Microorganisms are sensitive to heavy metal pollution as are other components of the
biota. However, most studies on the interactions between microbes and heavy metals
have been conducted in synthetic media or in altered (e.g., sterilized) environmental
samples and usually have used only single species. Few studies have evaluated the
effects of heavy metals on the activities of natural heterogeneous microbial populations,
both autotrophic and heterotrophic, in terrestrial and aquatic environments. These
latter studies have shown that heavy metals inhibit primary productivity, nitrogen
fixation, the mineralization of carbon, nitrogen, sulfur, and phosphorus, litter decomposition,
and enzyme synthesis and activity in soils, sediments, and surface waters. The potential
adverse effects of heavy metals on such microbe-mediated ecologic processes need to
be incorporated into the methodologies used by regulatory agencies, such as the U.S.
Environmental Protection Agency, to prepare environmental risk assessments which,
in turn, are used to formulate environmental criteria, such as the Water Quality Criteria,
and to evaluate the safety to the environment of exposure to "new chemical substances,"
as mandated by the U.S. Toxic Substances Control Act of 1976. To provide appropriate
data that can be assimilated into regulatory policy, it is essential that microbial
ecotoxicity tests be standardized, are neither costly nor difficult to train personnel
to conduct, and produce data that can be quantitated.