Environmental Assessments of Trace Metals in Sediments from Dongting Lake, Central China

To examine the degree of contamination in the Dongting Lake (洞庭湖) area, surface sediments samples were collected and investigated in this study. This lake lies in the south of the middle Yangtze River, and it is the second largest fresh-water lake in China. These samples were analyzed for the concentrations of the following 6 elements (Cd, Cr, Cu, Ni, Pb and Zn) collected from 46 locations. The index of geo-accumulation was used to assess the degree of contamination of the total trace elements and the assessments showed that the contamination of Cd reached strong to very strong pollution. The speciation of metal in sediments was analyzed using the modified BCR (Community Bureau of Reference) sequential extraction technology and the water column-contamination risk was evaluated by the calculated contamination factors. The results of the speciation of metal indicated that more easily mobilized forms (exchangeable, water soluble, and acid soluble) were predominant for Cd, especially in the samples from East Dongting Lake. In contrast, the largest amount of lead was associated with the iron and manganese oxide fractions, and Cu, Zn, Cr, and Ni analyzed were mainly distributed in residual phase at an average percentage higher than 60% of the total metals. The potential risk to the lake’s water contamination was the highest in East Dongting Lake based on the calculated contamination factors. The assessment results using geo-accumulation index were compared with the information obtained by trace metal speciation and both results were consistent.