| Fulvic acid（FA）is an important component of natural organic matter and widely exists in water,soil,sediment and other environments.Microorganisms can use FA as an electron donor or electron shuttle to participate in the iron redox process,thus driving the geochemical cycle of arsenic.The environmental geochemical behavior of arsenic is closely related to its occurrence form,so it is extremely important to study the effect of FA on arsenic form and its migration and transformation.In this paper,the effect of FA on arsenic migration and transformation in high-arsenic soils was taken as the main line,and a variety of anaerobic microcosmic systems were constructed with the sterilized soil-FA-Shewanella oneidensis MR-1（MR-1）as the main body,and the differential mechanism of FA-mediated arsenic migration and transformation in soils with different arsenic concentrations was studied under MR-1induction.It provides scientific basis for the biogeochemical cycle of arsenic in soils with high geological background.The main conclusions are as follows:1.The results showed that the Fe/As concentrations in the FA group were all higher than those in the sterilized soil group under non-biological conditions,indicating that the redox functional groups of FA could significantly promote the release and reduction of Fe/As in soil.Under the influence of MR-1,FA can significantly promote the reduction of Fe/As in different concentrations of soil,but FA plays the role of electron shuttle or electron donor and has significant difference in the reduction efficiency of As in different concentrations of soil.In addition,in both biological and non-biological groups,Fe obtained electrons preferentially than Arsenic in culture time,indicating that FA acted on iron first to produce reduction reaction,and then produced Fe（II）mediated reduction of arsenic.2.The results of parallel factor showed that the overlying DOM in all groups had four same components: The C1 component is humus-like（reductive quinones）,the C2 component is humus-like（terrigenous）,the C3 component is humus-like（related to microbial activities）,and the C4 component is fulminate-like.DOM in overlying water is mainly reduced quinones（accounting for more than 30%）,and DOM significantly affects the migration and transformation of arsenic.3.The results of arsenic speciation ratio showed that S6 was an important state interchanging with other states in soils of different concentrations.The abiotic effects of FA on arsenic speciation are most obvious in low concentration soil,while the biological effects of FA on arsenic speciation are more obvious when FA acts as an electron shuttle.4.The simulation results of PLS model showed that the transformation paths of arsenic form in soils with three concentrations were obviously different.As incorporated in amorphous iron oxides（S4）in low concentration soil significantly affected the arsenic content in overlying water,and FA significantly promoted the mutual transformation between As coprecipitated with AVS,carbonates,Mn oxides,and very amorphous Fe oxyhydroxides（S3）and As coprecipitated in crystalline iron oxides（S5）under the drive of MR-1.FA in medium concentration soil significantly promoted the mutual transformation between Fe related forms（S3-5）and its transformation in overlying water.As oxides and arsenic coprecipitated with silicates As（S6）and S5 in high concentration soil are the key forms affecting arsenic in overlying water.The effect of FA driven by MR-1 makes the remaining states more easily fixed to S6 and inert states（S7-8）.5.Under MR-1 driving,FA mainly regulates the migration and transformation behavior of arsenic by affecting the adsorption and desorption of arsenic,the mutual transformation between iron forms and the transformation between S6 and other forms.In this process,Fe（II）in soil is an important driving factor,and p H also has a certain effect on arsenic morphology. |
