Health risk assessment of heavy metal emissions from on-road vehicles in a metropolitan area in southeastern China
摘要
Heavy metals (HMs) in PM2.5 have been extensively studied for their toxicity and carcinogenic risk. In this study, the toxicity and spatial health risks of PM2.5-HMs from on-road vehicles were investigated in the Xiamen-Zhangzhou-Quanzhou (XZQ) metropolitan area in southeast China in 2021. The results show that the emissions of PM2.5 and PM2.5-HMs were 3219.54 and 89.48 t, with non-exhaust emissions contributing 62.1% and 87.6%, respectively. However, there were differences in the contribution of different sources to different HMs. The spatial distribution of PM2.5 was characterized by high levels in the urban centers with high traffic flow and population. The daily PM2.5 concentration could reach up to 6.85 μg/m3 in the area with heavy traffic. Wind speed and direction had a significant effect on the daily PM2.5 concentration, while hourly concentrations were more influenced by variations in vehicle activity. The annual average concentration of Cr(VI) (0.15 ng/m3, estimated as 12% of total Cr) in the hotspot grid was six times the limit (0.025 ng/m3) of China’s air quality standard. Other toxic metals such as As, Cd and Pb were well below their guidelines. The health risk assessment showed that there was no threat of non-carcinogenic risks, but the carcinogenic risks in some urban centers exceeded the safety level of 10–6. More than 90% of the carcinogenic risk came from Cr(VI), which mainly came from brake wear (55.7%) and diesel exhaust (32.5%). This study provides a scientific basis for the development of more effective pollution control strategies and public health policies.