Source-specific health risks of PM_2.5-bound toxic metals in Wuhai, a semi-arid city in northwest China

Quantifying the individual impact of each PM2.5-containing source on increasing health risk is essential for mitigating the harmful effects of atmospheric pollutants to human health. However, there remains a limited understanding of these health risks and their association with sources in semi-arid cities. To address this lack of understanding, 20 PM2.5-bound toxic metals (PTMs) were observed at six sampling sites in Wuhai, a typical semi-arid city in northwest China. The spatiotemporal variations, sources, and health risks of PTMs in Wuhai were investigated. Silicon (Si), Ca, Na, Al, Mg, and Fe were the predominant metals, accounting for 90.2 % of total metals. The contents of anthropogenic metals (Cd, Hg, and Pb) were higher during winter and autumn, whereas those of crustal metals (Si, Fe, Cu, Al, and Co) were higher during spring. The sources of PTMs in Wuhai were identified as soil sources (SS, 57.8 %), fugitive dust (FD, 23.3 %), vehicular emissions (VE, 13.4 %), metal smelting (MS, 3.9 %), and coal combustion (CC, 1.7 %). The hazard quotient of Mn and the hazard index of PTMs for children were >1, suggesting a non-carcinogenic health risk for children. The carcinogenic risk of Cr was >1 x 10(-6), suggesting a Cr-associated carcinogenic risk for both adults and children in Wuhai. The main sources of non-carcinogenic risk included VE (62.5 %), SS (18.4 %), MS (11.3 %), CC (4.6 %), and FD (3.2 %). Alternatively, the main sources of carcinogenic risks included MS (53.8 %), VE (15.9 %), SS (13.9 %), CC (8.8 %), and FD (7.6 %). Overall, this study suggests that natural sources (SS and FD) are significant contributors to the health risks of PTMs in semi-arid cities. In conclusion, this study provides a comprehensive understanding of PTMs in semi-arid cities and reveals the contribution of each potential source to corresponding health risks.