ethidium
bromide, benzo[a]pyrene, atrazine). Although Vetiver is not as effective as some other
species in heavy metal accumulation, very few plants in the literature have a wide
range of tolerance to extremely adverse conditions of climate and growing medium
(soil, sand, and tailings) combined into one plant as vetiver. All these special
characteristics make vetiver a choice plant for phytoremediation of heavy metals and
organic wastes.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/15226510902787302?prevSearch=mercury%2Bphytoremedi
International Journal of Phytoremediation
Volume 9, Issue 1, 2007
Capability of Selected Crop Plants for Shoot Mercury Accumulation from Polluted Soils:
Phytoremediation Perspectives
Luis Rodriguez, Jesusa Rincón, Isaac Asencio & Laura Rodríguez-Castellanos. pages 1-13
. High-biomass crops can be considered as an alternative to hyperaccumulator plants
to phytoremediate soils contaminated by heavy metals. In order to assess their
practical capability for the absorption and accumulation of Hg in shoots, barley, white
lupine, lentil, and chickpea were tested in pot experiments using several growth
substrates. In the first experimental series, plants were grown in a mixture of
vermiculite and perlite spiked with 8.35 μg g–1 d.w. of soluble Hg. The mercury
concentration of the plants' aerial tissues ranged from 1.51 to 5.13 μg g–1 d.w. with
lentil and lupine showing the highest values. In a second experiment carried out using
a Hg-polluted soil (32.16 μg g–1 d.w.) collected from a historical mining area (Almadén,
Spain), the crop plants tested only reached shoot Hg concentration up to 1.13 μg g–1
d.w. In the third experimental series, the Almadén soil was spiked with 1 μg g–1 d.w. of
soluble Hg; as a result, mercury concentrations in the plant shoots increased
approximately 6 times for lupine, 5 times for chickpea, and 3.5 times for barley and
lentil, with respect to those obtained with the original soil without Hg added. This
marked difference was attributed to the low availability of Hg in the original Almadén
soil and its subsequent increase in the Hg-spiked soil. The low mercury accumulation
yields obtained for all plants do not make a successful decontamination of the
Almadén soils possible by phytoremediation using crop plants. However, since the
crops tested can effectively decrease the plant-available Hg level in this soil, their use
could, to some extent, reduce the environmental risk of Hg pollution in the area.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/15226510601139359?prevSearch=mercury%2Bphytoremedi
Communications in Soil Science and Plant Analysis
Volume 42, Issue 22, 2011
Mercury Mobilization in a Contaminated Industrial Soil for Phytoremediation
Francesca Pedron, Gianniantonio Petruzzelli, Meri Barbafieri, Eliana Tassi, Paolo Ambrosini &
Leonardo Patata. pages 2767-2777
. The aim of this work was to investigate the possibility of using plants for mercury (Hg)
removal from a contaminated industrial soil, increasing the metal's bioaccessibility by
using mobilizing agents: ammonium thiosulphate [(NH4)2S2O3] and potassium iodide
(KI). The selected plant species were Brassica juncea and Poa annua. The addition of
the mobilizing agents promoted Hg uptake by plants, with respect to controls.
Treatments promoted Hg translocation to aerial parts. In the case of Poa annua,
greater Hg uptake was found in plants after the 100 mM KI treatment, reaching values
that were nearly 400 mg kg−1 in the aerial part. In contrast, Brassica juncea plants
accumulated in their aerial part the greatest Hg quantities, about 100 mg kg−1, after
treatment with 0.27 M (NH4)2S2O3. The ratio between the concentration of Hg in the
shoots and the initial concentration in the soil support the potential for successfully
applying Hg phytoextraction on this soil.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/00103624.2011.622823?prevSearch=mercury%2Bphytorem
. International Journal of Phytoremediation
Volume 14, Issue 2, 2012
Phytoremediation of Mercury- and Methyl Mercury-Contaminated Sediments by Water
Hyacinth (Eichhornia crassipes)
Sandip Chattopadhyay, Ryan L. Fimmen, Brian J. Yates, Vivek Lal & Paul Randall. pages 142161
. Phytoremediation has the potential for implementation at mercury- (Hg) and
methylHg (MeHg)-contaminated sites. Water hyacinths (Eichhornia crassipes) were
investigated for their ability to assimilate Hg and MeHg into plant biomass, in both
aquatic and sediment-associated forms, over a 68-day hydroponic study. The suitability
of E. crassipes to assimilate both Hg and MeHg was evaluated under differing
phosphate (PO4) concentrations, light intensities, and sediment:aqueous phase
contamination ratios. Because aquatic rhizospheres have the ability to enhance MeHg
formation, the level of MeHg in water, sediment, and water hyacinth was also
measured.
Hg and MeHg were found to concentrate preferentially in the roots of E. crassipes with
little translocation to the shoots or leaves of the plant, a result consistent with studies
from similar macrophytes. Sediments were found to be the major sink for Hg as they
were able to sequester Hg, making it non-bioavailable for water hyacinth uptake. An
optimum PO4 concentration was observed for Hg and MeHg uptake. Increasing light
intensity served to enhance the translocation of both Hg and MeHg from roots to
shoots. Assimilation of Hg and MeHg into the biomass of water hyacinths represents a
potential means for sustainable remediation of contaminated waters and sediments
under the appropriate conditions.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/15226514.2010.525557?prevSearch=mercury%2Bphytorem
ediation&searchHistoryKey=…. Diunduh 8/5/2012
CHEMISTRY AND ECOLOGY . Volume 9, Issue 1, 1994
Removal of Mercury from Polluted Waters by the Water Hyacinth (Eichhornia crassipes)
Humberto González, Martin Lodenius & Lisette Martinez. pages 7-12
The uptake of mercury by water hyacinth (Eichhornia crassipes) was studied in an
outdoor experiment for 25 days at different metal concentrations.
The removal of mercury from the water and uptake by plants was very effective during
the first hours and decreased rapidly thereafter.
The uptake of mercury was directly proportional to the initial concentration in the
water.
The highest concentrations were found in plant roots.
According to the results, water hyacinth could be used for treatment of mercurial
waste waters.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/02757549408038558?prevSearch=Sandip%2BChattopadhya
Toxicological & Environmental Chemistry . Volume 11, Issue 2, 1986. p. 125-135
Lead uptake by Eichhornia Crassipes
Christine Heaton, John Frame & James K. Hardy
Factors influencing uptake of lead(II) by the water hyacinth (Eichhornia Crassipes),
were examined.
Two phases of uptake were observed for the concentration range investigated (0.01–
1000 ppm).
The initial, rapid uptake phase of about 4 hours is followed by a slower, near linear
phase extending past 24 hours. Stirring the solution enhanced uptake, suggesting that
lead removal is in part diffusion limited. In the range of 4–8, pH has little effect on
uptake where as outside this range, uptake is reduced. Increased solution volume or
rootmass results in more metal being removed by the plant. The presence of strong
complexers blocks the initial rapid uptake phase as does the presence of Zn(II), Cd(II),
Hg(II), and Fe(III). Strong complexers can also strip a portion of any lead already
removed from solution by the plant.
Sumber:
http://www.tandfonline.com/doi/abs/10.1080/02772248609357125?prevSearch=Sandip%2BChattopadhya
Glutathione-Ascorbate Cycle for Phytoremediation of Mercury by Eichhornia crassipes
(Mart.) Solms
Upma Narang, A.K. Thukral, Renu Bhardwaj, S.K. Garg
Japanese Journal of Environmental Toxicology
Vol. 11 (2008) No. 1 P 1-9
The activities of ascorbate peroxidase, glutathione reductase, dehydroascorbate
reductase, monodehydroascorbate reductase, and ascorbic acid and glutathione
contents increased in response to mercury accumulation in E. crassipes .
This enhancement in the glutathione-ascorbate Cycle components was observed in
response to mercury in solution up to a concentration of 100 μg l-1, whereas, at a
concentration of 1000 μg l-1 the enzyme activities decreased.
Roots accumulated maximum amount of Hg, and there was a significant positive
correlation between Hg accumulated and components of the glutathione-ascorbate
cycle in E. crassipes , during phytoremediation of mercury.
Sumber: https://www.jstage.jst.go.jp/article/jset/11/1/11_1_1/_article…. Diunduh 8/5/2012
Environmental and Experimental Botany 62 (2008) 78–85
Phytofiltration of mercury-contaminated water: Volatilisation and plant-accumulation
aspects
Fabio N. Morenoa, Christopher W.N. Anderson, Robert B. Stewart , Brett H. Robinson.
Phytofiltration may be a cost-effective approach for treating Hgcontaminated wastewater.
We investigated the removal of Hg from solutions by Indian mustard [Brassica juncea
(L.) Czern.] grown in hydroponic conditions with solutions containing Hg
concentrations from 0 to 10 mg/L. Plants were enclosed in gastight volatilisation
chambers to assess the effect of Hg concentrations on plant transpiration,
accumulation and volatilisation.
We also determined the speciation and site of origin of volatilised Hg.
Solution Hg concentrations of 5 and 10 mg/L detrimentally affected transpiration.
Roots concentrated Hg 100–270 times (on a dry weight basis) above initial solution
concentrations. The plants translocated little Hg to the shoots, which accounted for
just 0.7–2% of the total Hg in the plants.
