Five-Year Ageing Effects on Tungsten Plant Uptake in Different Spiked Soils

This study investigated the evolution of tungsten plant uptake during a five-year ageing period using three agricultural soils differing mainly in pH and organic matter content. Soils previously amended with sodium tungstate at five contamination levels (10–100 mg W kg−1) were maintained under controlled greenhouse conditions and used annually to cultivate Zea mays L. under identical experimental conditions. Plant biomass, tungsten concentrations in shoots and roots, bioaccumulation factor (BAF), translocation factor (TF), and Freundlich uptake parameters were determined each year to evaluate temporal changes in plant exposure. Plant biomass remained unaffected throughout the study. In contrast, tungsten concentration progressively declined in both roots and shoots in all soils, demonstrating a continuous reduction in phytoavailability despite constant total soil concentrations. Although ageing similarly affected all soils, the amount of plant uptake remained strongly dependent on soil properties. Declining BAF and decreasing Freundlich affinity coefficients (Kf) confirmed the progressive stabilization of tungsten within the soil matrix, whereas TF remained consistently below unity, indicating preferential retention of tungsten in roots. Overall, the results show that soil ageing substantially reduces tungsten phytoavailability without detectable effects on plant biomass, highlighting the importance of considering temporal changes in soil–plant interactions when assessing the long-term environmental exposure and risk associated with tungsten-contaminated soils.