Nano Zero-Valent Iron Enhances the Mobilization and Absorption of Chromium in Rice (Oryza Sativa L.): Implication for Cr Risks Management in Paddy Fields

Abstract

Chromium (Cr) accumulating in soil caused serious pollution to cultivated land. At present, nano zero-valent iron (nZVI) is considered to be a promising remediation material for Cr-contaminated soil. However, the impact on the behavior of Cr in the soil-rice system under high natural geological background value remains unknown. We studied the effects of nZVI on the migration and transformation of Cr in paddy soil-rice by pot experiment. Three different doses of nZVI (0, 0.001% and 0.1% (w/w)) treatments and one dose of 0.1% (w/w) nZVI treatment without plant rice were set up. Under continuous flooding conditions, nZVI significantly increased rice biomass compared with the control. At the same time, nZVI significantly promoted the reduction of Fe in the soil, increased the concentration of dissolved Fe and bioavailable Cr, then facilitated the absorption of Cr in rice roots and the transportation to the aboveground part. In addition, the enrichment of Fe(III)-reducing bacteria and sulfate-reducing bacteria in soil provided electron donors for Cr oxidation, which helps to form bioavailable Cr that is easily absorbed by plants. There is an unexpected environmental risk associated with nZVI application to the high geological background contaminated paddy soil, and one should be aware this risk when applying nZVI aiming to minimize human Cr exposure health risks via rice consumption.

Keywords: Chromium, Paddy soil, Bioavailability, Nano zero-valent iron