Effect of individual and combined exposure of Fe2O3 nanoparticles and oxytetracycline on their bioaccumulation by rice (Oryza sativa L.)

Purpose

It has been reported the bioaccumulation of γ-ferric oxide nanoparticles (Fe₂O₃ NPs) or oxytetracycline (OTC) in crops. However, there have been little references investigating their uptake and bioaccumulation in crops after the combined exposure. The present study focused on Fe₂O₃ NPs and OTC accumulation on root surface and in the tissues of rice (Oryza sativa L.) seedlings under combined exposure. And, the interactive influence mechanism was also discussed.

Materials and methods

Hydroponic experiments were conducted to investigate the Fe and OTC accumulation on root surface and in rice tissues under individual and combined exposure of Fe₂O₃ NPs and OTC. The dynamic change of particulate Fe, ionic Fe, and Fe plaque concentrations on root surface was determined under the influence of OTC from Fe₂O₃ NPs and Fe-EDTA exposure. Fe²⁺ from Fe-EDTA was selected in order to compare the Fe bioaccumulation from ionic Fe and nanoparticle Fe exposure. Hydrodynamic diameter and ζ-potential of Fe₂O₃ NPs in solution were investigated when OTC was present or not, and the changes of OTC concentrations were also determined during hydroponic culture. SEM, XRD, and TEM were used to analyze Fe₂O₃ NP distribution on root surface and inside root under the influence of OTC.

Results and discussion

OTC promoted surface-Fe and shoot-Fe accumulation in Fe₂O₃ NPs treatments, which was just an opposite result from Fe-EDTA treatments. Upon Fe₂O₃ NP exposure, Fe plaque was formed through the direct adsorption of NPs on the outside root surface and then incorporated into plaque as its crystalline components. OTC elevated notably surface-Fe accumulation mainly through increasing adsorption and precipitation of Fe₂O₃ NPs on the root surface due to low repulsive electrostatic interaction between NPs and the root surface after adding OTC. Fe₂O₃ NPs increased surface-OTC and root-OTC levels. Compared to Fe-EDTA, surface-Fe from NP treatments can hold strongly OTC due to Fe₂O₃ particle precipitated on root surface with high specific surface area. NPs reduced shoot-OTC under 25 mg L^?1 OTC, but not under 100 mg L^?1 OTC.

Conclusions

This study clearly demonstrates that Fe/OTC accumulation in rice was always in the order root surface > shoot > root, whether Fe₂O₃ NPs/OTC was individual or combined exposure. The combined exposure will increase their root surface distribution comparing with individual exposure, and Fe₂O₃ NPs increased also root-OTC levels, which could pose a potential risk to food safety in subsequent growth of rice.