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A. D. Akpan

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Open access 2026

Seasonal Variation of Heavy Metal Concentrations in Soils and Cocoyam Tubers Around Selected Municipal Dumpsites: Assessment Using Translocation Factor and Contamination Indices

Municipal open dumpsites are major sources of heavy metal contamination, posing significant risks to agricultural soils and food safety in developing countries. This study evaluated the seasonal distribution, soil to tuber translocation, contamination indices and human health risks of Pb, Zn, Ni, Cu, Cr and Cd in soils and cocoyam (Colocasia esculenta) cultivated around three municipal dumpsites in Akwa Ibom State, Nigeria. Composite soil samples were collected at three depths (0–10, 10–20, 20–30 cm) from each dumpsite and a control site, in both dry and wet seasons, to assess vertical and seasonal metal variation. Cocoyam tubers were also harvested at each location. Metals were determined by Atomic Absorption Spectrophotometry after digestion. Transfer factor (TF), contamination factor (CF), degree of contamination (Cdeg), hazard quotient (HQ) and hazard index (HI) were computed to assess metal mobility and health risk. Metal concentrations generally decreased with soil depth, showing surface accumulation from waste deposition. The highest concentrations occurred at Ikot Ekpene (13.50 and 88.50 mg/kg in Pb and Zn, dry season), while Pb increased to 37.50 mg/kg in wet season. Transfer factors exceeded unity for Pb at Eket (TF = 1.22, dry season), and for Pb at Uyo (TF = 1.27) and Cr at Eket (TF = 1.43) in the wet season, indicating high translocation into tubers. Soil contamination was highest at Ikot Ekpene (Cdeg = 18.36 dry season; 37.77 wet season), while tubers recorded Cdeg values of 22.40–24.67 (dry season). Hazard indices exceeded the US EPA threshold (HI > 1.0) at all dumpsites, peaking at 11.29 (Ikot Ekpene, wet season), with Pb the major contributor to risk. Cocoyam cultivated around municipal dumpsites carries a high heavy metal exposure risk. Improved waste management and restrictions on food crop cultivation in contaminated areas are recommended.

A. D. Akpan, U. U. Ubong, Aniefiok E. Ite et al. · International journal of re... · 0 citations

Open access Jul 2026

Ecological Risk Assessment of Heavy Metals in Soils and Surface Waters of Oil-Producing Areas in Akwa Ibom State, Nigeria

Aim: This study assessed the ecological risk posed by six heavy metals [lead (Pb), zinc (Zn), nickel (Ni), copper (Cu), chromium (Cr), and cadmium (Cd)] in soils and surface waters. Study Design: Soil samples were collected at two depths (0–15 and 15–30 cm) from 12 stations across Onna, Mkpat Enin, Eastern Obolo, and Uyo in Akwa Ibom State. Surface-water samples were also collected, and Uyo served as the reference location. Methodology: Composite soil samples were collected using a stainless-steel soil auger. Following acid digestion, metal concentrations were determined by atomic absorption spectrophotometry (AAS). The contamination factor (CF), degree of contamination (C-deg), geoaccumulation index (Igeo), single-metal ecological risk factor, and comprehensive potential ecological risk index (RI) were calculated using average-shale background values and the methods of Müller and Hakanson. Results: Except for nickel at Onna Station 3 (57.5 mg/kg), which exceeded the adopted agricultural and residential soil guideline values, soil-metal concentrations were below the relevant limits. In surface water, lead and nickel exceeded the adopted WHO guideline values at all four locations, whereas chromium and cadmium exceeded the guidelines at two locations. Most CF and Igeo values indicated low contamination, although cadmium showed the greatest relative enrichment at several stations. Conclusion: Although several stations, including the reference location, showed moderate-to-considerable single-metal risk from cadmium, RI remained below 150 at all soil stations, indicating low overall potential ecological risk. The results provide baseline information for environmental monitoring and remediation prioritisation in the studied oil-producing areas.

U. U. Ubong, A. D. Akpan, U. G. Isotuk · Asian Journal of Physical an... · 0 citations