Quantitative evaluation of multi-walled carbon nanotube uptake in wheat and rapeseed

Highlights: ► Wheat and rapeseed accumulate MWCNT through root exposure, and translocate them to their leaves. ► Transfer factor of MWCNT from hydroponic solution to leaves never exceeds 0.005‰. ► MWCNT majorly accumulate in the most peripheral areas and in newly developed leaves. ► Accumulation of less than 200 ng MWCNT per g of leaf does not impact plant development and physiology. - Abstract: Environmental contamination with carbon nanotubes would lead to plant exposure and particularly exposure of agricultural crops. The only quantitative exposure data available to date which can be used for risk assessment comes from computer modeling. The aim of this study was to provide quantitative data relative to multi-walled carbon nanotube (MWCNT) uptake and distribution in agricultural crops, and to correlate accumulation data with impact on plant development and physiology. Roots of wheat and rapeseed were exposed in hydroponics to uniformly 14C-radiolabeled MWCNTs. Radioimaging, transmission electron microscopy and raman spectroscopy were used to identify CNT distribution. Radioactivity counting made it possible absolute quantification of CNT accumulation in plant leaves. Impact of CNTs on seed germination, root elongation, plant biomass, evapotranspiration, chlorophyll, thiobarbituric acid reactive species and H2O2 contents was evaluated. We demonstrate that less than 0.005‰ of the applied MWCNT dose is taken up by plant roots and translocated to the leaves. This accumulation does not impact plant development and physiology. In addition, it does not induce any modifications in photosynthetic activity nor cause oxidative stress in plant leaves. Our results suggest that if environmental contamination occurs and MWCNTs are in the same physico-chemical state than the ones used in the present article, MWCNT transfer to the food chain via food crops would be very low.