Investigation of Seasonal Changes and Ecological Risk Assessments of Neonicotinoid Pesticides in Rivers in Osaka, Japan

Concentrations of neonicotinoids and fipronil in river water were investigated in rural areas, the lower reach of the sewage disposal plant and principal rivers in Osaka Prefecture. As a result, pesticides other than nitenpyram and thiacloprid were detected at all sampling sites. Concentrations of imidacloprid increased drastically in June and concentrations of dinotefuran increased drastically from August to September. These periods were contemporaneous with spraying periods of these pesticides in rice fields. It was determined that none of the pesticide concentrations exceeded the water quality standards in Japan or Predicted Environmental Concentrations (PEC), which were calculated by the Ministry of the Environment, in all survey spots. On the other hand, more than 5% of the aquatic organisms are expected to be affected by neonicotinoids in rural area rivers from late May to June according to the calculation from species sensitivity distribution (SSD) of multiple influence of aquatic arthropods.