Distribution Characteristics And Source Analysis Of Trace Elements In Offshore Surface Sediments From Jiulong River

Distribution characteristic,speciation and source analysis of trace elements in surface sediments of Jiulong River were studied in this paper.Geo-accumulation index(Igeo),potential ecological risk index(RI)and the ratio of secondary phase to primary phase(RSP)were applied to evaluate the pollution degree and potential ecological risk of heavy metals in the sediments.Multivariate statistical methods and Pb-Sr isotopic compositions were applied to speculate the main source of these heavy metals.Geochemical characteristics of REEs and Nd isotopic composition were applied to probe the provenance compositions of the sediments.The main conclusions were summaried as follows:The distributions of heavy metals were different in four regions of Jiulong River(North River,West River,Coastal Wetland and Estuary),and most of these elements were rich in the sediments.The results of pollution assessment by geo-accumulation index revealed that the pollution degree of Cd was the highest and at a serious polluted level in 7.5% of the samplings.And the pollution degree of heavy metals showed the order of Cd>Bi>Li>Mn>Cu>Pb>Be>Co>Ni>Hg>Sr>Zn>Tl>U>Sb>Cr>Ga>Ba>Cs>Rb>Th>Fe>V>Mo.The assessment results of potential ecological risk indicated that the potential ecological risk of heavy metals showed the order of Cd>Hg>Cu>Pb>Ni>Co>Cr>Mn>Zn>V.Cd and Hg contributed the most to the total potential ecological risk,accounting for 75.8% and 13.4%,respectively.The results of the modified BCR protocol showed that most of the elements(Fe,Ni,V,Tl,Ba,Sb,Ga,Cr and Sr)existed mainly in residual fractions,and extractable fraction was dominant for Mn(83.8%),followed by Cd,Pb,Zn,Co and Cu.The results of dilute HNO3 method showed that the proportion of the dilute HNO3-extractable fractions of Pb,Mn,Cd,Co,Cu and Zn were higher.The assessment results of ratio of secondary phase to primary phase(RSP)indicated that Pb,Mn,Cd,Co,Zn and Cu in surface sediments of Jiulong River had higher ecological risk.Both the extraction methods have merits and demerits respectively.In generally,the dilute HNO3 method is enough to analyze the bioavailability andecological risk of heavy metals in sediments.The results of multivariate statistics analysis indicated that the source of Fe?Mn?Zn?Pb?Cu?Cr?Cd?Hg?Mo?Sb and Bi were mainly from mixed sources of agricultural activities,coal combustion and mining activities;the source of Ni?Co?Li?Rb?Sr?Tl?Ga?Be?V and Ba were mainly from burning fossil fuels;and the source of Th,U and Cs were mainly from the rock weathering of granite.The results of Pb isotopic compositions in sediment samples and potential sources showed that the Pb accumulated in the surface sediments of Jiulong River was mainly from parent material,coal combustion and Fujian Pb-Zn deposit,with the contribution rates of34.4%,34.0%,and 31.6%,respectively.The results of Pb isotopic compositions in HNO3-extraction suggested that dilute HNO3-extraction was more sensitive in identifying anthropogenic Pb sources than total digestion.The results of Sr isotopic compositions showed that Sr accumulated in the surface sediments of Jiulong River estuary mainly derived from external source and natural source(parent material)with the contribution rates of 57.5% and 42.5%,respectively.The REEs in surface sediments at different sites were similar in geochemical characteristics.The average(50)REEs in the surface sediments of Jiulong River was254.25 mg?kg-1,which is higher than those in Fujian soils while lower than deep-sea sediments.The high concentrations of(50)REE,high LREE/HREE ratios and negative Eu anomalies indicated that the surface sediments were derived from terrigenous sources.The chondrite-normalized and NASC-normalized REEs patterns of sediments indicated that the REEs in different areas of Jiulong River were of similar origin.The sediments were mainly derived from the local soils but not exclude anthropogenic effects.The enrichment factor,plots of La-Th-Sc,La/Yb-?REE and Nd isotopes suggested that the surface sediments were mainly from granite with minor contributions from basic rocks.