Uptake of Thallium(I) by Rice Seedlings Grown in Different Soils: Key Soil Properties Determining Soil Thallium Availability

Abstract

This study investigated the uptake of thallium (Tl) by rice seedlings grown in different soils with varying physiochemical properties and Tl levels to elucidate the key factors governing soil Tl availability and accumulation in rice plants. The bioconcentration factors of Tl in rice roots (2.5–25.6) and shoots (1.5–14.7) indicated high soil Tl availability and efficient uptake and translocation of Tl in rice plants, with significant variations across soil types. Growth suppression and visual toxic symptoms, such as stem buckling, yellowish leaf tips, and withering leaf edges, occurred at low soil Tl levels due to high Tl toxicity. The accumulation of Tl by rice plants was influenced by both soil and plant-related factors. Cation exchange reactions primarily influenced the concentration of Tl in soil solution, with potassium ions (K+) acting as competitors for cation exchange sites with Tl+ ions and effective inhibitors of Tl uptake by rice plants. Increasing soil K content may mitigate soil Tl availability in contaminated soils by reducing soil Tl(I) adsorption and plant uptake. This study elucidates the key mechanisms governing soil Tl bioavailability and highlights potential management strategies to reduce Tl accumulation in crops.