Volatilisation from planted vessels increased linearly as a function of Hg concentrations
in solutions. Most Hg volatilisation occurred from the roots. Volatilised Hg was
predominantly in the Hg(0) vapour form.
Volatilisation was dependant on root uptake and absorption of Hg from the ambient
solution. Production of Hg(0) vapour in the solutions may result from the activity of
root-associated algae and Hg-resistant bacteria.
Phytofiltration effectively removed up to 95% of Hg from the contaminated solutions
by both volatilisation and plant accumulation. However, Hg(0) vapours released from
living roots may have unforeseen environmental effects.
Sumber: …. Diunduh 8/5/2012
Water, Air, & Soil Pollution. Volume 56, Number 1 (1991), 15-20.
Mercury in plants, soil and atmosphere near a chlor-alkali complex
B. E. Maserti and R. Ferrara
. Recent studies have shown that mercury (Hg) levels in many fish from remote lakes
exceed the recommended guidelines for human consumption. Most of these studies
conclude that the source of contamination lies in the atmosphere. Kejimkujik National
Park (KNP), Nova Scotia, Canada, is considered to be a pristine ecosystem in which fish
and loon Hg levels are anomalously high. Studies in the park have shown that
atmospheric Hg concentrations may not be high enough to account for the Hg levels in
the biota, indicating that the park may be an unusual system in terms of Hg
distribution and migration. In an attempt to summarise and synthesise the numerous
Hg data sets which have been produced in the park over the last 5-10 years, a
geographic information systems (GIS) approach was used to create a common
database using the watersheds in the park as the common parameter. By using a GIS
database, new relationships and correlations are established and the spatial
distribution of Hg levels is more readily evaluated and quantified. The results indicate
that geological sources of Hg, arising from biotite-rich granite rocks, may play a larger
role in the contamination of the park than previously thought.
Sumber: http://www.springerlink.com/content/n143r7138u856g31/ …. Diunduh 10/5/2012
Water, Air, & Soil Pollution. Volume 56, Number 1 (1991), 219-233.
Mercury in abiotic and biotic compartments of an area affected by a geochemical anomaly
(Mt. Amiata, Italy)
R. Ferrara, B. E. Maserti and R. Breder
. Data both from the literature and from our own research are reported on the Hg
levels in the soil, waters, sediment , atmosphere and some plants of the mineralized
Monte Amiata region (Italy) with the aim of evidencing the interactions between the
different environmental compartments.
The presence of cinnabar in the soil affects the whole area, particularly near the mines,
roasted cinnabar deposits and at the steam jets used for the geothermal power plants.
Soil degassing represents the main source of atmospheric Hg which shows a
concentration range of 5 to 200 ng m−3.
Vegetables display high Hg levels (0.06 to 9.80 µg g−1) especially in
the leaves. The aqueous transport of dissolved mercury is of no
importance; suspended particulate matter, however, is able to
carry a significant load of Hg.
Sumber: http://www.springerlink.com/content/x455x32577658627/ …. Diunduh 8/5/2012
. Water, Air, & Soil Pollution. Volume 56, Number 1 (1991), 15-20.
Mercury in plants, soil and atmosphere near a chlor-alkali complex
B. E. Maserti and R. Ferrara
Natural emissions of Hg are attracting increased interest both for their
environmental implications and for possible applications in the exploration of
mineral, petroleum and geothermal fields. However, daily and seasonal
fluctuations in concentrations of Hg in the atmosphere, caused by
meteorological and environmental variables, has made it very difficult to assess
Hg anomalies by conventional analytical procedures.
Some species of widespread foliose lichens from an abandoned cinnabar
mining and smelting area (Mt. Amiata), geothermal fields (Larderello, Bagnore
and Piancastagnaio, Central Italy), and active volcanic areas (Mt. Etna and
Vulcano, Southern Italy) seem to be very suitable biomonitors of gaseous Hg;
especially as lichen thalli have an Hg content which reflects average values
measured in air samples.
We discuss the advantages of quantitative biological monitoring
by lichens with respect to conventional air sampling in largescale monitoring.
Sumber: http://www.springerlink.com/content/n143r7138u856g31/ …. Diunduh 8/5/2012
Phytoextraction and Accumulation of Mercury in Selected Plant Species Grown in Soil
Contaminated with Different Mercury Compounds
Y. Su, F. Han, S. Shiyab, D.L. Monts
WM’07 Conference, February 25 - March 1, 2007, Tucson, A.Z.
. The objective of our research is to screen and search for suitable plant species for
phytoremediation of mercury-contaminated soil. Currently our effort is specifically focused on
mercury removal from the U.S. Department of Energy’s (DOE) Oak Ridge Site, where mercury
contamination is a major concern in the Y-12 Watershed area. In order to cost effectively
implement those remediation efforts currently planned for FY09, it is necessary now to obtain an
improved understanding of biological means of removing mercury and mercury compounds from
the Oak Ridge ecosystem. Phytoremediation is a technology that uses various plants to degrade,
extract, contain, or immobilize contaminants from soil and water. In particular, phytoextraction
is the uptake of contaminants by plant roots and translocation within the plants to shoots or
leaves. Contaminants are generally removed by harvesting the plants. We have investigated
phytoextraction of mercury from contaminated soil by using some of the known metal
accumulating wild plants since no natural plant species with mercury hyperaccumulating
properties has yet been identified. Different natural plant species have been studied for mercury
uptake, accumulation, toxicity and overall mercury removal efficiency. Various mercury
compounds, such as HgS, HgCl2 and Hg(NO3)2, were used as contaminant sources. Different
types of soil were examined and chosen for phytoremediation experiments.
We have applied microscopy and diffuse reflectance spectrometry as well as conventional
analytical chemistry to monitor the phytoremediation processes of mercury uptake, translocation
and accumulation; and the physiological impact of mercury contaminants on selected plant
species. Our results indicate that certain plant species, such as beard grass (Polypogon
monospeliensis), accumulated a very limited amount of mercury in the shoots (<65 mg/kg), even
though root mercury accumulation is significant (maximum 2298 mg/kg). Consequently, this
plant species may not be suitable for mercury phytoremediation. Other plant species, such as
Indian mustard (Brassica juncea), a well-studied metal accumulator, exhibited severe chlorosis
symptoms during some experiments. Among all the plant species studied, Chinese brake fern
(Pteris vittata) accumulated significant amount of mercury in both roots and shoots and hence
may be considered as a potential candidate for mercury phytoextraction. During one experiment,
brake ferns accumulated 540 mg/kg and 1469 mg/kg in shoots after 18 days of growing in soils
treated with 500 ppm and 1000 ppm HgCl2 powder, respectively; no visual stress symptoms
were observed. We also studied mercury phytoremediation using aged soils that contaminated
HgS, HgCl2, and Hg(NO3)2. We have found that up to hundreds of ppm mercury can be
accumulated in the roots of Indian mustard plants grown with soil contaminated by mercury
sulfide; HgS is assumed to be the most stable and also the predominant mercury form in Oak
Ridge floodplain soils. We have also started to investigate different mercury uptake mechanisms,
such as root uptake of soil contaminant and foliar mercury accumulation from ambient air.
Sumber: http://www.wmsym.org/archives/2007/pdfs/7174.pdf …. Diunduh 8/5/2012
. Phytoremediation of mercury using Eichhornia crassipes (Mart.) Solms
Upma Narang, Renu Bhardwaj, S.K. Garg, A.K. Thukral
International Journal of Environment and Waste Management (IJEWM)
Jun. 28, 2011
Roots of Eichhornia crassipes were found to accumulate maximum content of mercury
(92.21 μg g−1
dry wt) in the roots of plants treated with 1000 μg l−1
concentration of mercuric acetate on 14th day of treatment. The bioconcentration
factor (BCF) was found to be highest for lowest mercury concentrations (1 μg l−1
) in the medium. The uptake of mercury follows dual pattern of ion uptake. Type-1
mechanism operates at mercury concentrations up to 100 μg l−1
, which is carrier-mediated and follows Michaelis?Menten kinetics. Type-2 mechanism
occurs at concentrations up to 1000 μg l−1
.
Sumber: http://www.environmental-expert.com/articles/phytoremediation-of-mercury-using-eichhorniacrassipes-mart-solms-251678/view-comments…. Diunduh 11/5/2012
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
Mercury (Hg) pollution is a global environmental problem. Numerous Hg-contaminated sites exist in
the world and new techniques for remediation are urgently needed. Phytoremediation, use of plants
to remove pollutants from the environment or to render them harmless, is considered as an
environment-friendly method to remediate contaminated soil in-situ and has been applied for some
other heavy metals. Whether this approach is suitable for remediation of Hg-contaminated soil is,
however, an open question. The aim of this thesis was to study the fate of Hg in terrestrial plants
(particularly the high biomass producing willow, Salix spp.) and thus to clarify the potential use of
plants to remediate Hg-contaminated soils.
Plants used for phytoremediation of Hg must tolerate Hg. A large variation (up to 30-fold difference)
was detected among the six investigated clones of willow in their sensitivity to Hg as reflected in their
empirical toxicity threshold, the maximum unit toxicity and EC50 levels. This gives us a possibility to
select Hg-tolerant willow clones to successfully grow in Hg-contaminated soils for phytoremediation.
