ZnO Nanoparticle Size-Dependent Effects on Swiss Chard Growth and Nutritional Quality

Understanding the interactions between nanoparticles (NPs) and plants is crucial in comprehending the impact of nanotechnology on agriculture, with a focus on plant toxicity concerns and risks to human health. Zinc (Zn) belongs to the micronutrients with poor bioavailability, though this element is essential for the vital functions of plants. In this respect, this research estimated the impact of the size of zinc oxide NPs (ZnO NPs) applied by foliar application on biomass production and nutritional qualities in baby leaf Swiss chard ( Beta vulgaris ssp. cicla L. cv. Barese). Plants were grown hydroponically in controlled environment growth chambers, and exposed via foliar spray to varying particle sizes of ZnO NPs (18, 35–45, and 80–200 nm) at a concentration of 200 ppm. Control plants were sprayed with distilled water. The results revealed that ZnO NPs improved fresh and dry biomass, leaf area, favored leaf chlorophyll and flavonol indexes, and improved the total soluble protein content in Swiss chard. The total phenolic content and antioxidant properties depended more on different sizes of ZnO NPs in the solutions used for spraying plants. ZnO NPs significantly increased the accumulation of Zn and Fe in edible tissues. Still, the hazard quotient values of Zn and Fe were lower than 1, which supports the safe consumption of Swiss chard after ZnO NP treatment. In conclusion, these results revealed that ZnO NPs could be applied in Swiss chard production to improve yield, quality, and nutraceutical properties.