Degradation Dynamics and Residual Safety Evaluation of Methidathion in Citrus and Soil

The tests of degradation dynamics and final residue for 40% methidathion EC were conducted in the Hunan Academy of Agricultural Sciences and the Zhejiang Academy of Agricultural Sciences in 2009,and the methidathion content was determined by gas chromatography.The results showed that the average fortified recoveries of methidathion in the fruit,pulp,peel of citrus and soil were 82.22%~86.72%,80.94%~83.08%,81.74%~91.01% and 84.58%~95.39%,respectively;the degradation rates of methidathion in citrus and soil were almost the same,and the degradation half-life of methidathion in the citrus and soil was 10.83~11.45 d and 9.34~11.31 d,respectively;applying 40% methidathion EC with the using dose(400 ai·mg/L and was diluted to 1 000 times with water) and high-dose(600 ai·mg/L and was diluted to 666.7 times with water) for 1 to 2 times and once every 14 d,the last application was done in the interval of 7 d before harvest,the residue of methidathion in the harvested orange was lower than 2.0 mg/kg,which indicating that it was safe to apply the methidathion to orange with both doses;the methidathion belonged to the pesticide that was easy to be degraded and its residue amount in citrus and soil had no significant correlation with its applying concentration and application times.