三峡库区典型农业区土壤重金属污染特征及风险评价

为了解三峡库区农业区土壤重金属污染现状及环境风险水平,该文以重庆市8个典型农业区县(铜梁、云阳、万州、丰都、城口、垫江、南川和江津)土壤为研究对象,共采集表层(0~20 cm)土壤样品160个,依照《土壤环境监测技术规范(HJ/T 166-2004)》和《土壤环境质量标准GB 15618-1995》分析了土壤样品中8种重金属(As、Cd、Cr、Cu、Hg、Ni、Pb和Zn)的含量,比较了不同区县8种重金属污染现状及差异,应用地积累指数法和潜在生态风险指数法探讨了研究区土壤重金属的累积特征及潜在生态风险等级。结果表明:该研究区农业土壤8种重金属含量平均值均未超过《土壤环境质量标准GB 15618-1995》二级标准,与土壤背景值相比,Cd、Cr、Cu、Hg和Zn均具有极显著差异(P0.01),As、Ni和Pb差异不显著,8个区县Cr均表现出极显著差异(P0.01),城口区多种重金属均表现出极显著差异(P0.01),8种重金属地累积指数平均值均小于0,研究区土壤受重金属污染水平为未污染等级,单个重金属潜在生态风险顺序为HgCdAsHgCuNiCrZn,Hg元素潜在生态风险指数平均值为43.840,属中等生态风险等级,其余元素生态风险指数值均小于40,属于低生态风险等级,8种重金属综合潜在生态风险指数平均值为108135,为低生态风险等级。综合研究结果表明:三峡库区典型农业区土壤Cd、Cr、Cu、Hg和Zn具有一定程度的累积,且表现为多种重金属复合累积现象,Cr累积具有普遍性,Hg是影响三峡库区农业土壤综合潜在生态风险的主要元素,但研究区土壤重金属总体处于低生态风险水平。

Characterization and risk assessment of heavy metal pollution in agricultural soils in Three Gorge Reservoir Area

Abstract: Over the past several decades, a large amount of agricultural production materials (such as chemical fertilizers, organic fertilizers, pesticides and agricultural films) has been used to increase the output of agricultural products. Therefore, the problems of soil pollution, especially heavy metal pollution in soils, have become problems. Those problems have exerted direct or indirect adverse effects on food safety, and health of human and ecosystem. Therefore, the problem of heavy metal pollution in agricultural soils has become a research hot spot in environmental studies and has since received more attention. Chongqing is an important agricultural production base in the Three Gorges Reservoir Area. The environmental quality of soils in Chongqing area directly affects the food safety and health of the local residents. Although there have been some studies on the quality of agricultural soils, few studies have investigated the status of heavy metal pollution in the agricultural areas of Chongqing. In order to understand the status of heavy metal pollution and the level of its environmental risk in typical agricultural areas in Chongqing, 160 surface soil samples (0 - 20 cm) were collected from the farm field of eight agricultural areas (Tongliang, Yunyang, Wanzhou, Fengdu, Chengkou, Dianjiang, Nanchuan and Jiangjin) based on the "Technical Specifications for Soil Environmental Monitoring (HJ/T 166-2004)". The concentrations of eight heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) in these soil samples were analyzed according to the "Environmental quality standard for soils GB 15618-1995". The status and differences in pollutions of these weight heavy metals among various regions were compared. In addition, geo-accumulation index and potential ecological risk index were used to evaluate the accumulation characteristics and potential environmental risk levels of heavy metals in the studied regions. The results showed that the average contents of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn in the soils of the typical agricultural areas in Chongqing were respectively 6.110, 0.146, 96.860, 35.346, 0.050, 30.596, 24.723, and 77.286 mg/kg soil. The average concentration of all these eight heavy metals in the agricultural soils of studied areas did not exceed the Tier II limit specified in GB 15618-1995. In addition, compared with the background level of the soils, the levels of Cd, Cr, Cu, Hg and Zn showed significant (P < 0.01) differences, while the levels of As, Ni and Pb showed insignificant (P > 0.05) differences. Furthermore, the levels of Cr in all areas showed significant (P < 0.05) differences. Moreover, the concentrations of all these eight heavy metals in soil from Chengkou County showed significant (P < 0.05) differences and the geoaccumulation index values, i.e., the average value of geo-accumulation index, of all eight heavy metals were less than 0, indicating that the overall condition of the soils was not polluted. However, the geoaccumulation index values of certain individual samples were between 0 and 1, indicating that the heavy metals were accumulated at some sampling points. In particular, the level of Pb accumulation was the lowest, with the presence of mild pollution in 3.75% of the samples. The proportions of samples showing mild pollution of Cd, Ni, Hg, As, Zn and Cr were 8.75%, 11.25%, 11.25%, 12.5%, 12.5% % and 15%, respectively, but the highest proportion of samples (42.5%) showed mild pollution of Cu. Therefore, the level of potential ecological risk posed by individual heavy metals was Hg> Cd> As> Hg> Cu> Ni> Cr> Zn. Specifically, as a heavy metal with a medium level of ecological risk, the average Eir value of Hg was 43.8, greater than 40. In addition, the average Eir values of all other heavy metals were less than 40, indicating the level of ecological risk posed by them was low. The overall mean potential ecological risk index (RI) of the eight heavy metals was 108, less than 135, which was at a level of low ecological risk. The results of this comprehensive study showed that Cd, Cr, Cu, Hg and Zn were accumulated to a certain extent in the typical agricultural areas of Chongqing and were manifested as a combined accumulation of multiple heavy metals. In particular, the accumulation of Cr was widely found, while Hg was the main element affecting the comprehensive ecological risk posed to the agricultural soils in Chongqing. Nevertheless, the overall ecological risk posed to the soils of typical agricultural areas in Chongqing was low. Based on a relatively large-scale and updated investigation and assessment of the environmental quality of heavy metals in the soils of typical agricultural areas in Chongqing, in this study, we analyzed the status of heavy metal pollution in the soils of Chongqing, and would provide a scientific basis for the prevention and treatment of soil pollution in Chongqing.