溶解有机质调控湿润铁铝土铁还原耦联苯氧乙酸类除草剂降解生物-化学机制

Phenoxyacetic acid herbicides (PHAH), the most commonly used herbicides, are the main organic pollutants in tropical ferralisols. Dissolved organic matter (DOM) represents one of the most reactive organic matter fractions, significant influencing iron(III) reduction, microbial respiration, and organic pollutants degradation. Based on two important properties (complexation; electron transfer) in DOM, and the evidence that reductive transformation is important degradation process of PHAH under anoxic environments, this project is proposing to study DOM-regulated biotic-abiotic mechanisms of PHAH degradation coupled with iron(III) reduction in ferralisols. 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxy acetic acid (MCPA) will be used as target herbicides. The specific objectives of this proposal are: i) to investigate the kinetics of iron(III) reduction and 2,4-D/MCPA degradation in the presence of different DOM fraction (classification by XAD-8 resin), which is considered as organic ligand, electron donor or electron acceptor in the anaerobic transformation process; ii) to analyze the correlations between structural characteristics and electrochemical properties of DOM and iron(III)/2,4-D/MCPA anaerobic transformation rate, to determine the different role of DOM fraction involved in iron(III)/2,4-D/MCPA transformation, and finally to reveal the biotic-abiotic mechanisms of 2,4-D/MCPA anaerobic degradation in the presence of DOM; iii) to explore the relationships among the maximum degradation rate of 2,4-D/MCPA, DOM fraction, and soil bacteria communities in ferralisols batch systems, and further to demonstrate our original hypothesis on anaerobic degradation mechanism of 2,4-D/MCPA in ferralisols amended with DOM. To our knowledge, this is a new research on describing the capacity of different fraction of DOM to influence 2,4-D/MCPA anaerobic degradation in iron(III)-rich soils. The results of this research will improve our general understanding in environmental behavior of typical organic pollutants in soils; and provide scientific evidences for exploring remediation technology of soils contaminated by herbicides based on DOM.

苯氧乙酸类除草剂(PHAH)是热区湿润铁铝土中的典型有机污染物。溶解性有机质(DOM)环境行为活跃，显著影响土壤中铁还原、微生物呼吸、有机污染物降解脱毒。本项目针对DOM具有络合及电子转移活性，以及PHAH还原转化特征，提出DOM调控湿润铁铝土中铁还原耦联PHAH厌氧降解的生物-化学机制假设。以2,4-二氯苯氧乙酸(2,4-D)、2-甲基-4-氯苯氧乙酸(MCPA)为目标农药，研究DOM各组分作为有机配体、电子供体、电子受体影响铁还原及2,4-D/MCPA厌氧降解动力学；分析铁还原及2,4-D/MCPA降解与DOM结构组成的关系，阐明DOM不同组分在影响2,4-D/MCPA降解中的角色与功能，揭示体系中2,4-D/MCPA降解的生物化学本质。进一步在土壤体系中探讨2,4-D/MCPA降解与DOM结构组成及土壤微生物优势群落的关系，验证DOM影响湿润铁铝土中铁还原耦联HPAH降解机制假设。

苯氧乙酸类除草剂(PHAH)是热区湿润铁铝土中的典型有机污染物。溶解性有机质(DOM)环境行为活跃，显著影响土壤中铁还原、微生物呼吸、有机污染物降解脱毒。本研究以铁铝土为研究对象，以2甲4氯(MCPA)和2,4-二氯苯氧乙酸(2,4-D)为目标农药，采用XAD分组法、红外光谱法、荧光光谱法、紫外光谱法等表征技术为手段联合探讨堆肥DOM、土壤DOM、秸秆DOM的结构成分，分析了DOM在铁铝土及其重要矿物铁氧化物上的吸附特性，揭示了DOM对铁铝土典型有机污染物PHAH吸附行为的影响，阐释了DOM影响铁铝土吸附PHAH的关键组分及机制，并阐释了DOM作为电子供/受体参与PHAH厌氧降解的生物-化学机制。.主要结论如下：.1）不同来源DOM成分结构差异较大。极性组分中，疏水酸性组分(HOA)是堆肥源DOM的主要组分，约占45.2~49.6%，亲水性组分(HIM)是土壤源DOM、植物残体源DOM的主要组分，约占46.2~52.2%，酸不溶组分(AIM)、疏水碱性组分(HOB)在3种DOM中的含量均较低。.2）铁铝土对DOM的吸附表现为暗红湿润铁铝土＞简育湿润铁铝土＞水稻土。疏水中性组分(HON)、AIM是铁铝土吸附的关键组分，高疏水性、芳香性、分子量和脂肪链状结构是DOM强吸附发生的关键性质。.3）DOM对铁铝土吸附MCPA、2,4-D具有抑制作用，DOM疏水性越强，抑制作用越强。其中HON、AIM是抑制MCPA吸附量的关键组分。DOM对MCPA的增溶效应及土壤微孔结构的堵塞效应是DOM抑制MCPA的关键机制。疏水作用力，范德华力、π电子共轭作用力，氢键结合等是此过程的关键作用力。.4）获得5株腐殖质还原耦联MCPA降解菌，鉴定为苏云金杆菌Bacillus thuringiensis M4、贝莱斯芽孢杆菌Bacillus velezensis M9、Bacillus wiedmannii M11、蜡样芽孢杆菌Bacillus cereus M14、Bacillus toyonensis M18。15 d对MCPA的降解率为16.1~43.6%，其中蜡样芽孢杆菌M14对MCPA的降解率最高(15天43.6%)，AH2QDS生成量可达0.763(OD450)。.本研究为理解铁铝土中苯氧乙酸类农药环境行为过程提供了积累，为建立基于溶解性有机质的苯氧乙酸类农药污染土壤的原位修复提供了