Source-specific health risks of PM2.5-bound heavy metals in a Chinese megacity impacted by non-ferrous metal mines

Non-ferrous metal mining and smelting are considered to be one of the largest sources of heavy metals (HMs) to the atmosphere, posing a serious threat to human health. For this reason, this study addressed the potential impacts in a Chinese megacity affected by non-ferrous metal mines, and explored the characteristics and health risks of HMs in PM_2.5 during summer, autumn, and winter from June 2019 to January 2020. The results showed that the average PM_2.5 concentration and total concentration of 10 associated HMs increased from 25.5 to 48.5 μg m⁻³ and from 51.5 to 133 ng m⁻³, respectively, from summer to winter. Combining methods for health risk assessment of elements and sources, we found that the total carcinogenic risk (CR) of six carcinogenic HMs (As, Cr, Co, Cd, Ni, and Pb) also exhibited a clear increasing trend from summer to winter. However, the total CR (1.12 × 10⁻⁵) in summer still exceeded the minimum acceptable risk level. The main contributors to CR in each of the three seasons were consistently industrial emissions and coal combustion, with their combined contributions exceeding 82.5%. Further analysis indicated that in all three seasons, the CR of industrial emissions mainly resulted from Cr, Co, and Cd, while the CR of coal combustion was primarily due to As, highlighting the significant challenges of controlling Cr-, Co-, and Cd-related industries and As emissions from combustion in areas affected by non-ferrous metal mines in the future.