Population and community responses in pesticide-stressed freshwater ecosystems

This paper illustrates the ecological impact of pesticide contamination on freshwater organisms and communities by presenting results of semi-field te sts with the urea herbicide linuron and the organophosphorous insecticide c hlorpyrifos. In addition, a literature review is presented of results of mi crocosm and mesocosm studies performed with other photosynthesis inhibiting herbicides and cholinesterase inhibiting insecticides. The most sensitive ecological endpoints for photosynthesis inhibitors (incl uding linuron) are responses related co oxygen metabolism and the populatio n structure of primary producers (phytoplankton, periphyton, macrophytes). For cholinesterase inhibiting insecticides (including chlorpyrifos) the mos t sensitive endpoints are population responses of crustaceans, insects and fish. These effects show a clear dose-response relationship in accordance w ith results of laboratory single species tests, suggesting a response due t o direct toxic effects. Indirect effects usually became apparent at concent rations that were more than a Factor 3-10 higher than critical threshold co ncentrations for direct effects. The criteria as set by the Uniform Principles appear to provide sufficient protection for freshwater ecosystems when exposed to an individual photosyn thesis inhibiting herbicide or cholinesterase inhibiting insecticide. Depen ding on the application regime and the persistence of the pesticide, recove ry of sensitive ecological endpoints in stagnant micro/mesocosms usually ta kes place within two months when the peak concentration is not higher than (0.1-1) x EC50 of the most sensitive standard test species.