Geochemistry Of Heavy-metal Contaminated Bed Sediments From Lower Reaches Of The Xiangjiang River(Hunan Of China):A Step-leaching Study

The Xiangjiang River is the longest river in Hunan province.lt also is one of the river that are most heavily polluted by heavy metals in China.In this paper,the total amount of heavy metal elements and the morphological analysis of heavy metal elements in the downstream of xiangjiang river sediments were analyzed by inductively coupled plasma mass spectrometer(ICP-MS).The following results are obtained:(1)Distribution characteristics of trace elements:The average content of heavy metal elements varies greatly,which is gradually reduced in accordance with the order from upstream to downstream.The average content of the elements in the sedimentary column ZX2 is the highest.The content of heavy metal U,Ba,Mn,Th,Sc and Co is relatively uniform in the sedimentary column,and the total element content does not vary with the depth.Except the Sr element content in the sediment column,HFSE on average higher than the background value,and the change of element Zr and Hf,Nb and Ta patterns tend to be highly consistent,suggesting that it may have the same source.The variation coefficient of sedimentary column ZX2 is greater than 0.5,which indicates that the disturbance to the anthropogenic activity of the sedimentary column ZX2 may be very large.The distribution pattern of chondrite meteorites shows that the sediment of different sedimentary columns has a basic and consistent distribution curve,namely,light rare earth enrichment,heavy rare earth deficiency,and obvious Eu negative anomalous right-leaning model.(2)Enrichment characteristics of trace elements:The enrichment factor(EF)indicates that heavy metal Sc,Cu,Zn and Pb has significant pollution,especially with the sedimentary column ZX2 being the most serious,and reaching the very strong pollution.The high field strong element Sr was slightly polluted in the sedimentary column ZX2,and the Zr and Hf contained light pollution in the sedimentary column SG1 and ZB6,and some of the sediments were moderately polluted.Heavy rare earth elements in sedimentary column ZX2(Tb,Yb,Lu)reach to moderate pollution,all the rest of the sedimentary column of rare earth elements are slightly polluted,but there are three significant enrichment layer,respectively is 42 cm of ZX2 sedimentary column,16 cm of ZB6 sedimentary column,2 cm of SG1 sedimentary column,similar to heavy metal enrichment layer exists,this shows that the rare earth element may be the important evidence of heavy metal pollution.(3)Speciation from characteristics of trace element:Heavy metal V,Cr,Ni,Ba are mainly in the forms of residual fraction.Co,Zn,Cu and U residual fraction have a proportion of over 50%,and the secondary fraction possesses a high proportion.Pb,Th,Sc,Cd are dominated by secondary fraction,residual fraction ratio is low,among them with Cd effective state proportion is the largest.In addition to the high secondary fraction of the element Sr,the remaining high field strong elements are dominated by the residual fraction.In addition to the element Er,the structure of rare earth elements has a high similarity,but it has a higher proportion of the reducible faction and the oxidizable fraction.The occurrence of heavy metal elements is complex and diverse,and high field strength and rare earth elements are highly consistent.(4)Activity characteristics of trace elements:The high density of the extractable fraction of Cd and Zn is related to the carbonate rock widely distributed in the basin.The extractable fraction is easily affected by pH,therefore its activity is high.The reducible fraction of Pb mainly with Xiangjiang basin are widely distributed in red and yellow soils,it can provide a lot of iron and manganese compounds and heavy metal ions in water to form iron and manganese oxides,and Fe Mn oxides is the main purification way of heavy metals in Xiangjiang basin.,the oxidizable fraction of Cu Sc,this is due to Cu,Sc has a particularly strong affinity for organic matter,the morphology in the oxidizing environment of Xiangjiang basin has a certain activity decomposition.(5)Potential hazard characteristics of trace elements:According to the composition characteristics and activity of the elements,there are four types of potential hazards,no potential hazard elements:Ge.Ga.Cs.Rb.Nb.Ta.Zr、Hf、Sr;low potential hazard elements:V、Cr、Ni、Ba、Co、U、Th、REE;high potential hazards elements:Cu、Sc;extremely high potential hazards elements:Zn、Pb、Cd.