Speciation characteristics and ecological risk assessment of heavy metals in sediments from Caohai Lake, Guizhou Province

Caohai Lake in Guizhou Province is a plateau wetland lake within a karst geological topography. It is in the lead-zinc enrichment zone in northwestern Guizhou The potential environmental risk of heavy metals, with high geological background levels, has been attracting attention. In this study, sediments in Caohai Lake were investigated to analyse the overall levels and chemical speciation of heavy metals (As, Cd, Cr, Cu, Hg, Pb, and Zn). In addition, the potential ecological risk of environmentally active heavy metals was investigated from the perspective of heavy metal speciation using the ratio of the secondary phase to primary phase combined with the ecological risk assessment code. The results showed that the overall levels of heavy metals in sediments in Caohai Lake were several to hundreds of times higher than the background values. However, the chemical speciation of heavy metals was mostly residual. Among heavy metals, Cd is a typical pollution stress factor in the region, with high total levels and a high proportion of environmentally unstable forms. The mean sediment quality guideline quotient of heavy metals in sediments ranged between 0.2 and 1.6, indicating mild to moderate toxic effects on benthic organisms. From the analysis of the forms that migrate in the environment, the heavy metals in sediments were mostly at the pollution-free or low-risk levels. Cd poses a high environmental risk, with an extremely high regional risk level. Therefore, different forms of heavy metals have different environmental risks. In the environmental impact assessment of heavy metals, it is necessary to consider the environmental activity and bioavailability of different chemical forms of heavy metals. Stability and passivation of Cd forms with high environmental activity should be the focus in the prevention and control of heavy metal pollution in Caohai Lake. [GRAPHICS] .