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http://www.princeton.edu/~chm333/2004/Bioremediation/Hydrocarbons.htm
Hydrocarbons
Where does hydrocarbon contamination come from?
Hydrocarbons can be introduced into the environment via incomplete combustion of fossil fuels,
accidental discharge during transport, the disposal of petroleum products and other organic
wastes, incineration of refuse and wastes, and various industrial processes. They can also be
produced as a result of natural processes including forest fires and volcanic eruptions. Certain
hydrocarbons known as polycyclic aromatic hydrocarbons (PAHs) are found in soil at wood
preservation plants and gas manufacturing facilities.
Why are hydrocarbons toxic?
The inertness of high molecular weight hydrocarbons coupled with low solubility in water and
strong lipophilic character lead to high accumulation levels and persistence. Some
hydrocarbons (such as benzene) have been shown to be carcinogenic. In the case of large
industrial oil spills, the oil can actually suffocate living organisms and destroy entire ecosystems.
Excess hydrocarbons in aqueous environments can deplete the supply of oxygenating
molecules, leading to anoxic conditions.
Why use bioremediation?
Although they can be eliminated abiotically through photooxidation, PAHs with more than three
rings are more difficult to remove. High-molecular weight PAHs have a low bioavailability due to
their strong adsorption onto the soil organic matter, high resonance energy, and toxicity.
Numerous microorganisms – bacteria, algae, and fungi – are capable of metabolizing
hydrocarbons.
http://www.princeton.edu/~chm333/2004/Bioremediation/HOS%20main.htm
Halogenated Organic Solvents
The halocarbons, both halogenated compounds and halogenated solvents, are widespread
pollutants found in air, water, soil, and sediment; they are recalcitrant molecules resistant to
mineralization because the carbon-halogen bond is so stable. The stability and chemical
inertness of many halogenated compounds is part of their appeal in many industrial processes,
however it also makes them slow to degrade once they are released into the environment. In
general, the more halogens there are on a molecule, the slower the degradation process. The
focus for bioremediation of halocarbons is to exploit ability of organisms that have the natural
capacity to mineralize these toxic contaminants into benign molecules.
Halogenated organic solvents have a wide range of uses including metal processing,
electronics, dry cleaning and paint, paper and textile manufacturing. They thus have the
potential to contaminate almost every aspect of the environment, particularly water and soil.
Since halogenated solvents are generally denser than water they tend to sink and accumulate in
groundwater sources (they are also known as DNAPLs or dense nonaqueous phase liquids.)
Acute overexposure to halogenated solvents has serious health consequences for humans,
including possible nervous system damage, heart failure, and increased rates of cancer. At
lower doses halogenated solvents are considered potential carcinogens for humans and have
been shown to cause cancer in laboratory animals. (Prince, 1998)
http://www.princeton.edu/~chm333/2004/Bioremediation/HOC%20main.htm
Halogenated Organic Compounds
The halocarbons, both halogenated compounds and halogenated solvents, are widespread pollutants found
in air, water, soil, and sediment; they are recalcitrant molecules resistant to mineralization because the
carbon-halogen bond is so stable. The stability and chemical inertness of many halogenated compounds is
part of their appeal in many industrial processes, however it also makes them slow to degrade once they
are released into the environment. In general, the more halogens there are on a molecule, the slower the
degradation process. The focus for bioremediation of halocarbons is to exploit ability of organisms that
have the natural capacity to mineralize these toxic contaminants into benign molecules
.
Halogenated compounds have been used for a variety of purposes for hundreds of different industrial
processes over the last 50 years. However they present a danger to human health and include such known
toxins and potential carcinogens as dioxins, pesticides and PCBs. One prevalent example of a halogenated
organic compound is the widely used pesticide DDT, which has been shown to bioaccumulate in animal
fat tissue, disrupt hormone function, and damage ecosystems. PCB’s, polychlorinated biphenyls, are
another type of halogenated organic compound that have a variety of industrial applications as coolants,
lubricants, plasticizers, and dies. PCB’s are toxic chemicals and exposure has been shown to cause cancer
in laboratory studies. PCB’s may also adversely effect human health by contributing to neurological,
immune system, reproductive system, and other organ damage (see the EPA for more detail on PCB
health effects ).
