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Cadmium concentrations constituting a threat to aquatic ecosystems were predicted from data collected at two levels of biological hierarchy. A population-level estimate was derived from single-species toxicity test data, and a community-level estimate was derived from toxicity tests on protozoan communities. Estimates were compared with each other and with an ecosystem-level estimate derived from reports of ecological health and ambient cadmium levels in rivers, lakes, and streams.
Estimates of permissible acute concentrations differed by an order of magnitude. Single-species toxicity test data suggested that 42 μg Cd/L would affect 5% of taxa. The corresponding estimate from the community-level test was 459 μg Cd/L. Similar estimates of permissible chronic concentrations were not significantly different (0.82 and 0.20 μg Cd/L, single-species and community-level tests, respectively). Both estimates of permissible chronic concentrations fell within a rational range, the minimum defined by median cadmium concentrations in healthy aquatic systems (0.05 μg Cd/L) and the maximum defined by median cadmium concentrations in damaged systems (9.2 μg Cd/L).
cadmium, hazard evaluation, microcosm, toxicity, validation
Laboratory Specialist, University Center for Environmental Studies, Virginia Polytechnic Institute and State University, Blacksburg, VA
Research Associate, Virginia Polytechnic Institute and State University, Blacksburg, VA
Professor of Zoology, Virginia Polytechnic Institute and State University, Blacksburg, VA
University Distinguished Professor, Department of Biology, and Director, University Center for Environmental Studies, Virginia Polytechnic Institute and State University, Blacksburg, VA