An overview of heavy metal pollution in Chaohu Lake, China: enrichment, distribution, speciation, and associated risk under natural and anthropogenic changes

Abstract

An exhaustive overview of heavy metal pollution in Chaohu Lake illustrating enrichment intensity, temporal and spatial distribution, chemical speciation, and ecological risk under natural and anthropogenic changes was conducted. Low concentrations of heavy metals excluding Hg were found in water whereas high Hg might be ascribed to surrounding coal-fired power plants. Copper, Pb, Zn, Cd, and Hg were enriched in sediment whereas Cr and Ni were comparable to background values. Besides, As demonstrated an equal accumulation from natural and anthropogenic fluxes. Heavy metals were at a low level prior to the 1950s; it increased gradually during the 1950s–1960s owing to population growth and agricultural expansion; then it displayed abrupt increase since the late 1970s due to rapid modern urbanization and industrialization and agricultural intensification. Spatial distribution of heavy metals was a good indicator of natural and anthropogenic changes, where higher enrichment was found in the western lake. Apart from fluvial input, anthropogenic disturbances such as land use changes, atmospheric deposition, and algae-derived organic matter, along with natural stressors including climate change, hydrological alteration, and soil erosion, made significant contribution to the biogeochemical cycle of heavy metals in the lake. Heavy metals mainly from anthropogenic sources were dominantly partitioned in non-residual fractions, whereas those mainly from natural sources were predominantly distributed in residual form. Mercury and Cd were below the threshold effect concentration (TEC) indicating that adverse effects were excluded. However, result of chemical speciation demonstrated Cd would pose a considerable potential ecological risk. Besides, most of the heavy metals were in the range of TEC-PEC suggesting possible toxicity.