Heavy Metal Contamination in Plants Associated with Battery Waste Disposal at a Recycling Site in Ogun State, South-western Nigeria

Abstract

Uncontrolled disposal and informal recycling of used lead-acid batteries are major sources of heavy metal contamination in peri-urban soils and food crops in Nigeria. This study quantified the bioaccumulation and health risks of nine metals (Mn, Fe, Cu, Zn, Pb, Co, Cd, Cr and Ni) in edible plants cultivated around a battery recycling site in Ogijo, Ogun State. During wet and dry seasons, randomly selected plants and paired soil samples were digested and analyzed using atomic absorption spectrometry; bioaccumulation factor (BAF), Metal Accumulation Index (MAI) and Health Risk Index (HRI) were used to assess soil-to-plant transfer, multi-metal accumulation and non-carcinogenic dietary risk. Concentrations of Zn, Cd, Pb, Cr and Co in all plant species exceeded FAO/WHO guideline values for vegetables in both seasons, with higher levels generally recorded in the dry season. MAI values showed severe multi-metal stress in all species, especially maize (Zea mays), cassava leaves (Manihot esculenta), cocoyam leaves (Xanthosoma sagittifolium) and spinach (Spinacia oleracea). BAF values for Cd, Pb and Zn were mostly below 1.0 in the wet season but exceeded 1.0 in several dry-season cases, confirming efficient transfer under low-moisture conditions. HRI values for Cd and Pb in cassava leaves, spinach and ewedu (Corchorus olitorius) far exceeded 1.0, indicating unacceptable dietary risks. In general, the study area is unsuitable for food-crop production underscoring
the need for stricter control, relocation and remediation of battery recycling activities.