Objective To investigate the concentration variation, source, and health risk of metal elements in ambient fine parti-culate matter (PM_2.5) in Wujin district, Changzhou, China.

Methods From 2016 to 2022, ambient PM_2.5 samples were collected from Wujin district every month. The mass concentrations of metal elements in PM_2.5 were determined by inductively coupled plasma mass spectrometry. The metal sources were analyzed by enrichment factor and principal component analysis. The health risks of metal elements were assessed.

Results A total of 610 valid samples were collected from 2016 to 2022. The M(P₂₅, P₇₅) of ambient PM_2.5 mass concentration in Wujin district significantly decreased in these years and the values were 70 (40, 110), 54 (41, 79), 56 (38, 85), 54 (41, 76), 41 (28, 58), 40 (28, 60), and 39 (28, 54) μg/m³, respectively (P<0.05). The concentrations of metal elements were in the order of aluminum>manganese>lead>chromium>nickel>antimony>cadmium. Except for chromium, the concentrations of metal elements were relatively high in winter and spring. The enrichment factor of manganese was between 10 and 100, while the enrichment factors of other elements were greater than 100 during certain months in different years and seasons. Principal component analysis showed that the first principal component was composed of antimony, aluminum, cadmium, lead, and manganese, the second principal component was composed of chromium, and the third principal component was composed of nickel. Their variance contribution rates were 52.91%, 15.46%, and 10.95%, respectively. The hazard quotients of metal elements were in the order of manganese>nickel>cadmium>aluminum>chromium>antimony. According to the median concentration, the hazard quotients of all metal elements were less than 1. The carcinogenic risks of chromium were greater than 10^-6, and the carcinogenic risks of cadmium were greater than 10^-6 in 2016 and 2018. According to the 95th percentile concentration, the hazard quotient of manganese was greater than 1, and the carcinogenic risks of chromium, cadmium, and nickel were greater than 10^-6.

Conclusion From 2016 to 2022, the concentrations of most metal elements in ambient PM_2.5 generally decreased in Wujin district of Changzhou. The main sources are industrial emissions, transportation emissions, coal combustion, iron and steel industry, and shipping emissions. High concentrations of manganese present a non-carcinogenic risk, while chromium, cadmium, and high concentrations of nickel present a potential carcinogenic risk.