Heavy metals pollution and potential ecological health risk assessment in the Yangtze River reaches

Since the construction of the Three Gorges Project, great changes have taken place in the hydrological situation along the Yangtze River and its tributaries. This paper analyzes the content level, temporal and spatial changes and potential ecological risk trends of heavy metal pollutants in surface sediments from 2015 to 2020. The results showed that the average contents of copper (Cu), lead (Pb), manganese (Mn), arsenic (As) and mercury (Hg) in the sediments along the Yangtze River were 23.2∼50.3 mg/kg, 19.6∼65.7 mg/kg, 154.3∼996.8 mg/kg, 6.98∼20.65 mg/kg, 0.198∼0.492 mg/kg, respectively. The average content of Cu, Pb, Mn, As and Hg in sediments of it’s tributaries was 22.3∼29.5 mg/kg, 15.3∼36.7 mg/kg, 456.3∼1123.4 mg/kg, 7.37∼17.15 mg/kg, 0.209∼0.345 mg/kg, respectively. There were obvious differences in the content of heavy metals in the surface sediments of the left and right banks of local river sections along the Yangtze River. The content of heavy metals in surface sediments along the Yangtze River and its tributaries fluctuated to a certain extent in different water periods. The contents of Cd, Cr, Cu, Pb, As and Hg in the back muscle tissue of seven main economic fishes were determined. The results showed that the contents of Cd, Cr, Cu, Pb, As and Hg were 0.02∼2.53 mg/kg, ND∼2.75 mg/kg, 0.0003∼4.1 mg/kg, ND∼1.03 mg/kg, ND∼0.03 mg/kg, ND∼0.03 mg/kg, respectively. Pb and Cd were the main elements of heavy metal pollution in Yangtze River fish. Crucian fish was the most polluted by heavy metals, while grass fish was the least. Various evaluations show that the heavy metals in the surface sediments along the Yangtze River and its main tributaries were generally at a medium enrichment level, and the potential ecological risk index of heavy metals except Ganjiang River changes little during most periods. The potential ecological risk index of heavy metals in Ganjiang River was at relatively high level in 2017, but declined and tended to be stable after 2017.