High contribution of non-exhaust emission to health risk of PM2.5-bound toxic metals in an urban atmosphere in south China

PM2.5-bound toxic metals are hazardous to human health due to their bioaccumulation and non-degradability. To investigate the sources and health risks of PM2.5-bound toxic metals at urban Dongguan in the Pearl River Delta region, a comprehensive campaign was carried out in this city in 2019 to measure hourly mass concentrations of PM2.5-bound toxic metals (e.g., V, Cr, Mn, Ni, As and Pb). The annual average mass concentrations of V (2.4 +/- 2.1 ng m- 3), Mn (18.5 +/- 12.1 ng m- 3), Ni (1.9 +/- 1.2 ng m- 3), As (4.6 +/- 3.8 ngm- 3) and Pb (17.8 +/- 15.4 ng m-3) met the guidelines proposed by the World Health Organization (WHO), while that of Cr(VI) (estimated as 1/7 of Cr, 0.66 ng m-3) was 2.6 times higher than the WHO guideline. Positive matrix factorization (PMF) analysis suggested that Cr (70 +/- 23%) and Mn (54 +/- 24%) mainly originated from non-exhaust emission, Ni (50 +/- 29%) and V (83 +/- 24%) from ship emission and As (54 +/- 28%) and Pb (55 +/- 28%) from coal combustion. The hazard index (HI) of PM2.5-bound toxic metals was 0.76, complying with the acceptable value of 1.0. The carcinogenic risks (CRs) associated with Cr(VI) and As for adults were 18.6 and 5.7 times higher than the threshold value of 1 x 10-6, respectively. However, the CRs for children were 3.5 and 0.5 times higher than the same threshold value, respectively. HI and CRs of these toxic metals were dominated by non-exhaust emission and coal combustion, suggesting emission reductions from these sources would effectively reduce the human health risks caused by toxic metals.