Non-carcinogenic and Carcinogenic Risk Assessment of Trace Elements of PM2.5 During Winter and Pre-monsoon Seasons in Delhi: A Case Study

This study focuses on exposures of metal constituents of particulate matter (PM) in the ambient air sample collected at Indian Institute of Technology Delhi (IIT Delhi), India, which might lead to occurrence of non-cancerous events and cancer events. A step-wise construction of risk assessment framework for estimating risks due to exposures of PM2.5 presented. Samples from winter and pre-monsoon seasons of Delhi region (28.5450 degrees N, 77.1926 degrees E) (duration 1: December 2013-February 2014; duration 2: March 2014-May 14) were collected. More than 12 samples were collected using PM2.5 sampler on an 8-h basis and analysed gravimetrically for determining mass content and chemically for determining metal content of PM2.5. Twenty-eight metals in samples were detected using Energy Dispersive X-Ray Fluorescence (ED-XRF). Using these values, health risks of hypotheticals exposures of PM2.5 in ambient air samples were estimated either in terms of hazard quotient (i.e. ratio of daily inhaled dose to daily acceptable dose) for exposures of non-carcinogenic metals or lifetime excess risk of cancer for exposures of carcinogenic metals. Dose-response information of different metals was taken from the U.S. EPA IRIS database. Among metals, S content was highest followed by Cl, Si, K, Ca and Fe, Zn and Pb. High S can be attributed to vehicular emission or particles generated from abrasion of tyres of vehicles. High contents of Si, Ca, Fe in PM samples may be contributed from resuspension road dust, while source of K may be local biomass burning for space heating in winter. Zn comes from vehicle and coal burning probably used by local residents for space heating. Chlorine used in lubricants and diesel fuel could be a source of high Cl content in samples collected in the present work. Small traces of Pb in samples might be coming from brake and tyre wear or resuspension of road dust contaminated with lead used earlier in diesel and/or petrol to improve combustion. Estimates of potential risk due to hypothetical exposure of adults and children to four carcinogenic metals of PM2.5 were found to be more than 1/10,000,000, indicating chance of cancer risks. Among metals, exposures to PM-associated Cd resulted in consistent cancerous risk in both seasons, whereas exposures to PM-associated Cr resulted in HQ value > 1 indicating chance of non-carcinogenic risks.