Soil and wheat grain trace metals under contrasting fertilization strategies: implications for food safety and human health risk.

Heavy metal accumulation in agricultural soils threatens food safety through its transfer to wheat grains. However, the extent to which contrasting fertilization strategies influence wheat productivity, soil heavy metal accumulation, metal transfer to grains, and the associated human health risks remains poorly understood, particularly in peri-urban agricultural systems. This study evaluated four nutrient management strategies conventional mineral fertilization, reduced fertilization, organic fertilization, and integrated nutrient management in a clay loam soil system located in Monshaet El Kanater, Giza Governorate, Egypt, during three consecutive winter growing seasons of 2022-2025. Soil and grain samples were analyzed for Cd, Pb, Ni, Cr, Cu, and Zn concentrations. Environmental contamination was assessed using enrichment factor (EF) and pollution load index (PLI), while human health risks associated with wheat consumption were estimated using estimated daily intake (EDI), target hazard quotient (THQ), hazard index (HI), and carcinogenic risk (CR) models. Integrated nutrient management produced the highest grain yield (8.12 t ha⁻1), whereas organic fertilization resulted in the highest grain protein content (13.15%). Soil heavy metal concentrations differed significantly among fertilization treatments, however, the relatively small quantitative differences indicated limited treatment-induced accumulation during the three-year experimental period. Heavy metal concentrations in wheat grains followed the order Zn > Cu > Ni > Cr > Pb > Cd, with organic fertilization resulting in slightly higher Cd and Ni concentrations than the other treatments, indicating greater transfer of these metals to the grain. Contamination factors identified Cd and Zn as the principal contributors to the overall soil metal load, while the recalculated PLI values (1.107-1.127) indicated a modest exceedance of the selected upper continental crust reference. Human health risk assessment revealed greater dietary exposure for children than for adults, with Cu and Zn were the principal contributors to non-carcinogenic risk, whereas Cd was the dominate contributor to carcinogenic risk, followed by Ni. These findings highlight integrated nutrient management as a promising strategy for enhancing wheat productivity while limiting heavy metal transfer to grain in peri-urban agricultural systems.