洞庭湖表层水和底泥中重金属污染状况及其变化趋势

Assessment of Heavy Metal Pollution in Surface Water and Sediment of Dongting Lake

为评价洞庭湖重金属污染程度,分析了洞庭湖湖区9个采样点表层水及底泥中Hg、Cr、Cd、As、Pb和Cu的浓度水平,并采用地积累指数法和潜在生态风险指数法对底泥中的重金属污染现状进行评价. 结果表明,洞庭湖表层水中重金属质量浓度远低于GB 3838—2002《地表水环境质量标准》一级标准限值,底泥中w（Hg）、w（Cr）、w（Cd）、w（As）、w（Pb）和w（Cu）均高于背景值,其平均值分别为背景值的5.0、3.1、22.7、2.2、2.5和1.9倍. 洞庭湖表层水中ρ（As）与底泥中w（As）呈显著正相关. 近30年来,洞庭湖底泥中除w（Hg）下降外,其他重金属质量分数均有所上升. 地积累指数法评价结果表明,洞庭湖底泥中不同种类的重金属Igeo（地累积指数）表现为Cd＞Hg＞Cr＞As＞Pb＞Cu,Cd和Hg的Igeo分别为3.92和1.73；不同区域的重金属Itot（综合地积累指数）呈虞公庙〉横岭湖〉洞庭湖出口〉东洞庭湖〉蒋家嘴〉鹿角〉万子湖〉南嘴〉小河嘴的分布特征,虞公庙和横岭湖的Itot均大于10.0.潜在生态风险指数法评价结果表明,各污染物对洞庭湖生态风险构成危害的影响程度为Cd＞As＞Cr＞Hg＞Cu＞Pb,整个洞庭湖区的RI（潜在生态风险指数）为99.0-696.7,平均值为281.8,属于中等潜在生态危害,其中南洞庭湖的虞公庙和万子湖的RI分别为696.7和565.9,已成为潜在生态风险区域.

The contents of heavy metals, including As, Cd, Cr, Cu, Hg and Pb, in the surface water and sediment of nine sample sites in Dongting Lake were analyzed, and the heavy metal pollution of sediment in Dongting Lake was evaluated by geoaccumulation index （Igeo） and potential ecological risk index （RI）. The results indicated that heavy metal concentrations in surface water were much lower than the standards of class Ⅰ of Environmental Quality Standards for Surface Water （GB 3838-2002）. The average values of w（Hg）, w（Cr）, w（Cd）, w（As）, w（Pb） and w（Cu） in sediments were uniformly higher than the background values, with the average values being 5.0,3.1,2.7,2.2,2.5 and 1.9 times larger than the background values, respectively. A significantly positive relationship was found between the concentrations of As in surface water and sediment. Although the mass fraction of Hg in sediment decreased, the others showed an increasing trend over the past thirty years. The values of Igeo in sediments of Dongting Lake were in the following order：Cd〉Hg〉Cr〉As〉Pb〉Cu, and the values of Igeo of Cd and Hg were 3.92 and 1.73, respectively. The decreasing order of the values of Igeo was as follows：Yugongmiao〉Hengling Lake〉Outflow of Dongting Lake〉East Dongting Lake〉Jiangjiazui〉Lujiao〉Wanzi Lake〉Nanzui〉Xiaohezui, and the values of Igeo of Yugongmiao and Hengling Lake were both more than 10.0.The evaluation results of potential ecological risk index showed that the degree of ecological risk to Dongting Lake resulting from pollutants was as follows：Cd〉As〉Cr〉Hg〉Cu〉Pb. The average potential ecological risk index was 281.8 （ranging from 99.0 to 696.7）, suggesting a moderate ecological risk. Yugongmiao and Wanzi Lake in South Dongting Lake have become potential ecological risk regions, with potential ecological risk indexes at 696.7 and 565.9.