Heavy metal pollution risk assessments and their transportation in sediment and overlay water for the typical Chinese reservoirs

To assess the metals (Cr, Mn, Cu, Zn, Cd, Hg and Pb) pollution risks and their transportation in sediment and overlay water from the typical reservoirs in the rapidly developing economic region of southeastern China, this study integrated an intact sediment core incubation and the sediment metals vertical distribution analysis in a drinking water reservoir (Drinking-Y) and an irrigation water reservoir (Irrigation-T). The results revealed that both studied reservoirs were severely polluted by heavy metals. Irrigation-T was at a considerable risk compared to Drinking-Y (a moderate or slightly considerable risk) reflecting higher concentration of metals in Irrigation-T versus Drinking-Y. Concentrations of Hg and Cd in the overlying water exceeded the World Health Organization (WHO) standard, contributing approximately 90% of the total potential ecological risk index (RI) for both metals in the sediment. Most of the metals continue to increase inputs into the reservoirs and metals can settle from water to sediment in 10-15 days by static incubation. The main anthropogenic pollution sources originated from fuel combinations and industry mills (6.4%) and agricultural activities (38%) for Drinking-Y and fuel combinations and industry mills (4.9%), agricultural activities (32.9%) and mines and quarries (62.1%) for Irrigation-T. To reduce the human health risks, therefore, the freshwater should be stored 10-15 days prior to drinking or irrigation. Our data indicated that all the current pollution sources require more attention for further reducing the human health risks.