Biogeochemical reductive release of soil embedded arsenate around a crater area (Guandu) in northern Taiwan using X-ray absorption near-edge spectroscopy

This study investigates biogeochemical reductive release of arsenate from beudantite into solution in a crater area in northern Taiwan,using a combination of X-ray absorption near-edge structure （XANES） and atomic absorption spectrometry.Total arsenic （As） concentrations in the soil were more than 200 mg/kg.Over four months of laboratory experiments,less than 0.8% As was released into solution after reduction experiments.The 71% to 83% As was chemically reduced into arsenite （As（III）） and partially weathering into the soluble phase.The kinetic dissolution and re-precipitation of As,Fe,Pb and sulfate in this area of paddy soils merits further study.

Microbial reduction and migration of As/Fe mediated by electron shuttle:Differences between incorporated and adsorbed As(V)

Metal-reducing bacteria play a central and important role in the biogeochemical cycle of arsenic(As)and iron(Fe).Research on As/Fe migration from arsenic-containing iron minerals mediated by electronic shuttles is of significance to groundwater protection and human health.Further,the redox activity and bioavailability of goethite with differing occurrence and distribution of arsenic have not been studied clearly.In this study,the function of electron shuttle AQDS in Fe(III)bioreduction was determined.It was found that acidic conditions were conducive to the growth and reproduction of strain D2201,which was beneficial to the reduction of As(V)/Fe(III).The OD600nm value of the bacteria at pH 6 exceeded twice that at pH 8.Then,three types of goethite,namely pure goethite(Gt),coprecipitated As(V)-goethite(Gt-As),and adsorbed arsenic-goethite(Gt*As),were compared for microbial reduction reactivity.X-ray photoelectron spectroscopy analysis illustrated the proportion of OH-content in Gt-As was much lower than that of Gt and Gt*As,indicating Gt-As carried more surface defects and had higher bioavailability.The Fe(II)content released from AQDS-mediated bioreduction of Gt-As was two-fold higher than that of Gt and Gt*As at pH 7.In addition,pH significantly affected goethite bioreduction efficiency and arsenic migration degree.The dissolved Fe(II)concentration for Gt-As was 0.98,0.133,and 0.139 mM at pH 6,7,and 8,respectively;corresponding to dissolved As(T)content of 3.51,1.48,and 1.31μM within 9 days of culture.This study highlights the significant influence of AQDS and mineral structure on the As/Fe biochemical cycle,which will help further develop the bioremediation of arsenic-contaminated sediments.