22 November 2023

Tomography helps detect microplastics in soil

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A German research team has developed a new method for detecting microplastics. The technique employs neutron beams and X-rays to generate a complete image

by Matteo Cavallito

 

Microplastics are a dangerous and widespread pollutant to the environment at present, with claimed damage to soil, the ecosystem and human health. But what happens to these particles in different soils? How are they transported once broken into smaller pieces, changing soil structures? A study from the University of Potsdam, Germany, tries to answer these questions.

The research, published in the journal Science of The Total Environment, specifically proposes a new method of investigation based on tomography using X-rays and neutron beams that, according to the authors, would overcome some of the problems associated with traditional systems.

A new method

“Increasingly, environmental research efforts seek to understand how the continuous input of microplastics into terrestrial environments alters soil physicochemical properties and affects plants and other soil biota,” the study states. “However, fundamental understanding is hampered by the destructive nature of current analytical techniques, which typically require the disruption of soil samples and often the removal of soil organic matter.”

All of this, however, results in the loss of essential information about soil microstructure and the spatial distribution of microplastic particles.

The group of scientists, led by Sascha Oswald and Christian Tötzke, professor and researcher respectively at the University of Potsdam, set up a unique instrument at the Institut Laue-Langevin in Grenoble. Here, points out a statement from the Helmholtz-Zentrum for the Study of Materials and Energy in Berlin, one of the institutions involved in the research, “samples can be analysed with neutrons and X-rays to create 3D tomographies simultaneously, i.e. without altering the sample. While neutrons visualise organic and synthetic particles, X-ray tomography shows the mineral particles and the structure they form.”

Nei tomogrammi neutronici le microplastiche sono chiaramente identificate. La tomografia a raggi X, invece fornisce una visione della disposizione dei grani di sabbia. Una volta sovrapposte, le diverse immagini forniscono una descrizione del campione di terreno. Foto: Christian Tötzke et al., "Non-invasive 3D analysis of microplastic particles in sandy soil — Exploring feasible options and capabilities", Science of The Total Environment Volume 907, 10 January 2024, 167927 CC BY 4.0 DEED Attribution 4.0 International https://www.sciencedirect.com/science/article/pii/S0048969723065543?via%3Dihub

In neutron tomograms, microplastics are clearly identified. X-ray tomography, on the other hand, provides a view of the arrangement of sand grains. When superimposed, the different images provide a description of the soil sample. Photo: Christian Tötzke et al., “Non-invasive 3D analysis of microplastic particles in sandy soil — Exploring feasible options and capabilities“, Science of The Total Environment Volume 907, 10 January 2024, 167927 CC BY 4.0 DEED Attribution 4.0 International

Two images superimposed

To test the method, Tötzke prepared a series of soil samples with sand, organic components such as peat or charcoal, and artificial microplastic particles. In neutron tomograms, the statement says, microplastics are clearly identified, as are some of the organic components. X-ray tomography, on the other hand, provides a view of the arrangement of the sand grains, while the organic and plastic particles are shown as diffuse voids. When superimposed, the two images provide a complete picture of the soil sample.

All this allows scientists to estimate the size and shape of the microplastic particles, as well as the changes to the soil structure caused by their incorporation.

The scientists also analyzed sandy soil from a field near Beelitz, near Berlin, by mixing pieces of a mulch film. That is, the classic plastic sheeting used to protect crops whose degradation generates soil contamination. “We were able to show that fragments of such films can change the water flow in the soil. Microplastic fibres, on the other hand, created small cracks in the soil matrix,” Tötzke explained.

Stima delle quantità annue di plastica utilizzata nei terreni agricoli mondiali divise per tipologie di prodotto. FONTE: Assessment of Agricultural plastics and their sustainability. FAO, 2021

Estimated annual amounts of plastics used in global agricultural lands divided by product type. SOURCE: Assessment of Agricultural plastics and their sustainability. FAO, 2021

Agriculture and microplastics

The problem of microplastic pollution is obviously linked to the continued widespread use of non-biodegradable synthetic materials in agriculture. Two years ago report by FAO showed that agricultural supply chains use 12.5 million tons of plastic products each year. Another 37.3 million tons are used in food packaging. The largest users are the various segments of agricultural production and livestock farming, with 10.2 million tons per year combined. This is followed by fisheries and aquaculture with 2.1 million tons and forestry with 200 thousand tons.

The U.N. agency’s study, of course, also pointed to the problem of managing worn-out sheets. The volume of which, in Europe alone, amounts to 15 thousand tons annually. This is also why the FAO itself has officially recommended the replacement of synthetic mulching films with biodegradable and compostable ones. Whose usefulness, by the way, was formally recognized by the European Parliament already in October 2017.