Fertilizer-derived uranium uptake in maize (Zea mays L.): Findings from pot and field experiments in Tanzania

Phosphate fertilizers can introduce uranium (U) into agricultural soils and potentially into edible crop tissues. This work evaluated U transfer from fertilizers into maize ( Zea mays L.) under Tanzanian field and pot conditions. Three fertilizers with contrasting intrinsic U concentrations (39–160 mg kg⁻¹) were assessed in a single-season field experiment and in a replicated pot experiment, together with measurements of calcium (Ca) and exploratory bark and kaolin amendment treatments to mitigate U transfer from soil to plant. In the field experiments, interpreted descriptively, U concentrations were highest in soil (2.07–3.96 mg kg⁻¹), intermediate in roots (0.99–2.20 mg kg⁻¹), stems (0.39–1.09 mg kg⁻¹), and leaves (0.17–0.48 mg kg⁻¹), and lowest in grain (0.09–0.26 mg kg⁻¹, ash basis). In the pot experiment, one-way ANOVA showed highly significant treatment effects for U in soil, root, stem, and leaf compartments (all p < 0.001), and fertilizer/amendment interactions were significant among fertilized pots, indicating treatment-specific responses. Transfer coefficients for U and Ca supported a consistent partitioning pattern of soil > root > stem ≈ leaf > grain and showed that U transfer to grain remained strongly attenuated in both systems. Several amendment treatments, particularly kaolin and tree bark sawdust, were associated with reduced U concentrations and reduced transfer beyond the root compartment in the pot experiments, although no mechanistic measurements were made. Overall, the results identified fertilizer sources and compartmental partitioning as key controls on maize U accumulation and provided regionally relevant baseline data for exposure assessment and for future testing of low-cost retention measures under field-relevant conditions.