Geochemical and Ecological Risk Assessment of Petroleum Hydrocarbons in Sediments of Forcados River, Delta State

Abstract

Petroleum hydrocarbon contamination remains a significant environmental issue in the Niger Delta due to intense oil exploration, transportation, and artisanal refining. This study examined the geochemical features and ecological risks associated with petroleum hydrocarbons in sediments from the Forcados River, Delta State, Nigeria. Eight surface sediment samples were collected from upstream, midstream, and downstream zones during the dry season and analysed for Total Petroleum Hydrocarbons (TPH), Total Organic Carbon (TOC), pH, and moisture content following USEPA Method 8015B protocols. Geochemical and risk indices—Contamination Factor (CF), Pollution Load Index (PLI), Ecological Risk Index (Er), and Hydrocarbon Pollution Index (HPI)—were used to assess the level and ecological impact of contamination. TPH levels ranged from 8.43 to 42.56 mg/kg (average: 23.78 ± 10.4 mg/kg), surpassing the Department of Petroleum Resources (DPR) target limit of 10 mg/kg but staying below the intervention threshold of 50 mg/kg. Sediments downstream showed higher hydrocarbon accumulation, linked to increased TOC (1.12–3.48%) and moisture content (18.4–25.2%). The average CF (3.97) and PLI (1.44) suggested moderate contamination, while Er (59.8) and HPI (184.4) indicated moderate to high ecological risks. Strong positive correlations between TPH, TOC, and moisture content (r \(\ge\) 0.7; p < 0.05) confirmed the influence of organic matter and sediment composition on hydrocarbon retention. The results reveal that sediments in Forcados River are moderately affected by petroleum hydrocarbons, mainly from human activities. Ongoing monitoring, enhanced waste management, and remediation of oil-impacted zones are recommended to safeguard sediment quality and maintain the ecological health of the river system.