【作者】 蔡喜运；

【导师】 刘维屏；

【作者基本信息】 浙江大学 ， 环境科学， 2006， 博士

【摘要】 农业生产中手性农药的广泛使用,使其不可避免地进入到附近的环境系统中。手性农药中对映体在生物过程中存在较大的差异性,使之表现出不同的生态毒理,为此,手性农药的使用与环境安全成为一个新的关注中心。禾草灵是一种具有代表性的手性芳氧丙酸类除草剂,但仍以外消旋的形式上市。本文首先合成了禾草灵和禾草灵酸的对映体化合物,研究了它们在藻液中的对映体差异性降解和毒理。并初步探讨了产生对映体差异性的机制。此外,还研究了农药慢性诱导作用对藻细胞的生长、通透以及降解性能的影响。 禾草灵快速地吸附在藻细胞表面上,催化水解生成毒性较低的禾草灵酸,禾草灵和禾草灵酸进一步降解生成毒性更强的酚类代谢产物,表明禾草灵的这种降解没有降低其环境风险。禾草灵及其转化产物的毒性差异与它们的理化性质有关。测定农药在环境中转化产物的生态毒理和环境归宿,有助于完整准确地评价农药化合物带来的原生和次生的环境风险。禾草灵和禾草灵酸的毒性以及在藻液中的降解表现出了对映体差异性。蛋白核小球藻选择性吸收农药的R型对映体,普通小球藻和斜生栅藻表现出相反的对映体选择性。这种对映体选择性与藻细胞的通透性能具有一定的相关性,与化合物的种类和受试生物的种类有关,主要是由藻细胞的主动吸收造成的。 通过多种技术手段,证实了环糊精与禾草灵和禾草灵酸之间存在包合作用。环糊精的包合作用增加了禾草灵的溶解度和稳定性,加快了农药的溶解速率,减少农药在土壤中的吸附。环糊精对水藻的生长影响不大,降低了藻细胞的被动吸收能力,减弱了藻细胞表面的疏水性,降低了农药的降解速率。实验结果表明环糊精的存在,可以使农药化合物更有效地表现出毒理效应,提高农药的药效。并且,环糊精改变了手性农药化合物在藻液中降解的对映体差异性。环糊精减少了藻细胞对禾草灵和禾草灵酸的吸收,但没有抑制它们的生物活性,显示了环糊精有望作为一种助剂,加快它们在植株中的传导,提高药效,降低使用量,从而降低使用过程中可能产生的生态风险。 腐殖酸是天然水体中可溶性有机质中的主要成分,它可能通过氢键作用和疏水作用吸附在藻细胞上,增加了藻细胞的通透性,减弱了藻细胞表面疏水性能,更多还原

【Abstract】 Widespread application of chiral pesticides results in their occurrence in adjacent environmenat systems such as atmosphere, soil, and surface water. In general, the enantiomers of chiral pesticides are different in some biological processes and thus pose enantioselective ecotoxicity to nontarget biology. Consequently, use and environmental safety of chiral pesticides have been a new point of scientific researches. In the present study, the enantiomers of diclofop methyl (DM) and diclofop (DC) prepared by ourselves were selected to investigate their enantioselective degradation and ecotoxicology in algal cell cultures.DM is rapidly adsorbed to algal cells and is catalytically hydrolyzed to less toxic DC which shows phytotoxicicty. They further metabolize to more toxic phenol metabolites, indicating an increase of environmental burden on DM degradation. DM and its transformation products have different toxicity to algae, associated with their physical chemical properties. Assessing the ecotoxicology and environmental fate of pesticide transformation products is necessary to accurately evaluate environmental risk of pesticides. Toxicology and degradation of chiral herbicides DM and DC is enantioselective, dependent of algae and chemicals. Chlorella pyrenoidosa preferentially uptakes or degrades (R)-enantiomers of DM and DC, however, Chlorella vulgaris and Scenedesmus obliquus have reverse enantioselelctivity with (S)-enantiomer degrading more rapidly than the R enantiomer. The enantioslelctivity of three algae is correlated with their respective cell permeability and is mainly ascribed to cell facilitated transport.Phase-solubility experiments and other methods or technologies demonstrate inclusion complexes between cyclodextrins (CDs) and DM/DC. The inclusion complexation of partially methylated cyclodextrin (MCD) enhances water solubility and stability of DM, improves solution rate of DM, and decreases adsorption of DM to soils, indicating an increase in pesticide bioavailability. MCD does not inhibit algal growth, and decreases passive uptake of algae and cell surface hydrophobicity, but reduces degradation rate of DM and DC in algal cell suspension solutions. The resultsshow that less pesticide have the same biological acitivity when MCD exists. Besides, MCD changes enantioselective degradation of chiral herbicides in alga cultures. Thus, MCD probably increases herbicidal acitivity of DM and DC as additives, reduces application rates of pesticides, and decrease ecological risk of pesticides caused by overdose.Humic acid (HA) is a major component of dissolved organic matter in natural aquatic systems. HA binds DM and DC, and reduces the free pesticide compounds. In the study, however, HA, adsorbed to algal cells, increases cell permeability of three algae, decreases hydrophobicity of algal cell surface, and changes growth character of three algae in different degrees. Data for degradation of DM and DC and algal biomass in Chlorella vulgaris cultures shows that HA increases degradation or uptake of these pesticides and enhance their bioavailability. These suggest that cell permeability induced by HA plays more important role in their bioavailability than the binding interaction between HA and pesticides. At the same time, HA change degradation of DC and its two enantiomers, dependent of HA concentration, algae, and types and concentration of pestcicide.DC at low dose or concentration stimulates the growth of algae. On the algae exposed to 0.10 mg L"1 of DCs enantiomers for two months, however, the induction by DC results in some changes of algal growth and cell permeability. Induction by two enantiomers of DC stimulates the growth of Chlorella pyrenoidosa, inhibits the growth of Chlorella vulgaris, and have no observable effect on Scenedesmus obliquus. In general, induction increases the uptake of the same substrate by algal cells, for example, algal cells induced by R-DC uptake more R-DC than CK. Moreover, induction by two enantiomers reduces or even reverses the enantioselective degradation of chiral pesticides in alga cultures.更多还原