Increasing trends in heavy metal risks in the Caohai Lake sediments from 2011 to 2022

The accumulation of heavy metals (HMs) in lakes can pose a serious risk to aquatic ecosystems. Caohai Lake is the largest plateau freshwater lake in Guizhou Province, China. However, the spatial and temporal dynamics and ecological risks of HM contamination in Caohai sediments in recent years remain unclear. Here, we analyzed the HM content of sediments in Caohai Lake in 2022 and collected historical (2011-2021) data from published articles to explore the spatiotemporal distribution characteristics, toxicity risks and potential sources of HMs. The mean concentrations (2011-2022) of Ni, As, Cd, Zn, Hg and Pb in the Caohai Lake sediments were all higher than the background values, and the values of As (32.0 mg/kg), Cd (14.19 mg/kg), Pb (87.6 mg/kg) and Zn (406.2 mg/kg) were 1.9, 4.0, 2.4 and 1.3 times their probable effect level (PEL) values, respectively. Sediment As and Cd concentrations in Caohai Lake showed significant decreasing and increasing trends from 2011 to 2022, with mutation points occurring in 2018 and 2020, respectively. The Caohai Lake sediment aquatic life risk index (TRI) for HMs showed a gradual increase until 2019, when it reached a sudden change point, leading to a very high toxicity risk in 2020, with Cd contributing the most to the TRI (43.66). Cd, Pb and Zn, the main pollutants in the sediments of Caohai Lake, originate from traffic, mining and agricultural sources. Our integrated results demonstrated the severity of HM pollution in Caohai Lake and can be helpful for formulating reasonable pollution prevention and control measures.