Assessment of crop-specific heavy metal transfer and dietary exposure in fertilized tropical smallholder soils in Kaduna State Nigeria.

Fertilizer-associated heavy metals may accumulate in edible crops, yet crop-specific transfer and dietary risks remain poorly characterized in tropical smallholder systems. This study quantified Pb, Cu, Fe, Zn, Cd and Ni in paired soil and edible tissues of okra, maize and cassava from fertilized farms across five locations in Kaduna State, Nigeria. Thirty paired samples were analysed by Flame AAS, and transfer factors, multivariate statistics and dietary risk indices were used to assess metal distribution, uptake and potential exposure. Mean soil concentrations were 20.54, 42.95, 3350.00, 116.47, 0.141 and 38.41 mg kg-1 for Pb, Cu, Fe, Zn, Cd and Ni, respectively, compared with 0.650, 15.83, 908.57, 50.07, 0.014 and 0.174 mg kg-1 in edible tissues. Maize showed greater Pb accumulation than cassava and okra, although Pb transfer remained low across all crops. Dietary screening yielded a THQ of 2.98 for maize, exceeding the non-carcinogenic screening threshold of 1 and driven mainly by Cu and Pb, while the combined Pb + Cd carcinogenic risk was highest in maize (3.17 × 10-5). Cassava also slightly exceeded the THQ threshold (1.07), whereas okra remained well below it (0.011). Overall, the findings identify maize and cassava as priority crops for continued monitoring of Cu and Pb in agricultural fields subject to routine fertilizer use.