Phytotoxicity of VO₂ nanoparticles with different sizes to pea seedlings

Vanadium dioxide nanoparticles (VO₂ NPs) have been massively produced due to their excellent metal-insulator transition characteristics for various applications. Pilot studies indicated the toxicity of VO₂ NPs to bacteria and mammalian cells, but the environmental hazards of VO₂ NPs to plants have been unrevealed to date. In this study, we reported the inhibitive effects of VO₂ NPs to the growth and photosynthesis of pea seedlings. Laboratory synthesized monoclinic VO₂ NPs (N-VO₂), commercial nanosized VO₂ NPs (S-VO₂), and commercial microsized VO₂ particles (M-VO₂) were carefully characterized for environmental toxicity evaluations. VO₂ particles were supplemented to culture medium for seed germination and seedling growth. All three VO₂ samples did not affect the germination rates of pee seeds, while serious growth inhibition of pea seedlings was observed at 10 mg/L for S-VO₂ and N-VO₂, and 100 mg/L for M-VO₂. VO₂ particles had no impact on the chlorophyll contents, but the photosynthesis of leaf was significantly decreased following the consequence of N-VO₂ > S-VO₂ > M-VO₂. The inhibition of photosynthesis was attributed to the damage of acceptor side of photosystem II by VO₂ particles at high concentrations. Abundant bioaccumulations of vanadium in roots aroused oxidative damage and changed the root structure. Our results collectively indicated that the phytotoxicity of VO₂ NPs was related to the concentration, size and crystalline degree.