Multi-Metal Speciation, Phytotoxicological Assessment, and Human Health Risk Profiling of an Abandoned Lead-Acid Battery Industrial Site in Southwestern Nigeria: Implications for Sustainable Soil Remediation and Agricultural Policy

Despite increasing global documentation of battery-industry soil contamination, there is a critical research gap regarding the simultaneous multi-metal speciation characterization, comparative phytotoxicological bioassay using dual crop species, and integrated probabilistic human health risk assessment at a single abandoned site in sub-Saharan Africa. This study, conducted at an abandoned lead-acid battery industrial site in Ibadan, Southwestern Nigeria, addresses this gap by integrating ICP-OES-based geochemical analysis with a structured six-week greenhouse bioassay using Celosia argentea (vegetable) and Abelmoschus esculentus (okra) as phytotoxicological bioindicators, and by applying the USEPA probabilistic risk framework across oral ingestion and dermal contact exposure pathways for both children and adults. Soil and water samples were collected from the abandoned battery site and a control location. Physicochemical parameters were determined using standard methods. Twenty-seven metallic elements were quantified by ICP-OES (Agilent 720). Plant bioassays were conducted for six weeks under greenhouse conditions using contaminated soil and site water. Human health risk (non-carcinogenic and carcinogenic) was assessed following USEPA guidelines. Extreme soil acidification (pH 3.98 ± 0.32) and catastrophic lead contamination (603,432.25 mg/kg, approximately 2,738× the guideline value) were detected. Physicochemical water quality exceeded WHO limits for alkalinity, chloride, and suspended solids. Complete growth inhibition was recorded in both crop species irrigated with site water, while stunted growth and chlorosis were observed in crops grown in contaminated soil. Hazard Index (HI) values for soil exposure reached 20,529,671 (adult, dermal) and 43,796,632 (child, dermal). Cancer Risk Index values for soil Pb (dermal) reached 15,840 for adults and 33,792 for children, far exceeding the USEPA acceptable limit of 1×10⁻⁴. The abandoned battery site represents an acute multi-hazard environmental disaster. The dual-crop bioassay confirms species-specific differential tolerance, with Abelmoschus esculentus showing marginally superior resilience. Urgent phytoremediation and bioremediation strategies, alongside regulatory enforcement, are recommended.