Heavy metal pollution in the surface water of the Yangtze Estuary: A 5-year follow-up study.

The temporal-spatial changes in the concentration and health risk of eight dissolved heavy metals in the Yangtze Estuary over a 5-year period were discussed based on large-scale sampling data. Special attention was paid to the differentiation of metal sources. Concentrations of the metals were present in the following order: Zn≫As>Cu>Cr>Ni>Pb>Cd>Hg, but the hazard quotient indices could be obviously divided into three gradients. More attention should be paid to As, Ni, Pb, and Cr because they increased yearly. Cu, Ni, Pb and As had higher health risks in the nearshore zones, while higher health risks of Zn, Cr, Cd, and Hg were observed in the estuarine channel. Correlations and hierarchical cluster analysis results of metal sources were consistent well with those obtained by temporal-spatial distributions. Shipping activities were the largest contributor to the elevated Zn concentrations in the estuary, while Megacity Shanghai significantly affected the Ni, Cu and As pollution. Yangtze River runoff was the primary source of Cu and As in the estuary. Cd and Cr pollution were closely related to the sediment release under the drive of the "salt-out effect".