Phytotoxicity, Translocation, and Biotransformation of NaYF ₄ Upconversion Nanoparticles in a Soybean Plant

The increasing uses of rare‐earth‐doped upconversion nanoparticles (UCNPs) have obviously caused many concerns about their potential toxicology on live organisms. In addition, the UCNPs can be released into the environment, then transported into edible crop plants, and finally entered into food chain. Here, the soybean is chosen as a model plant to study the subchronic phytotoxicity, translocation, and biotransformation of NaYF₄ UCNPs. The incubation with UCNPs at a relative low concentration of 10 μg mL⁻¹ leads to growth promotion for the roots and stems, while concentration exceeding 50 μg mL⁻¹ brings concentration‐dependent inhibition. Upconversion luminescence imaging and scanning electron microscope characterization show that the UCNPs can be absorbed by roots and parts of the adsorbed UCNPs are then transported through vessels to stems and leaves. The near‐edge X‐ray absorption fine structure spectra reveal that the adsorbed NaYF4 nanoparticles are relatively stable during a 10 d incubation. Energy‐dispersive X‐ray spectrum further indicates that a small amount of NaYF₄ is dissolved/digested and can transform into Y‐phosphate clusters in roots.