Distribution And Sources Of REE And Other Metal Elements In The Sediments In Yundang Lagoon And Western Xiamen Bay

The concentration,spatial distribution,faction of REE?rare earth element?and other metal elements in the sediments in Yundang Lagoon and Western Xiamen Bay were analyzed,and contamination conditions were evaluated by methods of the enrichment factor,potential ecological risk index,geoaccumulation and ratio of secondary phase to primary phase.Pb-Sr-Nd isotope tracing technique was employed to reveal the sources of REE and other metal elements in the sediments.The conclusions are summarized as follows,The range of?REE is 131.9²68.0 mg·kg^-1 in surface sediments in Yundang Lagoon,while 210.29²97.78 mg·kg^-1 in surface sediments in Western Xiamen Bay.The range of?REE is 173.2²72.7 mg·kg^-1 in core sediments in Western Xiamen Bay.These are all close to local REE background values.The results of the enrichment factor show that REEs of this study area are mainly from the local soil while human activities are a minimal contributor.The results of distribution patterns of chondrite-normalized REEs show that the REE distribution patterns in the sediments in Yundang Lagoon and Western Xiamen Bay are enriched in LREE?light rare earth element?.This pattern is similar to that of the REE distribution patterns of the continental shelf.LREE/HREE?HREE,heavy rare earth element?ratios are around 10,which are near that of background value in Xiamen soil.LREE has obvious fractionation,however HREE shows no obvious fractionation.Ce has no obvious abnormality,and Eu has obvious a negative abnormality.The results of REE fraction analysis show that REEs of the study area are mainly in the reducible fraction and residual fraction,and are influenced by the iron and manganese oxides.In the reducible state,Ce shows a positive anomaly.The distribution patterns of chondrite-normalized REEs of acid-extractable phase in the sediments are similar to those of total REEs and four fractions of REEs.Comparing?REE and Sr-Nd isotopes in this study and in petential sources,REEs in the sediments of this area are from the local soil.REE in the surface sediments in Yundang Lagoon are also affected by domestic sewage,dust,coal combustion,vehicle exhaust and ship painting.REEs in the sediments of Western Xiamen Bay are also affected by Pb-Zn deposit,domestic sewage,dust,coal combustion,vehicle exhaust and ship painting.In surface sediments in Yundang Lagoon,the average concentrations of metal elements Li,V,Cr,Co,Ni,Cu,Zn,Rb,Cd,Ba,Pb,U,Sb,Tl,Th,Ta,Sc,Cs,W,Li,Be,Ga,Rb,Mo,In,Bi are higher than the background values of Chinese shallow-sea sediments.The average concentrations of metal elements Mo,Bi,Cu,Zn,Cd,Tl,Pb,W and U are 5.8,5.8,5.0,3.6,7.9,3.4,3.3,3.0,3.0 times that of the background value,respectively,which means significant enrichment.Cu is dominated by reducible fraction;Zn is also mainly present in the reducible fraction;Cd is mainly present in acid-soluble and reducible fraction;Pb mainly exists in the reducible fraction,followed by the residual fraction;Co,Ni,U,Fe and Mn mainly exist in reducible and residual fraction;Li,V,Cr,Rb and Ba are mainly present in the residual fraction.Cd,Bi,Mo,V,Cu,Zn,Tl,Pb,Cr,W and U in the surface sediments in Yundang Lagoon are main metal elements pollutants by the method of ecological risk index method,geoaccumulation index method and enrichment factor method.Cd shows moderate pollution degrees.Bi,Mo,Cu,Zn,Tl,Pb show low to moderate pollution degree.U,W,Sb,Th,In,Ta,Ga show low pollution degree.The levels of potential ecological risk in Yundang Lagoon are as follows:the outer lake>ditch>inner lake.The results of Pb isotope tracing shows that Pb is mainly affected by vehicle exhaust,parental material and domestic sewage with the distributions of 0%⁴9%,0%⁶1%,2%¹00%,respectively,and are slightly affected by coal combustion.The results of Sr isotope,and Pb-Sr isotope show that Sr in Yundang Lagoon are mainly effected by domestic sewage,ocean resource and coal combustion,and are scarcely effected by vehicle exhaust and parental material.Whether REEs and charactioristic parameters can indicate the pollution of other metal elements is not conclusive.In surface sediments in study area,REEs and characteristic parameters cannot be used to indicate the pollution of metal elements,while in the core sediments in Western Xiamen Bay REEs and characteristic parameters can be used to indicate the contamination of some metal elements.