Heavy Metal Pollution Of Weihe River

With the rapid development of economy and acceleration of urbanization process,the pollution of China's urban areas' river is becoming more and more serious.Among the various contaminates, heavy metals have become more serious due to their toxicity and persistence.As the main accumulation of heavy metals in the water environment,sediments reflect the heavy-metal contamination of the water.We can determine the level of contamination and pollution sources in the research areas and know the spread of heavy metals according to studying contents and horizontal distribution of heavy metals in the sediment.Of course,we may know the history of heavy metals pollution in the research areas by way of studying their contents of core sediments in different vertical positions.Compared heavy metals contents of the core sediments with the background in non-contaminated areas,it reflects the change condition of human activities on the transportation amounts of heavy metals in different historical periods.Xianyang section of Wei River is regarded as the research-area in this thesis.According to full investigation,collecting samples and experimental analysis,it systematically studies the physical-chemical characteristics(pH value,conductivity,CaCO₃,susceptibility,particle size,loss on ignition) of this area for the first time.Total contents of Cu,Cr,Pb,Zn,Mn and Ni are determined by X-Ray fluorescence spectrograph.Chemical extractions of Cu,Cr,Pb,Zn,Mn and Ni in all of the sediments are studied by BCR four-step sequential extraction method.Also determined the fractionations of the six heavy metals in the area's samples by flame atomic absorption spectrometry (AAS).Through analyzing the interconnection between the heavy metals,heavy metals contents and their fractionation,as well as physical-chemical indicators of heavy metals,we want to provide a scientific reference for rational development of resources and prevention of heavy metals pollution in the Wei River.The main conclusions of this study are as follows:1.The results of analyzing physic-chemical indicators show that:the sediments of Xianyang section of Wei River are of alkaline.The sediments texture type is mainly the sand particle.The average value of various physic-chemical indexes is respectively:the pH value is 8.041,conductivity is 416μs/cm,loss on ignition is 4.160%,the low-frequency magnetic susceptibility(x_LF) is 83.22×10-8m3/kg,the high-frequency magnetic susceptibility(x_HF) is 82.18×10-8m3/kg,the frequency magnetic susceptibility(x_fd) is 1.31%,the clay content is 4.67%,the silty sand content is 39.81%,and the sand particle content is 55.53%,CaCO₃ is 91.40g/kg.2.Through the entire research river,the average contents of four heavy metals(Cr,Cu,Pb and Zn) in surface sediment from Xianyang section of Wei River are higher than environmental background value of the research area.The average contents Cr and Pb are higher than environmental background being worth 32.9%and 34.3%,The average content of Cu is higher than environmental background being worth 16.7%,The average content of Zn is a little higher than environmental background being worth 6.2%.The average contents of Mn and Ni are lower than environmental background,which shows that accumulated amounts of this two elements from man-made is relatively less on the entirety,however,some sections also show high concentration. Therefore,we also need some attention.The average contents of heavy metals in surface sediment from Xianyang section of Wei River are in the following order:Mn＞Cr＞Zn＞Cu＞Ni＞Pb.On the space distribution,the average contents of heavy metals in surface sediment assume that the trend rising first to reduce again,most of high value areas are located in the middle to lower sections of research area.The cumulative values of research sections are in the following order:section 2＞section 3＞section 4＞section 5＞section 1.The average contents of most heavy metals in each section are of twists and turns on the vertical distribution of core sediment from Xianyang section of Wei River.The total contents display the gradually changeable small trend from above to below,which indicates that heavy metals pollution in research area are aggravated in recent years.Cr assumes the jagged and irregular multi-peak distribution characteristic obviously in all sections,one or more significantly high peaks emerge with depth,which may be related to the deposition of Cr after