A major problem with halogenated compounds is that they belong to a class of molecules known as
POP’s, persistant organic pollutants, which tend to biodegrade very slowly. It was originally thought that
there were no natural sources of halogenated compounds in the environment, and hence no organisms that
had evolved to exploit them. However, it has recently been shown that this is not the case (organisms as
well as volcanic eruptions can produce these compounds,), and that natural production of chlorinated
phenols may actually be greater than anthropogenic sources. Since these compounds have in fact existed
for millions of years, there are naturally occurring strains of bacteria have evolved to break down
halogenated compounds, thus opening up the possibility for bioremediation treatment of contaminated
sites.
http://www.princeton.edu/~chm333/2004/Bioremediation/NON%20main.htm
Nonchlorinated Herbicides and Pesticides
The bioremediation of herbicides and pesticides is of practical use, as it offers a less expensive
and more environmentally friendly way of cleaning up potential problems associated with the
toxins. The process focuses on detoxification rather than waste translocation [Dzantor], thereby
reducing the cost and complications associated with the possible alternatives, such as offsite
movement of the chemicals, human exposure, and expensive disposal of contaminated soil as
hazardous waste [Moorman].
When pesticides, herbicides, and fungicides are applied correctly they are usually designed to
be biodegradable so that they do not accumulate in the food chain. However, when these
chemicals are introduced to the environment in large quantities from manufacturing, storage or
spills they do present a contamination problem. Furthermore some nonchlorinated pesticides
and herbicides may contaminate the water supply and pose a potential health hazard.
Contamination can also result from heavy rain fall in the spring that washes away pesticide and
herbicide residue from newly treated fields into streams. Bioremediation strategies can be
employed to mineralize these compounds at contaminated sites.
A contamination in drinking water can cause serious consequences, even to those who do not
immediately drink that particular water. The problem can quickly jump from phytoplankton
feeding on the contaminated water to humans, in just a few short steps (phytoplankton to clams
to fish to humans). Thus, the managing of storage and spills of toxins such as pesticides and
herbicides is critical to several different species.
http://www.princeton.edu/~chm333/2004/Bioremediation/Nitrogen%20Compounds.htm
Nitrogen Compounds
Sources of Nitrogen contamination:
Nitrogen contamination in the form of nitrate (NO3-) and ammonia (NH3) occurs as a result of
agricultural runoff from fertilizer or animal waste. It is highly soluble and easily percolates
through the soil, contaminating aquifers. This excess nitrate poses a problem since it leads to
eutrophication in streams and has some averse health effects in humans.
Nitrogen contamination also exists in the form of nitroaromatic compounds such as
nitrobenzene, nitrophenol, nitrotoluene, and nitrobenzoate which are used in the industrial
manufacture of pesticides, explosives, dyes, pharmeceuticals and plastics.
Trinitrotoluen (TNT)
Health problems:
Nitrate ingestion can cause blue-baby syndrome (methaemoglobinemia) since nitrate-reducing
bacteria in the intestine produce nitrite which bind with hemoglobin in blood. This inhibits the
red-blood cells from transporting oxygen to tissue cells. Nitroaromatics are also highly toxic as
they are mutanagenic, and carcinogenic.
Why use bioremediation?
Bioremediation of nitrogenous pollution is not a new idea; the decontamination of nitrate and
ammonia pollution by bacteria is a major part of the nitrogen cyle. In fact, wastewater treatment
plants take advantage of this biological process all the time to remove nitrogenous pollution from
water via aeration tanks - we simply don't usually label this process as bioremdiation.
Furthermore, wastewater treatment is an example of ex situ treatment since the contaminated
media is transported to a different location for remediation. While this treatment is effective, it
requires expensive machinery and pump systems. Thus much current research is investigating
potential strategies for in situ remediation.
http://www.princeton.edu/~chm333/2004/Bioremediation/Metals.htm
Metals
Metal contamination:
A variety of metal contaminents exist in groundwater, surface water, and soils resulting from
industrial and agricultural activity. Toxic metals such as lead, mercury, cadmium, arsenic,
chromium, and uranium can cause damage to human health and the environment.
How does metal contamination occur?
Perhaps the most prevalent and problematic form of metal pollution is acid mine drainage. This
occurs when the mining of coal and metal ores exposes metals and radionuclides to the
atmosphere allowing them to be oxidized by certain bacteria (Thiobacillus ferrooxidans). For
example pyrite (often exposed in coal mining) can be oxidized to iron hydroxide and sulfuric
acid:
FeS2 + 15/4 O2 + 7/2 H2O = Fe(OH)3 + 2H+ + 2HSO4The effluent produced, known as acid mine drainage, is highly toxic since it is not only acidic but
also contains toxic metals. Such effluents have been known to contaminate nearby watersheds,
killing much of the aquatic life. Streams containing acid mine effluent (pictured below) are often
discolored due to Fe(OH)3 or “ yellow-boy” contamination.
Why use bioremediation?
While metals cannot be broken down into non-toxic components like organic compounds,
bioremediation can be used to stabalize, extract, or reduce the toxicity of soil and groundwater
contaminated by acid mine drainage. Bioremediation strategies are often more beneficial than
traditional "pump and treat" strategies because it can be implemented in situ, providing a
simpler, less intrusive, and cheaper method of remediation.