Bioremediation of heavy- and
radioactive-metal contaminations
from soil and ground water
John Hanna
Bioremediation
The use of biological agents, such as bacteria, fungi, or green
plants, to remove or neutralize contaminants, as in polluted soil or
water
 Break
down contaminants into less substances (e.g.
Petroleum)
 Act
to accumulate the contaminants so they can be
easily removed
 Chemical
forms
reduction of heavy metal ions to insoluble
Risk-Benefit relationship between
contaminants versus nutrition from
the consumption of fish

Heavy metals (e.g Mercury)

Dioxins

Polychlorinated biphenyls (PCBs)

Poly-unsaturated fatty acids
(Omega-3) fatty acids such as
eicosapentaenoic acid (EPA) and
docosahexaenoic acid (DHA)

Undisputed heatlh benefits (e.g
coronary heart disease
Rate of CHD cohort study on risks
CHD in relationship consuming
fish or fish oil
Bioremediation methods
available today to remove heavy
metal contamination

Used for the removal of Mercury, among other
metals such as chromium, cadmium, Zinc and
radioactive Uranium from agricultural areas or
groundwater reservoirs

Naturally-occurring organisms or those that have
been engineered to enhance their bioremediation
capability (biotechnology)

Methods include: bio-bleaching, bio-precipitation,
bio-sorption, and bio-accumulation
Bio-bleaching

The use of bacteria and fungi to remove metals (e.g.,
Cadmium, Copper, Nickel, and Zinc) from
contaminated soil

Insoluble metals are solubilized with organic acids (e.g.
hydrogen cyanide) produced by the living organism to
generate a soluble metal ion
 Insoluble
Metal + HCN  Metal-CN + H+
Bio-precipitation or biomineralization

bio-precipitation/biomineralization involves the
formation of insoluble compounds following the reaction
of soluble metal ions with either inorganic phosphate,
carbonate, or sulfide that is released from bacteria

Selection of bacterial strains capable of enhanced
organic ion secretion greatly increases the effectiveness
of this method

Metal ion + HPO42-  Metal-HPO4

Metal ion + CO32-  Metal-CO3

Metal ion + H2S  Metal-S
Bio-sorption and bioaccumulation

The removal of soluble metals from solution by biological
material.

Process are not limited to live organisms but also dead
ones which in addition to bacteria also can be carried out
by algae and fungi

Examples include: Engineering bacterial cells to express
mercury binding protein (MerC) or phytochetalins to
enhance the removal of mercury, arsenic, or cadmium
Bioremediation with Plants or
plant/fungi combinations

Plants inoculated with specialized fungi form structures in the
plant root systems known as mycorrhiza.

Working together the fungi enhances the ability of the plants to
absorb materials from the soil
Bioremediation of Uranium
contamination from ground
water

Uranium is removed by the reduction of Uranium (VI) to
insoluble Uranium (IV)

Same process can be also used to remove selenium and
Cadmium contamination

In all cases, the chemical reduction of the contaminant is
coupled to the oxidation or an organic compound
produced by the organism (e.g. acetate, lactate,
pyruvate, glycerol, or ethanol)

Process can be greatly enhanced by biotechnological
methods
Conclusions

Bioremediation offers a safe and effective method to
remove contaminants from the environment.

The use of bioengineered microorganisms, plants, or
bacteria will continue to offer promising alternatives to
the scientific community and allow the bioremediation
of otherwise uninhabitable areas

However, in most cases bioremediation is not 100%
effective in removing the contaminants

Research is needed to establish the Risk/Benefit
relationships for individual contaminants in order to
make educated decisions to treat individual cases
References
1.
Mozaffarian D, Rimm EB (2003) Fish intake, contaminants, and human
health evaluating the risks and the benefits. JAMA, 296(15): 1885-1899.
2.
Gadd GM. (2010) Metals, minerals and microbes: geomicrobiology and
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3.
Dhankher OP, LI YJ, Rosen BP, Shi J et al (2002) Engineering tolerance
and hyper-accumulation of arsenic in plants by combining arsenate
reductase amd gamma-glutaminecysteine synthase expression. Nat
Biotechnol 20, 1140-1145.
4.
Lovely DR, Phillips EJP, Gorby YA, Landa ER (1991) Microbal reduction of
uranium. Nature 350, 413-416.
5.
Stolz JF, Oremland RS (1999) Bacterial respiration of arsenic and
selenium in microbial metabolism FEMS Microbiol Rev 23, 615-627.
6.
Thompson-Eagle ET, Frankenberger WT, Karlson U (1989) Volatilization of
selenium by Alternaria alternata. Appl Environ Microbiol 55, 1406-1413.
7.
Nevin KP, Finneran KT, Lovley DR. (2003) Microorganisms associated with
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Environ Microbiol. 69(6): 3672-3675.