川西平原还田秸秆DOM对典型有机污染物迁移行为的影响及机理

Dissolved organic matter (DOM) derived from crop straw, to a certain extent, has controlling effects on environmental geochemical behavior of organic contaminants (OCs) in farmlands. Previous reports neglected the environmental effects of straw DOM. Therefore, the understanding of interaction between DOM and OCs is far from comprehensive. DOM derived from the original and decomposed straws of rice, wheat and rape that are widely planted in West Sichuan Plain will be used as model DOM. Effects of the DOM on transfer of different kinds of OCs in farm soil are tracked to provide a better understanding on environmental behavior of OCs. Based on multiple methods, this study will clarify the sorption properties of OCs in the DOM-Soil system, and investigate the relationship between the characteristics of DOM and the transfer behavior of OCs. Different effects of DOM from the three kinds of straws on the sorption of OCs in soil are discussed, and their contributions are calculated, respectively. Effects of ion strength and pH in the systems will also be discussed. Based on this research, the dominant mechanism in this process can be addressed, and the controlling components or structures of DOM on OCs transfer will be also identified. Quantitative contributions of those components or structures to the transfer behavior of OCs may be obtained. Results of this study will provide further information for environmental health risk assessment of OCs in the agro-ecosystem.

农作物秸秆来源的溶解性有机质（DOM）在一定程度上控制了农田土壤中有机污染物（OCs）的环境地球化学行为。以往的研究忽视了还田秸秆DOM的环境效应，对DOM-OCs相互作用的理解是不全面的。本研究拟以川西平原主要农作物（水稻、小麦和油菜）的秸秆原始有机质及其腐解过程释放的DOM为代表，探讨该类DOM对不同性质的OCs在土壤中迁移行为的影响，增强对OCs环境行为的更深层次认识。结合多种研究手段，掌握OCs在秸秆DOM-土壤复杂体系中的吸附特征，探讨DOM性质的变化与OCs行为改变的关系；比较不同秸秆来源的DOM影响土壤对OCs吸附性能改变的差异性，并定量各自的贡献；理解离子强度和pH值在体系中的作用；阐明该类DOM对土壤中OCs迁移行为影响的主导机理，锁定DOM中起控制性作用的组分或结构，并尝试定量描述其贡献，为川西平原农田生态系统环境健康风险评价提供理论依据。

结合多元研究手段，阐明了农作物秸秆原始有机质及其不同腐解阶段DOM组分特征和化学特性，并剖析了变化机理。DOM中酚类、羰基类和羧酸类物质数量增加，使得DOM与有机污染物、金属离子的相互作用增强，进而调节水稻土有机污染物的迁移过程。阐明了不同性质OCs在DOM–土壤复杂动态体系中的吸附特性，构建了还田秸秆DOM性质变化与OCs在土壤中行为改变的关系。OCs在DOM-土壤体系中的吸附过程符合Langmuir模型、Freundlish模型和双室一级动力学过程。考察了DOM对OCs在土壤中吸附行为的影响，并对比了其贡献。DOM不仅增加了土壤有机质含量，还提升了累积吸附和共吸附作用，而这个过程是自发的、吸热的。尽管如此，它们的吉布斯自由能差异不明显。考察了离子强度和pH值在体系中的作用。阐明了影响OCs在土壤中迁移行为的关键因素。本研究揭示了农作物秸秆释放的DOM对川西平原水稻土中OCs迁移行为影响的主导机理，以及DOM中的控制性组分或者结构。农作物秸秆来源的DOM在一定程度上控制了农田生态系统中OCs的环境地球化学行为。本研究为川西平原环境健康风险评价提供了理论依据。