喀斯特地区土壤铅超常富集的微观形貌与同位素联合解析

Heavy metal lead accumulates significantly in soil of Karst area. It is a noteworthy question that whether the accumulation of lead is resulted from natural soil processes or primarily from anthropogenic input. Based on the data obtained by "Chinese geochemical baseline plan", this study aims to set up typical geochemical profiles in the background and enrichment areas respectively, to collect samples from rocks to soils in these profiles, measure the total amount of lead in samples and specific-speciation of lead in soil samples, study the variation characteristics of lead vertically, and find out the relationships and enrichment degrees of lead from rocks to soils. Then use scanning electron microscopy (SEM) to observe the microstructural characteristics of the magnetic particles in soil samples, use ICP-MS to determine lead isotope ratios of rocks, soils and anthropogenic end-member samples, establish the lead isotope tracer models to analyze the sources of lead, find out the contributions of natural and anthropogenic sources of heavy metal lead in the karst area. This study can be used to monitor the impact of human activities, provide important basis for environmental management and policy making, to effectively reduce the risk of heavy metal pollution and human health risks, which is of important significance.

喀斯特地区土壤中重金属铅显著富集，铅富集到底是由自然成土过程主导，还是主要来源于人为注入，这是值得关注的问题。本研究以“中国地球化学基准计划”获得的数据为依据，在背景区和富集区设置典型的地球化学剖面，采集从岩石到土壤剖面样品，测量样品铅元素总量及土壤样品铅形态，研究垂向上铅元素含量变化特征，查明从岩石到土壤的铅元素继承关系和富集程度。利用扫描电镜观察土壤样品中磁性颗粒的微观形貌特征，利用ICP-MS测定岩石、土壤及人为源端元样品的铅同位素组成，建立铅同位素示踪模型，对重金属的来源进行解析，查明喀斯特地区重金属铅自然源和人为源贡献。这可以用于监测人类活动的影响，为环境管理以及政策制定等提供重要依据，对于有效地降低重金属污染风险以及人类健康风险有重要的意义。

喀斯特地区表土铅存在超常富集现象，中国地球化学基准计划所获样品显示，广西省约7.2%的样品铅超常富集，48.2%的样品铅中等富集（本研究将Pb>150mg/kg认定为超常富集，Pb含量位于30至150mg/kg之间为中等程度富集，Pb含量小于30mg/kg为背景区）。本项目在铅超常富集区、中等富集区以及背景区分别选取一个典型流域，采集流域内典型岩石风化剖面样品、铅锌矿风化剖面样品以及污染端元样品，并对汇水域沉积物进行重访采样。系统开展铅同位素源解析、微观矿物学分析、铅形态分析、流域尺度多元素联合解析以及区域尺度机器学习源解析等研究，从多尺度对铅的来源及富集机制进行解析。阐明碳酸盐岩风化过程中铅的富集机理，查明铅超常富集及中等富集区的主要影响因素，明确了铅超常富集区铅的主要赋存形态。项目研究结果，将拓展和深化对铅的超常富集机理的认识，为喀斯特地区铅污染防控提供有力的理论依据，具有较强的科学价值和现实意义。