Ecological and Human Health Risk Assessment of Heavy Metal Contamination in Soils of a Former Auto-Mechanic Village in Old Nekede, Imo State, Nigeria

Abstract

Soils were sampled from the decommissioned auto-mechanic village in Old Nekede, Owerri, Imo State, Nigeria, and analysed for six trace metals (Co, Ni, Fe, Zn, Pb and Al) in both the topsoil (0–15 cm horizon) and subsoil (15–30 cm horizon). Sampling stations were established at minimum inter-station distances of 100 m on a georeferenced grid. Ecological risk was assessed using the Hakanson potential ecological risk index (RI) and the monomial potential ecological risk factor (Er). Human health risk via ingestion, dermal contact, and inhalation pathways was calculated for adult and child receptors at each station following established USEPA protocols. Residual concentrations of Fe and Zn dominated the contamination profile, with topsoil Fe reaching 1,267.25 mg/kg and topsoil Zn reaching 253.00 mg/kg. Pb and Ni were below the analytical detection threshold (<0.001 mg/kg) at all stations. Ecological risk index values (RI) ranged from 13.9 to 59.0, classifying the site as low-to-moderate ecological risk, with the highest individual Er associated with cobalt. Non-carcinogenic hazard indices (HI) exceeded the USEPA threshold of 1.0 for child receptors at three of the five stations investigated, driven primarily by the ingestion pathway and attributable to Zn and Co. Cobalt carcinogenic risk remained within the USEPA acceptable range (10−6 to 10−4) for both receptor groups at all stations. Passive site recovery over five years post-relocation has proven insufficient. Findings support the need for ecological restoration, groundwater management, and enforceable land-use policy.