Elemental Geochemistry Of Heavy-metal Contaminated Bed Sediments From The Lowermost Xiangjiang River,China

The concentrations of heavy metals,major and trace elements of sediments from the lowermost Xiangjiang River were analyzed using inductively coupled plasma mass spectrometer?ICP-MS?and X-ray fluorescence spectrometer?XRF?analysis techniques in this study.The results show that the contents of TiO₂,Fe₂O₃,MnO,CaO,Na₂O,P₂O₅,and LOI in the sediments are significantly variable,with CV?coefficient of variation?values>0.2,among which in sediments from Zhuzhou section have the highest CV values,with those from Xiangtan and Changsha sections the lower.The chemical index of alteration?CIA?is77.8 in average,indicating that the sediments were from the source regions where the chemical weathering was in a moderately degree of weathering.The heavy metals Cu,Pb,Zn,and Mn in bed sediments of the lowermost Xiangjiang River are of highly concentrated,which leads to significantly high enrichment of these metals in the sediments,while the enrichment of other heavy metals including V,Cr,Co,Ni,and Ba in the sediments is insignificant.The enrichment index of Cu,Pb and Zn in the Zhuzhou section is the highest,followed by the Xiangtan section and Changsha section.The rare earth elements?REE?distribution patterns in sediments show the light rare earth elements are relatively enriched,and the heavy rare earth elements are deficient,presenting a distinct negative Eu anomaly and a slight positive Ce anomaly.The results of the geoaccumulation index showed that the sediments of lowermost Xiangjiang River were seriously contaminated by Pb,Zn was the intermediate pollution,Cu and Mn reached the intermediate degree of pollution or the middle degree pollution,other heavy metal elements were mildly polluted or clean.The comprehensive pollution status of heavy metals in each section is as follows:Zhuzhou section>Xiangtan section>Changsha section.Health risk assessment shows that V,Mn,Pb of children constitute non carcinogenic risk threat significantly,especially the non carcinogenic risk value?HQ?of Pb to children was as high as 17.3 in Zhuzhou section,Cr,Co and Ni have a significant risk of cancer in children and adults,which threatens the health of local residents is relatively large,relevant departments should pay more attention to it.Stepwise regression analysis showed that Ba mostly hosted in ilmenite and K-feldspar,Co and Ni are mostly hosted in coarse grained quartz detrital minerals,V and Cr are mostly hosted in Ilmenite,Mn mainly occurs in the presence of manganese-containing minerals,Cu,Zn,Pb mostly hosted in the iron oxide,plagioclase and fine-grained minerals such as clay minerals.Based on the results of geo accumulation index evaluation,All of sediment samples would be divided into three types of heavily polluted?i?,moderate pollution?ii?and light pollution?iii?by the levels of pollution.The characteristics of trace elements in three kinds of sediments with different pollution levels are analyzed.The key chemical components that cause the major chemical difference between the three class samples were identified out by using the one-way ANOVA analysis.Combined study shows,the more tend to be in the direction of REE/Zr and Ti/Nb,the more serious the pollution,suggesting the REE and Ti/Nb can be used to indicate heavy metal pollution.In addition,linear correlations between Co/Th and Sc/Th can also be inferred to be contaminated by heavy metals.In order to determine the origin of heavy metals,Ni/Y as the abscissa and the heavy metal/Y as the ordinate for the scatter,The results showed that heavy metals of Cu,Zn and Pb were mainly anthropogenic sources,Co,V,Ba,Cr,Mn and so on are derived from natural weathering and anthropogenic activities.