Oxidative Potential of Metal-Containing Nanoparticles in Coal Fly Ash Generated from Coal-Fired Power Plants in China

The overwhelming magnitude of coal-fired power plants has caused an inevitable release of metal-containing nanoparticles (MNPs) into the atmosphere, which may be inhaled into the respiratory system and cause oxidative stress. In this study, MNPs and oxidative potential (OP) were analyzed in <1 μm fractions of 56 coal fly ashes collected from Chinese CFPPs. The particle number concentrations (PNCs) of Fe- and Ti-containing NPs, as the dominant MNPs in CFAs, were in the range of 1.5 × 10⁹ to 9.4 × 10¹⁰ and 6.4 × 10⁸ to 4.1 × 10¹⁰ particles/mg, with average particle sizes of 87 and 89 nm, respectively. Average OP values of <1 μm fractions were 1.4-2.2 nmol AA min^-1 μg^-1 for three simulated lung fluids, which were 2-3 orders of magnitude higher than those of urban atmospheric PM_2.5. According to structural equation model analysis, metal concentrations in <1 μm fractions, PNCs of Fe-/Ti-containing NPs, and their corresponding dissolved Fe/Ti (including NPs with minute sizes) can regulate OP of <1 μm fractions in CFAs. Elevated PNCs of MNPs in CFAs can be produced by CFPPs burning low-rank coals and with a low combustion efficiency boiler (e.g., circulating fluidized-bed boiler). Once entering lung fluids, they likely release more dissolved metals or tiny corresponding NPs, thus generating greater OP. This study provides the first comprehensive investigation of OP generated by MNPs in CFAs.