【作者】 马瑞雪；

【导师】 刘霞； 周志强； 王鹏；

【作者基本信息】 中国农业大学 ， 农产品安全， 2014， 博士

【摘要】 每年使用的大量农药中,手性农药的使用量也在上升,手性农药对映体在生物过程中存在较大的差异性,使之表现出不同的环境行为和生态毒理,为此,对它们的使用与环境安全的研究逐渐成为环境毒理学的研究热点。禾草灵(diclofop methyl, DM)是现在仍然大量使用的一种芳氧苯氧丙酸类(Aryloxyphenoxypropionates, AOPP)除草剂。目前大部分AOPP除草剂以外消旋形式生产使用,其作用机理、环境风险的研究都是基于外消旋体,针对非靶标生物在对映体水平上的毒理与环境风险知之甚少。有机氯农药六六六(Hexachlorocyclohexane, HCH)是二战后大量使用的一种杀虫剂,因其具有较长的半衰期和较高的生物富集性,因而在禁用长达数十年后仍可在各种环境基质及生物体中检测到,给生态系统带来了严重的风险。环糊精是一类重要的污染修复剂,同时,环糊精具有手性识别功能,它对手性污染物的对映体选择性环境行为会产生不对称的影响。研究手性农药对映体水平上的生态毒理和环境行为,以最大限度的减缓,控制或修复农药残留物对生态系统的影响,对手性农药的合理使用和正确评价生态安全均有重要的意义。本论文对α-六六六在麦穗鱼和鲫鱼体内的选择性富集、代谢及在各组织器官中的动态分布等环境行为进行了研究；探索了禾草灵、禾草灵酸对映体的水生毒理和对映体选择性环境行为,考察了环糊精对禾草灵毒理和环境行为的影响。选用三种淡水鱼和大型蚤考察了禾草灵对映异构体及禾草灵酸的选择性毒性。制备了禾草灵/β-环糊精包合物,并对包合物进行表征；考察包合物对禾草灵毒性的影响。从急性毒性结果来看,禾草灵都显示了一定程度的对映体差异：三种鱼类的试验结果为R-禾草灵的毒性高于S构型；而大型溞的急性毒性结果与此相反,S-禾草灵的毒性高于R-禾草灵。包合后的禾草灵的毒性显著减弱,对受试生物的LC50均有不同程度的增大,96h的毒性不足原来的1/4。环糊精可用于禾草灵的污染修复,包合作用可以降低禾草灵的水生态风险,考察两种染毒方式,第一种加入禾草灵原药,第二种加入等摩尔量的环糊精／禾草灵包合物,禾草灵在泥鳅体内的立体选择性环境行为。第一种染毒方式,泥鳅体内的禾草灵会立即转化为禾草灵酸,没有检测到禾草灵母体,禾草灵酸的两个对映单体含量差别显著,禾草灵酸对映体的代谢较快,半衰期约为0.3d,且R-DC降解速率快于S-DC；第二种染毒方式在初期阶段的泥鳅体内可以检测到生成的禾草灵酸和少量禾草灵母体。禾草灵的两个对映体含量接近,泥鳅在摄取包合物时没有立体选择性吸收。禾草灵／环糊精包合物较禾草灵原药不易被泥鳅吸收。在泥鳅体内检测到的禾草灵酸含量较低。禾草灵酸对映体代谢较缓慢,半衰期在1.2--1.5天,R-DC代谢速率慢于S-DC。采用体外肝微粒体孵育方式,对禾草灵外消旋体和单体及禾草灵酸在泥鳅肝微粒体中的酶促反应动力学和立体选择性代谢行为进行了研究,首先建立了禾草灵/禾草灵酸对映体在新型键合的手性色谱柱Chiralpak IC上的同时拆分的分析方法；肝微粒体酶促反应结果显示泥鳅肝微粒体催化禾草灵酸对映体的生成速率是不同的,且生成禾草灵酸的过程具有立体选择性。S-DM降解速率是其对映体的约4倍,在整个孵育时间内未观察到禾草灵酸的降解。反应过程中禾草灵对映体保持构型稳定,没有手性翻转现象。从毒性、生理生化和降解过程三个方面研究了环糊精对禾草灵对映体和四尾栅藻相互作用的影响,结果显示禾草灵对四尾栅藻的急性毒性存在立体选择性,S-禾草灵的毒性高于R-禾草灵；加入环糊精可以明显降低禾草灵对四尾栅藻的毒性,禾草灵对四尾栅藻SOD和CAT酶的活力有选择性诱导作用；加入环糊精后会改变禾草灵对四尾栅藻生理指标的影响。在培养单体禾草灵的试验中发现,生成的S-禾草灵酸部分转化为R-禾草灵酸,但R-禾草灵酸不会转化为S-禾草灵酸。环糊精会促进R-禾草灵酸的降解,并有助于S-禾草灵酸向R-禾草灵酸的单向转化。运用手性毛细管气相色谱柱结合GC-ECD,考察了α-六六六对映体麦穗鱼体内的立体选择性行为。体外暴露实验结果显示α-六六在麦穗鱼体内富集迅速,平均在1-2天内达到最大富集浓度,最大BCF1d为830,之后进入浓度逐渐降低并伴随重吸收的过程：α-六六六在泥鳅体内的代谢符合一级动力学,半衰期为1.2天左右；麦穗鱼在富集和代谢过程中均有不同程度的对映体选择性,(+)-α-HCH较(-)-α-HCH被优先吸收和代谢,导致富集阶段体内EF值大于0.5,而头部的α-六六六在代谢过程中EF值逐渐减小至0.5以下。对单次经口暴露α-HCH在鲫鱼体内的富集动态和分布规律研究发现,鲫鱼对α-HCH的富集很快,各组织器官中均可以检测到α-HCH的分布,且肝胰脏、肾脏和脑组织的富集能力最高;肝脏等组织器官中α-HCH的药代动力学用二室模型拟合结果较好；α-HCH在鲫鱼肝脏中富集和代谢最快,各组织器官中的半衰期从数小时到数天不等；α-HCH在鲫鱼体内的分布和代谢具有一定立体选择性,其中肝胰脏、肾脏和脑组织中选择性最明显,且脑组织中的手性分异和其他器官不同,显示出对(-)α-HCH的选择性积累。更多还原

【Abstract】 Along with the wide application of pesticides, the usage of chiral pesticides is also on the rise. The enantiomers of chiral pesticides are different in some biological processes and thus pose enantioselective behavior and ecotoxicity to non-target biology. Therefore, for their use and environmental safety, research on enantioselective behaviors has become the new focus of environmental toxicology. Diclofop-methyl (DM) is one kind of AOPP herbicides which is still of massive use. At present most of the AOPP herbicides are produced and used in racemic form. Although there are some reports about degradation