This paper is the result of agricultural geological survey engineering.

Objective Copper (Cu) is an essential micronutrient for plants and animals, playing a central role in key physiological processes such as photosynthesis, antioxidant defense, and energy metabolism. In the North China Plain, the high pH and calcium carbonate content of calcareous soils strongly inhibit the bioavailability of Cu, constraining wheat yield and quality while posing potential dietary risks. This study aimed to systematically elucidate the transport and partitioning mechanisms of Cu in the soil-wheat system and assess the health risks associated with its accumulation in grains, thereby providing a theoretical basis for safe production and precision management.

Methods A pot experiment was conducted using the wheat cultivar "Shixin 828" exposed to a gradient of exogenous Cu concentrations (0–3.6 mg/kg). The transport processes of Cu were systematically investigated by measuring its concentrations in soil and various plant tissues at different growth stages. The mechanisms governing Cu migration and partitioning were elucidated using bioconcentration factors, translocation factors, and correlation analyses.

Results The alkaline calcareous soil (pH 8.48) exhibited a strong immobilizing effect on Cu, significantly inhibiting its bioavailability. The allocation of Cu in wheat varied markedly between growth stages: at jointing, Cu was primarily enriched in leaves, whereas at maturity, it shifted to a root-dominated sequestration pattern. The Cu concentration in roots increased from 8.7 mg/kg at jointing to 12.9 mg/kg at maturity, with the bioconcentration factor rising from 0.36 to 0.56, while the translocation factor decreased from 2.11 to 1.01. The Cu concentration in grains remained stable within the range of 5.5–7.7 mg/kg, below the national food safety limit (10 mg/kg). However, under the 3.6 mg/kg exogenous Cu treatment, dietary intake reached 10.4% of the Tolerable Upper Intake Level for adults. Correlation analysis revealed a significant positive relationship between soil available Cu and grain Cu concentration (r=0.457, p<0.01).

Conclusions In the calcareous soil-wheat system, soil chemical immobilization and root physiological barriers synergistically form a dual mechanism safeguarding grain Cu safety. Wheat employs growth-stage-specific allocation strategies, significantly inhibiting Cu translocation to grains during the reproductive stage. Based on these findings, we recommend strictly controlling exogenous Cu inputs in high-background areas to mitigate risks, while implementing precision fertilization in low-background areas to harness the potential of Cu for nutritional biofortification.