Toxicity assessments of nanoscale zerovalent iron and its oxidation products in medaka (Oryzias latipes) fish

Iron-based nanotechnologies are increasingly used for environmental remediation; however, toxicologic impacts of iron nanoparticles on the aquatic ecosystem remain poorly understood. We treated larvae of medaka fish (Oryzias latipes) with thoroughly characterized solutions containing carboxymethyl cellulose (CMC)-stabilized nanoscale zerovalent iron (nZVI), aged nanoscale iron oxides (nFe-oxides) or ferrous ion (Fe[II]) for 12-14 days' aqueous exposure to assess the causal toxic effect(s) of iron NPs on the fish. With the CMC-nZVI solution, the dissolved oxygen level decreased, and a burst of reactive oxygen species (ROS) was generated as Fe(II) oxidized to ferric ion (Fe[III]); with the other two iron solutions, these parameters did not significantly change. CMC-nZVI and Fe(II) solutions caused acute lethally and sublethally toxic effects in medaka larvae, with nFe-oxide-containing solutions causing the least toxic effects. We discuss modes of toxic action of iron NPs and chronic toxic effects in terms of hypoxia, Fe(II) toxicity and ROS-mediated oxidative damage.