Cyhalofop In The Paddy Ecosystem Degradation

Cyhalofop-butyl, R- (+)-n-butyl-2- (4-(2-fluoro-4-cyanophenoxy) phenoxy} propionate, is one of the recently developed herbicides and belongs to aryloxyphenoxypropionic compound used for control of most graminaceous weeds in rice fields. It is rapidly hydrolyzed in environment to the corresponding ACID, which is the herbicidal active form. At present, the pesticide has been temporarily registered in China. In order to extend its use in the country, it is necessary to have full understanding of its behavior in the environment and obtain more information on the degradation pattern of cyhalofop-butyland its metabolites. Based on this, the research work reported herein was done on the following: (a) Analytical method of cyhalofop-butyl and its metabolites in water> soil and crops by HPLC; (b) hydrolysis of cyhalofop-butyl and ACID at different pHs and temperatures in aqueous buffer solutions; (c) photolysis of cyhalofop-butyl and ACID in different aqueous solutions (d)microbial degradation of the herbicide in pond water. The results were summarized as follows:1. At the same analytic condition, Cyhalofop-butyl and its 4 metabolites in water, soil and rice grain can be detected by HPLC technique and achieved a chromatographic separation. The detection limits of the 5 compounds in different samples varied from 0.02~0.002mg/kg, the recoveries for each compound across all fortified samples (0.01~5mg/kg) were 80~103%(see Chapter one). In short, the method established was simple, fast, accurate and suitable.2.Hydrolysis study showed that the first-order constants (k) were greatly dependent on pH and temperature. Cyhalofop-butyl was relatively stable in acid aqueous buffer solutions (pH5.0), and its stability decreased as pH increased in aqueous buffer solutions. The half-life of Cyhalofop-butyl in aqueous buffer solutions at 25癈 was 990.2 days at pH 5 and 16.6h at pHlO.O Half-life was greatly reduced at elevated temperatures. At 25 and 65 癈 (pH5.0), the k values were 0.0007 and 0.0281, respectively. Effect of pH and temperature on degradation of ACID in aqueous buffer wasn't evident. Hydrolysis was observed only at strong alkalicondition (pHll). The main hydrolysis products of cyhalofop-butyl in aqueous buffer solutions were ACID, AMIDE and DIACID whereas those of ACID were AMIDE and DIACID.3.The photolysis of cyhalofop-butyl and its acid were studied in aqueous solutions. The results for photolysis study showed that cyhalofop-butyl and its free acid undergoes very fast photochemical reaction in aqueous solution under UV light (254nm). The half-lives of cyhalofop-butyl and ACID in distilled water (pH=6.8) were 4.5 and 5.37min, respectively. To cyhalofop-butyl and its acid, acetone was found not to be a photosensitive agent. Photolysis products of cyhalofop-butyl and its acid were determined by HPLC and GC-MS. Possible degradation pathways were also analyzed.4.The microbial degradation of cyhalofop-butyl in sterile and non-sterile pond water at 25癈 and 35C was studied. A decrease of cyhalofop-butyl in the sterile and non-sterile pond water was found, but the degradation of cyhalofop-butyl in sterile pond water was slightly slower than in non-sterile. The half-life of cyhalofop-butyl in sterile water was found to be 9.8h (35C) and 19.0h (25癈), in non-sterile pond water 3.7h (35癈 ) and 8.0h (25癈). The degradation was also slightly faster at 35癈 than at 25癈. In addition, cyhalofop-butyl affected the total number of microbes. This study showed that the total number of bacteria increased with the decrease of cyhalofop-butyl residue in the non-sterile condition, but the amount of fungi and actinomycetes seldom changed. This indicates that microbial degradation is an important factor for the metabolism of cyhalofop-butyl in paddy rice ecosystem.