9 Evaluation of oxidative stress inducibility of total suspended particles (TSP) in urban air of Delhi

Abstract Particulate matter (PM) in the atmosphere has adverse effects on the respiratory and cardiovascular systems, posing a serious global health concern. To elucidate the chemical and toxicological characteristics of PM in highly polluted regions, this study evaluated the toxicity of total suspended particles (TSP) collected in Delhi, India, and compared them with PM2.5 samples collected in Japan. TSP samples were collected at the Indian Institute of Technology Delhi from November 4 to December 4, 2023, using a high-volume sampler (900 L min-−) for three time periods (morning, daytime, and nighttime). Thirty-five samples collected between November 4 to 18 were analysed for water-soluble organic carbon (WSOC), inorganic ions, and water-soluble/insoluble metals. Oxidative potential was assessed by the dithiothreitol (DTT) assay, and oxidative stress inducibility was evaluated using HO-1 gene expression in rat alveolar epithelial cells. The mean concentrations of PM2.5 and PM10 were approximately 250 and 380 µg m−3, respectively. Although the DTT activity per particle mass was lower in Delhi than in Japan, it was about twenty times higher per air volume due to elevated PM concentrations. In contrast, HO-1 expression was 40-fold higher per particle mass and 1,200-fold higher per air volume, suggesting substantial regional differences. High levels of Pb, Zn, Cu, Mn, and WSOC, particularly during daytime, may contribute to these effects.