Release of Hg into air by plants is a concern when using phytoremediation in practice. No evidence
was found in this study that Hg was released to the air via shoots of willow, garden pea (Pisum
sativum L.), spring wheat (Triticum aestivum L.), sugar beet (Beta vulgaris L.), oil-seed rape (Brassica
napus L.) and white clover (Trifolium repens L.). Thus, we conclude that the Hg burden to the
atmosphere via phytoremediation is not increased.
Phytoremediation processes are based on the ability of plant roots to accumulate Hg and to
translocate it to the shoots. Willow roots were shown to be able to efficiently accumulate Hg in
hydroponics, however, no variation in the ability to accumulate was found among the eight willow
clones using CVAAS to analyze Hg content in plants. The majority of the Hg accumulated remained in
the roots and only 0.5-0.6% of the Hg accumulation was translocated to the shoots. Similar results
were found for the five common cultivated plant species mentioned above. Moreover, the
accumulation of Hg in willow was higher when being cultivated in methyl-Hg solution than in
inorganic Hg solution, whereas the translocation of Hg to the shoots did not differ.
The low bioavailability of Hg in contaminated soil is a restricting factor for the phytoextraction of
Hg. A selected tolerant willow clone was used to study whether iodide addition could increase the
plantaccumulation of Hg from contaminated soil. Both pot tests and field trials were carried out.
Potassium iodide (KI) addition was found to mobilize Hg in contaminated soil and thus increase the
bioavailability of Hg in soils. Addition of KI (0.2–1 mM) increased the Hg concentrations up to about 5,
3 and 8 times in the leaves, branches and roots, respectively. However, too high concentrations of KI
were toxic to plants.
As the majority of the Hg accumulated in the roots, it might be unrealistic to use willow for
phytoextraction of Hg in practice, even though iodide could enhance the phytoextraction efficiency.
In order to study the effect of willow on various soil fractions of Hg-contaminated soil, a 5-step
sequential soil extraction method was used. Both the largest Hg-contaminated fractions, i.e. the Hg
bound to residual organic matter (53%) and sulphides (43%), and the residual fraction (2.5%), were
found to remain stable during cultivations of willow. The exchangeable Hg (0.1%) and the Hg bound
to humic and fulvic acids (1.1%) decreased in the rhizospheric soil, whereas the plant accumulation of
Hg increased with the cultivation time. The sum of the decrease of the two Hg fractions in soils was
approximately equal to the amount of the Hg accumulated in plants. Consequently, plants may be
suitable for phytostabilizationSumber:
of aged Hg-contaminated
soil, in which root systems trap the
…. Diunduh 11/5/2012
bioavailable Hg and reduce the leakage of Hg from contaminated soils.
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
. Mercury (Hg) pollution is a global environmental problem. Numerous Hg-contaminated sites exist
in the world and new techniques for remediation are urgently needed. Phytoremediation, use of
plants to remove pollutants from the environment or to render them harmless, is considered as an
environment-friendly method to remediate contaminated soil in-situ and has been applied for some
other heavy metals. Whether this approach is suitable for remediation of Hg-contaminated soil is,
however, an open question. The aim of this thesis was to study the fate of Hg in terrestrial plants
(particularly the high biomass producing willow, Salix spp.) and thus to clarify the potential use of
plants to remediate Hg-contaminated soils.
Plants used for phytoremediation of Hg must tolerate Hg. A large variation (up to 30-fold
difference) was detected among the six investigated clones of willow in their sensitivity to Hg as
reflected in their empirical toxicity threshold (TT95b), the maximum unit toxicity (UTmax) and EC50
levels. This gives us a possibility to select Hg-tolerant willow clones to successfully grow in
Hgcontaminated
soils for phytoremediation.
Release of Hg into air by plants is a concern when using phytoremediation in practice. No
evidence was found in this study that Hg was released to the air via shoots of willow, garden pea
(Pisum sativum L. cv Faenomen), spring wheat (Triticum aestivum L. cv Dragon), sugar beet (Beta
vulgaris
L. cv Monohill), oil-seed rape (Brassica napus L. cv Paroll) and white clover (Trifolium repens L.). Thus,
we conclude that the Hg burden to the atmosphere via phytoremediation is not increased.
Phytoremediation processes are based on the ability of plant roots to accumulate Hg and to
translocate it to the shoots. Willow roots were shown to be able to efficiently accumulate Hg in
hydroponics, however, no variation in the ability to accumulate was found among the eight willow
clones using CVAAS to analyze Hg content in plants. The majority of the Hg accumulated remained
in the roots and only 0.5-0.6% of the Hg accumulation was translocated to the shoots. Similar
results were found for the five common cultivated plant species mentioned above. Moreover, the
accumulation of Hg in willow was higher when being cultivated in methyl-Hg solution than in
inorganic Hg solution, whereas the translocation of Hg to the shoots did not differ.
The low bioavailability of Hg in contaminated soil is a restricting factor for the phytoextraction
of Hg. A selected tolerant willow clone was used to study whether iodide addition could increase
the plant-accumulation of Hg from contaminated soil. Both pot tests and field trials were carried
out. Potassium iodide (KI) addition was found to mobilize Hg in contaminated soil and thus increase
the bioavailability of Hg in soils. Addition of KI (0.2–1 mM) increased the Hg concentrations up to
about 5, 3 and 8 times in the leaves, branches and roots, respectively. However, too high
concentrations of KI were toxic to plants. As the majority of the Hg accumulated in the roots, it
might be unrealistic to use willow for phytoextraction of Hg in practice, even though iodide could
enhance the phytoextraction efficiency.
In order to study the effect of willow on various soil fractions of Hg-contaminated soil, a 5-step
sequential soil extraction method was used. Both the largest Hg-contaminated fractions, i.e. the Hg
Sumber:
Diunduh(43%),
11/5/2012
bound to residual organic matter (53%)
and ….
sulphides
and the residual fraction (2.5%), were
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
Hg - a global environmental pollutant: Sources of Hg pollutants
Mercury (Hg) is a global environmental pollutant that is present in soil, water, air and biota. Hg enters
the environment as a result of natural and human. The naturally occurring Hg can be released into the
atmosphere and then exchanged between the soil and water systems by the following processes
(Ebinghaus et al., 1999):
1. Wind erosion and degassing from Hg mineralized soil and rock formation
2. Volcanic eruptions and other geothermal activities
3. Evasion of Hg from the Earth’s subsurface crust whereas, anthropogenic sources of Hg can be
attributed as follows (Porcella et al., 1996):
4. Combustion of fossil fuels, wood, wastes, sewage sludge and crematories.
5. High temperature processes, e.g. smelting, cement and lime production
6. Manufacturing/commercial activities: e.g. metal processing, gold extraction, Hg mining, chloralkali plants, chemical and instrument industry (Hg chemicals, paints, batteries, thermometers,
process reactants and catalysts).
7. Other sources, e.g. agriculture (pesticides, fertilizers and manure).
Mercury-cycling in the environment.
Sumber:
1. Ebinghaus, R., Tripathi, R.M., Wallschläger, Lindberg S. E., 1999. Natural and anthropogenic mercury sources and
their impact on the air-surface exchange of mercury on regional and global scales. In:
2. Ebinghaus, R., Turner, R.R., Lacerda, L.D., Vasiliev, O., Salomons, W.(eds.) Mercury Contaminated Sites:
Characterization, Risk Assessment and Remediation. Springer - Verlag Berlin Heidelberg New York. pp 1–50.
3. Porcella, D.B., Chu, P., Allan, M.A., 1996. Inventory of North American mercury emissions to the atmosphere:
relationship to the global mercury cycle. In: Baeyens, W., Ebinghaus, R., Vasiliev, O. (eds.) Global and regional
mercury cycles: sources, fluxes and mass balances. NATO-ASI Series 2. Environment vol 21. Kluwer, Dordrecht,
The Netherlands. pp 179–190.
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
Current estimates of anthropogenic Hg emission range from about 50 % to 75% of the
total annual Hg emission to the atmosphere (Ebinghaus et al., 1999; Fitzgerald, 1995). The
atmospheric Hg burden has increased by a factor of three during the last 100 years (Fitzgerald, 1995).
The Hg released from both anthropogenic and natural sources is further distributed in the
environment (Fig. 1). The main pathway of Hg transport in the environment is air-surface exchange
with soils, ocean, fresh water and vegetation.
However, other transports like soil-vegetation exchange and water-vegetation exchange are very
important to human beings. The Hg accumulated in vegetation may enter the human diet either
directly or through fish, birds and livestock (Fig. 1). Moreover, the soilvegetation exchange of Hg (Fig.
2) gives a possibility to remove Hg from contaminated soil by plant uptake.
The role of terrestrial plants in the biogeochemical cycling of Hg.
Sumber:
1. Ebinghaus, R., Tripathi, R.M., Wallschläger, Lindberg S. E., 1999. Natural and anthropogenic mercury
sources and their impact on the air-surface exchange of mercury on regional and global scales. In:
2. Ebinghaus, R., Turner, R.R., Lacerda, L.D., Vasiliev, O., Salomons, W.(eds.) Mercury Contaminated Sites:
Characterization, Risk Assessment and Remediation. Springer - Verlag Berlin Heidelberg New York. pp 1–
50.
