The Effect Of Humic Acid On The Migration And Transformation Of Arsenic In Soil With High Arsenic Geological Background

As an important component of natural organic matter,humic acid is widely distributed in rivers,lakes and marine environments.It can act as an electron donor for microbial anaerobic respiration or as an electron shuttle between microbes and heavy metals.The oxidation-reduction process,in turn,has an important driving effect on the biogeochemical cycle of arsenic.The toxicity and bioavailability of arsenic are closely related to its form of occurrence.It is of great significance to carry out research on the transformation of arsenic and arsenic form by humic acid.This article focuses on the study of the influence of humic acid on the migration and transformation of arsenic in the soil with different arsenic concentration and high arsenic geological background,and constructs a multi-layer system based on MR-1(dissimilar iron reducing bacteria)-humic acid-high arsenic geological background soil.An anaerobic microcosmic culture system has carried out the research on the differential mechanism of humic acid-mediated arsenic migration and transformation under the action of microorganisms.It hopes to provide a theoretical basis for in-depth understanding of the environmental chemical behavior of humic acid-mediated iron and arsenic biogeochemical cycle,and to provide a scientific basis for the management and control of potential arsenic pollution risks in soils with high arsenic geological background.The main conclusions are as follows:1.The results showed that the maximμm reduction release of Fe(II)from the different types of soils were relatively close,while the maximμm reduction release of As(III)was significantly different.The maximμm reduction release of As(III)in soil C was 20.89 times that of soil A,respectively 7.8 times that of soil B.It shows that in the process of Fe(II)driven arsenic reduction and release,the total arsenic content is an important factor affecting the reduction and release of arsenic;2.In the soil biological groups with different arsenic concentrations,the Fe(II)and As(III)concentration of the overlying water in the humic acid system was significantly higher than that of the humic acid system,indicating that humic acid can significantly promote the effect of MR-1 on soil iron./Reductive release of arsenic.Among them,the effect of humic acid as an electron shuttle on the release and reduction of iron/arsenic is higher than that of its use as an electron donor,indicating that the electron shuttle characteristics of humic acid driven by microorganisms can play an important role in the reduction and release of soil Fe/As;3.The results of potential path analysis showed that humic acid in soils with different arsenic concentrations promoted the release of amorphous iron-aluminum oxide bound arsenic to overlying water when humic acid was used as an electron donor.It shows that humic acid as an electron donor can promote the reduction and dissolution of iron in amorphous iron-aluminum oxide by MR-1,thereby promoting the reduction and release of arsenic;when humic acid is used as an electron shuttle,it can promote the combination of crystalline iron-aluminum oxide The release of arsenic in the overlying water.It shows that when humic acid is used as an electronic shuttle,it has a stronger ability to reduce iron in crystalline iron-aluminum oxide,and promotes the release of arsenic by reducing and dissolving the crystalline iron-aluminum oxide;when humic acid is used as an electronic shuttle,it is different.The potential conversion pathways of arsenic in the soil with different arsenic concentrations are significantly different,but they all significantly promote the migration and transformation of stable arsenic to effective arsenic,thereby improving the bioavailability of arsenic and may increase the potential risk of arsenic.