Variation in the fungicide, 4,5,6,7-phthalide, in water was investigated in order to evaluate the runoff of the fungicide after aerial application to paddy fields by a radio-controlled helicopter. The survey was conducted for 4 months after the application. The average and maximum concentrations of phthalide were 3.7-4.4 microg/L and 30.5-33.8 microg/L in the paddy fields, 0.37-0.64 microg/L and 2.7-7.5 microg/L in the drainage channels, and 0.18 and 0.83 microg/L in a river, respectively. The runoff ratios of the aerially applied phthalide from the paddy fields into the drainage channels were calculated to be 1.7-2.4%.

Variation in the fungicide, 4,5,6,7-tetrachlorophthalide (phthalide), in paddy field soil was investigated in order to evaluate its decrease after aerial application by a radio-controlled helicopter. The maximum concentrations of phthalide were 309-320 microg/kg dry, which were 83%-96% of the applied phthalide. The organic carbon normalized soil sorption coefficient (K(oc)) was calculated to be 94-96 mL/g at 1 h after the application. The calculated K(oc) values increased to 620-1,300 mL/g from 1 through 9 days after the application and then 4,700-7,200 mL/g 14 days after the application. The half-life of the phthalide was calculated to be 20-31 days.

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