3. Fitzgerald, W.F., 1995. Is mercury increasing in the atmosphere – the need for an atmospheric mercury
network. Water, Air and Soil Pollution 80 (1-4), 245–254.
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
. Hg speciation in air, water, and soil
The most common gaseous forms of Hg are elemental Hg (Hg0) and dimethyl-Hg ((CH3)2Hg). On a
global scale, the atmospheric Hg cycle is dominated by elemental Hg (generally > 95% of total
airborne Hg), whereas only minor amount of other species (mainly particulate-phase Hg (Hg(p)) have
been detected (Stratton and Lindberg, 1995).
Both methyl-Hg and dimethyl-Hg have been detected in ambient air (Bloom and Fitzgerald, 1988).
However, the concentrations are far below those of the inorganic species. The total Hg concentration
in air at background levels is generally 1–4 ng m-3 (Table 1). The atmospheric Hg concentrations in
1990 were 2.25±0.41 and 1.50±0.30 ng m-3, respectively, in the northern and southern hemispheres
over the Atlantic Ocean (Slemr and Langer, 1992), and it was reported as 1.5 ng m-3 at the west coast
of Sweden in 2003 (Munthe et al., 2003). The atmospheric Hg concentration is generally higher in
urban and industrial areas, and it was reported to be 600 and 1500 ng m-3 near Hg mines and
refineries (WHO, 2000).
Background Hg concentrations in different media and general Hg speciation
Sumber:
1. Bloom, N.S., Fitzgerald, W.F., 1988. Determination of volatile mercury species at the picogram level by
low-temperature gas-chromatography with cold-vapour atomic fluorescence detection. Analytica
Chimica Acta 208 (1-2), 151–161.
2. Munthe, J., Wängberg, I., Iverfeldt, A., Lindqvist, O., Stromberg, D., Sommar, J., Gardfeldt, K., Petersen,
G., Ebinghaus, R., Prestbo, E., Larjava, K., Siemens, V., 2003. Distribution of atmospheric mercury species
in Northern Europe: final results from the MOE project. Atmospheric Environment 37, S9-S20.
3. Slemr, F., Langer, E., 1992. Increase in global atmospheric concentrations of mercury inferred from
measurements over the Atlantic Ocean. Nature 355 (6359), 434–437.
4. Stratton, W.J., Lindberg, S.E., 1995. Use of a refluxing mist chamber for measurement of gas-phase
water-soluble mercury (II) species in the atmosphere. Water, Air and Soil Pollution 80, 1269–1278.
5. WHO Regional office for Europe, 2000. Air quality guidelines – Second edition, Copenhagen, Denmark.
Chapter 6.9. pp 1–15.
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
Plant interaction with Hg
Plants are capable of extracting a variety of metal ions from their growth substrates, including Hg.
Many studies have showed that plant roots accumulate Hg when they were exposed to Hgcontaminated soils (Kalac and Svoboda, 2000). Laboratory studies showed that plant roots absorbed
Hg from solution and roots accumulated much greater amount of Hg than shoots (Cavallini et al.,
1999; Godbold and Hütterman, 1988). Both field and laboratory studies have demonstrated that
plants accumulate more Hg when it is introduced in organic form than in inorganic form (Ribeyre and
Boudou, 1994).
Leaves can absorb gaseous Hg via stomata, which has been shown in previous laboratory studies (
Cavallini et al., 1999; Du and Fang, 1982, 1983). Du and Fang (1982) reported that uptake of Hg0 by
the leaf increased with increasing Hg vapour concentration, temperature, and illumination. Leaves
can also absorb Hg after deposition of particulate Hg on the leaf surface (Fernández et al., 2000) and
release gaseous Hg into the atmosphere (Kozuchowski and Johnson, 1978). Furthermore, Hanson et
al. (1995) reported that at low external Hg concentrations in the air, the release of Hg from leaf to air
was higher than the leaf Hg absorption from the air in the tree species Picea abies L. Liriodendron
tulipifera L., Quercus alba L., and Acer rubrum L.. Similar results were also found by Ericksen and
Gustin (2004). This evidence suggests that foliage can manage both uptake and volatilization of
gaseous Hg.
Sumber:
1. Du, Sh.H., Fang, Sh.C., 1982. Uptake of elemental mercury vapor by C3 and C4 species. Environmental
and Experimental Botany 22 (4), 437–443.
2. Du, Sh.H., Fang, Sh.C., 1983. Catalase activity of C3 and C4 species and its relationship to mercury vapor
uptake. Environmental and Experimental Botany 23, 347–353.
3. Ericksen, J.A., Gustin, M.S., 2004. Foliar exchange of mercury as a function of soil and air mercury
concentrations. Science of the Total Environment 324 (1-3): 271–279.
4. Fernández, J.A., Aboal, J.R., Carballeira, A., 2000. Use of native and transplanted mosses as
complementary techniques for biomonitoring mercury around an industrial facility. Science of the Total
Environment 256 (2-3), 151–161.
5. Hanson, P.J., Lindberg, S.E., Tabberer, T.A., Owens, J.G., Kim, K.H., 1995. Foliar exchange of mercury
vapor: evidence for a compensation point. Water, Air and Soil Pollution 80, 373–382.
6. Kalac, P., Svoboda, L., 2000. A review of trace element concentrations in edible mushrooms. Food
Chemistry 69 (3), 273–281.
7. Kozuchowski, J., Johnson, D.L., 1978. Gaseous emissions of mercury from an aquatic vascular plant.
Nature 274, 468–469.
8. Ribeyre, F., Boudou, A., 1994. Experimental study of inorganic and methylmercury bioaccumulation by
four species of freshwater rooted macrophytes from water and sediment contamination sources.
Ecotoxicology and Environmental Safety 28, 270–286.
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
All physiological and biochemical processes in plants may be negatively affected by
Hg when plants are exposed to Hg-contaminated soil, water or air (Patra and Sharma,
2000). Elemental Hg (Hg0) does not react with most biomolecules unless first oxidized to
Hg2+, and this may be catalytically driven by peroxidase or catalase (Du and Fang, 1983). Hg cations have
a high affinity for sulphydryl (-SH). Because almost all proteins contain sulphydryl groups or disulphide
bridges (-S-S-), Hg can disturb
almost any function in which proteins are involved in plants (Clarkson, 1972). Organic Hg
is 1–2 orders of magnitude more toxic to some eukaryotes and is more likely to
biomagnify across trophic levels than ionic Hg (Hg2+) (Bizily et al., 2000).
The biophysical behaviour of organic Hg is thought to be due to its hydrophobicity and
efficient membrane permeability (Braeckman et al., 1998). Hg compounds can also bind to
RNA, several synthetic polyribosomes, and DNA (Cavallini et al., 1999). Hg is known to affect
photosynthesis, mineral nutrient uptake, and transpiration (Barber et al., 1973; Godbold, 1991, 1994;
Patra and Sharma, 2000). Plants can generally sequester toxic ions in complexes at the
cytoplasm to defend against their phytotoxicity. Glutathione (GSH)-related phytochelatins
(PCs) with the general structure (γ Glu-Cys)nGly (n=2-11) are the most dominant
molecules found so far to sequester the metal ions in cytoplasm and then transport them to
vacuoles (Rajesh et al., 1996; Zenk, 1996). Rajesh et al. (1996) reported that the strength
of Hg(II) binding to glutathione and phytochelatins ranked in order as follows: γ Glu-CysGly < (γ Glu-Cys)2Gly < (γ Glu-Cys)3Gly < (γ Glu-Cys)4Gly. Suhadra et al. (1993) found
that, compared with normal seedlings, those from Hg-treated seeds exhibited a larger
amount of nonprotein SH, indicating the possible involvement of phytochelatins in the Hgreduced
adaptive response. Organic acids (e.g. citrate) and amino acids (e.g. histidine)
existing in cytoplasm may also complex metal ions and reduce their toxicities to plants
(McGrath and Zhao, 2003).
Sumber:
1. Bizily, S.P., Rugh, C.L., Meagher, R.B., 2000. Phytodetoxification of hazardous organomercurials by genetically
engineered plants. Nature Biotechnology 18, 213–217.
2. Braeckman, B., Cornelis, R., Rzeznik, U., Raes, H., 1998. Uptake of HgCl2 and MeHgCl in an insect cell line (Aedes
albopictus C6/36). Environmental Research 79 (1), 33–40.
3. Cavallini, A., Natali, L., Durante, M., Maserti, B., 1999. Mercury uptake, distribution and DNA affinity in durum
wheat (Triticum durum Desf.) plants. The Science of the Total Environment 243/244, 119–127.
4. Godbold, D.L., 1991. Mercury induced root damage in spruce seedlings. Water Air and Soil Pollution 56, 823–831.
5. Godbold, D.L., 1994. Mercury in forest ecosystems: Risk and research needs. In: Watras, C. J., and Huckabee, J.
W., (eds) Mercury pollution – Integration and synthesis. Lewis Publishers, Boca Raton. pp 295–303.
