Characterization and Risk Assessment of Heavy Metals and Hydrocarbon Sludge in the Nsisioken Environment, Rivers State Nigeria

Abstract

This study focuses on the characterization and risk assessment of heavy metals and hydrocarbon sludge contamination in the Nsisioken River environment, Rivers State, Nigeria. Soil and water samples were analyzed using Gas Chromatography with Flame Ionization Detection (GC-FID) and Atomic Absorption Spectroscopy (AAS). The physicochemical parameters of the river revealed a mean pH of 7.29 ± 0.2, chemical oxygen demand (COD) of 47.5 ± 6.4 mg/L, and turbidity of 11.0 ± 2.4 NTU values that exceed WHO permissible limits for surface water quality. Soil samples showed high concentrations of cadmium (0.38 ± 0.10 mg/kg), chromium (46.99 ± 5.9 mg/kg), nickel (20.1 ± 2.8 mg/kg), lead (24.1 ± 4.0 mg/kg), and zinc (99.3 ± 8.0 mg/kg). Total Petroleum Hydrocarbon (TPH) fractions in soil ranged from 12.8 mg/kg (C25–C30) to 45.6 mg/kg (C13–C16), contributing to a cumulative TPH risk value of 486,741.67. For water, the TPH risk was lower at 49,750, but still considerable. Health risk assessments revealed alarming Hazard Quotient (HQ) values arsenic had an HQ_ingestion of 15,525.11 and a cancer risk (CR_ingestion) of 6.99, far exceeding the USEPA’s acceptable cancer risk range of 10⁻⁶ to 10⁻⁴. Lead also showed high non-carcinogenic risks (HQ_ingestion = 9432.49). These results indicate significant ecological and human health risks due to hydrocarbon and heavy metal pollution.