and environmental behavior of DM, the reports about aquatic toxicity at the level of enantiomers was rare. Hexachlorocyclohexane (HCII) had been extensively used as a classical organochlorine pesticide and was forbidden in the1960s, but it can be detected for decades in various kinds of environmental samples due to its persistence and higher bioaccumulation, posing a serious risk to ecosystem. Cyclodextrins (CDs) are a kind of very important remediation agents for environmental contamination. CDs also have chiral recognition ability, so they might have an asymmetric impact on the enantioselectivity of chiral contaminants. Our work focused on the environmental behaviors and eco-effects of two chiral pesticides a-HCH and diclofop-methyl, studied their enantioselective bioaccumulation and elimination in several fish and evaluate the effects of β-cyclodextrin on the toxicology of DM.Three kinds of freshwater fish as well as daphnia magna were employed to evaluate the aquatic toxicity of DM (diclofop-methyl) enantiomers and diclofop. The acute toxicity of DM shows a certain degree of enantioselectivity:for3species of fish, the acute toxicity of R-DM is higher than that of S-enantiomer; on the contrary, the toxicity of R-DM to daphnia magna was lower than its antipode. The inclusion complex of DM/β-cyclodextrin was prepared in solution and solid phase. The inclusion complexation enhanced the DM water solubility and reduced its acute toxicity to several aquatic organisms.In order to investigate the β-cyclodextrin effect on DM enantioselective behaviors in loach, two types of contamination were adopted. One group was spiked with racemic diclofop-methyl and the other was treated with cyclodextrin/DM inclusion complexation. The first group revealed DM in loaches immediately transformed into diclofop and no DM was detected. The concentration of diclofop enantiomers differed significantly. Loach metabolized DC enantiomers quickly, with half-lives of about0.3d and R-DC faster than S-DC; In the second group, a small quantity of DM could be detected in the initial stage, and loaches up-took the DM enantiomers with no stereoselectivity. DC enantiomers had relatively long half-lives of1.2-1.5days with R-diclofop degraded more slowly than S-diclofop.An efficient and stable method for the simultaneous chiral analysis of DM and DC enantiomers on Chiralpak IC column was developed. The degradation of racemic DM and single enantiomer as well as diclofop in loach liver microsomes in vitro was conducted. The results suggested that the biotransformation process was dominated by microsomal esterases. The rac-DM degradation in loach liver microsomes was enantioselective with the conversion rate of (S)-DM markedly greater than that of the R-enantiomer. No enantiomerization was observed, suggesting