REMEDIATION OF HEAVY METALS-CONTAMINATED SOIL
AHMED K. SALAMA, KHALED A. OSMAN AND NEAMA A. GUDA
LOGO
Faculty of Science, Majmaah University and Alexandria University
LOGO
This report is based upon work supported by the Basic Science Research Unit, Scientific Research
Deanship, Majmaah University 2015
ABSTRACT:
The currently used techniques for soil remediation such as landfilling or
metal extraction using toxic agents as well as the use of metal-chelating
bio-surfactant need to be replaced by green technology solution.
Therefore, the research was designated to study the ability of plants to
bio-accumulate, translocate and remove some metals such as copper,
zinc, lead and cadmium from contaminated soil. The herbal plant
ryegrass, Lolium multiflorum was investigated as a bio-accumulator
plant for these metals. The translocation of these heavy metals in
ryegrass was compared considering root to shoot transport and
redistribution of metals in the root and shoot system. The trace metal
contents from root and shoot parts were determined using atomic
absorption spectrometer. The results showed that the percent of copper,
zinc, lead and cadmium transferred to ryegrass plant were 96.01, 84.51,
51.39, and 74.57%, respectively, while those remained in the soil were 3.81,
14.42, 45.16 and 27.40 % following 60 days of treatment. The soil-plant
transfer index in root and shoot system of ryegrass was found to be 0.60
and 0.37 for copper, 0.51 and 0.32 for zinc, 0.32 and 0.20 for lead, and 0.50
and 0.25 for cadmium. These findings indicated that ryegrass is a
promising accumulator plant and able to uptake and translocate the
heavy metals copper, zinc, lead or cadmium from contaminated soil.
SPECTROSCOPIC ANALYSIS
Plant and soil samples were subsequently analyzed for heavy metal
contents, as dry weight basis, using an atomic absorption spectrometer
(AAS). Measurements were made using the hollow cathode lamps for
Cu, Zn, Pb, and Cd at the proper wavelength. Working solutions were
prepared by dilution just before the use of standard solutions for atomic
absorption spectroscopy (1000 ppm). For the determination, two solutions
were prepared for each sample and three separate readings were made
for each solution. The means of these figures were used to calculate the
concentrations.
INTRODUCTION:
Soil contamination by heavy metals is one of the most critical
environmental problems as it poses significant impacts to the human
health as well as the ecosystems. Heavy metal contamination in soils can
come from atmospheric fall-out, pesticide formulations, and
contamination by chemical fertilizers and irrigation with water of poor
quality (Marcovecchio et al, 2007). They cannot be destroyed biologically
but are only transformed from one oxidation state or organic complex
to another pollution poses a great potential threat to the environment
and human health. The contaminants are able to infiltrate deep into the
layer of underground waters and pollute the groundwater as well as the
surface water. Heavy metals in the soil subsequently enter the human
food web through plants and they constitute risk to the ecosystem as
they tend to bio-accumulate and can be transferred from one food chain
to another. Heavy metals are discovered in various food chains where
the results are usually detrimental to micro-organisms, plants, animals
and humans alike. The use of plant species for cleaning polluted soils has
gained increasing attention as an emerging effective and inexpensive
technology (Macek et al, 2000, Susarla et al, 2002 and Xia et al, 2003)
compared to other remediation methods, because it is a natural process
and does not usually produce toxic by-products. It also has a minimal
impact on the environment (McKinlay and Kasperek, 1999).
Phytoremediation technologies are needed to replace currently used
techniques of either landfilling or metal extraction using caustic or toxic
agents. These plants are called hyper-accumulators that keep
contamination from spreading to other areas through the action of wind,
rain and groundwater (Perez et al, 2002, Glick, 2003, Olowoyo et al, 2012,
Badr et al, 2012, Luo et al, 2012).
OBJECTIVES:
CONCLUSIONS:
Soil contamination by metals is one of the most critical environmental
problems. The currently used techniques either landfilling or metal
extraction using toxic agents as well as the use of metal-chelating biosurfactant for soil remedy need to be replaced by green technology
solution. Therefore, the research was designated to study the ability of
plants to bio-accumulate, translocate and remove some metals such as
zinc, copper, lead and cadmium from contaminated soil. This method
does not usually produce toxic by-products. It is also cheaper and
effective technology with minimal impact on the environment and can
be easily used for soil remedy.
METHODS & MATERIALS:
Soil were sieved, dried and the pH value and organic matter were
determined. Seedlings of herbal plants were cultivated in pots containing
100 g soil without any fertilizer and the plant left to grow under
greenhouse conditions. Metal salts of copper carbonate, zinc carbonate,
lead hydroxide carbonate and cadmium nitrate at different
concentration levels of
0, 100, 200, 400
and
600 µg/g soil were spiked
60 days and divided into roots
and shoots. Plant and soil samples were dried at 105 °C in an oven for
24 h and powdered and digested with nitric acid. Samples were put in a
muffle furnace at 600°C for ashing. The ash was rinsed with 1.0 M nitric
into the soil. Plants were removed after
acid and filtered to be ready for analysis.
The investigated herbal plant is a good accumulator for Cu, Zn, Pb or Cd.
The soil-plant transfer factor (the conc. of heavy metal in plant to the
conc. in soil) indicated that the mechanism of soil remedy using the
investigated plant is phytoextraction where the amounts of heavy
metals transferred by plant roots into the above ground portions were
higher than that remained in the soil. Phytoremediation offers green
technology solution to the problem because it does not usually produce
toxic by-products. In addition, it is cheaper and effective technology with
minimal impact on the environment and can be easily used for soil
remedy.
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