Historical trends of heavy metal contamination and their sources in lacustrine sediment from Xijiu Lake,Taihu Lake Catchment,China

Concentrations of Cd,Cr,Cu,Pb,Zn and Hg in Xijiu Lake sediment from the Taihu Lake catchment,China,were analyzed.Their contamination state was investigated based on the geoaccumulation index and enrichment factors.Statistical analysis was used to differentiate the anthropogenic versus natural sources of heavy metals (HMs),and the anthropogenic accumulation fluxes were calculated to quantify anthropogenic contribution to HMs.The results indicated that the lake sediment had been heavily contaminated by Cd,enrichment of Zn and Hg was at a relatively high level,while that of Cu and Pb was in the lower-to-moderate level and Cr was in the low enrichment level.Sources of Cr in the sediment were mainly from natural inputs,while other metals,especially Cd,were predominantly derived from anthropogenic sources.In the past century,anthropogenic accumulation fluxes of Pb,Zn and Hg increased by 0.1-47.3 mg/(cm2·yr),2.4-398.1 mg/(cm2·yr),and 3.7-110.3 ng/(m2·yr),respectively,accounting for most inputs of HMs entering the sediment.The contamination state of HMs varied with industrial development of the catchment,which demonstrated that contamination started in the early 20th century,reached the maximal level between the mid-1970s and mid-1990s,and decreased a little after the implementation of constraints on high contamination industries,although the contamination of some HMs,such as Cd,Zn and Hg,is still at high levels.