Relative tolerances of selected aquatic oligochaetes to individual pollutants and environmental factors

Abstract

Aquatic oligochaete distributions are a recognized indicator of environmental quality. The purpose of this study was to investigate the tolerances of 12 oligochaete species to specific pollutants and environmental factors and to relate tolerances to the use of oligochaetes as indicator species. Species were chosen for experimentation based on their present or potential importance as indicators of organic pollution. Acute toxicity data (96-h LC 50 values) were obtained for 9 freshwater ( Limnodrilus hoffmeisteri, Tubifex tubifex. Branchiura sowerbyi, Varichaeta pacifica, Quistadrilus multisetosus, Rhyacodrilus montana, Spirosperma nikolskyi, Spirosperma ferox and Stylodrilus heringianus) and 3 salt-water species ( Monapylephorus cuticulatus, Tubicoides gabriellae and Limnodriloides verrucosus). The tolerances of these species were determined for 5 pollutants (cadmium, mercury, pentachlorophenol, pulp mill effluent and sewage sludge) and 4 environmental factors (pH, temperature, salinity and anoxia) both with and without sediment. Species considered to be eutrophic indicators were the most tolerant to sewage sludge, and oligotrophic species were the least tolerant. However, this was not true for pulp mill effluent or the chemical pollutants. The results confirmed the use of present oligochaete assemblages to indicate the degree of trophy in natural systems, but also suggested new assemblages for indicating the presence of particular chemical contaminants. The presence of sediments resulted in increased tolerances for all species, demonstrating the role of sediments as important modifiers of toxic effects on oligochaetes.