Nanoscale zero-valent iron (nZVI) technology is promising for treating the oxidizing pollutants. Understanding the potential risk of nZVI in solution is important for in situ remediation. In this work, the impacts of nZVI on the chemical properties of solution and microorganism were investigated to assess the risk of environmental exposure of nZVI. The effects of salinity (NaCl), pH and humic acid on the chemical stability of nZVI were studied, the concentrations of released toxic ions within 36 days were examined, and the toxicity of solution was evaluated based on the luminous bacteria-based toxicity test. The results indicated that nZVI was chemically stable as the total chromium concentration was below 0.05 mg/L all along and the maximum concentration of released total iron ion was 0.22 mg/L. The results of the toxicity test showed that the reaction products were non-toxic to microorganism even if they existed in solution for a long-term time. (C) 2012 Elsevier B.V. All rights reserved.