Environmental Impact Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) and Heavy Metals in Rivers and Creeks around Gokana LGA, Rivers State

Abstract

This study assessed the environmental impact of polycyclic aromatic hydrocarbons (PAHs) and heavy metals in water, sediment, and biota from fifteen (15) sampling stations along the Bodo River in Gokana Local Government Area, Rivers State, Nigeria. The primary objective was to evaluate the concentration levels of PAHs and selected heavy metals (Pb, Cd, Cr, Ni, and Zn) and determine their ecological and public health implications. Systematic sampling was conducted across upstream, midstream, and downstream sections to capture spatial variations in pollution. All samples were collected, preserved, and analyzed using standard methods prescribed by the American Public Health Association (APHA, 2005) and the United States Environmental Protection Agency (USEPA, 1989) to ensure data accuracy and comparability. Results revealed that the physicochemical parameters of the Bodo River exceeded permissible limits in several locations. Electrical conductivity ranged from 5,820.6 to 16,480.9 µS/cm, while total dissolved solids (TDS) varied between 2,910.4 and 8,230.7 mg/L, indicating strong ionic and saline influence. Biochemical oxygen demand (BOD₅) ranged from 2.25 to 7.40 mg/L, and chemical oxygen demand (COD) from 56.70 to 112.50 mg/L, reflecting moderate to high organic pollution. The mean concentrations of heavy metals in water were Pb (0.285 ± 0.019 mg/L), Cd (0.013 ± 0.004 mg/L), Cr (0.044 ± 0.005 mg/L), Ni (0.056 ± 0.007 mg/L), and Zn (0.032 ± 0.006 mg/L). Among these, lead (Pb) and cadmium (Cd) exceeded both WHO (2011) and NSDWQ (2015) limits, signifying significant contamination from oil-related and anthropogenic activities. Sediment samples also exhibited elevated concentrations of these metals, while biota, including fish, crabs, and periwinkles, showed notable bioaccumulation, particularly for Pb (1.92 mg/kg) and Cd (0.84 mg/kg). The analysis of PAHs revealed that total concentrations in water ranged from 0.012 to 0.091 mg/L, and in sediments from 0.32 to 1.84 mg/kg, with a predominance of high molecular weight (HMW) PAHs, suggesting pyrogenic (combustion-related) and petrogenic (oil-derived) sources. Elevated levels of Benzo(a)pyrene, a known carcinogen, were detected in both sediment (0.42 mg/kg) and biota (0.18 mg/kg), indicating potential ecological and human health risks through food chain exposure. In conclusion, the Bodo River exhibited severe contamination from hydrocarbons and heavy metals, primarily driven by oil exploration, industrial effluents, and urban runoff. The study recommends the implementation of effective pollution control policies, regular environmental monitoring, community-based awareness programs, and remediation of contaminated sites to restore the river’s ecological integrity and safeguard public health.