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Water samples collected once a week from early April 1996 to the end of August 1996 from four sites on the Shinano River in Japan were analyzed for pesticides and their metabolites using a gas chromatograph-mass spectrometer. Among the total of 53 chemicals found, 22 were herbicides, 15 were insecticides, 11 were fungicides, and 5 were metabolites. The concentrations of chemicals found ranged from 3 ng/L (bromobutide) to 8200 ng/L (isoprothiolane). Herbicides were found primarily during May and June at all four sites. Insecticides and fungicides were found primarily during July and August at all four sites. The presence of pesticides in the river water correlated with the time of pesticide application to the rice fields near the river.

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