Ecological risks of pesticides in freshwater ecosystems; Part 2: insecticides

A literature review of freshwater model ecosystem studies with insecticides was performed to assess the NOEC ecosystem for individual compounds, to compare these threshold levels with water quality standards, and to evaluate the ecological consequences of exceeding these standards. Studies were judged appropriate for this purpose if the test systems simulated a realistic freshwater community, if the experimental design was generally sound (ANOVA or regression design; exposure concentrations described), and if published not earlier than 1980. Most studies dealt with organophosphates (predominantly single applications) and synthetic pyrethroids (mostly repeated applications) in standing waters. Structural endpoints were more sensitive than functional ones. The most sensitive taxa were representatives of the crustaceans, insects and fish. Most studies tested relatively high concentrations, with even lowest concentrations showing effects. An NOEC eco could therefore be established for a limited number of compounds only. Based on toxic units, safe threshold values were more or less the same for compounds with a similar mode of action. This also accounted for the nature and magnitude of direct effects at higher concentrations. Usually, indirect effects were reported at higher concentrations than those for direct effects. Although laboratory single species toxicity tests may not allow predictions on (exact) ecological effects, some generalizations on direct effects and recovery can be made with respect to the acute EC50 of the most sensitive standard test species. Safe concentrations, as set for water quality standards, appear to be protective. Depending on exposure regime, the NOEC eco is generally in the range of (0.1-0.01) x EC50 of the most sensitive standard test species. Recovery of sensitive endpoints usually takes place within two months after the last application when peak concentrations stay lower than (0.1-1) x EC50 of the most sensitive standard test species.