Thallium (Tl) is a trace metal with very high toxicity. As a part of an ongoing environmental investigation of copper (Cu) metallurgy impacts, thirty sediment samples of a previously dated sediment core retrieved from a heavily polluted urban lake (SE China) were analyzed to quantify the pollution of Tl and identify Tl transfer mechanism within the catchment. The results show that the lake has experienced serious Tl pollution during the past 60 years, owing to a large influx of

Tl-bearing wastes from a Cu smelter nearby. The distribution pattern of Tl contents in the sediment core correlated well with the production scale of Cu smelting activities. Further analysis by electronic microscopy and X-ray diffraction suggested that Tl was found mainly bound to quartz and alumino-phyllosilicates in both electrostatic dust of the Cu smelter and representative highly-polluted sediments from the depth profile. In addition, SEM-EDS analysis implied that a fraction of

Tl was also frequently present in diatom frustules of the sediments. It indicates a potentially significant role of biogenic silicates on Tl transferring in the sediment-water system. This is the first study to verify the coupling between Tl pollution in the lake sediments and Cu metallurgy activities from an urban lake in recent decades. The results also highlight the necessity of further environmental monitoring and regulations of Tl pollution in other similar scenarios susceptibly impacted by Cu smelting activities.

This project was supported by the National Natural Science Foundation of China (41573008; 41873015; U1612442) and the Guangzhou University's 2017 training program for young top-notch personnel (BJ201709)