6. McGrath, S.P., Zhao, F.J., 2003. Phytoextraction of metals and metalloids from contaminated soils. Current
Opinion in Biotechnology 14 (3), 277–282.
7. Patra, M., Sharma, A., 2000. Mercury toxicity in plants. The Botanical Review 66 (3), 379–421.
8. Rajesh, K.M., Jose, M.V., Ramana, K., Rizwana, A., Thomas, C.H., Priti, M., 1996. Optical spectroscopic and
reverse-phase HPLC analyses of Hg(II) binding to phytochelatins. Biochemical Journal 314, 73–82.
9. Suhadra, A.V., Panda, K.K., Panda, B.B., 1993. Residual Mercury in seed of Barley of methanesulfate, maleic
hydrazide, methyl mercury chloride and mercury-contaminated soil. Mutation Research 300 (34), 141–149.
10. Zenk, M.H., 1996. Heavy metal detoxification in higher plants – A review. Gene 179 (1), 21–30.
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
Plant chamber systems and Hg traps
A set of plant-chamber systems was established to study the Hg accumulation and the
translocation of Hg to the shoots in hydroponics. Hg can easily volatilize from solution
into air (Paper IV) and leaves can absorb gaseous Hg (Du and Fang, 1982; Wang and
Greger, unpublished). A transpiration chamber system (Fig. 4) was constructed to evaluate
the Hg accumulation, translocation and volatilization via leaves, which efficiently
prevented leakage of air into the upper cylinder from the chamber below (Paper I).
Another plant-chamber system with a gaseous Hg generator (i.e. a tube system with a drop
of metallic Hg inside) was used to study uptake of Hg via the shoot (Fig. 5; Wang and
Greger, unpublished).
The transpiration chamber (design II) used to study the volatilization of Hg from shoots
(Paper I).
Sumber:
Du, Sh.H., Fang, Sh.C., 1982. Uptake of elemental mercury vapor by C3 and C4 species. Environmental
and Experimental Botany 22 (4), 437–443.
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
The plant-chamber system used to study uptake of Hg from air via shoots (Wang and
Greger, unpublished).
Sumber: …. Diunduh 11/5/2012
Weibull function
To evaluate the differences in Hg tolerance among willow clones, a modified Weibull
model (Taylor et al., 1991) was used in Paper II to compare the dose-response curves.
The modified Weibull function has been shown to be an excellent tool to compare
doseresponse curves and estimate some important parameters such as the empirical
toxicity threshold (TT95b), the maximum unit toxicity (UTmax) and EC50. TT95b is the
concentration of Hg where growth is reduced by 5%, EC50 is the concentration of Hg
where growth was reduced by 50% and UTmax indicates the value of the maximum
slope of the dose-response curves (Fig. 6). Generally, a plant with higher values of
TT95b and EC50 and a low value of UTmax means it is less sensitive to Hg than the
plants with lower values of TT95b and EC50 and a higher value of UTmax.
Illustration of the empirical toxicity threshold (TT95b), the maximum unit toxicity
(UTmax) and EC50 in a dose-response curve. The growth of the shoot decreases with increased
Hg concentration in solution when roots were exposed to various concentrations of HgCl2.
* dy/dx indicates the slope of the curve.
Sumber:
Taylor, G.J., Stadt, K.J., Dale, M.R.T., 1991. Modelling the interactive effects of aluminium,
cadmium manganese, nickel and zinc stress using the Weibull frequency distribution. Canadian
Accumulation and distribution of various Hg species in willow
Willow clone Björn was used in this study. The short-term Hg-accumulation study
(Paper IV; Wang and Greger, unpublished) showed that Hg accumulation in the roots of
willow decreased according to its species in following order: CH3HgCl > HgCl2 ≈
Hg(NO3)2 > HgI2 (Fig. 8).
Accumulation of Hg in
willow roots during the
cultivation of plants in 1
μM CH3HgCl,
HgCl2, Hg(NO3)2, and
HgI2, respectively, for 4
h. The Hg solution was
changed every 30 min.
The Hg accumulation
rate is shown as the
slope of the line
between the two harvest
times. n=3,
± SE (data from Paper IV
and from Wang and
Greger (unpublished)).
Sumber: …. Diunduh 11/5/2012
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
According to our studies and the literature, all previously investigated plants have low
translocation of Hg to the shoots (Table 2; Papers I–IV; Beauford et al., 1977; Godbold
and Hütterman, 1988). It seems that the majority of the total accumulated Hg is trapped in the roots and that only
a minor amount can be translocated to the shoots. Ion uptake mainly occurred at the root tip, prior to the
formation of the Casparian band (Fig. 9), which is a zone allowing apoplasmic transport of heavy metals into the
stele (Marschner, 1995).
Illustration of the Casparian band in
root tip of willow.
(a) Diagram of longitudinal section
of a root tip (adapted from
Esau (1953));
(b) The diagram represents only a
symplastic transport of ions
from cortex cells to stele when
the endodermis cell wall is
deposited with suberin
lamellae (adapted
from Mauseth (1988));
(c) The diagram represents that the
Casparian band is a barrier of
apoplastic movements of water
and solutes from cortex to stele
(adapted from Mauseth (1988));
(d) Fluorescence microscopic
picture of a hand section of willow
root stained with berberine, bar =
50 μm (Wang and Greger,
unpublished).
Sumber:
1. Beauford, W., Barber, J., Barringer, A.R., 1977. Uptake and distribution of mercury within higher plants.
2. Physiologia Plantarum 39, 261–265.
3. Esau, K., 1953. Plant Anatomy. John Wiley & Sons, New York. p 493.
4. Godbold, D.L., Hütterman A., 1988. Inhibition of photosynthesis and transpiration in relation to
mercuryinduced root damage in spruce seedlings. Physiologia Plantarum 74, 270–275.
5. Marschner, H., 1995. Mineral Nutrition of Higher Plants. Academic Press, London.
6. Mauseth, J.D., 1988. Plant Anatomy. The Benjamin/Cummings Publishing Co., Inc., Menlo Park CA. pp
277.
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
Phytoremediation of Hg
Phytoextraction
In phytoextraction, metal-tolerant plants with high metal accumulation and high
biomass production are preferably used. Our results showed a large variation among
the six clones of willow in their sensitivity to Hg (paper II). The tolerant clone Björn was
used to study the phytoextraction of Hg both in pots with aged Hg-spiked soil or
industrial Hgcontaminated soil and in the field. Results showed that this willow clone
could grow successfully without significant measurable toxic effects except with 1mM
KI addition (Papers III and IV). The toxic effects found in the test with 1 mM KI addition
was thought to be mainly due to the toxicity of iodide to the plants (Paper IV). It
suggests that selected willow clones are able to tolerate Hg while being used for
phytoextraction of such types of aged Hg-contaminated soil.
The plants used for phytoextraction must have an ability to efficiently accumulate
metal via their roots. Our studies showed that willow roots efficiently accumulated Hg
in hydroponics, where they could accumulate more than 300 μg Hg g-1DW from of 1
μM Hg(NO3)2 (200 μg Hg L-1) within 4 hours and reduce the Hg concentration in
Hg(NO3)2 solution from initial 1 μM to 0.05 μM after 3 days of cultivation. Moreover,
willow could accumulate Hg by more than 1000 μg g-1DW in its roots without
significant toxic effects (Paper II).
The low bioavailability of Hg in contaminated soil is a restricting factor in
phytoextraction of Hg. Compared with chelating agents, e.g. EDTA, iodide is
more efficient in mobilizing Hg in soil, which mainly forms the soluble
complex HgI4= with a stability constant of 29.8 (Wasay et al., 1995).
Sumber:
Wasay, S.A., Arnfalk, P., Tokunaga, S., 1995. Remediation of a soil polluted by mercury with acidic
potassium–iodide. Journal of Hazardous Materials 44, 93–102.
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
Phytostabilization
In order to reduce the bioavailability or mobility of heavy metals, the plants used for
phytostabilization preferably have efficient root-accumulation of available metals in the
soil, low translocation of metals to the shoots, and a large root system. Willow roots could
efficiently accumulate Hg in hydroponics and had high affinities for Hg (Table 2; Papers
I–IV). Hg binds roots so hard that washing with 20 mM EDTA (30 min) only removed
less than 2% of total Hg in roots (Wang and Greger, unpublished). Therefore, willow roots
grown in Hg-contaminated soil were able to accumulate Hg and reduce its bioavailability
in soil (Table 7; Paper III). The exchangeable Hg and the Hg bound to humic and fulvic
acids decreased in the rhizospheric soil, whereas the plant accumulation of Hg increased
with the cultivation time.
The sum of the decrease of these two Hg fractions in soil after 76
days of cultivation was approximately equal to the amount of the Hg
accumulated in plants, which accounted for about 0.2 % of the total Hg in
soil. Moreover, the low translocation of Hg to the shoots detected makes
willow useful for phytostabilization of Hg-contaminated land, in which
root systems trap the bioavailable Hg and reduce the leakage of Hg from
contaminated soils. However, the Hg-accumulated root tissues may die
and become debris. Bacterial activities on debris of Hg-accumulated
tissues need to be taken into account in long term cultivation.
