降水中过氧化氢介导类Fenton反应对土壤典型除草剂的化学--生物耦合降解的机理研究

With increasing applied of herbicide and using more GM crops with herbicide resistance, concerns for herbicide contamination and its prevention and control are continuously increasing. Hydrogen peroxide exists in natural water bodies including surface waters, atmospheric droplets and precipitation and may come into contact with Fe(Ⅱ)in plant-soil system. Then the Fenton or Fenton-like chain reactions can take place and generate free radicals which are even more powerful than H2O2 in terms of oxidative capacity. Our previous work has demonstrated that low concentrations of hydrogen peroxide could induce Fenton effect and cause herbicide degradation. However, the coupled chemical–biological oxidation of herbicides in plant-soil system and its mechanism has not been well explored. The objective of this proposal is to discover the role of oxidation by hydrogen peroxide at micro molar level in natural farmland environment. The possible effects of this on environmental and chemical behavior of herbicides including the degradation of herbicides in rhizosphere-soil system will be studied by field investigation and greenhouse experiment. Compartmented root-bag culture systems and rhizospheric box will be used to study the effects of hydrogen peroxide on Fe (Ⅱ) in the oxidized iron sheet around plant root surface on the chemical and microbial oxidation process of herbicides in soil. Soil chemical –biochemical -microbiological parameters in plant rhizosphere compartments and rhizosphere soil, root surface area, soil pore water content, and herbicides biodegradable reaction products will be measured and quantified. Microbial population in rhizosphere soil and root-surface will be characterized. The mechanism related to the relationship of oxidation and herbicide change on leave surface, the interface between root and rhizosphere, and the chemical and biochemical activities behind will be revealed. The optimum soil environment and cultivation method will be explored. The result of this project will show us the feasibility in real-world environmental for the conversion and remediation of herbicides. It will provide a theoretical basis for management practices to reduce a wide range of organic pollutants like herbicides in agro-environment.

随着化学除草和抗除草剂转基因作物商品化的不断推进，除草剂污染与防控问题日益被关注。紫外辐射增加和大气污染上升会导致天然水中过氧化氢等活性氧物质浓度不断上升，并对环境中的化学物质发生各种氧化反应，影响污染物在环境中的迁移、转化和归宿，并影响其生态毒理效应。天然水中微摩尔浓度过氧化氢介导的类Fenton效应可能是土壤环境化学与生态过程的重要影响因素，会影响污染物的土壤环境行为与归趋，但迄今仍未被重视。本项目通过根箱模拟实验和大田小区试验，研究天然水中过氧化氢介导的农田中类Fenton反应对典型除草剂降解的影响，重点探究类Fenton反应对植物根/土界面和土壤中除草剂环境化学行为的影响，揭示现实环境下除草剂化学-生物氧化耦合降解的相关机理，并探讨人为强化类Fenton反应促进除草剂修复的农业栽培措施，以丰富现实环境下除草剂等有机污染物残留降解与修复理论与技术。

草甘膦使用量位居全球农药的首位，在世界范围内广泛应用导致其在土壤和水环境中无处不在，其降解中间体 AMPA 被证明比草甘膦本身更具持久性、流动性和毒性，而阿特拉津、敌草隆等具有这引起了公众对其安全性的持续关注。随着大气污染与全球变化，大气沉降中氧化性物质增加，氧化沉降介导类Fenton效应可能是影响土壤污染物环境行为与归趋的重要因素，但迄今仍未被重视。为此，本项目监测了周年降水事件中过氧化氢等氧化沉降物质的动态，研究了天然水中过氧化氢介导的农田中类Fenton反应对土壤典型除草剂阿特拉津、草甘膦等化学氧化和微生物氧化降解的影响，重点探究类Fenton反应对土壤中除草剂化学-生物氧化耦合降解的相关机理，并探讨了施用氧化尿素等强化类Fenton反应促进除草剂修复的效应。周年降水监测表明过氧化氢浓度在0.10-118.7 µM之间，过氧化氢随天然降雨进入水土环境与亚铁离子(Fe2+)等还原剂发生原位（类）Fenton效应，影响典型除草剂的环境迁移、转化和归宿，同时影响土壤微生物群落，间接影响污染物环境生物化学行为。模拟降水中微摩尔H2O2对土壤ATR及其降解产物的降解有促进作用，且土壤ATR降解残留量与土壤铁含量呈负相关。微生物氧化降解和双氧水介导的氧化降解均促进了ATR降解，且生物氧化与化学氧化存在耦合强化作用，辅助紫外光催化类芬顿反应进一步促进土壤ATR的降解。项目筛选获得了12株能够耐受高浓度草甘膦的菌株和1株丁草胺高效降解菌。微摩尔浓度过氧化氢介导Fenton效应参与了土壤草甘膦降解，强化了化学氧化降解，但抑制了草甘膦降解菌进而削弱了生物氧化降解；增加了土壤微生物群落多样性。施加过氧化尿素，特别是同时施加硫酸亚铁，显著加快旱地红壤和水稻土中草甘膦残留降解。研究结果为认识和丰富天然水中H2O2等外源氧化剂进入农田影响除草剂环境行为与修复机制提供了科学参考。