Disappearance of diazinon, isoxathion and cartap applied to rice plant

Abstract

Diazinon, isoxathion and cartap were sprayed on rice plants. The amount of the insecticides recovered from rice plants were measured by GLC at intervals. Furthermore, experiments to investigate the cause of pesticide disappearance from rice plants were also performed. Initial deposition ratios of diazinon, isoxathion and cartap on rice plants were 5.90, 18.4 and 7.79% respectively. In the case of organophosphates, the disappearance curve of pesticides on rice plants consisted of two periods apparently. In the initial period (0-1day), the amounts of diazinon and isoxathion decreased very rapidly, the half lives of these insecticides being 0.35 and 0.92 day, but in the later period (3-15 days), the disappearance of the insecticides was very slow, the half lives being 4.8 and 5.0 days, respectively. Photodecomposition and volatilization tests were carried out using test tubes (Pyrex glass tube covered with aluminum foil, Pyrex glass tube, and quartz tube) and Petri dishes. Diazinon, isoxathion and cartap were slightly decomposed by sunlight.. Diazinon was very volatile, and only 0.1% remained in Petri dishes 8 hours after application, but 92.0% of cartap remained in the Petri dishes 8 hours after application. In conclusion, volatilizaton was the most important factor, for the disappearance of diazinon and isoxathion on rice plants, while the role of photodecomposition was negligible.