PM_2.5-bound heavy metals around the Danjiangkou Reservoir: sources, transport pathways, and health risks

To investigate the potential impact of PM_2.5-bound heavy metals on the water source area, four monitoring sites were established in the Xichuan Reservoir area of the Danjiangkou Reservoir, a core component of the South-to-North Water Diversion Project. PM_2.5 samples were collected from June 2022 to April 2023 (n = 112), and concentrations of nine heavy metals (Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, and Pb) were analyzed. The study identified major pollution sources and atmospheric transport pathways and assessed potential health risks. Results indicated that the total average concentration of the nine heavy metals was found to be 1.9062 μg m^-3, with Zn and Fe being the most abundant, contributing 72% and 23% of the total mass concentration, respectively. Seasonal variations were observed, with higher concentrations during spring and lower levels in summer and winter. No non-carcinogenic health risks were detected for any of the metals. However, As and Cr(VI) exhibited measurable carcinogenic risks. PMF analysis resolved four primary emission sources: traffic (35%), agriculture (33%), dust (23%), and coal combustion (9%). Among the sources, agricultural emissions were predominantly of local origin, whereas traffic and dust sources resulted from a combination of local emissions and regional transport. In contrast, coal combustion sources were primarily attributed to long-range transport. Notably, despite it's relatively low mass contribution, coal combustion constituted the primary source of both carcinogenic and non-carcinogenic risk, accounting for 81% and 65-67%, respectively. These findings address a critical research gap regarding heavy metals in PM_2.5 within the reservoir area, providing a theoretical foundation and data support for future air pollution control measures in the Danjiangkou Reservoir region.