Uptake of metallic nanoparticles containing essential (Cu, Zn and Fe) and non-essential (Ag, Ce and Ti) elements by crops: A meta-analysis

The specific properties of nanoparticles can induce toxic or promoting effects on plant growth. We performed a meta-analysis of 173 studies to evaluate the uptake and accumulation of metallic nanoparticles (MNPs) by crops. Studies on the main cereal/vegetable crops (wheat, tomato, bean, maize, rice and cucumber) and Ag, Zn, Ce, Fe, Cu and Ti containing MNPs were mostly found; 63% of the studies used MNPs with size <30 nm, and root application accounted for 84% of all studies. Under root exposure, metal concentrations were reduced by up to 2 orders of magnitude from root through shoot to leaf. Moreover, the uptake preference of MNPs or dissolved metals was element-specific and varied among tissues. Plants accumulated generally higher concentrations of the three essential elements (Cu, Zn and Fe) than of the non-essential ones (Ag, Ce and Ti). Also, foliar application was more efficient than root exposure. Metal concentrations in shoots increased with decreasing particle size for non-essential elements, but showed a variable increase for essential elements as size decreased. Besides, the uptake of MNPs increased with more negative zeta potential (especially for Cu and Zn). Overall, the plant essential elements (Cu, Zn and Fe) were preferred taken up as MNPs, while for non-essential elements (Ag and Ce) uptake as dissolved metals was more common. We conclude that for plant nanofertilizers, foliar application of essential elements as small MNPs might be more efficient for crop uptake than the uptake of dissolved metals.HighlightsUptake of essential elements was significantly higher than that of non-essential elements.Metal accumulations increased with smaller particle size and more negative zeta potential.Non-essential elements (Ag and Ce) are acquired preferably as dissolved metals.Essential elements (Cu, Zn and Fe) are preferably taken up as nanoparticles.