Wheat plants absorb nanoplastics but they put up a fight

Plastic pollution in ecosystems and human health is a major societal concern. Plastic debris is made of polymer and additives which evolve through time.

Plastics can be present at the macroscale, microscale or at the nanoscale, the latter being formed by natural erosion of larger plastics through physical, chemical or biological processes or added to products like cosmetics, for example. Nanoplastics could have potential impacts on organisms as they behave differently than microplastics. Hence, the scientific community is trying to track these in different environments in order to get a clear picture of how nanoplastics may affect organisms.

However, nanoplastics are extremely difficult to study because of their small size and composition. Today, characterization techniques are limited. An international team of scientists from IMIDRA (Madrid), ETH (Zurich), Xploraytion (Berlin) and IsTerre and ESRF (Grenoble) has now used innovative imaging techniques to study these polymers in a non-destructive way on the beamlines. “Studying nanoplastics in plants using these techniques is a first step to be able to study what happens in real life”, explains Ana Pradas del Real, corresponding author of the publication and visiting scientist at the ESRF. “We have added palladium atoms to the nanoplastics, as they are easily detected using synchrotron techniques”, explains Pradas del Real.

The team grew some plants in a water solution with nutrients and the nanoplastics with palladium during four weeks. They then studied the plants’ roots on ID21, ID19 and ID16B at the ESRF using X-ray fluorescence, infrared spectroscopy and X-ray computed tomography. They found that the thickness of the cell wall of the root had increased considerably: “We think that the plant developed a ‘thicker skin’ as a mechanism of defense, as if it was trying to create a barrier so that the nanoplastics couldn’t go through”, says Hiram Castillo Michel, scientist at ID21 and co-author of the study.

Despite the plants’ strategy, the nanoplastics managed to penetrate inside the root. Further experiments carried out at ETH Zürich confirmed that the stem of the plant also contained nanoplastics. “These results lead us to think that nanoparticles ultimately may end in the grain of the plant, and so we may eat them”, explains Castillo Michel.  

In parallel to these experiments, the team carried out further investigations to confirm that the association of nanoplastics and palladium is very stable.

“This work sheds light on a reality that is present all around us and, unfortunately, it also affects food crops like wheat, which is a staple worldwide”, adds Pradas del Real. “It is worth noting that we still don’t know the impact of nanoparticles in human health because it is very complex to study”, she adds.

“Our next step will be to grow plants on soil and to try to detect the amount of plastic in the grains, which we hope to do with the array of techniques that we now have available”, concludes Pradas Real.

Reference:

A.E. Pradas del Real, Journal of Hazardous Materials, Volume 430, 15 May 2022, 128356. https://doi.org/10.1016/j.jhazmat.2022.128356

Text by Montserrat Capellas Espuny

Top image: Virtual slice done with X-ray tomography of a cross-section of a root from a wheat plant that has been grown with nanoplastics surrounding it. The red coloured regions correspond to higher density cell walls in response to nanoplastic exposure. Credits: B. Hesse