Comprehensive analysis of heavy metals in indoor PM2.5: Source identification and health risk assessment in Dhaka, Bangladesh

Indoor air pollution and its associated health risks have become a critical concern in developing countries. This study analyzed particulate matter (PM_2.5) collected from six indoor locations in Dhaka, Bangladesh. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used for measuring the concentration of thirteen heavy metals (Pb, Cd, Cr, Zn, Be, V, Ni, Hg, As, Co, Se, Mn, and Cu). Among these, Mn, Cd, Hg, and Pb exceeded United States Environmental Protection Agency (USEPA) guideline values, with Hg surpassing USEPA thresholds by over 50 times, Cd by more than 6-fold, and Pb by over fourfold, indicating substantial anthropogenic influence. Zn and Pb were identified as the primary contributors to indoor PM_2.5, with high enrichment of Zn, Pb, Hg, Se, and Cd indicating strong anthropogenic influence. Principal Component Analysis (PCA) revealed two major components, explaining 71.26 % of the total variance. Acidity-alkalinity analysis revealed that PM_2.5 in Dhaka was predominantly acidic, with greater concentrations of NO₃⁻ and SO₄²⁻ further supporting the role of anthropogenic activities. Non-carcinogenic risk assessment showed hazard index (HI) values exceeding 10 at three locations, with Ni, Mn, and Cd posing the greatest risks for both children and adults. For carcinogenic risks, Total Cancer Risk (TCR) values at all sites exceeded acceptable thresholds. Cr, Cd, and As were the dominant contributors to TCR, and adults consistently exhibited higher risks than children due to lifetime exposure. This study provides novel, policy-relevant evidence on indoor air quality challenges in Dhaka, highlighting the urgent need for targeted interventions to mitigate heavy metal exposure and safeguard public health in dense urban environments.