Cadmium and lead ions interaction: A model for assessing combined heavy metal contamination in soils for food safety risk evaluation

Extensive research has delved into the toxicity and risks associated with individual heavy metals. While some studies have explored the combined toxicity of various heavy metals, there remains a pressing necessity to establish protocols for evaluating the combined contamination of heavy metal mixtures in relation to agricultural food safety risks. Here, we investigated the combined toxicity of cadmium (Cd(II)) and lead (Pb(II)) to Triticum aestivum L. roots by hydroponic culture, and determined dose-dependent interaction behaviors in 20 Cd(II)-Pb(II) combined intervals. The results showed that when Cd(II) concentration was < 0.002 or 0.021-0.061 mg/L, the main interaction between Cd(II) and Pb(II) was additive; and when Cd(II) was 0.002-0.021 or > 0.061 mg/L, the interaction was a significant antagonistic effect. We further established a Cd(II) bioaccumulation model (BCF_Cd model) of wheat under the Cd(II)-Pb(II) combined pollution based on plant physiological characteristics. The effect of Pb(II) stress on wheat BCF_Cd was quantitatively analyzed by the maximum and minimum enrichment coefficients (K_max and K_min). Application of the model to three distinct soil types demonstrated its robust performance in quantifying wheat root uptake (R² = 0.84) and grain uptake (R² = 0.87) of Cd(II). These results affirm the suitability of the BCF_Cd model for application within the context of the soil-wheat system. This robust predictive tool shows considerable promise in establishing a comprehensive framework for evaluating food safety risk thresholds in the context of concurrent heavy metal contamination in soil environments.