the biotransformation was configurationally stable. In contrast, DC was not metabolized in liver microsomes even with NADPH present. Further research on the mechanism of DC metabolism and enzyme involved was needed.The impacts of β-cyclodextrin on interaction between DM and Scendesmus quadricauda were investigated through toxicity, enzymatic activity and degradation process. The results showed there were obvious differences in toxicity between DC enantiomers to S. quadricauda. The acute toxicity of S-DM was much higher than that of the R-DM. Compared to the control EC50values, the EC50values corresponding to every stage increased in the presence of cyclodextrin. DM exerted enantioselective induction effects on the activity of SOD and CAT of s. quadricauda. The degradation of DC by S. quadricauda was enantioselective but a bit slow. In single enantiomer cultivation, it was found that only S-DC could transform into R-DC. Cyclodextrin could accelerate the R-DC degradation and promote the R-DC conversion.The enantioselective bioaccumulation and degradation behavior of a-HCH in pseudorasbora parva was studied. A valid chiral residue analysis method for the a-HCH enantiomers in the water and fish samples was established using capillary column BGB-172combined with GC-ECD. The bioaccumulation of a-HCH in loach was quickly and the highest concentration point was reached within2days, with a maximum BCF1d of830. After that the body burden began to decrease and a companying re-uptake process was observed. The degradation kinetics of a-HCH fitted typical first order kinetic, and the half-life was about1.2days. Both the bioaccumulation and degradation processes showed obviously enantioselectivity.(+)-a-HCH was preferential accumulated and degraded than (-)-a-HCH with the EFs in fish head higher than0.5during bioaccumulation and lower than0.5during elimination.Crucian carp, a kind of edible freshwater fish was chosen to study the a-HCH bioaccumulation and metabolism behavior in various tissues through a single dose exposure. The fish were exposed to racemic a-HCH orally and the concentrations of its two enantiomers were measured in the liver, kidney, brain, muscle, skin and ovary at different time intervals. The absorption and elimination of a-HCH in liver were fast which can be characterized by a two-compartmental kinetic model. The accumulation rates were different among tissues depending on blood flow rate and fat content. Liver, kidney and brain tissue had the highest enrichment ability. The enantiomers distribution in most tissues suggested an apparent enantioenrichment of (+)-a-HCH. On the contrary, a-HCH in brain showed a significant enantioselectivity. The EFs for brain decreased dramatically after the exposure and reached to0.45, suggesting a preferential clearance of (+)-a-HCH.更多还原