Polymer coating and microbial community shift regulate nano zero-valent iron aging in soils. Polymer coating and microbial community shift regulate nano zero-valent iron aging in soils

Nano zero-valent iron (nZVI) has great potential for remediating metal(loid)-contaminated soils, but its aging in the soil ecosystem associated with microbial community shift is unclear. In this study, three types of nZVI particles [bare nZVI, nZVI coated with carboxymethyl cellulose (CMC), or polyacrylic acid (PAA)] were incubated in a soil matrix with different microbial compositions (realized by γ-radiation), and their aging was investigated using complementary microspectroscopic analyses. In addition, possible soil microbial communities involvement with nZVI transformation was addressed by employing next-generation sequencing. The results revealed drastic morphological change of the nZVI, which was transformed mainly into magnetite with rough morphology. CMC coating decreased nZVI aging, whereas PAA coating accelerated it and facilitated goethite and lepidocrocite formation. Soil microbial community change in response to γ-radiation slowed down nZVI oxidation (especially for PAA-nZVI). In return, nZVI presence and aging altered soil microbial communities. Iron-reducing/oxidizing bacteria (Bacillus, Shewanella, and Sediminibacterium) and fungal strains with capacity for siderophore production may participate in nZVI transformation. This study revealed nZVI particles aging in the soil ecosystem and their interactions with the soil microbial community, and thus, provides important information for the assessment of nZVI use in soil remediation.