the migration process.Cu,Ni and Zn in each section have the similar vertical distribution characteristic, which indicates them probably having the similar source.The vertical distribution characteristic of Mn and Pb in each section is not obvious.3.The results of analyzing fractionation of heavy metals in surface sediment from Xianyang section of Wei River shows that:In general the main fractionation of heavy metals is residual state. Each heavy metal in different forms under different relocation conditions are in the following order: in the acid extractable fractionations:Mn(38.49%)＞Pb(27.66%)＞Ni(13.3%)＞Zn(9.09%)＞Cu (7.93%)＞Cr(0.00%);in the reducible fractionations:Cu(26.36%)＞Pb(12.81%)＞Zn(11.81%)＞Mn(11.71%)＞Ni(7.23%)＞Cr(0.00%);in the oxidable fractionations:Ni(13.09%)＞Cu (7.47%)＞Zn(5.42%)＞Pb(5.14%)＞Mn(3.96%)＞Cr(2.61%);In the environmental media, the overall migration and transformations is in the following order:Mn(54.16%)＞Pb(45.61%)＞Cu(41.76%)＞Ni(33.62%)＞Zn(26.32%)＞Cr(2.61%).The result of analyzing fractionation of heavy metals in core sediment from Xianyang section of Wei River shows that:The vertical distribution of four fractionations of Cu,Cr,Pb,Zn,Mn and Ni are of twists and turns,most of heavy metals fractionations in shallower part are higher than deep part in the acid extractable fractionations, but it turns out just the opposite in the residual fractionation,the vertical distribution trend of oxidable and residual fractionations are not obvious.In most of sections,it shows that the proportion of "labile" fractionation in total contents in shallower part is higher than in deep part,which is basically the same as the above conclusions.4.The interconnection analysis among the heavy metals shows that:Cr has a positive relation to Pb,no relation to other four heavy metals.There are significantly positive correlations among five heavy metals(Cu,Zn,Pb,Mn and Ni).The correlation analysis between "labile" fractionation and total contents displays:There are significantly positive correlations between every two indicators in six heavy metals.The correlation analysis between total contents of heavy metals,fractionation, "labile" fractionation with physic-chemical indexes displays:most of the heavy metals fractionation shows significantly correlation with conductivity,loss on ignition,low-frequency magnetic susceptibility(x_LF),high-frequency magnetic susceptibility(x_HF),CaCO₃,the clay and the silty sand.The above phenomenon reflects that seven physic-chemical indexes are the main factors of influencing fractionations for heavy metals in sediment from Xianyang section of Wei River;Pb, Cu,Ni,Mn and Zn have significantly positive relation to the seven physic-chemical indexes,which also shows that seven physic-chemical indexes are the main influencing factors for heavy metals in sediment from Xianyang section of Wei River;At the same time,"labile" fractionation also shows significantly correlation with seven physic-chemical indexes,which is basically the same as other conclusions.5.The result of evaluating research area by using Ratio of Secondary Phase in surface sediments of beavy mental displays:Apart from light pollution of Mn,Pb and Cu,other heavy metal elements have no pollution in surface sediments of Xianyang section of Wei River.The pollution of Mn exists in four sections(section 2,section 3,section 4 and section 5).The RSP value of section 2 is the highest,amounting to 140%.The pollution of Pb exists in two sections(section 3 and section 4).Tbe RSP value of section 4 is the highest,amounting to 116%.The pollution of Cu exists in section 3.The RSP value is 116%.There are three pollution elements(Mn,Pb and Cu) in section 3. There are two pollution elements(Mn and Pb) in section 4.The pollution of Mn exists section 2 and section 5.6.According to the distribution region of heavy metals in research area,there are high concentration in section 2 and section 3.It reflects that the content of heavy metals is affected significantly by pollution sources in the sediment from this section of Wei River.Others have little change,which indicates that the sediment is mainly affected by natural factors,such as soil parent material characteristics.Moreover,there are significantly positive correlation among six heavy metals(Cr,Pb,Cu,Zn,Mn and Ni).So it can be concluded that:the content of heavy metals in sediment from XianYang section of Wei River is affected by parent material and pollution sources of the sediment.