Distribution of carcinogenic polycyclic aromatic hydrocarbons in urban soil across major cities of Bihar, India: seasonal variation, source apportionment, and health risk assessment

This study investigates the distribution of sixteen priority polycyclic aromatic hydrocarbons (PAHs), various sources of PAHs, and their probable cancer-causing risks in the soil samples collected from urban cities in Bihar, India. During the winter season, the ∑₁₆ PAH concentration was dominant and ranged from 979.36 to 5149.37 ngg⁻¹ with a mean value of 2684.79 ngg⁻¹, while for the summer season, it ranged from 690.06 to 4539.55 ngg⁻¹ with a mean value of 2194.31 ngg⁻¹. The (4-ring) PAH compounds were the major contributors, accounting for 40% and 37% in the winter and summer seasons, respectively followed by (5- and 6-ring) PAHs at 30% and 32%, and (2- and 3-ring) PAHs at 29% and 30% in the respective seasons. Carcinogenic PAHs constituted ~ 50% of the ∑₁₆ PAHs, with mean values of 1353.97 ngg⁻¹ and 1098.09 ngg⁻¹ for the winter and summer seasons, respectively. Positive matrix factorization (PMF) confirmed the dominance of fossil fuel burning and biomass burning as a primary source in the urban soil of Bihar. Total mean benzo(a)pyrene equivalent (BaP_eq) values for the ∑₁₆ PAHs were 312.04 ngg⁻¹ for the winter season and 262.83 ngg⁻¹ for the summer season. These values were higher in current study sites as compared with other studies. However, the concentration range fell within the limit set by the Canadian soil quality standard (700.00 ngg⁻¹) and exceeded the limit of the Dutch target value (32.96 ngg⁻¹). The Incremental Lifetime Cancer Risk (ILCRs) from dermal and ingestion pathways were approximately 10⁴ to 10⁵ times lower than the inhalation pathway, suggesting greater risk. The study revealed higher mean cancer risk values for children (1.16 × 10⁻⁵) and adults (1.03 × 10⁻⁵) in the winter season, falling within the unacceptable range (10⁻⁶ and 10⁻⁴) of carcinogenic risk that might lead to human health risk in the study sites.