Phytotoxicity of ionic, micro- and nano-sized iron in three plant species

• Nanoremediation activities use nano-zerovalent iron (nZVI).
• Knowledge of nZVI effects on macrophytes are still scarce.
• Standard phytotoxicity tests (72 h exposure) showed no adverse effects of nZVI.
• Micro-sized iron showed no significantly different effects from nZVI.
• Apparent uptake of ZVI detected by microscopy.

Potential environmental impacts of engineered nanoparticles (ENPs) can be understood taking into consideration phytotoxicity. We reported on the effects of ionic (FeCl3), micro- and nano-sized zerovalent iron (nZVI) about the development of three macrophytes: Lepidium sativum, Sinapis alba and Sorghum saccharatum. Four toxicity indicators (seed germination, seedling elongation, germination index and biomass) were assessed following exposure to each iron concentration interval: 1.29–1570 mg/L (FeCl3), 1.71–10.78 mg/L (micro-sized iron) and 4.81–33,560 mg/L (nano-iron). Exposure effects were also observed by optical and transmission electron microscopy. Results showed that no significant phytotoxicity effects could be detected for both micro- and nano-sized zerovalent irons, including field nanoremediation concentrations. Biostimulation effects such as an increased seedling length and biomass production were detected at the highest exposure concentrations. Ionic iron showed slight toxicity effects only at 1570 mg/L and, therefore, no median effect concentrations were determined. By microscopy, ENPs were not found in palisade cells or xylem. Apparently, aggregates of nZVI were found inside S. alba and S. saccharatum, although false positives during sample preparation cannot be excluded. Macroscopically, black spots and coatings were detected on roots of all species especially at the most concentrated treatments.