Studies On Sediment Quality Criteria Of Heavy Metals In Lake Chaohu, China

The lake sediment is not only the important part of the lake ecosystem but also thecenter link of the circulation of nutrients. As primary containers of heavy metals inlakes, sediments can reflect the status of contamination of heavy metals of the lake byheavy metal pollution situation and the history of water pollution. In this paper,sediments taken from the typical shallow eutrophic lake of the eastern plain lakearea-Lake Chaohu were studied. The main effcets were focused on the distributioncharacteristics of heavy metals associated with different fractions. The film diffusiongradient technology （DGT） and the equilibrium partitioning approach （EqPA） wereused to derive the sediment quality criterias of heavy metals in order to providetheoretical basis for the protection of the ecological environment, management andrepair of Lake Chaohu. The main research results are as follows:（1） The results indicated that the pollutions of metals of Cr, Cu, Zn, Ni, Pb, Cd,Co, V and As were mostly existed in the east and west part of the lake while lowercontents in the middle part which also were proved by the dendrogram. The results ofcorrelations analysis showed that Co and V were found to have different origins anddistributions with the other metals studied. Potential ecological risk indices for nineheavy metals investigated were in the order: Cd>As>Pb>Co>Cu>Ni>Zn>V>Cr. Cdhad high potential ecological risk and contributed most to potential ecological indexcompared with the other heavy metals. Based on the geoaccumulation index of heavymetals, the degree of heavy metal pollution decreased in the order ofCd>Zn>Pb>Co>Cu>As>V>Ni>Cr. The Igeo values suggested “unpolluted” of Cr, V,As and Ni (mean I_geo<0),“unpolluted to moderately polluted” of Co, Cu, Zn and Pb（0<mean Igeo<1）, and “moderately polluted” of Cd (1<mean I_geo<2), and somesampling sites in the west-half of Lake Chaohu have to be considered as “moderatelyto heavily polluted”. Based on the SQCs, concentrations of heavy metal were higherof sediments in the east and west parts near the estuary the lake. The concentrations ofNi, Zn, Pb and Cr were obvious exceeded the PEL values and the situation must bepaid enough attention.（2） Different fractions of nine heavy metals （Cr, Co, Ni, Cu, Cd, Zn, V, Pb and As） of Lake Chaohu sediments at twelve sampling sites were studied using BCR（European Communities Bureau of Reference） sequential extraction procedure. Theresults shown that Cr, As, Ni, V and Cu were present mainly in the residual fractionwith the proportion of73.75%,73.54%,67.80%,73.24%and59.46%, respectivelywhile Co, Pb, Zn and Cd were associated with the non-residual fraction （soluble,reducible and oxidizable fractions） dominantly and the proportions were56.54%,70.97%,65.55%and91.6%, respectively. The results of correlation analysis indicatedthat, total amounts of heavy metals were greatly affected by the contents ofnon-residual fractions. Cr, Ni, Cu, Cd, Zn, Pb and As were found to have the sameorigin and distribution, nevertheless Co and V have different origins and distributionswith the other metals studied.（3） The concentrations of AVS and SEM in sediments of the west lake weresignificantly higher than that in sediments of the east lake. Zn contributed most toSEM and was opposite to Cd. Concentrations of five heavy metals were in thesequence of Zn>Cu>Ni>Pb>Cd. The concentrations of AVS and SEM wereinfluenced by the contents of TOC, TN, TP and particle sizes. Meanwhile, it showedsignificant correlation between AVS and the non-residual fraction. This indicated thatthe non-residual fraction could be extracted during the extraction process of AVS.Results of sediment biological toxicity assessment shown that ions were released fromsediments which could cause adverse biological effects and it should cause enoughattention.（4） The concentration of the heavy metal in the interstitial water （CIW） wasdetermined by the film diffusion gradient technology （DGT）. The CDGTwas lowerwhen compared with the concentration determined by centrifugation. The averageratios of DGT method measured concentrations (C_DGT) to the concentrationsmeasured by centrifugation （C_F） of Cr, Cu, Pb, As, Zn, Cd were0.19,0.42,0.21,0.19,0.61and0.22, respectively. It suggested that the release rates of these metals fromsolid phase to solution followed the sequence of Zn>Cu>Cd>Pb>Cr=As. Sediments inLake Chaohu were in part of the buffer state, and Zn could be supplied rapidly fromsediment solid phase to interstitial water when it was absorbed by the DGT. Theeffective concentrations of Cr and Cu were affected by the contents of the reduciblefraction and total amounts of the two, respectively. Meanwhile, the release of Cu wasmainly influenced by organic matter.（5） The values of the metal partitioning coefficient （KP） for Cr, Cu, Pb, Zn, Cd and As were3924.84,2276.23,17811.30,738.35,10986.54and718.74L/kg,respectively. The Equilibrium Partitioning Approach （EqPA） approach was used toderive the sediment quality criteria （SQC） recommended values of six heavy metals（Cr, Cu, Pb, Zn, Cd and As） for surface sediments taken from Lake Chaohu. SQCvalues for Cr, Cu, Pb, Zn, Cd and As based on Chinese surface water quality criteria（GB3838-2002） were derived with the values of78.53,56.95,362.93,74.68,23.90and71.84mg/kg, respectively and the applicability of the values were preliminarilyconfirmed.