Historical Trends In Atmospheric Heavy Metals Pollution In The West Of Northeast China As Reconstructed From Lake Sediments

Atmospheric heavy metal is one of the main issues of environmental today.Limited of data,there is little research on atmospheric heavy metal pollution in remote areas in China.Located in remote areas and are sensitive to atmospheric heavy metal pollution,the alpine lakes are good carrier for reconstructing the history process of atmospheric heavy metal pollution.This article studies the history of atmospheric heavy metal pollution in the past millennia by analysing the content of the elements Al,Ti,As,Cd,Cr,Cu,Hg,Ni,Pb,Sb,Zn and Pb isotope in the sediment cores of the three crater lakes?Tuofengling Tianchi,Moon Lake,and Aershan Tianchi?in the northwestern region of Northeast China.The results show that the 11 metals?or metalloid?have similar combinations in sediments in three lakes,and according to the results of the cluster analysis,they can be simply divided into two groups.One group is Al,Ti,Cr,Cu,Ni,whose contents in the sediments cores of the three lakes have similar historical trends which was relatively stable before 1880s,and has been decreasing since 1880s in core of YL and TC.Contents of elements in core of TFL were decreasing from 1850s.The temporal trends of the enrichment coefficient of elements?EF?are stable in this group?<1.1?,and from natural sources.The other group includes As,Cd,Hg,Pb,Sb and Zn,in which the content of Hg of three sediments have similar historical changes,relatively stabled before 1880s,and gradually increased from 1880s.The EFs of Hg have a consistent historical change trend with contents.The EF values have gradually increased since 1880s,and are 0.8-5.9,0.9-4.7,0.9-4.4 in three cores.Hg is one of the main pollution elements in the sediment.Based on regional comparison and potential source analysis,Hg pollution is considered to be affected by both global and regional sources.The average anthropogenic Hg deposition flux in the three cores at the top of the core?since 1980?is 7.76-20.39 ug/m²/a.The difference in the anthropogenic Hg deposition flux in different lake sediments may be related to the concentration effect of the sediments,and the ratio of the atmospheric Hg deposition flux in morden air was about 6.62 ug/m²/a after the correction of the sedimentation effect by the way of watershed/lake area,which was at a moderate pollution level compared with Eastern China,Western China and South China,but lower than that in Europe and the United States.The contents of As,Cd,Pb,Sb and Zn were relatively stable before 1930s,and with varying degrees of increasing since 1930s.The EF results are basically consistent with the historical trends of content changes,which have gradually increased since 1930s.Among them,Cd and Pb have higher EF values in three cores,which are the main pollution elements.Historical trends of ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb are consistent with those of the Pb contents and EFs,and have increased since the 1930s.Different from cores of TFL and YL,the core of TC have peaks in anthropogenic heavy metal pollution trends during 1920-1950s,which may be related to local deforestation.Based on the comparison of atmospheric pollution in different regions and the potential pollution sources,and combined with the analysis of Pb isotopes,it is believed that As,Cd,Sb,and Zn are mainly derived from regional coal burning and non-ferrous metal smelting,and Pb is mainly derived from the use of leaded gasoline,coal burning and non-ferrous Metal smelting.The anthropogenic sedimentation fluxes of As,Cd,Pb,Sb and Zn in the top of cores?since 1980s?are 0.49-0.78 mg/m²/a,0.040-0.083 mg/m²/a,1.86-3.94 mg/m²/a,0.042-0.095 mg/m²/a and 3.76-8.58 mg/m²/a,which are lower than North China,Northeast China,Southwest China,Northwest China and other parts of China and the world.