Predicting the behavior of paddy pesticides in a river basin using a simulation model (PADDY-Large): Application to a tributary of the Chikuma River under rice cultivation

• Published in: Journal of Pesticide Science 2011/08/25, Vol.36(3), pp.413-427
• Main Authors: Inao, Keiya, Hojyo, Toshihiko, Annoh, Hirochika, Miyazaki, Satoe, Saito, Takeshi, Park, Ho-Dong
• Format: Article
• Language: eng ; jpn
• Subjects: environmental fate; mathematical model; metabolite; paddy pesticide; river basint; runoff and drif
• ISSN: 1348-589X; 1349-0923
• DOI: 10.1584/jpestics.W11-15

Eleven paddy pesticides and 3 of their metabolites were monitored in Hiroi stream (a tributary of the Chikuma River in Japan) during rice cultivation season for 5 years (2001–2005). An improved simulation model for predicting pesticide behavior in drainage canals and rivers based on PADDY-Large was developed to include the metabolic pathways and drift process following aerial and unmanned helicopter spraying and applied to herbicides as well as nursery-box- and foliage-applied fungicides and insecticides. The nursery-box-applied insecticide carbosulfan was rarely detected in stream water during the monitoring period, whereas a clear peak for its metabolite (carbofuran) was observed. Detection of herbicides other than cyhalofop-buthyl was dependent on the timing of herbicide application. The fungicide tricyclazole, the insecticide trichlorfon, and the trichlorfon metabolite (dichlorvos) were detected at a few dozen μg L−1 immediately after aerial spraying and the concentrations decreased rapidly. In contrast, these peak concentrations sprayed by unmanned helicopter were one-tenth to one-half of those by aerial application. The improved PADDY-Large model successfully simulated changes in concentrations of paddy pesticides and 3 of their metabolites in stream water during the rice cultivation season, although there were some discrepancies between simulated and measured concentrations.