Cadmium Accumulation and Transfer in Soil-Vegetable Systems in Peri-Urban Farming Areas of Kaduna State, North West Nigeria

This study investigates cadmium accumulation in soils and its transfer to commonly consumed vegetable crops in peri-urban farming areas of Kaduna State, located in Nigeria's North West geopolitical zone. Cadmium is a toxic trace element that accumulates in agricultural soils from phosphate fertiliser use, atmospheric deposition, and irrigation water, and its transfer into food crops, particularly leafy vegetables, poses dietary health risks that are poorly documented for Nigerian peri-urban farming systems. Using a field sampling and controlled pot experiment design, surface soils from 50 peri-urban vegetable farms across Kaduna North, Sabon Gari, and Igabi local government areas were analysed for total cadmium by ICP-MS, EDTA-extractable cadmium (bioavailable fraction), soil pH, organic carbon, and clay content. Bioconcentration factors were calculated for spinach, amaranth, and waterleaf grown on representative farm soils in a greenhouse pot experiment. Dietary exposure was estimated for a typical adult consumer. Findings revealed total soil cadmium ranging from 0.08 to 1.84 mg/kg, with 22 percent of farms exceeding European Union soil guideline values for agricultural soils. Leafy vegetables accumulated cadmium most readily, with amaranth bioconcentration factors above 2.0 in 40 percent of tested soils. Estimated weekly dietary cadmium intake from vegetable consumption in high-exposure scenarios exceeded the JECFA provisional tolerable weekly intake of 2.5 micrograms per kilogram body weight in adult consumers. Soil pH was the strongest negative predictor of cadmium bioavailability. The study recommends soil liming as the priority cadmium risk reduction strategy and advocates mandatory cadmium monitoring of peri-urban vegetable soils in Kaduna State. Keywords: cadmium accumulation, vegetable crops, peri-urban farming, bioconcentration, Kaduna State.