Spatial distribution, contamination and ecological risk assessment of heavy metals in surface sediments of Erhai Lake, a large eutrophic plateau lake in southwest China

Abstract

The concentrations of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) and major metals (Al, Fe and Ti) in 42 surface sediment (0–2cm) samples from Erhai Lake, a large eutrophic plateau lake in southwest China, were analyzed. The heavy metal contamination was studied by comparing the multivariate statistical analysis and enrichment factor (EF) results, and the potential eco-risks were comparatively discussed by combining the sediment quality guidelines (SQGs), potential ecological risk index (Er and RI) and EF indices. The heavy metal concentrations displayed obvious spatial diversity in the surface sediments due to human contamination and variations in sediment texture, such as grain size and organic matter content. Principal component analysis (PCA) indicates that Cr, Cu and Ni were mainly lithogenic in origin and that the As, Cd, Hg, Pb and Zn levels were influenced by anthropogenic contamination. The EFs show that Cu, in addition to As, Cd, Hg, Pb and Zn, was also influenced by anthropogenic contamination. The contamination levels of the metals were zero to minor for Cu, Pb and Zn and moderate to significant for As, Cd and Hg on a whole lake basis. The different origins assigned to Cu by the PCA and EF results suggest that the PCA is less effective at differentiating pollutants when the pollution level is low. Anthropogenic As in the surface sediments was derived primarily from agricultural sources, and the other anthropogenic metals were mainly from atmospheric deposition and secondarily from industrial discharges. The mean concentrations of As and Cd are above the threshold effect concentrations (TECs) of the SQGs, suggesting adverse effects of the metals are likely to occur, which is in agreement with the Er assessment. The mean concentration of Hg is lower than the TEC; however, it may also pose adverse effects to the organisms because of its high contamination level (mean EF=6.7) and toxicity, which is supported by the Er value. The RI values (average 431) indicate that the heavy metals may pose very high eco-risks, with higher contributions from As, Cd and Hg. Generally, As, Cd and Hg are suggested to be the most concerning metals with respect to environmental monitoring and management in Erhai Lake due to their high contamination levels and potential eco-risks.