Size Distribution Of Water-Soluble Metals In Atmospheric Particles In Xi'An, China: Seasonal Variations, Bioavailability, And Health Risk Assessment

The water solubility of potentially toxic elements is associated with biological effects and thus should be a major toxicity evaluation criterion for elements. The size distribution and potential health risk of particle-bound watersoluble metals (Cr, Ni, Zn, Fe, Pb, Ba, Mn, Cu, and Ti) in nine particle sizes ( 0.43, 0.43-0.65, 0.65-1.1, 1.1-2.1, 2.1-3.3, 3.3-4.7, 4.7-5.8, 5.8-9, and 9 mu m) were investigated from December 2018 to November 2019 in Xi'an, China. Water-soluble metals exhibited a typical bimodal distribution, with a dominant peak in the coarse mode (4.7-5.8 mu m) and a minor peak in the fine mode (0.43-0.65 mu m). Most measured water-soluble metals (Ni, Fe, Pb, Ba, Mn, Cu, and Ti) exhibited a peak-shifting tendency from 0.43 to 0.65 to 0.65-1.1 mu m (summer to winter) because of the high relative humidity and high concentrations of gaseous precursor. The bioavailability index (BI) indicated that Zn (44.3%), Mn (37.3%), Ba (34.3%), and Pb (33.6%) had higher bioavailable fractions. Cu (29.4%) and Fe (10.4%) had the highest BI at <0.43 mu m in autumn. Water-soluble Cr and Pb exhibited obvious noncarcinogenic health risks to both children and adults. Water-soluble Cr also had a concerning incremental lifetime carcinogenic health risk of 8.68 x 10-6 caused primarily by the elements in fine particles (<0.65 mu m). Furthermore, the relative contributions of elements in fine particles had a larger effect on bioavailability and health risks than those in coarse particles did, indicating that closer attention should be paid to fine-particle-size elements in Xi'an.