Nano-sized Fe_2O_3/Fe_3O_4 facilitate anaerobic transformation of hexavalent chromium in soil–water systems

The purpose of this study is to investigate the effects of nano-sized or submicro Fe_2O_3/Fe_3O_4 on the bioreduction of hexavalent chromium（Cr（VI）） and to evaluate the effects of nano-sized Fe_2O_3/Fe_3O_4 on the microbial communities from the anaerobic flooding soil.The results indicated that the net decreases upon Cr（VI） concentration from biotic soil samples amended with nano-sized Fe_2O_3（317.1 ± 2.1 mg/L） and Fe_3O_4（324.0 ± 22.2 mg/L） within21 days,which were approximately 2-fold of Cr（VI） concentration released from blank control assays（117.1 ± 5.6 mg/L）.Furthermore,the results of denaturing gradient gel electrophoresis（DGGE） and high-throughput sequencing indicated a greater variety of microbes within the microbial community in amendments with nano-sized Fe_2O_3/Fe_3O_4 than the control assays.Especially,Proteobacteria occupied a predominant status on the phylum level within the indigenous microbial communities from chromium-contaminated soils.Besides,some partial decrease of soluble Cr（VI） in abiotic nano-sized Fe_2O_3/Fe_3O_4 amendments was responsible for the adsorption of nano-sized Fe_2O_3/Fe_3O_4 to soluble Cr（VI）.Hence,the presence of nano-sized Fe_2O_3/Fe_3O_4 could largely facilitate the mobilization and biotransformation of Cr（VI） from flooding soils by adsorption and bio-mediated processes.