Heavy metal characteristics and health risk assessment of PM2.5 in three residential homes during winter in Nanjing, China

Both indoor PM(2.5 )concentrations and its chemical compositions are of great concern to human health. This study was conducted to characterize PM2.5 in three residential homes with different HVAC-filter (HVAC: Heating, Ventilating and Air-Conditioning) scenarios and one outdoor environment in terms of mass concentration, heavy metal composition (Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Hg and Pb), enrichment factors (EFs) and health risk assessment. The results verified that the utilization of HVAC-filter system helped to improve indoor air quality significantly with the mean reductions of mass concentration, heavy metal contents and related health risks of indoor PM2.5 -22.1%, 29.1%, and 48.0% of the atmospheric PM2.5 respectively. However, the EFs in the home with HVAC-filter system were the highest among the tested indoor and outdoor air PM2.5 which reminded the potential pollution related to stainless ventilation ducts and particle characteristics (smaller than 2.5 mu m). No evident contributions of the independent household floor heating facility were found to the improvement or the deterioration of indoor air quality from the comparative analysis (p > 0.05). Fe, Zn, Ni, and Mn were the main constituents of the metal elements and accounted for more than 80% of the total elements while Cd was the most enriched metal. Smelting furnaces and coal combustion were the main sources of Cr, Ni and As. Health risk assessment indicated that carcinogenic risks of selected metals in all tested homes (1.22 x 10(-6) similar to 3.32 x 10 -4 ) were unacceptable while non-carcinogenic risks were within the safe range.