Pollution characteristics of heavy metals and the risk assessment for the surface sediments from Lake Chaohu and its main tributary rivers

Abstract

Shallow lakes are important freshwater resources and have the functions of flood control, transportation, agriculture, aquaculture, tourism, drinking and ecological protection. The environmental quality of shallow lakes is highly related to human health and sustainable development of social economy. Rapid urbanization and economic development have resulted, progressively, in deteriorating freshwater conditions. Lake Chaohu is the fifth largest freshwater lake in China. In order to characterize the pollution characteristics of heavy metals in surface sediments of Lake Chaohu, 33 and 7 sediment samples were collected in April 2013 from Lake Chaohu and its main tributary rivers, respectively. The contents of eight heavy metals (Cu, Zn, Pb, Cr, Cd, As, Hg and Ni) in the samples were analyzed and the risk of heavy metal contamination was evaluated using geo-accumulation index, Hảkanson potential ecological risk index and sediment quality guidelines. The mechanization level of various components or elements was analyzed. The results showed that the average contents of heavy metals in surface sediments of the main tributary rivers were higher from 1.18 to 5.15 times than the contents in the whole lake surfaces. The contents of Cu, Zn, Pb, As and Hg in surface sediments of Nanfei River were even higher than those of other rivers, and were 3.53, 16.98, 3.98, 5.84 and 23.11 times greater than the background values, respectively. The average contents of Cu, Zn, Pb, Cd and Hg in the west regions were higher than those of the east regions, and also higher from 1.04 to 1.45 times than those of the whole lake. The results using the geo-accumulation index and the potential ecological risk assessment both indicated that Cd and Hg were the main contribution of the potential ecological risk elements, and they had reached the serious risk level (43.17-3870.94 and 29.96-924.57). The results of source analysis revealed that contents of Cu, Zn, Pb, Cr, Hg and As were highly positively related each other, indicating that they have the same sources which may be from industrial and domestic sewage.