Bioavailability of Nanomaterials to Plants: Importance of Particle Size and Surface Coating.

We used the model organisms Nicotiana tabacum L. cv Xanthi (tobacco) and Triticum aestivum (wheat) to investigate plant uptake of 10, 30 and 50 nm diameter Au manufactured nanomaterials (MNMs) coated with either tannate (T-MNMs) or citrate (C-MNMs).  Nanomaterial size and surface charge were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), and electrophoretic mobility measurements.  Plants were exposed to NPs hydroponically for 3 or 7 days for wheat and tobacco, respectively.  Volume averaged Au concentrations were determined using inductively coupled plasma mass spectrometry (ICP-MS).   Spatial distribution of Au in tissue samples was determined using laser ablation ICP-MS (LA-ICP-MS) and scanning x-ray fluorescence microscopy (µXRF).  Both C-MNMs and T-MNMs of each size treatment bioaccumulated in tobacco, but no bioaccumulation of any treatment was observed in wheat.  These results indicate that MNMs of a wide range of sizes and with different surface chemistries are bioavailable to plants and raise questions about the importance of plant species to MNM bioaccumulation.