Distribution, bioaccessibility, and health risk assessment of heavy metals in PM2.5 and PM10 during winter heating periods in five types of cities in Northeast China.

PM2.5 and PM10 samples were collected from the outdoor environment of five types of cities (provincial central cities, regional central cities, resource-based cities, agricultural cities, and forested cities) situated in Northeast China. Based on bioaccessibility and respiratory deposition fluxes, health risks of PM2.5- and PM10-bound six heavy metals [HM6: Arsenic (As), Chromium (Cr), Cadmium (Cd), Nickel (Ni), Cobalt (Co), and Lead (Pb)] were studied. Cobalt (Co) and Cr were found to be the most abundantly bioaccessible fraction among HM6 after extraction of simulated lung fluids. After inhalation exposure, among HM6, Co mainly contributed 88.39-93.19% to the non-carcinogenic risk, while Cr account for 82.92-93.72% of cancer risk. The estimated daily intake of bioaccessible HM6 in outdoor environment during the heating period was calculated to be 293.11 ± 121.03, 117.08 ± 32.46, 105.57 ± 32.49, 100.35 ± 25.58 and 83.11 ± 17.64 ng/h for provincial central cities, regional central cities, agricultural city, resource-based cities and forested cities, respectively, for local residents. During the heating period of 180 days, non-carcinogenic risks (As, Cr, Cd, Ni, Co) in outdoor environment of 0.5 residence time were below the safety threshold (HQ < 1). Cancer risks for Cr and Co were above 10-5 in the five types of cities, but in the assumable range (< 10-4). Our study highlighted the wide range of measures needed to cut airborne particles pollution to safer levels.