南方典型高铊(Tl)异常土壤中铊在降雨条件下迁移释放过程与机制

Thallium (Tl) is one of the most toxic heavy metals which appear on the list of priority pollutants in many countries. It is reported that high thallium concentrations in soil are of either pedogeochemical origin (i.e. natural rock weathering) or anthropogenic origin (e.g. mining-smelting, coal burning). Prior studies on thallium geochemical behavior found that thallium tends to be easier to mobilize than the other heavy metals. Rainfall-runoff is assumed as a vital controlling factor for thallium transport. However, the physical and chemical mechanisms of thallium release from soil and transport to surface runoff are still unclear. Many evidences of thallium anomalies in soils have been found in southern China, e.g. the thallium contents in soils in Lanmuchang, Guizhou province, are tens and hundreds times higher than Chinese background values. The processes of soil thallium release will be enhanced in those monsoon areas with a high temperature, plenty of precipitation, and typically frequent acid rainwater. Bearing this in mind, this proposal will analyze the transport processes and mechanisms of thallium release from soil to water and transport to surface runoff under rainfall condition. Anthropogenic thallium polluted soil in Yunfu, Guangdong province and lithogenic thallium enriched soil in Lamuchang, Guizhou province, were selected for immersion experiments and artificial rainfall experiments. The objectives of this research are threefold: (1) to figure out thallium mobility and its release and transport processes due to rainfall; (2) to elucidate how chemical properties of soil and water (e.g. pH, SOM) and physical processes, such as diffusion and soil particle erosion by raindrop splash, control the release and transport processes; and (3) to model and predict the risk of the thallium transport processes from soil to surface runoff. The results of this study will hopefully benefit our understanding on soil thallium transport, fate and behavior. In addition, some results can be learned for other areas with similar thallium pollution.

重金属元素铊（Tl）因其剧毒性所带来的中毒和环境污染事件而备受关注。以往Tl环境地球化学研究发现其活动能力比常见重金属强，且水文作用是影响土壤Tl迁移扩散的重要动力。然而，已有研究结果难以从物理化学机制上解释降雨-径流中土壤Tl的迁移释放的过程。自然风化和人为活动影响下，湿热多雨且暴雨频发的我国南方局地土壤Tl高值异常明显。基于此，本研究以广东云浮硫铁矿附近人为Tl污染土壤和贵州兴仁滥木厂地区富含原生Tl的土壤为实验土壤，通过静态浸泡实验、人工降雨实验以及数学模拟手段，分析降雨条件下来源迥异的Tl在土水环境中的迁移活性、迁移释放过程；探究土水环境中的化学因素和溶出-扩散及土壤颗粒溅蚀等理化过程的作用；模拟预测其向地表径流的扩散风险。本项目将有助于深入理解Tl的表生地球化学迁移行为，将为我国南方及同类地区土壤Tl的污染防控提供科学依据和理论指导，具有较强的科学研究价值和现实意义。

水沙携带是土壤中有毒有害元素在径流迁移扩散的重要途径。本项目以高铊（Tl）土壤中的Tl为目标元素，通过室内实验和数学模型来探究水土环境中Tl“污染流”释放/运移过程。本研究通过分析广东和贵州不同理化性质的实验土壤中（类）重金属释放/运移的实验数据发现，颗粒态是（类）重金属在地表径流运移的主要形式，土壤（类）重金属赋存形态决定着其溶出及向径流释放的能力，同时受pH、有机碳（质）不同程度的影响。本项目系统探究了以棉花秸秆为代表的生物炭添加污染修复对土壤水文特性、雨滴溅蚀及重金属Tl释放运移的影响。实验表明，生物炭影响着实验土壤的水力渗透性和地表径流产流率以及雨滴作用下的土壤颗粒溅蚀强度。水沙条件变化以及生物炭钝化作用可能导致生物炭添加抑制或促进土壤Tl溶出及向地表/下渗径流的释放。项目耦合了Hydrus水运动、Rose土壤溅蚀及Gao溶质运移方程构建降雨过程的产流、产沙和“产污”模型，模拟计算了降雨实验中的水流、泥沙和重金属Tl释放动态过程。本项目的研究结果有助于深入理解水土环境中污染物环境地球化学行为，能为降雨事件中污染物空间上的扩散预测提供数学模拟手段，同时为目前广泛开展的生物炭修复污染土壤提供一定的借鉴。