Variation of 4,5,6,7-tetrachlorophthalide in water after aerial application to rice cultivation area

Fate of pesticides in combined paddy rice-fish pond farming systems in northern Vietnam

During the last decades, high population growth and export-oriented economics in Vietnam have led to a tremendous intensification of rice production, which in turn has significantly increased the amount of pesticides applied in rice cropping systems. Since pesticides are toxic by design, there is a natural concern on the impact of their presence in the environment on human health and environmental quality. The present study was designed to examine the water regime and fate of pesticides (fenitrothion, dimethoate) during two consecutive rice crop seasons in combined paddy rice-fish pond farming systems in northern Vietnam. Major results revealed that 5 and 41% (dimethoate), and 1 and 17% (fenitrothion) of the applied mass of pesticides were lost from the paddy field to the adjacent fish pond during spring and summer crop seasons, respectively. The decrease of pesticide concentration in paddy surface water was very rapid with dissipation half-life values of 0.3 to 0.8 and 0.2 d for dimethoate and fenitrothion, respectively. Key factors controlling the transport of pesticides were water solubility and paddy water management parameters, such as hydraulic residence time and water holding period. Risk assessment indicates that the exposure to toxic levels of pesticides for aquaculture (, ) is significant, at least shortly after pesticide application.

Daily variation of pesticides in surface water of a small river flowing through paddy field area

The daily variations in the insecticides, i.e., buprofezin, etofenprox, fenitrothion, fenobucarb and pyridaphenthion, and fungicides, i.e., flutolanil, isoprothiolane, mepronil, pencycuron, phthalide and tricyclazole, were investigated in order to evaluate the short periodic variations in the pesticide concentrations of small river waters. The mean and maximum concentrations were 0.05 microg/L (pyridaphenthion)--1.2 microg/L (isoprothiolane) and 0.30 microg/L (pyridaphenthion)--13 microg/L (flutolanil), respectively. The concentration at 10:00 a.m. could be regarded as the representative daily concentration of the day. However, the concentration could markedly vary during the day or the day following the pesticide application. Therefore, the mean concentrations at 10 a.m., 2 p.m. and 6 p.m. were recommended as the best representative values of the day.

Decrease of 4,5,6,7-tetrachlorophthalide in paddy field soil after aerial application

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.