Are the new atmospheric health risk substances EPFRs oxidatively toxic? : Results from a large urban road dust study in Northwest China

Atmospheric particulate matter (PM) is an important factor of premature human mortality due to PM inhalation. However, the toxic and hazardous components contained within the atmospheric PM are still not fully identified. Environmental persistent free radicals (EPFRs), a novel environmental health risk substance in the atmosphere, have been hypothesized to be important contributors to human respiratory health risks due to their potential to enhance the oxidation potential of PM, but this hypothesis has not been compelling confirmed in the actual atmospheric environment. Therefore, the fugitive characteristics of EPFRs in dust and their potential oxidative toxicity were investigated by using road dust from a mention city in northwest China. The research results showed that the road dust in Xi'an is rich in C-centered EPFRs ((6.6±5.0) ×1017 spins/g), and its half-life can reach 4.5 years. Water-insoluble dust was the main contributor (71%) to the oxidative toxicity of road dust, showing a rapid toxicity-producing process, while the rate of oxidative toxicity production was more constant for water-soluble dust. The contribution of the EPFRs dominant factor to the total dust oxidative toxicity was estimated to be 17% based on the positive matrix factorization (PMF) model, and up to 33% for water-insoluble dust oxidative toxicity. Metals and organic carbon were the main contributing components to the oxidative toxicity of the WS fraction. Summarily, this study demonstrated that the EPFRs are an important contributor to the oxidative toxicity of in actual atmospheric PM, and their oxidative toxicity is dependent on the type of free radicals, providing important insights into what other potentially toxic substances contribute to the oxidative toxicity of atmospheric PM.