First estimation of thallium contamination in sediments affected by uranium mining/hydrometallurgical activities

Thallium (Tl), a typical highly toxic heavy metal, poses emerging contamination risks near uranium (U) mining areas, yet its geochemical behavior remains poorly characterized in the surface sediment environment near the U processing sites. Herein, the migration pattern of Tl was comprehensively investigated in surface sediments from a decommissioned U hydrometallurgical site, China. The results showed that the downstream sediments were notably contaminated by Tl, surpassing both local background and international thresholds by several times. Sequential extraction revealed relatively high Tl bioavailability in these sediments, and the geo-accumulation index assessed Tl contamination as moderate to strong degree. Additionally, thallium isotopic compositions suggested that multiple sources contributed the Tl contamination in the studied sediments. The PMF modeling further identified three primary sources: industrial discharges (51.8%), agricultural activities (29.4%), and natural weathering (18.8%). Quantitative analysis estimated that the potential Tl contamination loads exceeding 100 tons in major U-producing nations (China, France, Germany, and Spain), with Germany reaching 151 tons. These findings underscore the necessity for enhanced environmental monitoring of Tl in U processing regions and establish a scientific foundation for Tl pollution management and remediation strategies in similar mining areas worldwide.