Concentrations of microplastics measuring between 1 and 100 micrometers in Lake Geneva and its surrounding rivers may have been underestimated - - 2024 EPFL/Jamani Caillet - CC-BY-SA 4.0
A new technique developed by EPFL has revealed that tiny microplastics in Lake Geneva and surrounding waterways are far more abundant than previously thought.
Microplastics are plastic particles smaller than five millimeters that originate either from manufactured products or from the breakdown of larger plastic items. We can now find them everywhere, from oceans and rivers to soils and indoor air. Because most plastics degrade very slowly, these particles can remain in the environment for decades or centuries.
While larger microplastics can be detected and classified relatively easily, estimates suggest that microplastics larger than 100 microns, roughly the thickness of a human hair, represent only about 3% of the total plastic particles present in the environment. However, characterizing particles smaller than 20 microns still represents a major challenge. "We need to be able to detect well below 100 microns. Otherwise, we are only observing the tip of the iceberg," explains Christel Hassler, former scientific coordinator at EPFL.
To improve the detection of tiny particles, a team led by Hassler and Florian Breider, director of the EPFL Central Environmental Laboratory, has developed a new AI-based technique that can identify and classify six types of polymers, which are very long molecules made of many small repeating units linked together, as small as five micrometers. Since microplastic abundance increases exponentially as particle size decreases, the results were used to estimate pollution levels for microplastics between 1 and 100 micrometers. The method is published in Nature Partner Journals Clean Water.
Using water samples from Lake Geneva and its surrounding rivers, the researchers found that concentrations of microplastics measuring between 1 and 100 micrometers may have been underestimated by more than 650-fold.
Risk at the threshold
Evaluations carried out by EMPA show that out of the 38 samples analyzed, around six exceeded the ecotoxicological thresholds used to assess environmental risks. Hassler sees these findings as an important warning sign: "We are not in an alarming situation, but we might be at the threshold where we should worry."
The immediate question that arises is whether such high concentrations pose some risk to the population and ecosystems. Although the effects of small microplastics have been extensively studied in laboratory settings, understanding their impact on natural ecosystems remains challenging and requires accurate measurements of environmental concentrations. "The entire food chain may be exposed to microplastics. In some cases, it is not only the bioaccumulation of plastics but also other substances, such as additives that are transported by them," says Breider.
Previous studies estimate that more than 15,000 chemicals are used in plastic manufacturing. In Switzerland, some of these substances are banned, such as some additives used to give some texture to the plastics. The picture becomes even more complex because microplastics interact with many other pollutants already present in aquatic environments. "It is the cocktail of substances that is problematic. Studying its toxicity is extremely complex, and even more so its impact on the whole ecosystem," says Breider.
AI-assisted classification
This new methodology is based on AI tools that help identify and classify different types of small polymers. Researchers used two different algorithms. The first algorithm helped identify and separate microplastics from biological material also found in the water samples. Once detected, a second algorithm classifies samples into six major polymer categories, allowing researchers to characterize them with a greater level of accuracy than previous techniques.
This new and evolutive method improves existing methods and will enable researchers to detect even smaller particles and new types of polymers.
Smaller and smaller
Breider points out that, "we need to develop new methods to have a complete picture of the complex problem of microplastics." With this goal in mind, researchers now aim to track how microplastic concentrations evolve over time across the Geneva Leman watershed and to determine whether pollution levels are increasing. At the same time, researchers also expect to be able to classify other types of polymers and to increase the sensitivity to detect microplastics at the nanoscale. Hassler thinks that no single technique is likely to cover the full-size range of microplastics or capture the complexity of the problem.
