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Abstract The Chaohu is one of the largest fivefreshwater lakes in China. It provides freshwaterfor agriculture, life, and part of industry. Thequality of water becomes worst and worst dueto the toxic matter. In this study, we collectedthe samples from the sedimentary mud in thelake. The distribution of some potential hazardoustrace elements (Cu, Ni, Cr, As, Pb, Cd, and Hg) inthe sediments of western Chaohu Lake, has beendetermined and studied, and the enrichment fac-tors, the index of geoaccumulation, and potentialecological risk were analyzed and calculated. Theresults show that: the levels of selected potentialhazardous trace element vary from different sam-pling sites and significant anthropogenic impact ofPb and Cd occur in sediments. The contaminationrank of Pb and Cd are moderate, and Pb has alight potential ecological risk, but Cd is heavy.The total potential ecological risk of the selectedhazardous trace elements in this study in Chaohu Lake is moderate. Cluster and correlation analy-sis indicate that the selected potential hazardoustrace element pollutant has different source andco-contamination also occur in sediments.Keywords Heavy metals • Sediments •Chaohu Lake • Potential ecological riskIntroductionThe Chaohu Lake, which is one of the five mostfamous largest freshwater lakes in China, lies inthemiddle ofAnhui province, with longitude fromE 117◦16 54 to E 117◦51 46 and latitude fromN31◦43 28 to N 31◦25 28 , which belongs totypical geological fault constructional lake.35846
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Thelake is between the Yangtze River and HuaiheRiver, with the area of 9,130 km2(913,000 ha),whose basin covers 11 cities and towns, and thereare seven main rivers flowing into the lake. Theclimate of Chaohu Lake belongs to sub-tropicalmonsoon climates, the annual average rainfall is1,120 mm and the annual average temperature is15∼16◦C.The Chaohu Lake is a large freshwater lakewhich plays an important part not only in inten-sive commercial fishing, but also for water sup-ply, irrigation navigation, tourism, and recreationas well as being of great conservation value inits wildlife and wetland system. Unfortunately, Chaohu Lake, which before the 1960s was a clearand beautiful lake supporting rich biopersitiesof fish and other aquatic species, is now the mainrecipient of pollutants from cities and towns alongthe lake, especially fromtheHefei City, the capitalof Anhui Province, China, west of the lake. Asan example, one of the biggest pollutant influx tothe lake is the Nanfei River which discharges alarge amount of untreated domestic sewage andindustrial wastewater with a total of 1.8 × 108tonsper year from Hefei City into the west regionof the lake (Fig. 1). Annually the quantities ofsewage discharged into the lake from the cityare about 18,360 tons of total nitrogen (TN) and1,050 tons of total phosphorus (TP; Xu et al. 2005).Although numerous studies have indicated thatthe Chaohu Lake is both organically polluted andhighly enriched in nitrogen and phosphorus, andaverage concentrations of TN, TP, and CODMn inthe whole lake were 2.30, 0.204, and 12.7 mg/L, re-spectively (Tu et al. 1990;Yin and Bernhardt 1992;Han 1998; Chen and Wang 1999;Xuetal. 2005),few documents pay attention to the potential haz-ardous trace element contamination of ChaohuLake except Cao et al. (2004) who reported thePb contamination in the eastern Chaohu Lakeand Wang et al. (2003) who determined severalsediment samples from two stations of the westregion.The focus of this project was to (1) provide theconcentration and distribution of some potentialhazardous trace elements in western Chaohu Lakesediments;
(2) evaluate the contamination degreeand the potential ecological risk for the selectedpotential hazardous trace elements; and (3) pro-vide the possible sources of pollutant inputs, andalert environmental authorities of areas of spe-cific environmental concern. This specific reportfocuses on Cu, Ni, Cr, As, Pb, Cd, and Hg levelsin surface sediments from different locations thatthe rivers entering into the western Chaohu Lake.Materials and methodsSample collection and pre-treatmentIn order to obtain the possible pollution sourcesdata on the selected potential hazardous traceelements (Cu, Ni, Cr, As, Pb, Cd, and Hg), andevaluate their potential ecological risk, six sur-face sediments samples were collected from dif-ferent stations of the western Chaohu Lake, four among six sampling stations were selected on theentrance which rivers are via into the westernChaohu Lake, the other two sampling stationswere selected on the Tangxi and the centre of thewestern Chaohu Lake (Fig. 1 and Table 1).The sampling sites were positioned by globalpositioning system (GPS). The surface sedimentsamples (approximated 2–5 cm in depth) werecollected using a grab sampler and stored in glassbottles. These samples were thoroughly mixedto create composite samples for each site, whichwere then subsequently processed by air dryingand manually disaggregated after being broughtback to laboratory.All samples ground in an agatemortar to pass through a 100 mesh screen andreserved in the airer.Analytical methodsThe digestion method was used to determine thetotal content of these selected potential hazardoustrace elements in the sediments.