Spatial Distribution And Risk Assessment Of Heavy Metals In Eastern Dongting Lake Wetland

Eastern Dongting Lake is one of the most important wetland in china and the most important agricultural production area in Hunan province. Because of increased population, reclaiming land from lake, developing mining industry and the paper industry in nearly two decades, a tremendous amount of waste was discharged to the lake resulting in serious environmental problems. Heavy metals were paid close attention because of the toxicity, wide sources, non-biodegradable properties and accumulative behaviors.Wetland is a main place for accumulating heavy metals. Investigating the content, time-space distribution of heavy metals in wetland would make a great contribution to understanding the heavy metal resources, pollution status and the affect to the ecosystem, and was an important link of preventing the wetland pollution and protecting the environment.The spatial distribution and sources of eight heavy metals (Cu、Zn、 Pb、Cr、Cd、Ni、Hg、As) were analyzed in Eastern Dongting Lake wetland. Geoaccumulation index, potential ecological risk and healthy risk on the basis of total contents were applied to assess the pollution and potential ecological risk of heavy metals in the wetland soil. The main conclusions were summed up as follows:Generally, the mean values of soil heavy metals in two layers of0-20cm and20-40cm in Eastern Dongtong Lake wetland were higher than native background value. Heavy metal contents in Lujiao port,Chenglingji port and Yueyang urban were higher than those in other areas.The orders of mean values of heavy metal in the layers of0-20cm and20-40cm were Zn>Cr>Cu>Ni>Pb>As>Cd>Hg. The results of relevance analysis, factor analysis and clustering analysis indicated that heavy metal elements in wetland soil were mostly related with TP, TN and organic matter. As、Hg、Cd、Pb、Zn mainly came from waste water discharged from mining, industry factories and traffic exhausting. Cu、 Ni、Cr mainly came from natural wethering of geochemistry and had been little effected by human activities.Based on total heavy metal in wetland soil, in the study three assessment methods were adopted to assess heavy metal pollution in the layers of0-20cm and20-40cm in Eastern Dongting Lake. In the layer of0-20cm,Cu、Ni、Cr、As、Hg、Pb、Zn were classified to zero-light pollution level and Cd belonged to moderate pollution level by using accumulation index. In the layer of20-40cm, As、Cu、Pb、Ni、Cr、Hg、 Zn belonged to zero-light pollution level and Cd belonged to heavy pollution level. Meanwhile, Cd、Hg were main pollutants in this area. The order of pollution level of heavy metals was Cd>Hg>As>Cu>Pb>Ni> Zn by using potential ecological risk index assessment. From perspective of RI mean values, ecological risk of Eastern Dongting Lake wetland was classified to moderate pollution level and Cd was the most serious pollution index.The order of potential ecological risk of heavy metal of sub-area was Lujiao port>Chenglingji port>Yueyang urban> Reed Field of Lu Lake>farm of Tuanzhou>tourism area of Jun Moutain>Matang town> wetland protection area in Caisang. By applying health risk evaluation method to assess non-carcinogenic risk and carcinogenic risk of both children and adults, the results indicated that the order of non-carcinogenic risk index was Ni>Cr>Pb>Cu>Zn>Hg. From perspective of elements, As had caused more damages to human health comparing to Cd and As was the main damaging element. The risk index of heavy metals for adults had not been far lower than threshold value, so that carcinogenic risk and non-carcinogenic risk of heavy metal should not be ignored, especially for adults.Values for adults were higher than childrens’because adults’contact areas were bigger than that of children.The study results provided referent statistics for environment department and applicable measures for restoring heavy metal pollution in Eastern Dongting Lake wetland. It was very significant for managing polluted wetland.