Phytostabilization may also partly result from physical effects, as the vegetation
cover can promote physical stabilization of a substrate, especially on sloping
ground. Willow has a massive root system, which helps to bind the soil. In
addition, transpiration of water by the willow reduces the overall flow of water
down through the soil, thus, helping to reduce the amount of Hg that is
transferred to ground- and surface waters.
Sumber: …. Diunduh 11/5/2012
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
Illustration of phytostabilization of Hg.
Sumber: …. Diunduh 11/5/2012
PHYTOREMEDIATION OF MERCURY BY TERRESTRIAL PLANTS
A doctoral dissertation to be public defended 21 December 2004 at 10:00 in the lecture hall
at the Department of Botany, Stockholm University
Faculty opponent: Professor Douglas Godbold, School of Agricultural & Forest Sciences,
University of Wales, UK.
FOLIAGE FILTRATION
Our present study showed that willow leaves were able to continuously absorb Hg
from air, and Hg concentrations in leaves and branches increased with prolonged
exposure time. Hence, on a global scale, vegetation may function as a foliage filtration
of Hg in the air. However, relatively few data have been published so far on airvegetation exchange.
The amount of Hg removed from the atmosphere by vegetation regionally or globally is
virtually unknown.
In consideration of food safety, uptake of Hg in vegetation from air contributes to part
of the intake of Hg by humans. Furthermore, atmospheric deposition is considered to
dominate the Hg input to most soils and lakes in the boreal forest zone, which causes
Hgcontamination of fish (Meili et al., 2003). Therefore, global efforts are needed to
reduce the emission of Hg into the atmosphere.
1.
Meili, M., Bishop, K., Bringmark, L., Johansson, K., Munthe, J., Sverdrup, H., de Vries, W., 2003.
Critical levels of atmospheric pollution: criteria and concepts for operational modelling of
mercury in forest and lake ecosystems. Science of the Total Environment 304 (1-3), 83–106.’
. PHYTOEXTRACTION PROCESS
Phytoextraction is a subprocess of phytoremediation in which plants remove
dangerous elements or compounds from soil or water. This article will specifically
address phytoextraction of heavy metals. The MSDS defines heavy metals as, "any
metallic chemical element that has a relatively high density and is toxic, highly toxic or
poisonous at low concentrations."[1]
Heavy metals are also a major problem world wide, especially in developing countries
who do not have the money to remove the heavy metals from their drinking water. In
2001, the British geological survey recorded that in Bangladesh 57 million out of 129
million people were being poisoned by heavy metals in their groundwater.[2]
The heavy metals that plants extract are extremely poisonous to them as well, which
makes phytoextraction of heavy metals extremely dangerous for plants. Also there are
a group of plants called hyper-accumulators that sequester extremely large amounts of
dangerous heavy metals. This invariably leads researchers to two questions: why and
how do plants accomplish this useful task, since it seems to be so evolutionarily unfit?
Referensi:
1. http://www.ilpi.com/msds/ref/heavymetal.html
2. British Geological Survey. Phase 2 Groundwater studies of Arsenic Contamination in Bangladesh.
Nottingham, UK: British Geological Survey, 2001.
Sumber: http://en.wikipedia.org/wiki/Phytoextraction_process…. Diunduh 11/5/2012
WHY HEAVY METALS ARE A PROBLEM
Heavy metals are a major problem for any biological organism.
Once heavy metals get into a biological system they are reactive with a number of
chemicals used in essential biological processes.
They can also break apart other molecules into even more reactive species (such
as:Reactive Oxygen Species) which will also disrupt biological processes.
Figure is a reaction scheme showing how Fe2+ and Fe3+ can react with common
molecules such as O2 and H2O2. These reactions will deplete the concentration of
important molecules and also produce dangerously reactive molecules such as the
radicals O. and OH..
So heavy metals are fatally toxic for most organisms which makes any organism that
hyper-accumulates heavy metals interesting. Why in the world would any organism
purposely sequester large amounts of dangerous compounds?
In light of this it is important to realize that non-hyper-accumulators will also absorb
some concentration of heavy metal. The reason for this is that the heavy metals that
are absorbed are chemically similar to other metals that are essential to the plants life.
The way that the Periodic Table of Elements is organized puts chemically similar
compounds in the same column. From looking at this Periodic table you can see that all
of the toxic heavy metals which are absorbed by plants share columns with essential
elements. For example; Nitrogen (N) and Phosphorus (P) are essential elements that
share column 15 with Arsenic (As) a dangerous heavy metal, Zinc (Zn) shares column
12 with Cadmium (Cd) and Mercury (Hg).
Sumber: http://en.wikipedia.org/wiki/Phytoextraction_process…. Diunduh 11/5/2012
. The absorption process
In order for a plant to extract a heavy metal from water or soil, five things need to
happen.
The metal needs to be dissolved in something the plant roots can absorb
The plant roots need to absorb the heavy metal
The plant needs to chelate the metal in order to both protect itself and make the metal
more mobile(this can also happen before the metal is absorbed)
Chelation is a process by which a metal is surrounded and chemically bonded to an
organic compound. This process is displayed in the figure titled "Metal-EDTA Chelate"
The plant moves the chelated metal to a place to safely store it
Finally, the plant must adapt to any damages the metals cause during transportation
and storage
Metal-EDTA chelate
The chelate effect describes the enhanced affinity of
chelating ligands for a metal ion compared to the
affinity of a collection of similar nonchelating
(monodentate) ligands for the same metal.
Consider the two equilibria, in aqueous solution,
between the copper(II) ion, Cu2+ and
ethylenediamine (en) on the one hand and
methylamine, MeNH2 on the other.
Cu2+ + en ====== [Cu(en)]2+ (1)
Cu2+ + 2 MeNH2 ======= [Cu(MeNH2)2]2+ (2)
In (1) the bidentate ligand ethylene diamine forms a
chelate complex with the copper ion. Chelation
results in the formation of a five–membered ring.
In (2) the bidentate ligand is replaced by two
monodentate methylamine ligands of approximately
the same donor power, meaning that the enthalpy
of formation of Cu—N bonds is approximately the
same in the two reactions.
(diunduh dari: http://en.wikipedia.org/wiki/Chelation)
Sumber: http://en.wikipedia.org/wiki/Phytoextraction_process …. Diunduh 11/5/2012
DISSOLUTION
In their normal states, metals cannot be taken into any organism. They need
to be dissolved as an ion in solution to be mobile in an organism (1).
Once the metal is mobile, it can either be directly transported over the root
cell wall by a specific metal transporter or carried over by a specific agent.
The plant roots mediate this process by secreting things that will capture
the metal in the rhizosphere and then transport the metal over the cell wall.
Some examples are: phytosiderophores, organic acids, or carboxylates (2).
If the metal is chelated at this point, then the plant does not need to chelate
it later and the chelater serves as a case to conceal the metal from the rest
of the plant. This is a way that a hyper-accumulator can protect itself from
the toxic effects of poisonous metals.
Referensi:
1. Misra V., Tiwari A., Shukla B. & Seth C.S. (2009) Effects of soil amendments on the bioavailability
of heavy metals from zinc mine tailings. Environmental Monitoring Assessment 155, 467–475.
2. Han F., Shan X.Q., Zhang S.Z., Wen B. & Owens G. (2006) Enhanced cadmium accumulation in
maize roots – the impact of organic acids. Plant and Soil 289, 355–368.
Sumber: http://en.wikipedia.org/wiki/Phytoextraction_process…. Diunduh 11/5/2012
ROOT ABSORPTION
The first thing that happens when a metal is absorbed is it binds to the root cell wall
(1).
The metal is then transported into the root. Some plants then store the metal through
chelation or sequestration. Many specific transition metal ligands contributing to metal
detoxification and transport are up-regulated in plants when metals are available in
the rhizosphere (2).
At this point the metal can be alone or already sequestered by a
chelating agent or other compound.
In order to get to the xylem the metal then needs to pass through the
root symplasm.
Referensi:
1. Clemens S., Palmgren M.G. & Krämer U. (2002) A long way ahead: understanding and engineering
plant metal accumulation. Trends in Plant Science 7, 309–315.
2. Seth, C. S., et al. "Phytoextraction of Toxic Metals: A Central Role for Glutathione." Plant, Cell and
Environment (2011)SCOPUS. Web. 16 October 2011.
Sumber: http://en.wikipedia.org/wiki/Phytoextraction_process…. Diunduh 11/5/2012
ROOT-TO-SHOOT TRANSPORT
The systems that transport and store heavy metals are the most critical systems in a
hyper-accumulator because the heavy metals will damage the plant before they are
stored. The root-to-shoot transport of heavy metals is strongly regulated by gene
expression. The genes that code for metal transport systems in plants have been
identified. These genes are expressed in both hyper-accumulating and non-hyperaccumulating plants. There is a large body of evidence that genes known to code for
the transport systems of heavy metals are constantly over-expressed in hyperaccumulating plants when they are exposed to heavy metals (1).
This genetic evidence suggests that hyper-accumulators over-develop their metal
transport systems. This may be to speed up the root-to-shoot process limiting the
amount of time the metal is exposed to the plant systems before it is stored.
These transporters are known as heavy metal transporting ATPases (HMAs) (2).
