Comparative mobilization and bioaccumulation of cadmium and lead in apple orchards and associated screening level ecological and human health risks

Lead (Pb) and cadmium (Cd) accumulate in agricultural soils through long-term agrochemical use, posing ecosystem and food-safety risks; whether these inputs elevate Pb and Cd in edible fruit had not previously been quantified for Iranian apple orchards. This screening-level, multi-index study assessed Pb and Cd across the fertilizer/pesticide–soil–fruit continuum in Padena, Semirom, combining paired soil and root-stem-fruit tissue analysis ( n = 36) with ecological and deterministic human health risk indices for adults and children. Results showed that mean soil concentrations were 22.5 ± 2.9 mg/kg for Pb and 2.12 ± 1.07 mg/kg for Cd, both above regional background levels, with the two elements almost perfectly correlated in soil (Spearman ρ = 0.996). Despite its ~ 10-fold lower concentration, Cd drove most ecological risk, reaching the very-high category in 83% of samples, while Pb stayed low. Pb showed low bioconcentration and near-unity translocation between tissues, consistent with restriction at the root; Cd was more root-mobile but sharply restricted from stem to fruit. Fruit Cd remained below its permissible limit, while mean fruit Pb, on a wet-weight basis, reached ~ 98% of the Iranian national limit. Hazard indices (0.06–0.08) and cancer risks (8.0–10.9 × 10⁻⁶) for both age groups stayed within or only marginally above internationally accepted thresholds. Pesticides accounted for 99.2% of the combined annual agrochemical load, yet a mass-balance check showed they could explain only 15.6–17.0% of soil Pb enrichment and 6.5–7.1% of Cd enrichment, pointing to additional, unquantified sources. Continued monitoring of fruit Pb is recommended.