Abstract
Thirty-nine paddy pesticides and 11 of their metabolites were monitored in the Sakura River during the rice cultivation season in 2007 and 2008. Pesticide concentrations in the river water depended on the timing of pesticide application. Herbicides that were shipped to Ibaraki Prefecture in large amounts or had high water solubility, a low soil adsorption constant value, or large usage rates were detected at high peak concentrations. The concentrations of nursery-box-applied fungicides and insecticides peaked immediately after transplanting. The concentrations of pesticide metabolites, such as bromobutide-desbromo, cafenstrol-descarbamoyl, clomeprop-propionic acid, carbofuran, and fenthion-sulfoxide depended on the degradation rates and metabolic pathways of the parent compounds and on the stability of the metabolites in water and soil. Clomeprop-propionic acid, carbofuran, and fenthion-sulfoxide, which were formed from rapidly degradable pesticides, were detected at much higher peak concentrations than the parent compounds.
