Long-term Monitoring of Thallium Uptake and Phytoremediation Potential of Robinia pseudoacacia

This study investigates the spatial and temporal variation of thallium (Tl) accumulation in different tissues (outer bark, inner bark, and wood) of Robinia pseudoacacia growing in the city center of Düzce, Türkiye, a region known for severe air pollution. Sampling was performed by sectioning the main trunk at approximately 50 cm above ground level, and Tl concentrations were analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES). Variance analysis revealed significant differences in Tl concentrations depending on organ type and directional exposure (p <0.001). The highest concentrations were generally detected in the northern orientation, with the outer bark showing particularly elevated accumulation. Temporal evaluations across twelve time periods from 1963 to 2022 indicated a decreasing trend in Tl levels after 2008, suggesting improved environmental conditions in recent years. The results highlight the ability of Robinia pseudoacacia to reflect both spatial and historical patterns of Tl contamination, supporting its use as a medium-sensitivity biomonitor. Additionally, the wood tissue showed a potential to represent long-term cumulative Tl exposure. Overall, these findings suggest that Robinia pseudoacacia could be an effective candidate for phytoremediation and biomonitoring strategies in urban and industrial areas with thallium contamination.