Transport of Zn in a sandy loam soil treated with ZnO NPs and uptake by corn plants: Electron microprobe and confocal microscopy studies
The manufacture and multiple uses of zinc oxide (ZnO) nanoparticles (NPs) will represent a possible source of soil contamination. Little is known about how these NPs transport in soil and plants. In this research, the transport of Zn/ZnO NPs in sandy loam soil and the uptake by corn plants (Zea mays) was investigated. Results showed that ZnO NPs exhibit low mobility in a soil column at various ionic strengths. Elution curves suggest that some of the adsorbed ZnO NPs/Zn were released in the presence of chemical perturbations. The breakthrough of released Zn coincided with Fe and Al (indicator of soil colloids) suggesting that soil colloids may act as carriers of strongly adsorbed NPs. By using electron microprobe, Zn/ZnO NPs aggregates were visualized associate with soil clay minerals. The uptake (mg/kg) of Zn by one-month old corn plants varied from 69 to 409 in roots and from 100 to 350 in shoots, respectively, in soils contaminated with different concentrations of ZnO NPs (from 100 to 800 mg NPs/kg soil). Confocal microscope images showed that ZnO NPs aggregates penetrated the root epidermis and cortex through the apoplastic pathway; however, the presence of some NP aggregates in xylem vessels suggests that the aggregates passed the endodermis through the symplastic pathway.