Microbial community characteristics of cadmium speciation transformation in soil after iron-based materials application

Although numerous studies on the stabilization of heavy metals in contaminated soil with iron-based materials have been conducted, the role of microorganisms in iron species and Cd speciation transformation has not been fully elucidated. Here, 2-line ferrihydrite (MGE) and goethite (GE) were prepared and used to stabilize Cd in contaminated soil. Based on the microbial community characteristics in the early, middle, and later stages, the role of microorganisms in Cd speciation transformation was explored. The exchangeable Cd decreased by 10.73 %–51.31 %, while the iron‑manganese oxide-bound speciation, and the residual speciation increased after MGE/GE application. The relative abundance of Proteobacteria, and Sphingomonas were obviously increased, and Trichoderma and Mortierella were decreased in the MGE group. The outcome in the GE group was the opposite. The complexity of the bacterial and fungal community network was increased in the MGE and GE groups. The lignin in MGE could stimulate the growth of iron-reducing bacteria (FeRB) and promote the reduction of iron minerals to Fe2+. The Fe2+ in the soil was oxidized and hydrolysed, which might lead to an increase in the soil pH. During the process of iron species transformation and iron redox mediated by FeRB, Cd was transformed to more stable speciation.