TRACE-METAL MOBILIZATION IN SOIL BY BACTERIAL POLYMERS

Enhanced transport of trace metal in porous media can occur in the pre sence of a ligand or ''carrier'' that has a high affinity for binding the pollutant, is dispersed and mobile in the soil environment, is rec alcitrant with respect to microbial degradation, and is acceptable to the public. These aspects of the facilitated transport to trace metals are discussed with respect to a naturally occurring carrier: extracel lular polymers of bacterial origin. The literature is reviewed regardi ng the production and composition of bacterial extracellular polymers, the processes relevant to the facilitated transport of trace metals i n soil by bacterial polymers, and potential for transformation of poly mers in soils by microbial degradation. Model calculations of contamin ant retardation are presented for the case of polymer-mediated transpo rt of cadmium in a sandy aquifer material. The available information s uggests that extracellular polymers can bind metal ions and are mobile in the soil environment. Extracellular polymers also appear to be rel atively slowly degraded by soil microorganisms. These properties and t he supporting model calculations indicate that extracellular polymers of bacterial origin merit consideration as agents that may be applied to contaminated soils to enhance trace meta mobility.