Polycyclic aromatic hydrocarbons in selected rivers in southwestern Nigeria: Seasonal distribution, source apportionment and potential risk assessment

Abstract

The river sediment has been identified as major potential threats to ecosystem and human health due to its repository ability towards pollutants including polycyclic aromatic hydrocarbons (PAHs). A total of 72 surface sediment samples from six major rivers within south-western Nigeria were collected during both wet and dry seasons. Sixteen USEPA priority PAHs were analyzed using GC–MS for profile composition, potential sources, and ecological and human health risks on seasonal basis. PAHs were detected in all analyzed sediments at varying concentrations: ∑16 PAHs ranging from 1226 to 13,093 μg/kg (mean: 1356–12,850 μg/kg) and 1495 to 13,845 μg/kg (mean: 1536–13,671 μg/kg) across all locations during the dry and wet seasons respectively. However, the spread of PAH differs from each location. The carcinogenic PAHs (∑PAH7C) dominated the high molecular weight (HMW) PAH profile (≥ 97%) and accounting for 28 to 45% of the Σ16PAHs, presenting a high carcinogenic potential. Elevated Σ PAHs and ΣPAH7C were observed during the wet season. The study observed varied benzo(a) pyrene (BaP eq) equivalent concentrations across the rivers, suggesting variability in carcinogenic potency. Six-ring PAHs constituted the least composition in all the rivers (< 0.08–0.53 μg/kg) while three and four-ringed PAHs dominated the composition profile. Carbonaceous materials such as black carbon and particulate organic carbon notably influenced PAHs distribution (R2≥0.733, p < 0.05 ). Results of diagnostic ratios suggested the predominance contributions of coal and biomass combustion to PAHs distributions over petrogenic sources by positive matrix factorization (PMF). Further studies on the levels of PAHs in edible seafood transportation processes of PAHs is recommended for developing appropriate risk analysis approaches.