土壤吸附对残留农药生物可用性的影响及机制

Sorption is generally recognized as a key to controlling concentrations of a pesticide in soil solution, and hence its availability to a receptor. However, most research to date concerning effect of soil sorption on bioavailability of pesticides has focused on apparent and empirical description about the relationship between soil sorption and the bioavailability of pesticides. Little work has been done to describe mechanistically the processes soil sorption govern the bioavailability of these chemicals. In the present study, therefore, the insecticide chlorpyrifos, the herbicide metolachlor and the fungicide myclobutanil widely used in China are chosen to research the effect and mechanism of soil sorption on bioavailability of residue pesticides using batch equilibration technique, root-box technique,and microcosmos technique based on the theoretical basis of pesticide environmental toxicology and soil pollution chemistry. The objectives of this work are (i) to determine characteristics and mechanisms of effect of dissolved organic matter,straw-derived ash,mineralclay and surfactants on sorption of pesticides in soil, (ii) to determine characteristics and approaches of microbial degradation, plant uptake and earthworm cumulation of pesticides in soil, (iii) to explore the quantitative relationship between soil sorption and availablility of pesticides to microorganisms, plants and earthworms, and (ⅳ) to reveal the effect and mechanism of soil sorption on bioavailability of residue pesticides in soil, and to interpret the function of soil sorption in the transfermation and fate of the pesticide in environment. The results of this work will have great important significance for developing theories and methods of pesticides environmental toxicology, richening research contents of soil pollution chemistry, rationally assessing and predicting the risk level of residue pesticide contamination, exploring the controll strategy of soil pesticide contamination, guiding the rational use of pesticides and the synthesis of new pesticides.

本项目选用我国常用的杀虫剂毒死蜱、除草剂异丙甲草胺和杀菌剂腈菌唑为代表农药，以农药环境毒理学和土壤污染化学为理论基础，采用批量平衡法等方法，着重研究可溶性有机质、草木灰、矿物粘土和表面活性剂对土壤吸附农药的影响规律及其机理，以及微生物降解、植物吸收和蚯蚓富集农药的规律及途经，探明微生物、植物及蚯蚓利用农药途经与土壤吸附作用之间的量化关系，以揭示土壤吸附对残留农药生物可用性的影响及其机制，阐释土壤吸附作用在残留农药的环境转移归趋中的功能作用。项目成果对发展农药环境毒理学和土壤污染化学的理论和方法、丰富农药环境化学的内容、合理评价和预示土壤残留农药的污染水平、探讨土壤农药污染的治理策略、指导农药的合理使用及新农药的合成均具有重要意义。

本项目选用我国常用的杀虫剂毒死蜱、除草剂异丙甲草胺和杀菌剂腈菌唑为代表农药，以农药环境毒理学和土壤污染化学为理论基础，采用批量平衡法等方法，研究探明微生物、植物及蚯蚓利用农药途经与土壤吸附作用之间的量化关系，阐释土壤吸附作用在残留农药的环境转移归趋中的功能作用。项目研究主要结果如下：（1）土壤吸附农药的影响规律及其机理：土壤有机质、可溶性有机质（DOM）、表面活性剂（SF）、草木灰（SDA）和蒙脱石矿物粘土（MC）是影响供试农药在土壤上吸附附行为的主要因素；DOM和SF增加了供试农药的表观溶解度、降低了Kow值，而SDA和MC则刚好相反。（2）土壤吸附对微生物降解残留农药的影响及其机制：分离到嗜麦芽寡养单胞菌Stenotrophomonas maltophilia和蜡状芽孢杆菌Bacillus cereus两株降解菌；土壤吸附菌株的量随土壤中有机质、SDA和MC含量的增加而增加，随DOM和SF含量的增加而降低；菌株对土壤-溶液中农药的降解速率与土壤性质、土壤溶液中菌株数量、农药浓度及老化时间有关；菌株降解农药的半衰期与它们各自的吸附系数（Kf）有较好的正相关关系（R>0.968）。（3）土壤吸附对小麦吸收残留农药的影响及其机制：小麦对土壤中供试农药的吸收量有随土壤有机质含量和老化时间的增加而降低的趋势，DOM和SF均能明显提高小麦吸收土壤中农药的残留量，SDA和MC则相反，小麦对供试农药的生物浓缩系数(BCF)与它们各自的Kf有较好的负相关关系（R>-0.916）。（4）土壤吸附对蚯蚓吸收残留农药的影响及其机制：蚯蚓对土壤中供试农药的吸收利用与土壤性质、老化时间及摄食方式密切相关；DOM和SF均能明显提高蚯蚓吸收土壤中异丙甲草胺和腈菌唑的残留量、SDA和MC则相反，而添加低剂量DOM、SF、SDA和MC对蚯蚓吸毒死蜱残留量的影响不大；异丙甲草胺和腈菌唑的BCF与Kf有较好的负相关关系（R>-0.947），而毒死蜱的BCF与Kf则有较好的正相关关系(R=0.987)。