Health Effects of Combined Respiratory and Internal Exposure to Multiple Metals in PM2.5 and PM0.25 in Solid Fuel Combustion Household Environment

Respiratory exposure to heavy metals is an important health risk factor; however, the impact of co-exposure to multiple metals on internal exposure and health remains unclear. Here, we evaluated the relationship between exposure to nine metals (K, Ca, Fe, Cr, Mn, Zn, Pb, Se, and Hg) in PM2.5, PM0.25, and urinary metals with health biomarkers, i.e., 8-hydroxy-2′-deoxyguanosine (8-OHdG), vascular endothelial growth factor (VEGF), interleukin-8 (IL-8), and C-reactive protein (CRP), in rural housewives in Yuncheng City, northern China. K, Ca, Cr, Mn, Zn, and Hg were primarily present in PM0.25. Fe, Pb, and Se showed the higher concentrations in PM2.5, indicating that these elements mainly existed in the coarser fraction of PM2.5. The correlation of metals in the two particle sizes was decent, but only K and Se in PM2.5 and PM0.25 were significantly correlated with their respective concentrations in urine. Most metals in the urine were negatively correlated with biomarkers representing inflammation and oxidative stress. Based on the Bayesian kernel machine regression mixed effect model, we found that the co-exposure of nine metals in PM0.25 was significantly negatively correlated with VEGF, with Hg and Cr having the highest posterior inclusion probability, which may be due to the synergistic effect of these two metals. We recommend minimizing the use of solid fuels at home and regularly replacing utensils, which can have a certain effect on reducing exposure to heavy metals. This study offers a theoretical foundation and practical exposure case for quantitatively assessing the effects of particulate matter-bound metals on human health during the combustion of solid fuels in rural households.