Effects of chronic low concentrations of the pesticides chlorpyrifos and atrazine in indoor freshwater microcosms

Effects of chronic low concentrations of chlorpyrifos (0.1 μg.L−1) and atrazine (5 μg.L-−1) were studied in indoor freshwater microcosms. Test concentrations were based on a factor of 0.1 multiplied by the lowest available L(E)C50 of standard aquatic test organisms. We tested whether this safety factor was sufficient to protect aquatic communities in the-microcosms in the case of a chronic exposure regime. Effects on plankton, macro-invertebrates and physico-chemical parameters during the seven weeks of treatment are summarized in this paper. Chlorpyrifos treatment resulted in primary effects on the zooplankton taxa Cyclopoida and Daphnia galeata and the macro-invertebrate Gammarus pulex, and secondary effects on the rotifer Keratefia quadrata. No effects of chlorpyrifos on phytoplankton or on physico-chemical parameters were found. Atrazine exposure caused a slight shift in the functional parameters: DO, pH, alkalinity and conductivity, indicating a small decrease in photosynthetic activity. No effects of atrazine on the species composition of the ecosystem were found. In case of a chronic exposure to chlorpyrifos, a safety factor of 0.1 appeared to be insufficient to protect the aquatic community.