| Fenoxanil which is used in most areas planted rice is recommended as a fungicide in China. In order to evaluate the eco-environment of fenoxanil in rice paddies, this paper had systematically studied the residual degradation of fenoxanil and its preparation in paddy water, paddy soil and paddy straw, and adsorption rules and the influence factors in five different types of tested soils. The studies comprehensively, accurately estimated the safety of fenoxanil after it was applied in rice field. The results could provide some fundamental datas for scientific application of fenoxanil. The main conclusions were as follows:(1) The methods of GC-NPD analysis of fenoxanil and the extraction and purification were established.The samples were extracted by acetone and water separately, then purified by a florisil column, finally detected with GC-NPD. The minimum detectable amount of fenoxanil were 1×10-7mg and the lowest detectable concentrations in paddy water, paddy soil, paddy straw, rice hull and brown rice were 0.005 mg/L,0.025,0.05,0.05,0.025mg/kg, respectively. When the additive amount of fenoxanil rang from 0.05 to 5.00mg/kg, the average recoveries rang from 84.27% to 108.67% and the coefficient of variations were from 0.54% to 5.56% among different kinds of tested samples.(2) The degradation of fenoxanil followed a equation of one-grade chemical reaction dynamics in the different kinds of paddy samples which collected form Hunan Changsha, Zhejiang Hangzhou and Guangxi Nanning. The average degradation half-life of fenoxanil was 7.66 d in paddy water,7.65 d in paddy straw, and 12.87 d in paddy soil. The results showed that fenoxanil was an easily degradable pesticides (T1/2<30 d). The recommend amount of usage was 210 g/hm2 and higher usage was 315 g/hm2 (20% SC) for prevention diseases of rice during the growth period. The pesticide should be used 3 and 4 turns, and the interval time should be 7 days. The residues of fenoxanil in the brown rice and paddy soil were less than 0.50 mg/kg and the residue of fenoxanil in the paddy straw and rice hull were less than 1.00mg/kg. The residues of fenoxanil in brown rice were lower than the corresponding MRL value (1.00mg/kg), so it was thought that it was safe to be used in the rice fields (the dose of fenoxanil was 20%SC).(3) The adsorption of fenoxanil in five kinds of soils were consistent well with the Freundlich isotherm equation and Linear isotherm equation; the adsorption of fenoxanil was strongest in the black soil from Heilongjiang, and its mobility was weakest; the adsorption was weakest in the red soil from Hunan Changsha, and its mobility was strongest; the impact factor which affect the adsorption of fenoxanil was the organic matter, pH and cation exchange capacity.The degree of the adsorption of fenoxanil was organic matter, pH, cation exchange capacity; the free energy of adsorption of fenoxanil in five kinds of the tested soil was less than 40 kJ/mol. It indicated that the adsorption of fenoxanil in soil belonged to physical adsorption process.(4) The adsorption of fenoxanil to soils were increased with Cu2+or Zn2+in five kinds of tested soils. When copper ions existed, the adsorption of fenoxanil was strongest in the cinamon soil from Shandong Qingdao, the adsorption was weakest in the red soil from Hunan Changsha. When zinc ions existed, the adsorption of fenoxanil was strongest in the cinamon soil from Shandong Qingdao, the adsorption was weakest in the cinamon soil from Henan.The free energy of adsorption of fenoxanil in five kinds of the tested soil was less than 40 kJ/mol. It indicated that with Cu2+ or Zn2+ existed the adsorption of fenoxanil in soil belonged to physical adsorption process. |
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