Photodegradation of herbicide metamifop in aqueous solution

Abstract

This work is a laboratory study of the abiotic degradation by photolysis of metamifop in aqueous solution. In direct photolysis, half-life of metamifop, (R)-2-[4-(6-chloro-1,3-benzoxalzol-2-yloxy)phenoxy]-N- (2-fluorophenyl)-N-methyl propionamide, was 248 days and quantum yield was 1.10×10-5 under sunlight. In indirect photolysis, degradation of metamifop was enhanced by chemical sensitizer. Half-life of metamifop were 128 days for synthetic humic water, 122 days for paddy water, and 18.8 days for acetonecontaining water under sunlight. Photodegradation of metamifop was increased greatly under UV-B (312nm) and C (254nm) lamp, but UV-A (365nm) was not affected to its degradation. In aqueous acetonitrile solution, half-life were 63.6 and 29.6 min under UV-B and C, respectively. In acetonitrile solution, halflife were 43.9 and 20.5 min under UV-B and C, respectively. In methanol solution, half-life were 38.7 and 18.8 min under UV-B and C, repectively. In order to investigate metabolites, highly concentrated solution (250ppm, in acetonitrile) was irradiated under UV-C, and then 7 metabolites were identified as 4-(6-chloro-benzooxazol-2-yloxy)-phenol, N-(2-Fluoro-phenyl)-2-hydroxy-N-methyl-propionamide, N-(2- Fluoro-phenyl)-2-(4-hydroxy-phenoxy)-N-methyl-propionamide, 3HBenzooxazol- 2-one, 2-[4-(Benzooxazol-2-yloxy)-phenoxy]-N-(2- fluoro-phenyl)-N-methyl-propionamide, 6-chloro-3H-benzooxazol-2- one. Key words : Metamifop, photolysis, direct photolysis, indirect photolysis, acetone, UV-A, UV-B, UV-C, photoproducts