One of the most well-documented HMAs is HMA4, which belongs to the Zn/Co/Cd/Pb
HMA subclass and is localized at xylem parenchyma plasma membranes (3).
HMA4 is upregulated when plants are exposed to high levels of Cd and Zn, but it is
down regulated in its non-hyperaccumulating relatives (4). Also, when the expression
of HMA4 is increased there is a correlated increase in the expression of genes
belonging to the ZIP (Zinc regulated transporter Iron regulated transporter Proteins)
family. This suggests that the root-to-shoot transport system acts as a driving force of
the hyper-accumulation by creating a metal deficiancy response in roots (5).
Referensi:
1. Rascio, N., and F. Navari-Izzo. "Heavy Metal Hyper-accumulating Plants: How and Why do they do
it? and what Makes them so Interesting?" Plant Science 180.2 (2011): 169-81. SCOPUS. Web. 16
October 2011.
2. K.B. Axelsen and M.G. Palmgren, Inventory of the superfamily of P-Type ion pumps in Arabidopsis.
Plant Physiol., 126 (1998), pp. 696–706.
3. Rascio, N., and F. Navari-Izzo. "Heavy Metal Hyper-accumulating Plants: How and Why do they do
it? and what Makes them so Interesting?" Plant Science 180.2 (2011): 169-81. SCOPUS. Web. 16
October 2011.
4. A. Papoyan and L.V. Kochian, Identification of Thlaspi caerulescens genes that may be involved in
heavy metal hyper-accumulation and tolerance. Characterization of a novel heavy metal
transporting ATPase. Plant Physiol., 136 (2004), pp. 3814–3823.
5. M. Hanikenne, et al. Evolution of metal hyper-accumulation required cis-regulatory changes and
triplication of HMA4. Nature, 453 (2008), pp. 391–395
Sumber: http://en.wikipedia.org/wiki/Phytoextraction_process…. Diunduh 11/5/2012
ENERGETICS OF NUTRIENT TRANSPORT
In some cases, molecules can be transported across a plasma membrane via
diffusion, which is passively down a concentration or chemical gradient.
Diffusion is enhanced by two types of transmembrane proteins: channels serve
as selective pores, whereas carrier proteins bind the molecule on one side of
the membrane and release it on the other side.
If ions are used quickly once they cross into the cytoplasm (such as
incorporation of phosphate into nucleic acids), then the driving force for
diffusion may be maintained.
General schematic of membrane transport proteins:
channels, carriers, and pumps.
(Adapted from L. Taiz and E. Zeiger, Plant Physiology, 4th ed., Sinauer,
Sunderland, MA, 2006)
Sumber: …. Diunduh 11/5/2012
Storage
Remember, the systems that transport and store heavy metals are the most
critical systems in a hyper-accumulator because the heavy metals will
damage the plant before they are stored. Often in hyper accumulaters the
heavy metals are stored in the leaves.
Sumber: http://en.wikipedia.org/wiki/Phytoextraction_process…. Diunduh 11/5/2012
BASIC MECHANISM OF PHYTOEXTRACTION OF HEAVY METALS
The first step in the general mechanism of hyperaccumulation via phytoextraction involves absorption
of heavy metals from soil into the apoplast of roots, followed by translocation of the heavy metals
into root tissue (1,2). With the help of chelators such as histidine, malate and citrate, metal
transporters carry complexed metals from root cells across the endodermis and casparian strip into
the xylem apoplast, where other metal transporters subsequently translocate the complexed metals
from the xylem apoplast into the shoot symplast (2). Once in the shoot cells, chelators sequester the
heavy metals by binding them and storing them in various locations within the cell to protect the
plant from the potential damage caused by the metal (1,2).
The symplast of a plant is defined
as the all the cells that are
connected to plasmodesmata,
both directly and indirectly (3).
The plasmodesmata are narrow
vessels in the plant connecting
the cyptoplasms of adjacent cells,
facilitating intercellular
communication and transport of
nutrients (4). The apoplast, on
the other hand, is a semipermeable membrane that
separates the symplast from the
non-living parts of the plant, that
is, the xylem, phloem, cell walls
etc (3).
References
1. Cherian S, Oliveira MM. Transgenic plants in phytoremediation: Recent advances and new
possibilities. Environ Sci Technol. 2005; 39: 9377-90.
2. Eapen S, D'Souza SF. Prospects of genetic engineering of plants for phytoremediation of toxic
metals. Biotechnol Adv. 2005; 23: 97-114.
3. Erickson RO. Symplastic Growth and Symplastic Transport. Plant Physiology. 1986; 82: 1153.
4. Raven PH, Johnson GB, Losos JB and Singer SR. Biology. 7th ed. New York: McGraw Hill Higher
Education; 2005. p. 140.
5. Clemens S, Palmgren MG, and Kramer U. Along way ahead: understanding and engineering plant
metal accumulation. Trends in Plant Science. 2002; 7: 309-315.
Sumber: http://bio349.biota.utoronto.ca/20079/20079bio349sasha/phytoextraction.html…. Diunduh 11/5/2012
Part of a wheat root transaction in the region of mineral absorption and
transport to xylem (pathways denoted by arrows). (Adapted from K. Esau,
Plant Anatomy, John Wiley & Sons, New York, 1965)
The cytoplasmic regions of plant cells are interconnected via plasmodesmata, which
are microscopic channels that form a continuous body referred to as the symplast.
Water and solutes within the cytoplasm can move freely from cell to cell through
osmosis/diffusion across the symplast without having to cross the plasma membrane.
Outside the plasma membrane, the apoplast is another continuous body formed from
a network of cell walls and extracellular spaces. Water and nutrients can move readily
from the soil solution through the apoplast, except where, as at the endodermis, the
cell walls are impregnated with waxes.
The endodermis thus restricts the apoplastic movement of water and nutrients to the
xylem. To enter the xylem for transport to the rest of the plant, mineral nutrients must
pass through a plasma membrane (that is, symplastic absorption) external to the
endodermis.
Sumber: http://accessscience.com/content/Plant-mineral-nutrition/523500 …. Diunduh 11/5/2012
. Phytoremediation is the use of plants to clean up environmental contamination of
surface soils. It is more cost-effective and environmentally appealing than other
currently available methods for soil detoxification. The most common approach for soil
cleanup involves the excavation and removal of polluted soil to a chemical treatment
facility or a long-term storage landfill facility. This method is very costly for large-scale
decontamination and can be destructive to the environment. Phytoremediation, on
the other hand, costs significantly less and does not require the same degree of
environmental perturbation.
1.
2.
3.
Melinda A. Klein, US Plant, Soil, and Nutrition Laboratory and Department of Plant Biology,
Cornell University, Ithaca, New York
Ashot Papoyan, US Plant, Soil, and Nutrition Laboratory and Department of Plant Biology,
Cornell University, Ithaca, New York
Leon V. Kochian, US Plant Soil, and Nutrition Laboratory, Cornell University, Ithaca, New York
Sumber: accessscience.com…. Diunduh 11/5/2012
The processes involved in plant assimilation and metabolism of all chemical elements, with the
exception of carbon, hydrogen, and oxygen. The latter elements are typically excluded from the
discussion of plant mineral nutrition because they are assimilated from the atmosphere and from
water. Mineral nutrients are so named because they are primarily derived from the weathering of
minerals of the Earth's crust, with the exception of nitrogen, which is primarily derived from
atmospheric nitrogen. Taken together, these nutrient elements are critical for the processes of plant
growth and hence are key to the capturing of solar energy, which is the basis of nearly all life on
Earth.
Sumber: …. Diunduh 11/5/2012
Phytoextraction of metal-contaminated soil relies on the use of plants to extract and translocate
metals to their harvestable parts (Figure 1). The aim of phytoextraction is reducing the concentration
of metals in contaminated soils to regulatory levels within a reasonable time frame. This extraction
process depends on the ability of selected plants to grow and accumulate metals under the specific
climatic and soil conditions of the site being remediated. Two approaches have currently been used
to reach this goal: the use of plants with exceptional, natural metal-accumulating capacity, the socalled hyperaccumulators, and the utilization of high-biomass crop plants, such as corn, barley, peas,
oats, rice, and Indian mustard with a chemically enhanced method of phytoextraction (Huang et al.,
1997; Salt et al., 1998; Lombi et al., 2001; Chen et al., 2004).
Referensi:
1. CHEN, Y.; LI, X.D.; SHEN, Z.G. Leaching and uptake of heavy metals by ten different species of
plants during an EDTA-assisted phytoextraction process. Chemosphere, v.57, p.187-196, 2004.
2. HUANG, J.W.W.; CHEN, J.J.; BERTI, W.R.; CUNNINGHAM, S.D. Phytoremediation of leadcontaminated soils: role of synthetic chelates in lead phytoextraction. Environmental Science and
Technology, v.31, p.800-805, 1997.
3. LOMBI, E.; ZHAO, F.J.; DUNHAM, S.J.; MCGRATH, S.P. Phytoremediation of heavy-metal
contaminated soils: natural hyperaccumulation versus chemically enhanced phytoextraction.
Journal of Environmental Quality, v.30, p.1919-1926, 2001.
4. SALT, D.E.; SMITH, R.D.; RASKIN, I. Phytoremediation, Annual Review Plant Physiology Plant
Molecular Biology, v.49, p.643-668, 1998.
