Risk Assessment of Polyaromatic Hydrocarbon (PAH) in Asiko River, in Ajaokuta, Kogi State, Nigeria

Polyaromatic hydrocarbons (PAHs) are persistent environmental pollutants with significant health risks due to their toxicity, carcinogenic potential, and resistance to degradation. This study assessed PAH contamination in the Asiko River, situated in Ajaokuta, Kogi State, Nigeria, by analyzing water samples from five designated points (S1-S5) for hydrophobic PAH concentrations. The collected water samples were preserved in dark brown glass vials containing preservatives and transported to the laboratory. PAHs extracts were isolated through a liquid-liquid extraction method and then the extract was subjected. The results indicated varying PAH levels across sampling sites, with S1 recording acenaphthylene (1.28 ± 2.3 × 10⁻⁵ mg/L), acenaphthene (2.30 ± 2.9 × 10⁻⁵ mg/L), and pyrene (2.60 ± 1.2 × 10⁻⁵ mg/L), while S2 and S3 had notable detections of naphthalene (5.445 ± 5.7 × 10⁻⁵ mg/L and 3.00 ± 2.7 × 10⁻⁵ mg/L, respectively). S4 exhibited the highest diversity of PAHs, including naphthalene (2.28 ± 5.7 × 10⁻⁶ mg/L) and pyrene (3.32 ± 2.9 × 10⁻⁵ mg/L), whereas S5, serving as the control, showed fluoranthene (13.70 ± 2.2 × 10⁻⁵ mg/L). The concentrations exceeded the Agency for Toxic Substances and Disease Registry (ATSDR) permissible level of 0.2 μg/L and the US Environmental Protection Agency (USEPA) limit of 0.1 μg/L, indicating significant pollution. Risk assessment parameters, including average daily dose (ADD), hazard quotient (HQ), and lifetime average daily dose (LADD), were computed following USEPA methodologies. The ADD values for adults and children ranged from 0.39 to 0.56 and 1.20 to 2.29, respectively, while LADD values were below the threshold of 10⁻³, suggesting no immediate health risks. The cancer risk (<10⁻⁶) and HQ (<1) were within acceptable limits, indicating that despite contamination, local inhabitants are not currently at high risk of carcinogenic effects. These findings underscore the necessity of stringent regulatory measures to mitigate PAH pollution and protect aquatic ecosystems and human health. Continuous monitoring, pollution control strategies, and public awareness are recommended to reduce PAH exposure in the Asiko River region.