Abstract
Fenitrothion was sprayed by helicopter on the paddy field in Katahigashi, Nishikanbara, Niigata Pref., in Aug., 1997 and Aug., 1998. The concentration of fenitrothion in the atmosphere was measured. The air was trapped into silica gel column, and fenitrothion was eluted with acetone and was determined by FPD-GC. The maximum concentration of fenitrothion at the spray area, 1.0-2.3μg/m3, was observed for 3-22 hours after the application, and the concentration decreased over time. The maximum concentration of fenitrothion outside of the spray area, 0.7-1.8μg/m3, was observed for 22-47 hours after the application. Therefore, the concentration at the outside of the spray area was 1/2-1/10 of the concentration at the spray area. The meteorological parameters at air sampling, geographic parameters and physical chemical parameter were used as the area source plume model (ASPLM) . The emission rate (Q) was calculated by the use of empirical equations with a vapor pressure of fenitrothion and the elapsed time after application. Q, wind speed, distance between air sampling point and emission point, diffusion width and plume height were used as the point source plume equation to calculate the diffusion from a point source in the area source. And the predicted concentration was calculated by summing up concentration diffused from all emission points. It was observed that the predicted pesticide concentrations at the spray area were equal to observed values. The predicted concentration at the outside were slightly lower than observed ones and the prediction error slightly increased with distance from sprayed border line. The predicted values ranged from 1/11 to 11 times of observed them. Therefore, it was proved that the ASPLM was useful for predicting the concentration of pesticides after application on paddy field.
