贵州省典型污染区土壤中镉的空间分布及影响机制

Spatial Distribution and Effect Mechanisms of Cadmium in Soils in Typical Contaminated Areas,Guizhou Province

镉(Cadmium)是自然环境中普遍存在且毒性极强的重金属元素,几乎所有土壤、地表水和植物体内均含有镉。选择贵州碳酸盐岩地质条件下的典型重金属污染区(铅锌矿区、煤矿区、赤泥坝区、污灌区等)为研究对象,探索在镉的地球化学高背景下,不同来源镉在土壤中的空间分布及其影响机制研究。结果表明,研究区域内72%土壤镉含量超过国家土壤质量二级标准,其中都匀铅锌矿区由于存在独立镉矿床,故其镉含量平均值高达23.36 mg kg-1;镉在土壤水平方向上的含量分布受污染源的影响较大,以污染源为中心向四周呈呈幅射状递减;镉在土壤剖面上的含量分布呈现表层高,在0.80 m内逐渐降低,后在0.80~1.20m之间镉含量急剧升高,出现明显的淀积层,镉在土壤剖面上的分布主要受土壤pH、黏粒积累和底部滞水层等因素影响;在酸性土壤的铅锌矿区和污灌区,镉的赋存形态主要以与铁锰结合的易还原态和酸可交换态为主,占总量的60%~80%,容易从土壤进入食物链和水体,存在较高的人体健康风险和环境风险。

Cadmium is known to be both extremely toxic and ubiquitous in natural environments. It occurs in almost all soils, surface waters and plants. Several typical heavy metal contaminated areas were selected to study the spatial distribution of Cd in soil from different sources and their effect mechanisms. The contaminated areas located in carbonate rock region with high geochemical background value of Cd in Guizhou Province, which were mining area,Pb-Zn mining area, red mud dam and sewage irrigation area. Compared with the second level of the Chinese Soil Environment Quality Standard(GB 15618-1995), the proportion of Cd content over its limit value in all soil samples was 72%. Due to the independent cadmium deposits existed, average Cd content of Duyun lead-zinc mining area was up to 23.36 mg kg-1. The results showed that the horizontal distribution of Cd might be affected by the pollution sources, in which cadmium content was almost highest in the center and decreased gradually from the center to around. The content of Cd was much higher in the topsoil. It gradually reduced within the depth of 0.8 m, then increased sharply between 1 m to 2 m, sequentially precipitated at the bottom of the soil profile. Cd distribution in soil profile was mainly affected by soil pH, clay accumulation and bottom stagnant water. In acid soils of sewage irrigation and lead-zinc mining, Cd mainly existed in reducible Fe-Mn oxides and acid exchangeable Cd accounted for 60-80%, which could easily transfer from soil to food chain or water. This issue could lead to human health and environmental risks.