Effects of damming on riverine heavy metals and environmental risks in the world’s largest hydropower engineering, China

With the increasing demand for clean energy and water resources, hydropower engineering is gradually expanding worldwide. Revealing the status and toxic risks of riverine pollutants is of considerable theoretical importance for water safety management. However, damming complicates the geochemical behavior of pollutants in river water, especially in large reservoirs with intensive anthropogenic activities. Whether damming amplifies the environmental risks of pollutants needs to be clarified. This study selected heavy metals (HMs) as major pollutants, combining positive matrix factorization (PMF) and Monte Carlo simulation (MCS), identifying the damming impacts on riverine HMs in the Three Gorges Reservoir (TGR). The average concentrations of most HMs increased manyfold than the background, and the HMs loading rates of outflow was increased, suggesting the obvious disturbance by human activities. Through PMF, about 70% of Cu came from industrial wastewater discharges, and more than half of As, V, Mo and Ni were contributed by agricultural activities. The risk assessment results indicated that the concentration of most riverine HMs during the study period did not pose human health damage, children exposed to As have an 9.8 ± 0.9% occurrence probability of non-carcinogenic risk. The results coupled with PMF and MSC showed agricultural activities contributed most (51.3 ± 0.3%) to inducing HMs health hazard. In addition, the contribution rate of each potential source of HMs along the river remained relatively stable, suggesting that damming has limited impact on the risk occurrence. Overall, agricultural activities and the drinking water quality from TGR source should to be constraint preferentially for HMs risks prevention.