Study On Residue And Degradation Of Shachongdan In Soil-water-paddy System

Shachongdan is a new pesticide invented by China. At present there is no effective analytical method and reasonable application criterion. An analytical method was established for determining residue of Shachongdan by the gas chromatography under the optimized conditions, and a set of application criteria in paddy were recommended for 80% Shachongdan SP according to the field experiment.Fortified recover)7 was carried out with soil, water, rice plant, rice and chaff as material. The RC and CV range for the method were 86.7-94.3% and 3.54%~12.4%, respectively. The method was convenient, quick, sensitive and accurate.The results indicated that under 1200g.ai/h application Shachongdan could be degraded quickly in field water and soil with half-lives of 0.83 and 0.90 days respectively. But it was degraded slowly in simulative water and rice plant with half-lives of 1.89 and 2.72 days. Shachongdan degradation in rice plant, field water, simulative water and soil followed the first-degree reaction model.The results also indicated that under 600g.ai/h and 1200g.ai/h application, the sampling interval apart from last application was 20 and 30 days, the residue was ND~0.2577mg/kg in rice, ND~0.4760mg/kg in chaff, ND~0.7829mg/kg in rice plant, ND~0.5426mg/kg in soil. As a52general rule, the residue in rice plant was slightly higher than that in rice, chaff or soil. The residue with larger dose, more application and shorter sampling interval from last application was slightly higher than its counterpart.Referring to the maximum residue limit (MRL) of shachongshan in rice, the MRL of shachongdan in rice is temporarily suggested to be 0.2 mg/kg. Under 600gai/h application in paddy, using twice or three times. the sampling interval apart from last application being 20 days and 30 days, the residue was lower than 0.2mg/kg. If under 1200g.ai/h application, using twice or three times, the residue would be possibly higher than 0.2mg/kg. The recommended application criterion is that 80% Shachongdan SP was sprayed under 600g.ai/h application, at most three times per season crop, with a 15 days' interval between two applications and with a longer than 20 days' interval between last application and harvest.