沉积物的粒度分布特征及砷的次生富集机制OA

The differential distribution of sediment grain size is a key factor controlling the spatial heterogeneity of arsenic(As)distribution in sediments and is the most sensitive indicator for reconstructing sedimentary environments and tracing the sources of As in sediments.Studying the particle size distribution of sediments as well as the distribution of As in different grain size fractions helps trace the source-sink relationship and release-migration processes of As.This study focused on 68 sediment samples from seven boreholes with different sedimentary facies in the Baoding Plain.The grain size distribution and geochemical characteristics of the sediments were analyzed,and the factors controlling the heterogeneous distribution of the sediment chemical composition were clarified.The main carriers of As in the sediments were identified,and the sources of As in the sediments were elucidated using the As/Fe ratios.The results showed that the grain size distribution of the sediment samples was mainly controlled by lithology,with little difference in grain size distribution among sediments of the same lithology in different sedimentary facies.The heterogeneous distribution of the chemical composition of the sediment was strongly controlled by hydrodynamic sorting.The fine fraction(grain size<0.062 mm)in the fine-grained(clay to silty sand)and coarse-grained sediments(fine sand to gravel)accounted for(85±12)%and(22±5)%,respectively.The proportion of the fine sediment fraction was significantly positively correlated with the total organic carbon(TOC),total As,and HCl-extractable As/Fe/Mn.The As content in the sediments ranged from 0.5 to 29.5 mg/kg,with an average of(7.6±4.7)mg/kg.The As sediments were primarily derived from the lithosphere,with secondary Fe/Mn oxides as the main carriers.This mobilizable Fe/Mn oxide-loaded As poses a high risk of As release into groundwater.