Impact of pretilachlor herbicide and pyridaphenthion insecticide on aquatic organisms in model streams.

To detect the impact of pesticides on aquatic organisms, model streams (3m wide, 20 m long) were established in paddy field in Japan. More than 100 species of aquatic organisms were generated in the model streams. Field tests with pretilachlor herbicide and pyridaphenthion insecticide were carried out in the streams for 3 yr (2001-2003). Exposure of pretilachlor (max. 0.382 mg/L) showed little density changes in algae with a Bray-Curtis percent similarity in the range 81.6-93.3% for algae. Exposure to high concentrations (>0.1mg/L) of pyridaphenthion produced visible density reductions in Cladocera zooplankton species. Reduction of individual aquatic insects in the model streams by pyridaphenthion caused an increase of chlorophyll a greater than that of the control streams. The pesticides used showed no substantial differences in the ecosystems of model streams exposed to maximum environmental concentrations (e.g., 0.01 mg/L) detected in real rivers.