Toxicological Chemistry of Cadmium in Agricultural Food Chains of Bauchi State: Exposure Assessment, Metabolic Transformation, and Epigenetic Mechanisms

Cadmium accumulation in the agricultural food chain of Northern Nigeria, driven by phosphate fertiliser application and atmospheric deposition from mining regions, poses chronic health risks whose mechanistic underpinnings remain unexplored at the molecular level. This dissertation investigates the toxicological chemistry of cadmium in the agricultural food chain of Bauchi State from soil geochemistry through crop bioaccumulation to human exposure, combining field chemistry with in vitro toxicological mechanistic studies. Soil cadmium fractionation across 48 farmland sites was conducted using BCR sequential extraction. Crop bioaccumulation was quantified in sorghum, cowpea, and groundnut harvested from characterised soils, and dietary exposure was estimated using consumption surveys from 300 households. Human biomonitoring of urinary cadmium was performed in 180 farming household members, stratified by age and sex. In vitro toxicological studies employed primary human renal tubular epithelial cells exposed to cadmium at environmentally relevant concentrations to investigate metallothionein induction, mitochondrial membrane potential, reactive oxygen species generation, and DNA methylation changes at selected gene promoters by bisulphite pyrosequencing. Proteomic analysis by two-dimensional gel electrophoresis and mass spectrometry characterised differential protein expression patterns in cadmium-exposed cells. Results show that urinary cadmium in high-exposure farming communities approaches tubular dysfunction thresholds, with women showing higher retention. In vitro studies confirm that sub-toxic cadmium induces persistent DNA hypermethylation at CDKN2A and MLH1 promoters. Original contributions include a mechanistic epigenetic toxicology framework linking environmental cadmium exposure to potential long-term carcinogenicity through epigenetic silencing of tumour suppressor genes. Keywords: cadmium, food chain, epigenetics, toxicological chemistry, Bauchi State