Research On Geochemical Characteristics Of Heavy Metals In Lake Water Of Yunnan Plateau

The research on heavy metal pollution and water quality of typical plateau lakes in Yunnan is helpful to understand the status quo and development trend of heavy metal pollution in plateau lakes.The paper systematically analyzed the water quality survey data of typical plateau lakes in Yunnan Province,such as Dianchi Lake,Fuxian Lake and Xingyun Lake.The paper selected twelve kinds of heavy metals(Co,Ni,Cu,Zn,As,Mo,Sb,Pb,Th and U)in the water of the three lakes were used to analyze the mass concentration and distribution of heavy metals in lakes.The water quality index and health risk were evaluated for heavy metal pollution in three lakes.By combining physical and chemical index value of water quality such as nitrogen and phosphorus nutrients,water temperature,electrical conductivity,pressure,depth,pH,Eh,turbidity,chlorophyll-a and DO,etc.The present situation and possible sources of heavy metal pollution in three different eutrophication lakes are discussed by using multivariate statistical method.It is hoped that the paper can provide a useful scientific reference for the prevention of water pollution in the plateau lakes of Yunnan Province.The main conclusions of this thesis are as follows:(1)The content range of TN is 1.41-1.89ug/ml,the content range of TP is 0.01-0.13ug/ml,The content range of TOC is 4.59-5.85ug/ml in Dianchi Lake region.The content range of TN is 1.29-3.72ug/ml,the content range of TP is 0.21-0.32ug/ml,The content range of TOC is 7.85-9.85ug/ml in Xingyun Lake region.The content range of TN is 0.68-4.54ug/ml,the content range of TP is 0.01-0.01ug/ml,The content range of TOC is 0.67-4.81ug/ml in Fuxian Lake region.A comparison was made between TN,TP and TOC in the three lakes.Dianchi Lake is still a eutrophic lake,followed by Xingyun Lake and Fuxian Lake.(2)The content of heavy metals in three lakes did not exceed the grade I quality standard of surface water such as Mn,Fe,Zn,As,Cu,Mo,Sb.Ni,Pb,Co.The large value of Mn in Dianchi Lake water body in DL1,DL3 and DL6.The heavy metal Zn in Dianchi Lake water body is concentrated in DL1,DL2,DL3 and DL4.The contents of Fe,Mn and Zn in the southeastern waters were higher than other heavy metals.Sequence of the other 8 heavy metals is As>Cu>Mo>Sb>Ni>U>Pb>Th>Co.The large value of Mn in Xingyun Lake water body in XL3 and XL4.The heavy metal Zn in Xingyun Lake water body is concentrated in XL2,XL3 and XL4.The maximum of heavy metal Cu was found in XL5.Sequence of the 12 heavy metals in Xingyun Lake is Fe>As>Zn>U>Ni>Mn>Cu>Sb>Mo>Co>Pb>Th.Sequence of the 12 heavy metals in Fuxian Lake is Fe>As>U>Zn>Mn>Ni>Cu>Pb>Mo>Sb>Co>Th.(3)The dissolved heavy metal such as Mn,Cu,Zn,Pb,Ni,Co,Th mainly exists in the form of free ions in Fuxian Lake,Dianchi Lake and Xingyun Lake.The ratio of Th4+ to total dissolved Th is between 81.84%and 87.52%,The ratio of the other six heavy metal’s free state ions between 99.16%and 99.68%.MSO4 is the most important inorganic compound form of dissolved heavy metals in lake water.The proportion of MSO4 to total dissolved M is Dianchi lake>Fuxian lake>Xingyun lake.The occurrence of Fe is obviously different from that of other heavy metals,the ratio of Fe3+ to total dissolved Fe is only between 17.97%and 22.80%.Humic acid bound heavy metals also exist in lakes.(4)The water quality index of heavy metal pollution level in three lakes was evaluated,and the results showed that the average value of WQI in water samples of Dianchi Lake,Fuxian Lake and Xingyun Lake were 0.27,0.49 and 0.11.The pollution level of heavy metals in the three lakes is Dianchi Lake>Xingyun Lake>Fuxian Lake.The WQI values of heavy metals in three lakes were less than 1,respectively.The health risk assessment model of USEPA and the classification system of IARC were used in the three lakes.The annual risks of As in DL2 and DL6 of Dianchi Lake are higher than the maximum acceptable risk level of 5.00 × 10-5a-1 recommended by ICRP.The annual risks of As in XL6,XL2 and XL4 of Xingyun Lake are higher than the maximum acceptable risk level.The average annual risk of As in Fuxian Lake is 3.41 × 10-5a-1 which is lower than the maximum acceptable risk level.The individual annual risks of all the non-carcinogenic substances,Cu,Pb,Mn and Zn,are much lower than the maximum acceptable risk level.(5)Using multivariate statistical method to analyze the sources of heavy metals:the higher value of heavy metal Cu,Sb,Mo,U in the west bank and south bank of Dianchi Lake is from agricultural point source pollution and agricultural chemical fertilizer pollution.The higher value of heavy metal Pb,Th,Zn,Fe,Co in the east bank of Dianchi Lake,the main sources of pollution are industrial pollution sources.The higher value of heavy metal As,Mn and Ni in the main urban area of Kunming in the north,and the sources of pollution are urban life emissions.The heavy metals in the middle of Fuxian Lake are mainly natural sources.The source of Pb and Zn in the northern part of the lake is human activities and factory pollution.The heavy metals in Xingyun Lake except Pb,Ni and U are larger in the southwest lake area,the sources of pollution are urban life emissions.The high value of Zn,Fe and Pb in the eastern waters,and the source of pollution is industrial pollution sources.