Distribution and ecological risk assessment of cadmium in water and sediment in Longjiang River, China: Implication on water quality management after pollution accident.

In early January 2012, the Longjiang River was subjected to a serious cadmium (Cd) pollution accident, which led to negatively environmental and social impacts. A series of measures of emergency treatment were subsequently taken to reduce water Cd level. However, little information was available about the change of Cd level in environmental matrices and long-term effect of this pollution accident to aquatic ecosystem. Thus, this study investigated the distribution of Cd in water and sediment of this river for two years since pollution accident, as well as assessed its ecological risk to aquatic ecosystem of Longjiang River. The results showed that it was efficient for taking emergency treatment measures to decrease water Cd concentration to below the threshold value of national drinking water quality standard of China. There was high risk (HQ > 1) to aquatic ecosystem in some of reaches between February and July 2012, but low or no risk (HQ < 1) between December 2012 to December 2013. Cd concentration in sediment in polluted reaches increased after pollution accident and emergency treatments in 2012, but decreased in 2013. During flood period, the sediment containing high concentration of Cd in Longjiang River was migrated to downstream Liujiang River. Cd content in sediment was reduced to background level after two years of the pollution accident occurrence. The study provides basic information about Cd levels in different media after pollution accident, which is helpful in evaluating the effectiveness of emergency treatments and the variation of ecological risk, as well as in conducting water management and conservation.