HEAVY METAL TOXICITY AND NUTRIENT ANTAGONISM IN NIGERIAN COCOA (Theobroma cacao L.): SOIL–PLANT TRANSFER, FOOD SAFETY RISK AND MULTIVARIATE ASSESSMENT IN ABIA AND OYO STATES

Abstract

Heavy metal contamination and nutrient antagonism in cocoa ecosystems have become a critical environmental and food safety concern in tropical agricultural systems because of the increasing anthropogenic activities, prolonged agrochemical use, and declining soil quality maintenance. This study evaluated heavy metal toxicity, nutrient interactions, soil–plant transfer, and associated food safety risks in cocoa (Theobroma cacao L.) plantations across Abia State and Oyo State respectively. Soil and cocoa plant parts (roots, barks, leaves, beans, and pod husks) were analyzed for selected macro/micronutrients and heavy metals using standard analytical procedures. Pollution and ecological risk indices including Bioaccumulation Factor (BAF), Transfer Factor (TF), Contamination Factor (CF), Geoaccumulation Index (Igeo), Pollution Load Index (PLI), Daily Intake of Metals (DIM), and Hazard Quotient (HQ) were computed using internationally accepted background values and toxicological reference doses. Multivariate statistical analyses involving principal component analysis, hierarchical clustering, correlation matrix, and analysis of variance were further used to identify metal sources, transfer patterns, and nutrient antagonism within the cocoa ecosystem. Results revealed significant variations (p < 0.05) in metal accumulation among cocoa plant tissues and between the two states. Elevated Fe and Mn concentrations were associated with reduced Zn and Cu availability which indicates strong nutrient antagonistic interactions under acidic soil conditions. Bioaccumulation and transfer indices suggested differential mobility of metals from soil to edible cocoa tissues, while contamination indices indicated varying degrees of ecological enrichment across sampling locations. Although most hazard quotient values remained below critical thresholds, continuous accumulation of Pb and associated metals may constitute long-term food safety concerns. The study exclusively highlights the need for sustainable soil management and continuous monitoring of heavy metals in Nigerian cocoa production systems.