S C

IE N

T IF

IC H

IG H

LI G

H T

S X

-R A

Y N

A N

O P

R O

B E

8 7 I H I G H L I G H T S 2 0 2 2

Tracking low-level toxicity of nanoplastics in crop plants

X-ray mapping and tomography and infrared spectroscopy techniques were used to track nanoplastics in wheat plants. The study showed that the nanoplastics were absorbed in the roots and transferred in leaves. The results could help us to understand the fate and impact of plastic pollution on living organisms.

Plastic pollution is a major threat for ecosystems and human health. It affects not only aquatic systems and oceans but also agricultural soils, which are particularly affected due to the use of plastic films for mulching and the reuse of sewage sludge as fertiliser. Plastics can be present at the macroscale, microscale or at the nanoscale, the latter originating from release of consumer products such as cosmetics and from weathering of larger plastics through physical, chemical or biological processes.

Nanoplastics could have potential impacts on organisms as they behave differently than microplastics. The behaviour of nanoplastics in the environment, and their impact and possible transfer in living organisms is poorly known. Indeed, nanoplastics are extremely challenging to detect in complex environmental matrices and in living organisms because of their small size and chemical composition (they are made of light elements only).

In this study, scientists used an original combination of infrared (IR)- and X-ray-based techniques to study the fate and impacts of nanoplastics in a model crop plant, wheat. To overcome the difficulty of detecting the nanopolymers, they used nanoplastics with a palladium-doped core, the palladium acting as a tracer. Wheat plants were grown for four weeks in a nutrient solution with and without nanoplastics. This is a first step before studying more realistic systems such as soils.

Chemical analyses evidenced the uptake of nanoplastics by the roots and their translocation in shoots. Using scanning electron microscopy (SEM) on the wheat roots, the researchers showed an agglomeration of nanoplastics on the root surface, associated with filaments produced by roots and/or associated bacteria (Figure 78). Elemental mapping by micro-X-ray fluorescence (µXRF) carried out at beamline ID21 confirmed the presence of nanoplastics on the root surface, and also inside the roots (Figure 79). With nano-CT performed at beamline ID16B, it was not possible to distinguish nanoplastics from nanostructures also present in the control, corresponding to polyphosphate granules, small vesicles, etc. These results bring into question the validity of some of the previously published data regarding the detection of nanoplastics in plant tissues using transmission electron microscopy (TEM).

Classical markers of phytotoxicity were marginally affected by the exposure to nanoplastics. Finer markers

PRINCIPAL PUBLICATION AND AUTHORS

Elementary growth mechanisms of creep cavities in AZ31 alloy revealed by in situ X-ray nano- tomography, R. Kumar (a,b), P. Lhuissier (b), J. Villanova (a), L. Salvo (b), J.J. Blandin (b), Acta Mater. 225, 1177760 (2022); https:/doi.org/10.1016/j.actamat.2022.117760 (a) ESRF (b) Univ. Grenoble Alpes, CNRS, Grenoble INP, SIMAP, Grenoble (France)

REFERENCES

[1] M.E. Kassner & T.A. Hayes, Int. J. Plast. 19, 1715-1748 (2003). [2] T.G. Langdon, Mater. Sci. Eng. A 137, 1-11 (1991). [3] R. Lapovok, Y. Estrin in C. Bettles, M. Barnett (Eds.), Adv. Wrought Magnes. Alloy., Woodhead Publishing, 144-185 (2012).

five evolution types emerged (Figure 77), and it was seen that one cavity generally grew by a combination of several evolution types (for example, in Figure 76, the cavity shown grew by three different evolution types, indicated by different symbols). Individual evolution types were further linked to plausible growth mechanisms and compared with appropriate models. This indicated a combination of diffusion and grain boundary sliding to be the primary growth mechanism responsible for creep cavity growth in the tested conditions.

While grain boundaries are not directly resolved with X-ray tomography, in a very specific case, indirect evidence for grain boundary sliding was spotted near a cavity, thanks to the observed motion of intermetallics in the observed direction (green intermetallics in Figure 76a). In addition to growth, a very unconventional phenomenon was observed, where several cavities showed a decrease in volume during deformation. This was attributed to sintering of cavities via diffusion due to reduced local stress.