Assessing the impact of PM2.5 constituents in its overall toxicity in the urban region of Indo-Gangetic Plain 

A detailed physio-chemical investigation of ambient PM2.5 constituents was conducted in order to identify the factors affecting its toxicological endpoints. The PM chemical components for various inorganic ions (SO42-, NO3-, NH4+, etc.), PAHs, water-soluble organic carbon (WSOC), water-soluble nitrogen (WSN), elemental and organic carbon (EC/OC) were analysed. The indicators mentioned above were assessed using ambient PM2.5 samples (n=30) collected from October to December 2021, over urban Kanpur region in the Indo-Gangetic Plain. To assess the toxicity of PM, cell viability assays were conducted on three distinct cell lines, namely NIH-3T3, B16-F0, and A549. It was found that PM chemical composition was major determinant in toxicity assessment rather than its mass concentration. PM2.5 samples containing greater amounts of OC and high-molecular-weight PAHs (4-6 rings) exhibited a more pronounced toxicity. Elevated concentrations of SO42- and NO3- were concurrent with these samples. The observed association between OC, SO42- and NO3- with cell toxicity suggests that chemical processing has the potential to increase the toxicity of PM2.5 particles. This was further validated by analysing the light absorption spectra of PM2.5 samples (350–500 nm), which revealed that samples with reduced cell viability exhibited more absorption in the spectra. Further, the spectrum analysis of higher toxicity samples indicated the possible presence of nitroaromatic and HULIS type chromophores causing toxicity in PM2.5. The other PM components, particularly EC, exhibited no association with any of the PM2.5 components which may be due to its inert nature. Therefore, EC and low-molecular-weight PAHs (2–3 rings) had the least impact on PM2.5 toxicity. This study revealed that the primary factors contributing to the toxicity of PM2.5 are the existence of organic molecules and their subsequent secondary transformations in the presence of SO42-, NH4+, and NO3-. Further, the study improves our understanding regarding the toxicity profiling of particulate matter, which may help in policy formulation to mitigate its impact.