Assessment of heavy metals concentrations in soils and cassava(Manihot esculenta) from crude oil-polluted soils in Akwa Ibom State, Nigeria.

Abstract

This study assessed the concentrations and transfer dynamics of selected heavy metals—Iron (Fe), Manganese (Mn), Zinc (Zn), and Copper (Cu)—in soils and cassava (Manihot esculenta) grown in crude oil-polluted areas of Akwa Ibom State, Nigeria. Soil samples were collected at depths of 0–15 cm and 15–30 cm from six locations, alongside corresponding cassava samples. Standard laboratory procedures were employed to determine physicochemical properties and metal concentrations, while transfer factors (TF) and geo-accumulation indices (Igeo) were used to evaluate bioaccumulation and contamination status. Results revealed that the polluted soils were predominantly sandy loam, with elevated pH, organic matter, and electrical conductivity compared to the control (Etinan). Heavy metal concentrations followed the order Fe > Mn > Zn > Cu in both soil and plant tissues. The highest metal accumulation in cassava was recorded for Fe (134.51 mg/kg in Ibeno) and Mn (31.55 mg/kg in Ikot Abasi), while transfer factors indicated moderate to high bioavailability, particularly for Zn and Cu. Geo-accumulation indices suggested moderate to strong contamination in some locations, notably Ikot Abasi and Esit Eket, although all levels remained within permissible limits set by WHO/FAO. The study concludes that while cassava from these oil-impacted areas is currently within safe consumption thresholds, continued monitoring is essential to prevent long-term health risks. It recommends cautious cultivation practices and environmental management in crude oil-exploited zones to safeguard food safety and soil health.