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. Plants may use two strategies to deal with high metal concentrations adjacent to their roots: 1)
exclusion (avoidance) mechanisms by which the uptake and/or root-to-shoot transport of metals are
restricted; and 2) internal tolerance mechanisms that immobilize, compartmentalize or detoxify
metals in the symplasm through production of metal binding compounds (Marschner, 1995). Given
that the goal of phytoextraction is to maximize metal accumulation in plant tissues, mechanisms of
internal tolerance are likely to be important.
Internal tolerance to metals is thought to be based on several mechanisms rather than one alone, and
the lack of a comprehensive understanding of this complex metal homeostatic network in plants
remains a major bottleneck in the development of phytoextraction technologies (Hirschi et al., 2000;
Krämer, 2003). Compartmentation in the vacuole and chelation in the cytoplasm are among the most
significant mechanisms proposed to be related to metal accumulation by plants.
Metal transport from the cytosol to the vacuole is considered an important mechanism of both metal
tolerance and accumulation in plants. For this reason, much work has been dedicated to investigating
subcellular localization of metals in hyperaccumulators (Vázquez et al., 1992; 1994; Küpper et al.,
1999; 2000; Hirschi et al., 2000; Krämer et al., 2000; Sarret et al., 2002). Krämer et al. (2000) isolated
vacuoles from Ni-tolerant T. goesingense and Ni-sensitive T. arvense aiming directly to address the
role of vacuolar Ni storage in Ni tolerance. They found that T. goesingense accumulated two-fold
more Ni in the vacuole than T. arvense. Since protoplast and apoplast Ni contents were similar in both
species, vacuolar compartmentalization in T. goesingense seems to play a major role in Niaccumulation and tolerance.
Referensi:
1. HIRSCHI, K.D.; KORENKOV, V.D.; WILGANOWSKI, N.L.; WAGNER, G.J. Expression of Arabidopsis
CAX2 in tobacco. Altered metal accumulation and increased manganese tolerance. Plant
Physiology, v.124, p.125-133, 2000.
2. KRÄMER, U. Phytoremediation to phytochelatin - plant trace metal homeostasis. New
Phytologist, v.158, p.4-6, 2003.
3. KRÄMER, U.; PICKERING I.J.; PRINCE R.C.; RASKIN, I.L.; and SALT, D.E. Subcellular localization and
speciation of nickel in hyperaccumulator and non-accumulator Thlaspi species. Plant Physiology,
v.122, p.1343-1353, 2000.
4. KÜPPER H.; LOMBI E.; ZHAO F.J.; MCGRATH S.P. Cellular compartmentation of cadmium and zinc in
relation to other elements in the hyperaccumulator Arabidopsis halleri. Planta, v.212, p.75-84,
2000.
5. MARSCHNER, H. Mineral nutrition of higher plants. 2.ed. San Diego: Academic Press, 1995.
889p.
6. SARRET, G.; SAUMITOU-LAPRADE, P.; BERT, V.; PROUX, O.; HAZEMANN, J.L.; TRAVERSE, A.S.;
MARCUS, M.A.; MANCEAU, A. Forms of zinc accumulated in the hyperaccumulator Arabidopsis
halleri. Plant Physiology, v.130, p.1815-1826, 2002.
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Role of root exudates in metal phytoextraction
Chemical compounds likely to occur in the rhizosphere are clearly associated with increase of metals
uptake from soil and their translocation to shoots (Lin et al., 2003; Wenzel et al., 2003).
Low molecular-weight organic acids are probably the most important exudates in natural
phytoextraction systems. They influence the acquisition of metals by either forming complexes with
metal ions or decreasing the pH around the roots and altering soil characteristics. Despite the fact
that metals uptake may be increased due to decreasing pH, it is clear that the complexing capacity of
organic acids, rather than their capacity to decrease pH, is the main factor related to mobilization of
metals in soil and their accumulation in plants (Quartacci et al., 2005). Indirect effects of root
exudates on microbial activity, rhizosphere physical properties and root growth dynamics may also
influence ion solubility and uptake (Walker et al., 2003). For instance, microorganisms have been
shown to mobilize Zn for hyperaccumulation by Thlaspi caerulescens (Whiting et al., 2001) via
dissolution of Zn from the non-labile phase in soil.
Some plants release specific metal-chelating or reducing compounds into the rhizosphere to aid the
absorption of Fe and Zn when availability of these micronutrients is low (Marschner, 1995). Other
environmental stimuli have also been associated with root exudation of organic acids, including
anoxia (Marschner, 1995) and exposure to Al (Piñeros et al., 2002). It is thought that metal
accumulators may enhance metal solubility by releasing chelators from the roots. However, only a
few reports on the involvement of specific exudates in the uptake and accumulation of potentially
toxic metals by plants are known so far. In addition, the exudation rates and chemical composition of
exudates of hyperaccumulator species are virtually unknown.
Referensi:
1. LIN, Q.; CHEN, Y.X.; CHEN, H.M.; YU, Y.L.; LUO, Y.M.; WONG, M.H. Chemical behavior of Cd in rice
rhizosphere. Chemosphere, v.50, p.755-761, 2003.
2. PIÑEROS, M.A.; MAGALHÃES, J.V.; ALVES, V.M.C.; KOCHIAN, L.V. The physiology and biophysics of
an aluminum tolerance mechanism based on root citrate exudation in maize. Plant Physiology,
v.129, p.1194-1206, 2002.
3. QUARTACCI, M.F.; BAKER, A.J.M.; NAVARI-IZZO, F. Nitrilotriacetate- and citric acid-assisted
phytoextraction of cadmium by Indian mustard (Brassica juncea (L.) Czernj, Brassicaceae).
Chemosphere, v.59, p.1249-1255, 2005.
4. WALKER, T.S.; BAIS, H.P.; GROTEWOLD, E.; VIVANCO, J.M. Root exudation and rhizosphere biology.
Plant Physiology, v.132, p.44-51, 2003.
5. WENZEL W.W.; UNTERBRUNNER R.; SOMMER P.; SACCO P. Chelate-assisted phytoextraction using
canola (Brassica napus L.) in outdoors pot and lysimeter experiments. Plant and Soil, v.249, p.8396, 2003.
6. WHITING, S.N.; DE SOUZA, M.P.; TERRY, N. Rhizosphere bacteria mobilize Zn for
hyperaccumulation by Thlaspi caerulescens. Environmental Science and Technology, v.35, p.31443150, 2001.
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Sci. agric. (Piracicaba, Braz.) vol.63 no.3 Piracicaba May/June 2006
http://dx.doi.org/10.1590/S0103-90162006000300014
PHYTOEXTRACTION: A REVIEW ON ENHANCED METAL AVAILABILITY AND
PLANT ACCUMULATION
Clístenes Williams Araújo do Nascimento ; Baoshan Xing
Phytoextraction has emerged as a novel approach to clean up metal-polluted
soils in which plants are used to transfer toxic metals from soils to shoots.
This review provides a synthesis of current knowledge on phytoextraction of
metals from soils and their accumulation in plants. The objective is to integrate
soil-related (root exudates and chemical amendments) and biological advances
to suggest research needs and future directions.
As far as can be deduced from the literature, it will be some time before
phytoextraction may be established as a commercial technology. For chemicallyassisted phytoextraction, research has not shown easily biodegradable
compounds to overcome the risks associated with the use of EDTA for poorly
available metals in soils.
On the other hand, significant progress has been made on the physiological and
molecular aspects regarding tolerance and phytoaccumulation of metals in
plants.
A multidisciplinary approach is warranted to make
phytoextraction a feasible commercial technology to
remediate metal-polluted soils.
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IMPLICATIONS OF MERCURY SPECIATION IN THIOSULFATE TREATED PLANTS
Jianxu Wang, Xinbin Feng, Christopher W. N. Anderson, Heng Wang, Lirong Zheng, and Tiandou Hu
Environ. Sci. Technol. April 11, 2012
Mercury uptake was induced in two cultivars of Brassica juncea under field conditions
using thiosulfate.
Analysis was conducted to better understand the mechanism of uptake, speciation of
mercury in plants, and redistribution of mercury in the soil. Plant mercury and sulfur
concentrations were increased after thiosulfate treatment, and a linear correlation
between mercury and sulfur was observed.
Mercury may be absorbed and transported in plants as the Hg–thiosulfate complex.
The majority of mercury in treated plant tissues (two cultivars) was bound to sulfur in a
form similar to β-HgS (66–94%). Remaining mercury was present in forms similar to Hgcysteine (1–10%) and Hg-dicysteine (8–28%).
The formation of β-HgS may relate to the transport and assimilation of sulfate in plant
tissues. Mercury–thiosulfate complex could decompose to mercuric and sulfate ions in
the presence of free protons inside the plasma membrane, while sulfide ions would be
produced by the assimilation of sulfate. The concomitant presence of mercuric ions
and S2– would precipitate β-HgS.
The mercury concentration in the rhizosphere decreased in the treated
relative to the nontreated soil.
The iron/manganese oxide and organic-bound fractions of soil mercury were
transformed to more bioavailable forms (soluble and exchangeable and
specifically sorbed) and taken up by plants.
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