Koptsik, G., Lofts, S., Karavanova, E., Naumova, N., Rutgers, M.
Heavy metals in forest soils: Speciation, mobility and risk assessment. Chapter 6.

In: I. Ahmad, S. Hayat, J. Pitchel (Eds.), Heavy metal contamination of soil: Problems and remedies. New Delhi: Oxford & IBH Publishing Co. Pvt. Ltd., 2005. P. 105-156.

Annotation:

Contamination of soils and deeper sediments by toxic metals, metalloids, and radionuclides is a worldwide problem due to improper disposal practices, spills, atmospheric deposition of combustion emissions, and intentional application of sludges, fertilizers, or other materials. Such soil contaminants can pose various ecological problems, leach into drinking and agricultural water sources, or enter the food chain via plant uptake and bioaccumulation in plants or animals. The potential for causing ecological damage or negative human health consequences is largely a function of metal redox state, solubility, speciation, and other physicochemical properties. Although many of these contaminants are strongly sorbed by secondary clay minerals, metal oxides, carbonates, and humic substances in soils, their mobility can be strongly affected by microbial activity by a variety of mechanisms.

Changes in metal mobility can result from direct microbial oxidation or reduction of the metal, direct sorption by microbial biomass, uptake and bioaccumulation of metals, indirect microbially mediated changes in metal redox state, indirect stimulation of mineral precipitation by microbial surfaces, and/or indirect changes in groundwater and sediment geochemistry as a result of microbial metabolic processes. Microbial reduction of chromate, for example, may convert highly mobile Cr(VI) to less mobile Cr(III). In other cases, changes in metal redox state may be indirectly caused by microbial activity. Cr(VI), for example, may also be indirectly reduced to Cr(III) by Fe(II)-containing minerals formed by the activity of iron reducing bacteria. Microbial metabolism can also produce complexing ligands and carbonate species that may alter aqueous metal speciation or solubility, and release or immobilize metals as a result of dissolution and precipitation events. All of these processes may be accelerated by the presence of humic compounds which may both serve as metal complexants and electron shuttles between the bacterial respiratory system and the mineral surface. Considered together, these various mechanisms present a variety of options for the microbially mediated mobility of contaminant metals in soils and sediments.

For soil scientists, ecologists, biologists, biogeochemists and forestry specialists.

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