Sulfate Reducing Bacteria Mediated Adsorption-Desorption Characteristics Of Diphenylarsinic Acid On Different Iron Minerals And Soils

Diphenylarsinic acid(DPAA)is one of the most important organoarsenic pollutants in the soil from the regions where residual chemical weapons were buried since World War(?).Due to its high toxicity,it seriously threats the natural environment and human health.Iron minerals in the soil play a key role in affecting the migration of DPAA in the environment.Changes in the speciation and composition of arsenic-bearing iron minerals caused by iron reduction could significantly affect the dynamic redistribution process of arsenic binding and releasing in the soil.Sulfate reducing bacteria(SRB)are active microorganisms in the soil,which can catalyze multiple redox reactions such as sulfate reduction and iron reduction in the soil.However,studies on the adsorption and desorption characteristics of DPAA on iron minerals and soil particles mediated by SRB are very limited.This study focused on the scientific issue of the coupling mechanism between sulfate and iron reduction and DPAA adsorption-desorption processes in the soil mediated by SRB.Modern spectroscopy and chromatography techniques such as fourier transform infrared spectroscopy and high performance liquid chromatography-tandem mass spectrometry were used to study the SRB mediated adsorption-desorption characteristics of DPAA on two kinds of iron minerals(ferrihydrite and hematite),as well as on two different types of soils(Acrisol and Phaeozem).The coupling mechanism of SRB mediated sulfate reduction,iron reduction and DPAA desorption and releasing was investigated.The main results of this study:The synthesized ferrihydrite samples were in reddish-brown spherical shape with the size ranges 20?100 nm as observed by scanning electronic microscopy.Some nano-scale ferrihydrite particles can aggregate into large particles and exist in the form of amorphous particle polymers.The purchased hematite is a spherical aggregate with a loose porous structure on the surface.The amount of DPAA adsorbed on ferrihydrite is significantly higher than that on hematite.For ferrihydrite,the inoculation of SRB could significantly reduce the adsorption of DPAA on ferrihydrite,while for hematite,it shows a trend of firstly decreasing and then increasing.The inoculation of SRB shows the characteristics of first inhibition and then promotion of DPAA desorption on ferrihydrite.While for hematite,DPAA desorption was significantly promoted at first and then gradually weakening with the addition of SRB.Inoculation of SRB could also lead to the pH increasing,Eh decreasing,as well as enhanced sulfate reduction and iron reduction in the aqueous solutions of ferrihydrite and hematite,which could further affect the adsorption and desorption of DPAA on iron minerals.The adsorption capacity of DPAA on Phaeozem was higher than that on Acrisol despite the inoculation of SRB or not.SRB inoculation could significantly reduce the adsorption potential of DPAA on both soils.Inoculation of SRB could also significantly reduce the desorption capacity of DPAA from Phaeozem,along with the increasing of pH,the reduction of Eh,the enhancement of sulfate reduction and iron reduction in the soil solution.The results of this study could provide theoretical basis and technical principles for the research and development of technologies for bioremediation of soils contaminated with organoarsenic pollutants in chemical weapons burial areas in China.