Ecological and human health risks from railway-associated contaminants: a case study of trace metal and PAH pollution along a commuter line in Chittagong, Bangladesh.

Railway operations significantly contribute to soil contamination with trace metals and polycyclic aromatic hydrocarbons (PAHs). This study aims to assess the distribution of 16 PAHs using Gas Chromatography Mass Spectrometry (GC-MS) and six trace metals (Ni, Pb, Cd, Co, Cu, Zn) using Atomic Absorption Spectrometry (AAS) in surface soil samples across eight railway stations along the Chittagong University commuter rail line, which links Chittagong Central Station with Chittagong University and associated human and ecological risk. The total PAH concentration was 393.3 µg/kg in RS6 and 1666 µg/kg in RS5, raising environmental concerns Specific PAHs, including phenanthrene (Phe) and fluoranthene (Flu), exceeded the Effects Range Low (ERL) thresholds at these stations, indicating potential ecological risks. The highest burden of carcinogenic PAHs (cPAHs) was detected at RS1, with a concentration of 206.0 µg/kg, suggesting localized areas of elevated toxicological risk. Multi-metal pollution was notably severe at site RS1, where lead (Pb) concentrations ranged from 27.8 to 77.8 mg/kg, exceeding the threshold effect level TEL and ERL at all stations. Nickel (Ni) levels at RS1 reached 148.0 mg/kg, significantly higher than the global average, while copper (Cu) and zinc (Zn) concentrations also surpassed ERLs, averaging 74.1 mg/kg and 124.0 mg/kg, respectively. PAHs and metals emissions were attributed to railway operations. Notably, children exhibited the highest Chronic Daily Dose (CDD) ingestion levels for Cu and Ni, at 8.12 × 10⁻5 and 6.35 × 10⁻5 mg/kg/day, respectively, highlighting urgent public health implications.