Urban Road Dust as a Cross-Media Pollutant Reservoir: PM10 Oxidative Potential and Stormwater Metal Contamination in Kolkata

Abstract

Road dust in urban megacities represents a significant non-point source of both airborne and waterborne pollution. This study presents an integrated assessment of road dust in Kolkata, India, to evaluate its potential associations with the oxidative potential (OP) of ambient PM₁₀ and its role as a persistent urban metal reservoir associated with stormwater contamination. Road dust and runoff were collected from 16 diverse urban zones, while ambient PM₁₀ sampling was conducted at a representative commercial site during the pre-monsoon season. This study provides an integrated cross-media assessment by combining chemically resolved PM₁₀ oxidative potential measurements obtained during the pre-monsoon period of 2022 with road dust, stormwater runoff, and surface water samples collected during the pre-monsoon season of 2024. Given the non-concurrent sampling periods, the study evaluates persistent environmental patterns and cross-media consistency rather than direct event-specific transport across compartments. Positive Matrix Factorization (PMF) source apportionment identified road dust as the largest individual resolved contributor to PM₁₀ (20%). PM₁₀-road dust bound redox-active metals such as Fe, Mn, and Ni were strongly correlated (r: 0.6 to 0.75) with the volume normalized oxidative potential (OP_v) (average OP_v : 12.9 nmol DTT \({\text{m}\text{i}\text{n}}^{-1}{\text{m}}^{-3}\)), suggesting a potential contribution of these redox-active metals to PM₁₀ oxidative potential. Simultaneously, stormwater road runoff analysis revealed high concentrations of Pb (up to 1.22 \({\text{m}\text{g} \text{L}}^{-1}\)), Cr (0.85 \({\text{m}\text{g} \text{L}}^{-1}\)), and Fe (up to 98.7 \({\text{m}\text{g} \text{L}}^{-1}\)) particularly in landfill and industrial areas. Post-runoff measurements showed metal accumulation in nearby aquatic systems, with Pb levels increasing from 0.097 to 0.154 \({\text{m}\text{g} \text{L}}^{-1}\) in urban canals. The East Kolkata Wetlands, a Ramsar site, also showed signs of increased contamination. These findings underscore road dust as a persistent urban contaminant reservoir, influencing both atmospheric and aquatic pollution pathways. The study highlights the potential value of considering chemically relevant indicators such as OP alongside mass concentration in urban air-quality assessment and implementing stormwater interception measures to mitigate environmental and health risks in South Asian cities experiencing rapid urbanization.