Distribution and residue of 35S-methamidophos in simulated Rice-Azolla-Fish system

Distribution and residue of 35S-methamidophos in simulated Rice-Azolla-Fish System have been studied. The results show: (1) when 2 x 50g of 50% methamidophos emultion/mu are sprayed on the early rice, there is 0.01 ppm in the brown rice, and 0.55 ppm in the fish; (2) when 3 x 50g of 50% methamidophos emultion/mu are sprayed on the late rice, there is 0.04 ppm in the brown rice, and 0.40 ppm in the fish. ADI of methamidophos is 0.0006 mg/kg body according to FAD/WHO recommendation in 1985, so Maximum Residue Limit (MRL) in the rice is 0.078 ppm, MRL in the fish is 2.3 ppm. The residue in the rice and fish does not exceed the MRL by FAO/WHO recommendation, when the amount of used methamidophos was controlled. 35S-methamidophos in the simulated system disappears as exponential function. The half-life of 35S-methamidophos on the Azolla, water, fish and straw are 1.5, 2.8, 6.2 and 2.2 days respectively