Monitoring sources, discharges, and fluxes of, and assessing the risks from, pesticides in the Kurose and Ashida Rivers, Japan

Because pesticide-contaminated water can harm living organisms, pesticide residues need to be monitored, their sources need to be identified, and the risks they pose should be assessed. In this study, the sources, fluxes, and discharges of, and risks from, pesticides were monitored and assessed during the rice-growing season (from April to October) in the Kurose and Ashida Rivers in Hiroshima, Japan. Water samples were collected monthly, subjected to solid-phase extraction, and then analyzed by gas chromatography-mass spectrometry and high-performance liquid chromatography to determine the presence and concentrations of pesticides. The fluxes of the detected pesticides were also estimated at each site in the Kurose and Ashida rivers, and the discharges of these pesticides from different sources were determined. The potential ecotoxicological risks from the detected pesticides to the aquatic systems were also evaluated. Thirteen pesticides were detected in the Kurose River. Of these, the mean concentrations of diroun (970 ng/L) and butamifos (4.7 ng/L) were the highest and the lowest, respectively. Eleven compounds were detected in the Ashida River. Again, the mean concentration of diuron (860 ng/L) was the highest, while that of flutolanil (5.5 ng/L) was the lowest. The pesticide fluxes were the highest in the Ashida and Kurose Rivers in October and May, respectively. The main sources of pesticide discharges were rice paddies, orchards, and vegetable fields. The results of the ecotoxicological risk assessment indicated that fenitrothion, diuron, dichlorvos, and benthiocarb posed high risks to the aquatic environment in the Ashida and Kurose Rivers.