Study of metals in radical-mediated toxicity of particulate matter in indoor environments of Pune, India

Abstract

The concentration of coarse and fine indoor particulate matter (PM) was measured along with that of metals (Fe, Cu, Zn, Mn, Pb, Cd, Co, Ni, and Cr) collected from rural and urban residential environments of Pune City with the purpose of examining their free radical generation and its related toxicity. The average mass concentration of indoor PM10 and PM2.5 was ∼3.3 and ∼4.5 times higher than the threshold limits of the Indian National Ambient Air Quality Standards (NAAQS) at urban and rural sites, respectively. The concentration of metals was found to be higher in the fine fraction of PM collected from the rural site. Metal analysis revealed the dominance of Fe concentrations in both PM10 and PM2.5 followed by Zn, Ni, and Cu. Electron paramagnetic resonance (EPR) was used to evaluate the presence of free radicals in samples collected from both the sites. EPR spectra for these particles were attributed to both Fe3+ (g = 1.99∼2.0) and free radicals (g = 2.0023 and g = 2.003) in PM samples. Dithiothreitol (DTT) assay was also performed which supports the presence of higher redox activity in the fine fraction of PM at the rural site. Significant DNA damage was observed by both fractions of PM when tested in the controlled experiment, with averages of 43 and 30.9 % for PM10 and 55.3 and 40.5 % for PM2.5 at the rural and urban sites, respectively. This study articulates a significant amount of evidence to understand the importance of size and composition (especially metals) of indoor PM in the toxicological mechanism.