Environmental and Toxicological Risk Assessment of Heavy Metals in Eleme Agricultural Soils

Abstract

Heavy metal inputs from petrochemical industries, fertiliser plants, oil and gas operations, and intensive farming increasingly impact agricultural soils in industrialised parts of the Niger Delta. These metals persist in soils, influence soil quality, and pose ecological and human health risks through direct exposure and food-chain transfer. This study assessed the physicochemical characteristics, heavy metal concentrations, and associated environmental and toxicological risks of agricultural soils in Eleme Local Government Area, Rivers State, Nigeria. Composite soil samples were collected from five agricultural sites during dry and wet seasons at depths of 0–20 cm. Soil pH, electrical conductivity, organic matter, cation exchange capacity, and texture were determined using standard methods. Heavy metals (Fe, Pb, Cd, Cr, Ni, Zn, and Cu) were analysed after mixed-acid digestion using flame Atomic Absorption Spectrophotometry. Contamination factor, geo-accumulation index, pollution load index, enrichment factor, and potential ecological risk index were applied. Human health risks for adults and children were evaluated using USEPA exposure models for ingestion and dermal contact. Soil pH ranged from 5.4 to 6.9, with electrical conductivity between 82 and 214 µS/cm and organic matter content of 1.21–3.84%. Mean metal concentrations (mg/kg) were Fe 13,280 ± 3,140, Pb 54.8 ± 21.3, Cd 1.38 ± 0.71, Cr 52.9 ± 18.5, Ni 41.7 ± 16.2, Zn 112.5 ± 39.8, and Cu 35.9 ± 15.4. Cadmium exceeded the WHO/FAO limit of 0.8 mg/kg and showed strong contamination (CF = 6.9, Igeo = 2.8). The potential ecological risk index was 233.9, indicating considerable ecological risk. Hazard quotients for children exceeded unity for Pb (1.41) and Cd (2.18), while carcinogenic risk values (e.g., Cd: 2.4 × 10⁻⁵–5.7 × 10⁻⁵) remained within acceptable limits. Industrial activities have significantly degraded soil quality in Eleme, with cadmium posing the greatest ecological and health concern. Continuous monitoring and targeted soil management are urgently required.