Application Of BCR Sequential Extraction Procedure On Heavy Metal Speciation In Surface Sediments Of The Lhasa River Catchments

As the most important "sink" of heavy metals in water system,the composition and structure of sediment are relatively stable.It so can reflect the pollution of water environment to a certain extent.The form of heavy metals in sediment directly affects their chemical behavior and potential biological toxicity.Therefore,metal speciation in river sediments were studied for identifying the potential bioavailability of the metals.In this study,surface sediment samples were collected along the Lhasa River course.BCR sequential extraction procedure was applied for metal speciation and contents of different forms of metals,including Al,As,Ag,Ba,Be,Bi,Cu,Cr,Co,Cd,Fe,Ga,Hg,Li,Mn,Mo,Ni,Pb,Rb,Sn,Sr,Sb,Tl,Ti,U,V,W,Zn and Zr,were analyzed by Inductively Coupled Plasma Mass Spectrometry(ICP-MS).Among them special attention was paid for ten elements(i.e.Al,As,Ba,Cu,Cr,Fe,Mn,Pb,Ti and Zn),since contents of the others were very low and could be ignored.Spatial and temporal distribution characteristics and potential bioavailability of these metals was studied.Meanwhile,the correlation analysis between the physical and chemical parameters of the river water and different forms of these elements was carried out.The results were as following:(1)except Cu,the other nine elements in the surface sediments of the Lhasa River catchments were mainly dominated by the residual fraction.Cu existed,almost totally in a non-residual fractions.In contrast,Cu,Pb,Zn,Mn and As had a high potential bioavailability.Under the influence of different water periods,the trends of acid extractable,reducible fraction and oxidizable fraction were all in the sequence of dry season > flat water period >wet season.The residual fraction sequence was as wet season > flat water period > dry season.At the sampling points where the human disturbance was more obvious,these elements were mainly presented in the form of acid extractable and reducible fraction.(2)only water turbidity showed a significant relation with non-residual fractions of the studied elements in the correlation analysis.Overall,elements/heavy metals in the surface sediments of the Lhasa River catchments,except for the Cu,demonstrated a low bioavailability.Cu with its non-residual fractions presented in the sediments indicated a high potential risk to the environment.