The effects of co-exposures of Zea mays plant to the photon-upconversion nanoparticles; does the size or composition play an important role?

Abstract

This work thoroughly describes how three different types of photon-upconversion nanoparticles (UCNPs) that differ in size or composition influence a model plant Zea mays. This plant was treated with an aqueous dispersion of nanoparticles in a hydroponic short-term toxicity test (168 h) in three different concentrations (0.5, 5, and 25 μg/mL of yttrium). The plants were exposed in a single toxicity test as well as in so-called co-exposures where the plants were in direct contact with the nanoparticles of different sizes (hydrodynamic diameter 25.9 nm and 58.2 nm) or with different compositions (doped with gadolinium and thulium or with erbium ions) at the same time. After the exposure, basic macroscopic toxicity end-points were monitored. The translocation of nanoparticles across the whole plant was evaluated by Laser-Induced Breakdown Spectroscopy (lateral resolution of 26 and 100 μm) and by photon-upconversion microscanning (lateral resolution of 40 μm). Also, the total content of elements contained in plants was measured for the underground (root and coleoptile) and above-ground (primary leaf) parts separately using Inductively-Coupled Plasma Optical Emission Spectroscopy. Afterwards, bioaccumulation and translocation factors were evaluated. Our results indicated significant toxicity of all tested exposures groups for Z. mays plant. The main bioaccumulation site was the underground part, whereas the transfer to the above-ground part was minimal. Also, the UCNPs showed a low stability and led to a notable release of ions.