Pollution Evaluation Of Heavy Metals In Chaohu Lake And Phytoremediation Of Heavy Metals Pollution In Water

Chaohu Lake is one of the five largest fresh lakes in China.In order to know the pollution condition of heavy metals in the water,sediments and aquatic plants of Chaohu Lake,the spatial distribution of heavy metals and the potential ecological hazard in the sediments of Chaohu Lake,a survey was conducted to evaluate the contents of heavy metals(Cd,Cr,Pb,Cu,Zn,Mn,Fe) in the water,sediments and aquatic plants of Chaohu Lake.Pollution degree of heavy metals was also evaluated based on the Potential Ecological Risk Index.And for knowing the modality distribution characteristic of heavy metals in surface sediments of Chaohu Lake,a study was conducted to estimate the contents of heavy metals' different modalities.The results indicated that the content of the heavy metals in the water in the investigated areas meet classâ…¢criterion for surface water evaluation.Different kinds of aquatic plants in the sampling sites had different enrichment by the different heavy metals. According to the assessment of enrichment coefficient,the average enrichment coefficient of Cd,Cu,Mn contamination in aquatic plants was relatively higher than the other.The results also indicated that the sediments in rivers(esp.the Nanfei River) flowing into lakes were polluted more seriously than that in lakes by heavy metals.In the terms of concentration,the analyzed heavy metals followed a decreasing order of Fe＞Mn＞Zn＞Cr＞Pb＞Cu＞Cd.The potential ecologic risk index was used to evaluate metals pollution in the sediments of Chaohu Lake.By means of the risk assessment methodology,based on available data,it was demonstrated that Nanfei River was exposed to a very high potential ecological risk.Among the analyzed heavy metals Cd exhibited the highest pollution degree.Few section belonged to very high potential ecology risk.And the vertical distributions of pollutants in sediments were investigated.The highest concentration was in layer 0-8cm in depth.The results showed that the heavy metals concentration decreased with the increasing sampling depth.This paper investigated the speciation of heavy metals in selected contaminated surface sediments from water body by the BCR three-step sequential extraction procedure. The results showed that heavy metals(Cu,Cr,Zn,Fe) were associated mainly with residual form.Among these heavy metals,more than 60%of Cu,Fe.Pb were associated mainly with the Fe-Mn oxides bound form and the organic form.And more easily mobilized forms(the acid exchangeable form and the carbonate bound form) of Mn,Cd were dominant.While the percentage of the exchangeable Cd that was easily bioavailable was the highest.Compared with other metals,Cd,Mn and Pb in Lake Chaohu were more bioavailable,though the total concentrations of the three metals were not higher than others. It also found that the modality distribution of Zn was obviously influenced by human activities.Combination contamination of heavy metals is one of the important soil contamination types.A greenhouse experiment was carried out to determine the degree of tolerance of Pteris vittata L.to Pb,Cd and Cr and whether it could be applied to phytoremediation an revegetation of water contaminated with heavy metals.Results shown that:Concentrations of heavy metals in Pteris vittata L.all increased progressively with the increase of supply levels.Pteris vittata L.had good tolerance and could absorb the heavy metals mentioned above in various degrees.The Pb²⁺,Cd²⁺,and Cr⁶⁺ removal rates were 38.9%,31.5%and 35.2%.So,it was suggested that Pteris vittata L.was a potential pant for remedy Pb,Cd and Cr contaminated water.