Natural and anthropogenic factors exacerbating mercury ecological risk in the Qilian Mountain Rivers: A threat to water resources

The Qilian Mountains function as a vital ecological barrier in western China, and examining environmental contaminants within this region is pivotal for safeguarding its ecological integrity. However, our knowledge regarding the concentration levels of mercury (Hg) in river waters and the associated environmental risks in this region is quite limited. To evaluate the current status of ecological and health risks of Hg, we collected 84 river water samples from 6 river basins within the Qilian Mountain region for comprehensive Hg analyses. The average total Hg (THg) and total methylmercury (TMeHg) concentrations in the river water samples were 25.74±68.84 and 0.25±0.43 ng L−1, respectively. THg and TMeHg primarily existed in the particulate form and were significantly controlled by the total suspended particulate (TSP) content mainly derived from soil erosion. TSP contributed to 86% and 47% of the variances in THg and TMeHg concentrations, respectively. We also found that Hg in river water downstream of town areas may be influenced by both agricultural and industrial activities. When considering these interactions, the explanatory power of anthropogenic activities interaction with TSP for MeHg increases to 72%. Ecological risk assessments indicated that Hg in river water of the Heihe River Basin showed the highest ecological risk, with 52% of the sites exhibiting chronic medium risk of Hg exposure. Under the influence of climate change and escalating urban pollution, the risks of Hg exposure in this region may intensify in the future.