MICROBIAL SOLUBILIZATION AND IMMOBILIZATION OF TOXIC METALS - KEY BIOGEOCHEMICAL PROCESSES FOR TREATMENT OF CONTAMINATION

Microorganisms play important roles in the environmental fate of toxic metals with a multiplicity of physico-chemical and biological mechani sms effecting transformations between soluble and insoluble phases. Su ch mechanisms are important components of natural biogeochemical cycle s for metals and metalloids with some processes being of potential app lication to the treatment of contaminated materials. This paper will c oncentrate on three selected aspects which illustrate the key importan ce of microorganisms in effecting changes in metal(loid) solubility, n amely toxic metal sulfide precipitation by sulfate-reducing bacteria, heterotrophic leaching by fungi, and microbial transformations of meta lloids, which includes reduction and methylation. The basic microbiolo gy of these processes is described as well as their environmental sign ificance and use in bioremediation.