Heavy Metal Contamination and Human Health Risk Assessment of Farmland Soils in Ndele, an Oil-Producing Community in the Niger Delta, Nigeria

Abstract

Agricultural soils in oil-producing regions of the Niger Delta may receive persistent trace-metal inputs from petroleum-related activities and other anthropogenic sources, creating potential implications for soil quality, crop production and human exposure. This study assessed cadmium (Cd), lead (Pb) and arsenic (As) concentrations and associated human health risks in farmland soils of Mgbu-Oluwa and Mgbu-Ela communities in Ndele, Emohua Local Government Area, Rivers State, Nigeria. Composite topsoil samples (0–15 cm) were collected monthly from four farmland locations for six months (March–August 2025), giving 24 composite samples. Soil pH and temperature were measured in situ, while Cd, Pb and As were determined after acid digestion using atomic absorption spectrophotometry. Data were summarized using descriptive statistics and compared between communities using an independent-samples t-test. Human health risks were evaluated using a United States Environmental Protection Agency (USEPA)-based framework for adult (dermal exposure) and child (soil-ingestion plus dermal exposure). Cadmium was the dominant contaminant, with mean concentrations of 2.19 and 2.77 mg/kg in Mgbu-Oluwa and Mgbu-Ela, respectively. Corresponding mean concentrations were 0.32 and 0.89 mg/kg for Pb and 0.30 and 0.35 mg/kg for As. Differences between communities were not statistically significant for Cd (p=0.64), Pb (p=0.38) or As (p=0.84). Soil pH remained slightly acidic (5.95 6.25), while temperature declined during the sampling period. Using Nigerian petroleum-sector target values and FAO/WHO soil benchmarks, Cd exceeded the Nigerian target value in 17 of 24 samples, whereas Pb and As remained within the comparison values. Non-carcinogenic hazard quotients and hazard indices were below unity for both population groups; child HI values were 0.0425 and 0.0537 in Mgbu-Oluwa and Mgbu-Ela, respectively. Arsenic cancer-risk estimates were within the USEPA acceptable range. The findings indicate localized cadmium contamination without evidence of unacceptable health risk under the assessed exposure assumptions, emphasizing the need for continued soil monitoring, pollution prevention and crop-safety surveillance in Ndele.