Quantifying the adsorption and uptake of CuO nanoparticles by wheat root based on chemical extractions

Extensive application of metal nanoparticles is attracting more attention because of their potential environmental risks. Many studies have focused on the uptake of metal nanoparticles (NPs) by plant, but the adsorption of nanoparticles on root surface is often mistakenly regarded as their uptake. This study optimized the methods to distinguish the adsorption and uptake of CuO-NPs on the wheat root by applying different metal competing ions (Na+, Mg2+, and La3+), surfactant (i.e., sodium dodecyl benzene sulfonate, SDBS), or complexing agents like NaOAc and Na4EDTA, as well as ultrasonic technique. The results indicated that some CuO-NPs is strongly adsorbed on the plant root surface, and part of them by mechanical adhesion. Competing ions could not desorb the CuO-NPs from the root surface, while NaOAc and Na4EDTA well dissolved the adsorbed CuO-NPs. In addition, the uptake and adsorption of CuO-NPs increased with increasing exposure concentrations of CuO-NPs in the range of 5-200 mg/L. The amount of CuO-NPs adsorption is always lower than that of their uptake.