西南高镉地质背景区残坡积型土壤镉的迁移富集机制研究

There are many regions with high Cd background in southwest China, where residual soils were important parts of local arable soils, but the soils were threatened by Cd accumulation and pollution. However, the studies of Cd enrichment and migration in residual soils were limited, and the pollution mechanisms were still not clear. Therefore, a representative area with high Cd background in Chengkou County is selected as the study area in this project, the samples of weathering profiles, residual soils and soil waters are systematically collected. Based on the techniques of elemental, mineral and isotopic analysis, the soil physical-chemical characters, Cd concentrations, chemical species and isotopic compositions of samples are investigated. The purposes of this study are: 1) to reveal the mobility of Cd in weathering and migratory processes; 2) to illustrate the enrichment mechanism, transport processes and pollution mechanism of Cd in the residual soils and the constrained factors, 3) to verify the indication of Cd isotopic compositions to the environmental processes of Cd in soils. The findings of this research will expand and deepen the theories of Cd supergene geochemistry and isotopic geochemistry. The results are significant for providing scientific basis and guidance of the soil pollution prevention in high Cd background area of southwest China.

我国西南地区有大面积的高镉地质背景区，母岩风化形成的残坡积型土壤是区域农田的重要组成部分，镉富集与污染形势严峻，但迄今仍缺乏针对残坡积土壤镉迁移富集过程机制的深入研究，污染机理尚不明晰。本申请项目拟以重庆市城口县黑色岩系高镉地质背景区为研究区，系统采集母岩风化剖面、残坡积土壤等样品，利用元素分析、矿物分析、镉同位素分析等技术手段，系统开展风化剖面与残坡积土壤中镉的含量、土壤理化参数、赋存形态、镉同位素组成研究，对残坡积土壤镉的环境地球化学过程进行精细刻画，揭示母岩风化成土与残坡积运移过程中镉的迁移过程规律，阐明残坡积土壤镉的富集过程机制、污染机理及影响因素，查清镉同位素组成对土壤中镉迁移富集地球化学过程的指示意义。项目研究成果，将拓展和深化对镉的表生地球化学与同位素理论的认识，为西南高地质背景区残坡积型土壤镉污染防控提供有力的理论依据，具有较强的科学研究价值和现实意义。

西南地区是我国典型的高镉地质背景区，区内母岩近源风化形成的残坡积型土壤是农田的重要组成部分，且镉富集与污染形势严峻。然而，目前对残坡积型土壤中镉迁移富集过程的理论认识不足，污染机理不明。项目以西南典型黑色岩系高镉地质背景区为研究区，首先，研究了富镉母岩的地球化学组成、矿物及其微观形貌、镉赋存形态，揭示了黑色岩系中镉赋存状态及其对土壤镉富集与环境活性的影响；在此基础上，研究了风化成土过程镉赋存形态与镉同位素组成的变化规律及其对关键生物地球化学过程的响应，揭示了风化成土过程中镉的动态变化与再分配过程，利用镉稳定同位素组成示踪了土壤空间运移与镉生物地球化学循环过程；进一步研究了不同地形、不同成因土壤中镉的同位素组成、形态与含量分布特征，阐明了典型山区不同地形土壤镉的地球化学分异过程机理；基于此，阐明了残坡积型土壤镉富集机制与污染机理；最后，研究了农田土壤-作物系统镉迁移、富集与分布及土壤镉赋存形态与生物有效性，揭示了残坡积型土壤镉形态与生物有效性变化规律及其主控因素，查明了黑色岩系风化土壤中镉生物活性较高的原因。项目对典型高镉地质背景区域残坡积型土壤中镉迁移富集过程的精细刻画，拓展和深化了对镉的表生地球化学过程的理论认识，可为西南高镉地质背景区农田镉污染风险防控和污染土壤安全利用提供理论支撑。