Roles of nanoparticles in arsenic mobility and microbial community composition in arsenic-enriched soils

Environmental effects of nano remediation engineering of arsenic (As) pollution need to be considered. In this study, the roles of Fe₂O₃ and TiO₂ nanoparticles (NPs) on the microbial mediated As mobilization from As contaminated soil were investigated. The addition of Fe₂O₃ and TiO₂ NPs restrained As(V) release, and stimulated As(III) release. As(V) concentration decreased by 94% and 93% after Fe₂O₃ addition, and decreased by 89% and 45% after TiO₂ addition compared to the Biotic and Biotic+Acetate (amended with sodium acetate) controls, respectively. The maximum values of As(III) were 20.5 and 27.1 µg/L at 48 d after Fe₂O₃ and TiO₂ NPs addition, respectively, and were higher than that in Biotic+Acetate control (12.9 µg/L). The released As co-precipitated with Fe in soils in the presence of Fe₂O₃ NPs, but adsorbed on TiO₂ NPs in the presence of TiO₂ NPs. Moreover, the addition of NPs amended with sodium acetate as the electron donor clearly promoted As(V) reduction induced by microbes. The NPs addition changed the relative abundance of soil bacterial community, while Proteobacteria (42.8%-70.4%), Planctomycetes (2.6%-14.3%), and Firmicutes (3.5%-25.4%) were the dominant microorganisms in soils. Several potential As/Fe reducing bacteria were related to Pseudomonas, Geobacter, Desulfuromonas, and Thiobacillus. The addition of Fe₂O₃ and TiO₂ NPs induced to the decrease of arrA gene. The results indicated that the addition of NPs had a negative impact on soil microbial population in a long term. The findings offer a relatively comprehensive assessment of Fe₂O₃ and TiO₂ NPs effects on As mobilization and soil bacterial communities.