Daily variation of pesticides in surface water of a small river flowing through paddy field area.

The daily variations in the insecticides, i.e., buprofezin, etofenprox, fenitrothion, fenobucarb and pyridaphenthion, and fungicides, i.e., flutolanil, isoprothiolane, mepronil, pencycuron, phthalide and tricyclazole, were investigated in order to evaluate the short periodic variations in the pesticide concentrations of small river waters. The mean and maximum concentrations were 0.05 microg/L (pyridaphenthion)--1.2 microg/L (isoprothiolane) and 0.30 microg/L (pyridaphenthion)--13 microg/L (flutolanil), respectively. The concentration at 10:00 a.m. could be regarded as the representative daily concentration of the day. However, the concentration could markedly vary during the day or the day following the pesticide application. Therefore, the mean concentrations at 10 a.m., 2 p.m. and 6 p.m. were recommended as the best representative values of the day.