洞庭湖区表层沉积物重金属污染特征与风险评价

Pollution characteristics and risk evaluation of heavy metals in surface sediments of Dongting Lake

长江经济带的人口和经济总量占比均超过全国的40%,处理好长江流域洞庭湖水系开发与治理的关系,是实现长江经济带“共抓大保护,不搞大开发”的重要环节之一。为了解洞庭湖水系重金属污染特征与生态风险,2017年8月对洞庭湖水系24个点位表层沉积物进行了采样,分别对研究区域中Hg、As、Cr、Cd、Pb和Cu等6种重金属含量进行了评价和来源分析。结果表明:①表层沉积物重金属平均质量分数表现为Cr>Pb>Cu>As>Cd>Hg,Hg、As、Cr、Cd、Pb的含量分别为背景值的7.0,2.0,9.3,2.2,2.3倍,湖区Hg、As、Cr、Cd、Pb平均含量均略高于入湖水系,是入湖水系沉积物重金属含量的1.1~1.5倍。②地累积指数和潜在生态指数评价显示:重金属RI值从大到小的顺序为Cd>Hg>Cu>Pb>As>Cr;Cd处于中度污染,重生态风险,Hg处于偏中度污染,重生态风险,表明Cd、Hg是主要污染物;mPEC-Q均值为0.43,表明研究区域内发生生物毒性不利影响的可能性在15%~29%之间。③来源分析表明:As、Pb、Cd、Cu等重金属具有同源性,主要来自“四水”流域工业废水,需进一步推动企业转型升级;为降低Cr含量,应加强生物灭螺实际应用研究。

The population and economy in Yangtze Economic Belt accounts for more than 40% of whole China. Balancing the relationship between development and management of the water systems of Dongting Lake in the Yangtze River Basin is an important link in implementing the principle of promoting well-coordinated environmental conservation and avoiding excessive development. In order to understand the characteristics and ecological risks of heavy metal pollution in Dongting Lake water system, 24 sediment samples were collected in August, 2017. The content characteristics and the pollution status of heavy metals in the study area were analyzed by the method of Igeo, RI and mPEC-Q, and the interrelation and source of heavy metals were evaluated by CA and PCA. The results showed that:① The concentrations of heavy metals in the surface sediments from high to low were Cr, Pb, Cu, As, Cd, Hg. The concentration of Hg, Cr, Cd, Pb, Cu were 7.0, 2.0, 9.3, 2.2, 2.3 times of the background values, respectively. The average concentration of Hg, As, Cr, Cd, Pb in surface sediments of the lake areas were 1.1~1.5 times of that in the main inflowing rivers.② The results of geo-accumulation index method and the potential ecological risk evaluation indicated that Cd and Hg were considered as the dominant pollutants. The RI values from high to low were Cd, Hg, Cu, Pb, As, Cr. The mean value of mPEC-Q was 0.43, indicating that the sediments in all of the sampling sites had a 15%-29% probability of toxcity.③ Source analysis showed that As, Pb, Cd and Cu were homologous and mainly came from the industrial wastewater from the Xiangjiang River, Zijiang River, Yuanjiang River, and Lishui River, indicating that further promoting the transformation and upgrade of enterprise is necessary, and the practical application of biological snail control should be strengthened to reduce the concentration of Cr.