Lithium isotopic records of anthropogenic activity in the Xiaoqing River basin, eastern China

The environmental impact of the discharge of lithium (Li) by anthropogenic activity has been overlooked. By analyzing Li concentrations and isotope compositions (δ⁷Li) of water and sediment samples, this study evaluates the influence of anthropogenic Li discharge on the Xiaoqing River and Laizhou Bay, which are heavily polluted areas in China. High Li concentrations of the river water (up to 7.8 μmol/L) should be linked to anthropogenic Li discharge. However, no profound δ⁷Li anomalies were observed, preventing identification of the exact discharge sources. In the river sediments, Li concentrations (19.0-45.0 μg/g) were weakly correlated with Zn, Cu, and Cr concentrations, whereas δ⁷Li values ranged from 0.6 ‰ to 13.9 ‰ with high values being accompanied by high contents of total organic carbon and heavy Cr isotope compositions (δ⁵³Cr). All these point to significant influence of anthropogenic activity on the Li budget of river sediments. A simple mass balance calculation indicates that smelters, Li-bearing therapeutic drugs, and secondary Li-ion batteries are the main anthropogenic Li sources. In contrast to river sediments, marine sediments in the Laizhou Bay were broadly homogeneous at both spatial and temporal scales, indicating no significant influence of anthropogenic Li discharge. Overall, our data indicate that Li isotope systematics in river sediments, especially sediments near intense anthropogenic activity, are effective at tracing potential Li pollution and can help obtain accurate results for environmental inspection.