Pollution characteristics and human health risks of PM2.5-bound heavy metals: a 3-year observation in Suzhou, China

Abstract

This study aimed to analyze the temporal trends, pollution levels, and health risks associated with eleven PM_2.5-bound heavy metals (Sb, Al, As, Hg, Cd, Cr, Mn, Ni, Pb, Se and Tl). A total of 504 PM_2.5 samples were collected in Suzhou from January 2019 to December 2021. The pollution levels were estimated based on enrichment factors (EFs) which can be used to calculate the enrichment of heavy metals in PM_2.5 and determine whether the concentrations of PM_2.5-bound heavy metals are influenced by the crustal or anthropogenic sources, and the health risk of PM_2.5-bound heavy metals via inhalation was assessed following US EPA's Risk Assessment Guidance for Superfund (RAGS). The annual average concentration of PM_2.5 was 46.76 μg m^-3, which was higher than the WHO recommended limit of 5 μg m^-3. The average of the sum of eleven PM_2.5-bound heavy metals was 180.61 ng m^-3, dominated by Al, Mn, and Pb. The concentration of PM_2.5 in 2020 was significantly lower than that in 2019 and 2021. The PM_2.5 and PM_2.5-bound heavy metal concentrations in winter and spring were significantly higher than those in autumn and summer. The EF of As, Cr, Cd, Hg, Ni, Pb, Sb, Mn, Se, and Tl was higher than 10, indicating they were mainly from anthropogenic sources. Exposure to a single non-carcinogenic heavy metal via inhalation was unlikely to cause non-carcinogenic effects (HQ < 1), but the integrated non-carcinogenic risks should be taken seriously (HI > 1). The cumulative carcinogenic risks from the carcinogenic elements were exceeding the lower limit (1 × 10^-6) of the acceptable risk range. The carcinogenic risks of As and Cr(VI) contributed 60.98% and 26.77%, respectively, which were regarded as two key carcinogenic risk factors. Overall, the government policies and countermeasures for the PM_2.5 pollution control should be performed not only based on the PM_2.5 concentration but also based on the PM_2.5-bound heavy metals and their health risks for the local residents.

Keywords: Health risk assessment; Heavy metals; Inhalation exposure; PM2.5; Suzhou.