氰氟草酯在稻田生态系统中的降解研究

【作者】 赵莉；

【导师】 朱国念； 叶兴祥；

【作者基本信息】 浙江大学 ， 农药学， 2001， 硕士

【摘要】 农药是重要的农业生产资料，如果使用不当，可能对环境造成损害。农药进入环境以后在环境诸因子（水、光、微生物等）的影响下降解生成各种代谢物，同时农药也不可避免地进入生物体内，进行各种各样的变化。有的代谢产物毒性降低，有的代谢产物毒性比母体更大。因此，在使用一种新农药之前，必须了解其在环境及生物体内的降解和代谢途径，这对评价该药剂的环境安全性以及寻找控制农药污染的途径提供科学依据。 氰氟草酯（Cyhalofop-butyl）是美国陶氏公司最新开发的芳氧苯氧羧酸酯类除草剂，可有效地防除稻田的多种禾本科杂草，尤其对千金子、稗草有特效。目前氰氟草酯在我国已获得临时登记，但是关于该药剂的残留分析方法、稻田使用后的残留情况以及环境行为特征，国内外尚未见公开报道。为了氰氟草酯在我国推广应用，研究其环境行为对评价其环境安全性及安全合理使用是十分必要。 本文首次研究并建立了氰氟草酯母体及其4种代谢物在稻田水、土壤及水稻样品中的残留分析方法。在同一色谱分析条件下，可同时检测5种化合物，样品前处理过程简单，方法准确可靠，灵敏度、准确度达到农药残留检测的要求。氰氟草酯母体及其4种代谢物在上述样品中的检测极限均在0.02～0.002mg/kg之间（详见第一章），方法添加回收率均在80～102.1％之间。 本文还研究了氰氟草酯的水解动力学，光解和微生物降解，并对其具在杀草活性的代谢产物ACID的水解动力学和光化学降解作了进一步研究，探讨了氰氟草酯及ACID的水解、光降解作用机理。 水解研究结果表明，氰氟酯在酸性条件下比较稳定，而在微酸性及中性条件下水解速度加快，在碱性条件下，氰氟草酯水解迅速。ACID在酸性及中性条件下比较稳定，在弱碱条件下缓慢水解，只有在强碱条件下水解较快，提高温度均促进氰氟草酯及ACID水解。采用HPLC法，鉴定了氰氟草酯及ACID的水解产物。氰氟草酯的水解产物主要是ACID，并有少量AMIDE、DIACID产生，ACID水解产物主要是AMIDE以及少量DIACID。可能的水解途径是亲核加成反应。 在紫外光（λ=254nm）下，氰氟草酯及ACID在不同水介质中均容易光解，半衰期约4～6min，丙酮存在时，氰氟草酯及ACID的光解速度反而减慢，说明丙酮不是氰氟草酯及ACID的光敏催化剂。利用HPLC和GC－MS鉴定出7种光解产物，光降解途径是醚键断裂、酯健水解、脱梭及光异构化。 水中的微生物可有效地促进氰氟草酯降解，氰氟草酯对池水中某些细菌的生长有一定刺激作用，而对放线菌和真菌的生长影响不明显。通过对不同种属细菌的培养和鉴定发现，氰氟草酯在池塘水中的降解微生物主要是假单胞菌和葡萄球菌属，代谢机制可能以生长代谢为主。 厦门、杭州两年两地的消解动态和最终残留试验结果表明，常规施药浓度下，在稻田使用氰氟草酯，到作物收获时对稻谷的食用是安全，也不会对稻田环境造成不良影响。 以上研究结果说明，氰氟草酯在自然环境中降解迅速，残留期短，在稻田生态系中的降解可有多条途径，但主要是生物降解和光解，其次是水解。 本论文的研究结果无论是在理论上，还是在实践上均有一定的应用和参考价值。更多还原

【Abstract】 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.更多还原