W11 PM Advances in Biorestoration Strategies for Contaminated Sediments
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 343-344

(TAB-1118-252764) Microbial - Metal Interactions Affecting Bioremediation of Metal Contamination of Soils and Sediments.

Tabak, H¹, van Hollenbusch, E², Dejonghe, W³, ¹ US EPA, ORD, NRMRL, Cincinniti, OH, USA² Universite de Liomoges, Laboratoire des Sciences de l’Eau et de l’Environment, Limoges, France³ Flemish Institute for Technological Research, VITO, Belgium

ABSTRACT- The last 15 years have seen an increase in the types of contaminants to which bioremediation is being applied, including solvents, PAHs and PCBs. Now, microbial processes are beginning to be used in the cleanup of radioactive and metallic contaminants of soils and sediments. Microorganisms can interact with these contaminants and transform them from one chemical form to another by changing their oxidation state through the addition of (reduction) or moving (oxidation) of electrons. . In some bioremediation strategies, the solubility of the transformed metal or radionuclide increases, thus increasing the mobility of these contaminants and allowing them to more easily be flushed out from the environment. In other strategies, the transformed metal or radionuclide may precipitate out of the solution, leading to immobilization. Both kinds of transformations present opportunities for bioremediatioin of metals and radionuclides in the environments - either to immobilize or to accelerate their removal. Metal contamination of soils and sediments is especially problematic because of the strong adsorption of many metals to their particles. Due to the difficulty of desorbing metal contaminants, some traditional remediation methods, simply immobilize metals in contaminated soils, by the additioin of cement or chemical fixatives, by capping with asphalt, or by in-situ vitrification.. Alternatively, soils are often isolated by excavation and confinement in hazardous waste facilities. Although rapid in effect, both of these options are expensive and destroy soil’s future productivity. The success of soil washing and pump-and-treat technologies to remove metals is severely limited by the slow desorption kinetics of adsorbed metals, with the result that additional additives (acids, chelates and reductants) are often used to promote metal transfer to the aqueous phase. These agents improve cost effectiveness but may introduce further harmful chemicals. A primary strategy of bioremediation is the use of similar metal-immobilizing agents in conjunction with soil washing, with advantage that they pose no known environmental threat themselves. Biopolymers have been discovered that bind metals with high affinity and travel relatively unimpeded through porous medium. Certain mecroorganisms transform strongly-adsorbing metal species into more soluble forms and plants are being recruited that act as self-contained pump-and-treat systems. Other methods employ enzymatic activities to transform metal species into volatile, less toxic or insoluble forms. Techniques for soil bioremediation are usually designed to be used in-situ, lowering costs; they avoid the use of toxic chemicals, and in nearly all cases, the soil structure and potential for productivity are preserved. This review paper provides a detailed information on the metal-microbe interactions and the application of these interactions for bioremediation of the metal contaminated soils and sediments. The paper describes: (1) microbial processes effecting bioremediation of metals and radionuclides and influencing their toxicity and transport (metal biotransformation, metal biosorption, metal bioaccumulation and biomineralization via microbially-generated ligands - degradation and synthesis of organic ligands of toxic heavy metals); and (2) microbial mechanisms involwed in bioremediation of metal and radionuclide contaminated soils and sediments (dissimilatory metal reduction. microbial metabolism of iron bacteria, microbial metal leaching, microbial polymers and their use in bioremediation of metal contamination and microbial metal volatilization).

Key words: bioremediation, metal contamination, metal-microbe, soils