Once praised for its undeniable advantages, plastic no longer appears as “fantastic” as it once was. Since the first studies in the 1970s reported the presence of microscopic plastic particles in marine ecosystems, evidence has steadily accumulated, showing that this form of pollution is widespread. Microplastics have been detected in water, air, soil, food, beverages, human organs, and biological tissues. Nothing is spared in this regard.

“Microplastics are everywhere, and we must understand how they affect human health, without forgetting environmental health,” said Christian Laforsch, PhD, professor and chair of Animal Ecology I at the University of Bayreuth, Bayreuth, Germany, and spokesperson for the German Research Foundation Collaborative Research Center 1357 “Microplastics.”

“We also know that these microplastic particles break down into even smaller particles, such as nanoparticles or highly crystalline oligomers. As a result, we may have detected only the tip of the iceberg so far,” he added.

These issues were central to discussions at a scientific meeting organised by BelTox, the Belgian Society of Toxicology and Ecotoxicology, and the Belgian Environmental Mutagenesis Society (BEMS). Experts have highlighted major challenges related to definitions, detection methods, and risk assessment.

A Definition Problem

Assessing the toxicity of synthetic plastic particles remains complex, beginning with the definition of microplastics themselves. They are generally described as plastic particles smaller than 5 mm. However, experts at the BelTox and BEMS meetings agreed that this definition is insufficient from a toxicologic perspective.

“From a toxicological point of view, there is a major difference between the mode of action of a 5 mm particle and that of a 5 µm particle,” said Todd Gouin, PhD, Environmental Fate and Exposure Modelling specialist at TG Environmental Research, Sharnbrook, England.

“The former may pose a choking risk, whereas the latter can be absorbed by the body and affect internal organs. The current definition does not adequately reflect this difference in scale,” he said.

Differences in size are not the only challenges faced by researchers and toxicologists. “Microplastics differ not only in size but also in shape,” said Nelly Saenen, PhD, assistant professor at Hasselt University, Hasselt, Belgium, and secretary of the BEMS.

“Their composition can vary, as can the additives used during manufacturing, such as plasticisers."

Even particles that appear to be identical may behave differently. Laforsch described a study analysing polystyrene beads from eight different manufacturers.

“In principle, they were all made from the same polymer, had the same diameter, and the same shape. However, their physicochemical properties differ considerably depending on the manufacturer,” he said.

Detection Challenges

Another major obstacle is the lack of standardised detection and characterisation methods.

“The foundations are there, but they need to be optimised,” said Erik Van Miert, PhD, senior toxicologist or risk assessor at dsm-firmenich in Brussels and secretary of BelTox.

“We still lack a standard detection method, which makes comparisons between studies very difficult,” said Gouin.

“We often end up comparing apples and oranges, so caution is needed when interpreting the data.”

“Each laboratory has developed its own sample pretreatment protocols, which directly influence the identification and characterisation of particles,” said Milica Velimirovic, PhD, senior researcher at the Flemish Institute for Technological Research in Belgium.

“We are still facing many analytical challenges, but progress is being made,” Velimirovic said.

“The technology is evolving, and we are beginning to have tools that allow us to go further, faster, and with greater precision in microplastic analysis.”

These analytical difficulties are compounded by the substantial risk for contamination.

“Microplastics are ubiquitous. They can contaminate samples during collection and processing,” Laforsch said. His laboratory has been specifically designed to address this issue.

“The air entering the room must be filtered, and the room must be kept under positive pressure to prevent dust from entering. All water entering the room must be prefiltered. We also need to avoid plastic laboratory equipment, which is a real challenge,” he acknowledged.

Biological Effects

Despite these limitations, the risks associated with microplastic pollution are undeniable.

“Even if results are sometimes contradictory, we can confirm that a risk exists,” said Caroline De Tender, PhD, associate professor in the Department of Biochemistry and Microbiology, Ghent University, Ghent, Belgium, who specialises in soil microbiota and plant interactions.

“Effects have been observed on plant growth and germination, as well as on soil microbial communities. The problem is that we often still do not know the magnitude of that risk,” she said.

The absorption of microplastics and nanoplastics has also been demonstrated in invertebrates, aquatic food webs, and other living organisms, raising concerns about contamination and potential human exposure.

“Effects such as oxidative stress, inflammatory responses, and metabolic disturbances have been reported,” Gouin stated.

Laforsch and colleagues examined microplastic contamination in bivalve molluscs, a seafood group widely consumed in Belgium, to better characterise potential dietary exposure in the general population.

“We analysed mussels sold in supermarkets, whether frozen, preserved in oil, or in tomato sauce, and found between 10-250 microplastic particles/100 g of muscle tissue,” he said.

Although these particles appear to be eliminated through natural pathways, the same does not apply to the associated monomers and chemical substances. According to Laforsch, these compounds adversely affect the gut microbiome.

More concerning is the formation of a layer of natural organic and biological molecules, known as an eco-corona, spontaneously on the surface of plastic particles. The translocation of such microplastics from the intestine to other tissues has been observed, suggesting that they may more readily enter body cells.

Risk Management

Van Miert argued that risk assessment alone is insufficient.

“It is unrealistic to think that society can completely eliminate plastics,” he said.

“Research must also contribute to better risk management, including identifying polymers that pose the lowest risk to human health and the environment.”

Given the complexity of microplastic exposure, experts at the annual BelTox and BEMS meetings emphasised the need for interdisciplinary collaboration.

“Microplastic research involves physicists, chemists, materials engineers, and toxicologists,” said Saenen.

“An interdisciplinary approach is essential if we are to make progress.”

This story was translated from MediQuality, part of the Medscape Professional Network.