PM2.5 exposure characterisation around opencast coal mines: leveraging health risk and toxicity assessment

Introduction and background

Opencast coal mining accounts for more than 85% of coal production in India. Heavy transportation and mining activities have been identified as a significant contributor to the emission of fugitive dust and fine particulate matter (PM_2.5) leading to a decline in air quality and negative health impacts within densely populated coal mining regions. PM_2.5-bound species which are not routinely monitored such as elemental carbon (surrogate for diesel particulate matter, a Class I carcinogen), toxic metals and PAHs (poly aromatic hydrocarbons) may pose significant risk to the inhabitants around these areas raising serious health and regulatory concerns.  

Methodology

PM_2.5 samples were collected from roadsides and residential sites near an active coal mining area in Eastern Maharashtra, India at 2, 5 and 10 kms from the mine site comprising of a typical coal haul roadside, an urban roadside, and residential locations. Collected PM samples were analysed for elemental and organic carbon (EC & OC) through thermo-gravimetric analysis, water-soluble metals through ICP-MS and PAHs through GC-MS. Carcinogenic and non-carcinogenic risk was estimated for these species and PM toxicity was measured through acellular assays (Dithiothreitol and Ascorbic Acid).  

Results and conclusions

Five-folds higher PM_2.5 exposure levels (~500 ± 190 µg/m³) were observed near coal-haul road than at the residential sites. PM_2.5 concentration at 2 and 5 km residential sites was comparable (100-120 µg/m³), but 2-3 times lower at the 10 km site and the residential background location. Average DPM concentration (measured as EC) across the sites was 11.3 ± 12.2 µg/m³, with 3 times higher levels at the coal haul road due to the dominance of diesel-powered trucks. Cr (20 ± 2.3 µg/m³), Ni (5.6 ± 0.3 µg/m³), Cd (7.2 ± 1.5 µg/m³), As (2.8 ± 1.6 µg/m³), and Pb (3.7 ± 0.9 µg/m³) emerged as important carcinogenic metals across the sites likely attributable to coal combustion and vehicular exhaust. Average levels of Benzo(a)pyrene, a priority pollutant, was observed to be 15 ± 2.3 ng/m³ at the community sites. Toxicity of PM—measured as OP_vol^AA and OP_vol^DTT—was higher at the roadside (2.3 ± 0.6 nmol min^-1 m^-3 and ~1.9 ± 0.8 nmol min^-1 m^-3 respectively) compared to residential sites (~0.76 ± 0.01 nmol min^-1 m^-3 and 0.94 ± 0.2 nmol min^-1 m^-3 respectively) against the background 0.6 ± 0.2 nmol min^-1 m^-3 (OP^AA) and 0.9 ± 0.12 nmol min-1 m-3 (OP^DTT). The inhalation risk for PM_2.5 was observed to be 4 x 10^-4 indicating a significant risk to the population. The study highlights the high exposure to PM_2.5 and potential health risks in communities around opencast coal mines. It further underscores the need for considering PM composition and toxicity in environmental regulations to safeguard public health from the adverse impacts of industrial activities in data scarce low- and middle-income countries.