Centurial sedimentary record of Cd sources and deposition in Chaohu Lake: insights from Cd stable isotopes.

Understanding the sources and deposition processes of cadmium (Cd) in freshwater lakes is essential for effective pollution management. This study investigated the Cd concentrations and isotopes in a sediment core from Chaohu Lake, spanning the past 200 years. The results revealed that the Cd concentrations in the sediments decreased with depth, ranging from 1.04 μg/g to 0.26 μg/g, whereas the δCd values fluctuated significantly (-0.18 ± 0.04‰ ∼ 0.75 ± 0.04‰). The elevated EF and I values of Cd indicate that the degree of Cd pollution in sediments has reached medium to strong level. In the 0-8 cm section, the notably high Cd concentrations and heavy Cd isotope compositions are primarily linked to the inputs of slags (smelting and/or coal burning) and smelting wastewater since the 1960s. A notable decrease in the δCd value at the depth of 6 cm suggests that phosphate fertilizers used in the Chaohu Lake watershed in the 1970s may also have contributed to Cd pollution. In the 10-40 cm section, the effects of adsorption/coprecipitation/organic processes on Cd isotope fractionation are no obvious, indicating that the Cd deposition in Chaohu Lake in the early periods (before 1960s) is relatively complex and needs further research. Finally, this study highlights the significance and future prospects of Cd isotope application in freshwater lake systems, including the reconstruction of Cd sources and deposition pathways, as well as indications for the risk management of re-released Cd from sediments.