Health risk assessment of metals and metalloids in PM_2.5 during heating season from 2014 to 2018 in Baoding

Background Among the 72 large and medium-sized cities monitored in China, the air pollution of Baoding is still high, and the pollution of PM_2.5 in heating season is more serious than that in non-heating season.

Objective This assessment focuses on the health risks of metals and metalloids in PM_2.5 during heating season in Baoding, aiming to provide scientific evidence for air pollution control.

Methods During the heating season (15 November to 15 next March) from 2014 to 2018, PM_2.5 samples were collected on the roof of a four-storey school building of Lekai Primary School in Baoding City from 10 to 16 every month, totaling 145 d. The concentration of PM_2.5 was calculated by weight difference before and after sampling and sampling volume of quartz fiber filter membrane. The concentrations of 12 metals and metalloids were determined by inductively coupled plasma mass spectrometry (ICP-MS), including antimony (Sb), aluminum (Al), arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb), manganese (Mn), nickel (Ni), selenium (Se), and thallium (Tl). The non-carcinogenic risks of metals (Pb, Hg, and Mn) and the carcinogenic risks of metals and metalloids (As, Cd, Cr, and Ni) were evaluated by the health risk assessment model for inhalation exposure.

Results The daily average concentrations of PM_2.5 in the five heating periods from 2014 through 2018 were 2.00×10², 1.79×10², 2.05×10², 1.14×10², and 1.19×10² μg·m^-3 respectively, all above the national secondary standard limit of Ambient Air Quality Standards (GB 3095-2012). The daily average concentrations of Pb were 3.41×10^-1, 1.44×10^-1, 1.31×10^-1, 5.22×10^-2, and 8.49×10^-2 μg·m^-3, respectively, all within the national secondary standard limit (GB 3095-2012). The total concentrations of metals and metalloids were 9.21×10^-1, 8.15×10^-1, 5.61×10^-1, 3.58×10^-1, and 4.49×10^-1 μg·m^-3, accounting for 0.46%, 0.46%, 0.27%, 0.31%, and 0.38% of the concentration of PM_2.5 respectively. The concentrations of PM_2.5 and metals and metalloids in the heating periods of 2017 and 2018 were lower than those in the other three heating periods. The hazard quotients (HQs) of Pb, Mn, and Hg in the five heating periods were 4.00×10^-4-2.08×10^-1, 4.00×10^-4-8.77×10^-2, 4.00×10^-4-7.98×10^-2, 1.00×10^-4-3.18×10^-2, and 1.00×10^-4-5.77×10^-2, respectively, all below 1. Pb generated the highest HQ, followed by Mn and then Hg. The carcinogenic risks (R) of As, Cd, Cr, and Ni in the five heating periods were 2.20×10^-7-1.68×10^-4, 1.30×10^-7-3.20×10^-5, 8.00×10^-8-3.51×10^-5, 5.00×10^-8-2.82×10^-5, and 3.00×10^-8-1.70×10^-5, respectively. From 2014 to 2015, the order of carcinogenic risk was Cr>As>Cd>Ni, and in the other heating periods, it was As>Cr>Cd>Ni; the ranks of As and Cr was slightly different, and Ni was always at the bottom. The health risks of metals and metalloids to adult men was the highest, followed by adult women and then adolescents.

Conclusion In Baoding during heating periods, the non-carcinogenic risks of Pb, Mn, and Hg and the carcinogenic risk of Ni are acceptable; metalloid As and metals Cr and Cd may pose potential carcinogenic risks; both carcinogenic and non-carcinogenic risks of the selected elements show a downward trend over time.