Can Diffusive Gradients in Thin Films (DGT) Technique and Chemical Extraction Methods Successfully Predict both Zn Bioaccumulation Patterns in Plant and Leaching to Groundwater in Soils Amended with Engineered ZnO Nanoparticles?

The interactions of nanoparticles (NPs) with different soil components have impact on their fate, transport, and behavior. The present study was conducted to find operational extraction procedures for effective assessment of both plant availability and leaching to groundwater of Zn applied to soils from zinc oxide (ZnO) NPs. A greenhouse experiment was performed in lysimeters with different ZnO-NPs amounts (3, 20, and 225 mg Zn kg −1 ) in two typical soils in Central Spain. The experiment was carried out spanning the whole plant life-cycle of cherry tomato and common bean. The soil extractable Zn amounts were measured using chemical extraction procedures (the rhizosphere-based low-molecular-weight organic acids—LMWOAs—, CaCl 2 , DTPA-TEA, water-soluble—WS—, and NH 4 Ac) and the diffuse gradients in thin films (DGT) technique. The regression studies between extractable Zn concentrations and Zn concentrations in plant tissues showed that LMWOAs, CaCl 2 , WS, and the DGT technique successfully predicted Zn concentrations in all the different parts of plants. The prediction capacity of the DTPA-TEA and NH 4 Ac approaches were strongly influenced by soil type and plant species. LMWOAs, CaCl 2 , WS, and the DGT technique were the most robust approaches for evaluation of Zn bioavailability from the soils treated with ZnO-NP. Although LMWOAs and WS reagents were also able to estimate the total quantities of Zn that were leached to groundwater, the correlation improved when soil type was included as a categorical variable. DTPA-TEA and NH 4 Ac were able to predict the Zn concentrations in the plant tissues only if soil type was considered as a categorical factor. Graphical Abstract