Characterization, health risk of heavy metals, and source apportionment of atmospheric PM2.5 to children in summer and winter: an exposure panel study in Tianjin, China

To identify the health risks of heavy metals and potential sources of children's exposure to PM2.5, 36 students aged 9-12 were recruited in 2010 for a panel study in Tianjin, China. Si, Fe, Al, Mg, Ca, Ti, Zn, Pb, Mn, Cr, Ni, As, Cd, Co, nitrate (NO3-), sulfate (SO42-), organic carbon (OC), and elemental carbon (EC) were analyzed. Potential health risks of heavy metals were calculated and sources were identified by positive matrix factorization (PMF). PM2.5 exposure to children in winter (122.4 mu g m(-3)) was higher than in summer (74.7 mu g m(-3)) (p < 0.05). The 14 elements, ions (NO3- and SO42-), OC, and EC represented 14, 38, 40, and 4 % and 19, 39, 31, and 7 % of PM2.5 mass in summer and winter, respectively. Average NO3-/SO42- ratios were 2.3 and 0.6 in summer and winter, respectively, indicating a seasonal shift in the predominance of mobile and stationary sources. Cr and Mn posed the highest carcinogenic and non-carcinogenic risks, respectively. The integrated carcinogenic and non-carcinogenic risks were, respectively, 3.4 x 10(-3) and 2.8 in summer and 4.1 x 10(-3) and 4.9 in winter, which indicated that attention should be paid to both carcinogenic and non-carcinogenic risks of heavy metals for children. In summer, secondary sources, vehicle exhaust, crustal dust, industrial source, and vehicle additives contributed 30, 29, 13, 21, and 7 %, respectively, to children's PM2.5 exposure, while in winter, the contributions of the first four sources together with coal combustion and road dust were 26, 24, 14, 10, 20, and 5 %, respectively.