Heavy Metal Pollution Of Surface Water And Its Risk Assessment In Youhe River Wetland

Youhe River,an important tributary of the Weihe River,is the main source of drinking water for urban residents in Weinan City.The study on the heavy metal pollution of Youhe River wetland as well as the precise analysis on the heavy metals along the river and scientific evaluation of polluted river wetland is of significance to the protection of Weinan City drinking water source,the security of urban household water as well.At the same time,the author hopes that the study can provide a basis for the management of Youhe River wetland pollution and the protection for ecological environment of Youhe river basin and also offer some experiences and references for the research of heavy metal pollution in Guanzhong district of Shaanxi Province.On the basis of data collection and analysis through field investigation,this thesis selects the Youhe River Wetland as the research object.Sampling are carried out twice,respectively in May and September in 2016 including eight kinds of heavy metals,such as Cu,Zn,Pb,Cd,Mn,Cr,Hg,As as evaluation index.27 sampling transects are set up in the surface of water respectively during dry seas and wet season and relevant sampling analysis is made on the comprehensive evaluation of heavy metal contamination in Youhe River Wetland,by respectively using the method of single pollution index and potential ecological risk index,in order to analyze the present characteristics of heavy metal pollution in river wetland.The risk evaluation of harm on human caused by heavy metal pollutant that enters into body through drinking water are made,adopting the health risk assessment model recommended by the USEPA Environmental Protection Agency.Finally,a comprehensive evaluation of water quality is made about water sections in Youhe River Reservoir monitored during the period from 2011 to 2015 through the introduction of fuzzy matter element evaluation model of water environmental quality which is based on entropy.The main research results are as follows:(1)After analyzing the contents of these eight heavy metals,it is found that there exists a quite low content of heavy metals in Youhe River wetland,which meets the national health standards for drinking water and environmental quality(class I standard)of surface water.(2)The evaluation results gained by single pollution index show that the contents of heavy metal in wetland water are quite low and all the all the single contaminate index of heavy metal was<1.0,of which the single pollution coefficient of Pb is the largest,the maximum value is 0.97.The comprehensive pollution index in wetland water is between 0.057 and 0.174,which indicates that Youhe River is slightly polluted by heavy metal pollution.(3)The potential ecological risk index indicates that the potential ecological risks of heavy metals like Pb,Cd,and Hg,as are relatively high,of which the content of Pb is maximum and Cu is minimum.The single potential ecological risk of all heavy metals is below 40,and the comprehensive index is under 150.The above analysis shows the ecological risk in this region is not serious.(4)The evaluation of water environmental health risk shows that among the cancer-causing chemical elements Cd?Cr and As,Cr,to a large extent causes the greatest risk through drinking water,and the toxic chemical Pb has great influence on the health.The research comes to the conclusion that the risk of the heavy metals in this region mainly come to the chemical carcinogen.(5)The comprehensive evaluation of water environmental quality shows the water quality of Youhe River from the year of 2011 to 2015 meets the first class of water environmental quality standard,with the best water quality in 2013.