Toxicity of pesticides to aquatic microorganisms: A review

Microorganisms contribute significantly to primary production, nutrient cyc ling, and decomposition in estuarine ecosystems; therefore, detrimental eff ects of pesticides on microbial species may have subsequent impacts on high er trophic levels. Pesticides may affect estuarine microorganisms via spill s, runoff, and drift. Both the structure and the function of microbial comm unities may be impaired by pesticide toxicity. Pesticides may also be metab olized or bioaccumulated by microorganisms. Mechanisms of toxicity vary, de pending on the type of pesticide and the microbial species exposed. Herbici des are generally most toxic to phototrophic microorganisms, exhibiting tox icity by disrupting photosynthesis. Atrazine is the most widely used and mo st extensively studied herbicide. Toxic effects of organophosphate and orga nochlorine insecticides on microbial species have also been demonstrated, a lthough their mechanisms of toxicity in such nontarget species remain uncle ar. There is a great deal of variability in the toxicity of even a single p esticide among microbial species. When attempting to predict the toxicity o f pesticides in estuarine ecosystems, effects of pesticide mixtures and int eractions with nutrients should be considered. The toxicity of pesticides t o aquatic microorganisms, especially bacteria and protozoa, is an area of r esearch requiring further study.