Effectiveness and limitation of A-nZVI for restoration of a highly As-contaminated soil

Abstract To restore highly degraded soil with severe arsenic (As) contamination, effective mitigation of As mobility and bioavailability is considered as the primary step. In this study, the capability of an air-stabilized nano zero-valent iron (A-nZVI) to decrease soil As solubility and leachability was investigated. Further, the effect of A-nZVI on recovery of soil biological function was analyzed by measuring changes in dehydrogenase activity, bacterial community and development of two pioneering plant species. Results showed that A-nZVI exhibited a prominent sorption capacity for both arsenite and arsenate (92.4 and 44.1 mg g-1). With A-nZVI application at ≥0.2%, 44.2–74.7% decline in soil As solubility was achieved in neutral water extraction, while consistently higher As extractability was determined with synthetic precipitation leaching procedure (SPLP, pH 4.2). Compared to adjacent forest soil (F-CK), microbial community of the tested soil was featured by 66% lower abundance of Actinobacteria while an elevated richness of Gemmatimonadetes, both of which showed apparent shift toward F-CK with A-nZVI. 0.2% A-nZVI was most effective in promoting dehydrogenase activity and ryegrass growth. Further, by two-dimensional mapping with the Zr-oxide diffusive gradients in thin films (DGT), averaged DGT-As in rhizosphere of alfalfa (a green manure species) decreased by 47.1% with 0.2% A-nZVI. These results highlight that A-nZVI is critically essential for fixation of soil labile As and thus provides a favorable starting point for recovery of soil health.