Microplastic particles in the environment and in our food and drinking water are extremely diverse and complex. This makes it difficult to determine the risks to humans and the environment. Researchers of Wageningen University & Research now provide the first mathematical framework to assess the risks of these particles.
Worldwide, microplastic debris has been found in the oceans, soils, surface waters and in our food. Emissions are expected to increase by orders of magnitude in the coming years. Fragmentation leads to smaller and smaller particles, which eventually reach the submicron scale. At these very small dimensions, plastic particles can pose unforeseen risks. They are also so incredibly complex that until now there was no method to determine the risks of these small particles for humans and the environment.
Wageningen researcher prof. Bart Koelmans: "We already knew that microplastics are transported around the globe, potentially affecting aquatic life and human health. Now we have assembled the tools that helps us to understand if and when this actually happens. This is important in order to design mitigation strategies for microplastic debris."
Apples and oranges
So far, studies comparing the exposure and effects of microplastic particles have compared apples and oranges. This is because two microplastic particles are never the same, and the methods used to measure exposure and effects are all different. They use different types of microplastics, all of which are very different from the mixtures we are exposed to.
In their recent paper, published in the journal Nature Reviews Materials, Bart Koelmans and colleagues discuss and summarize ways to solve all these misalignments using mathematical approaches that are new to microplastic research. "This provides a way to represent all of this data as just apples so that they can be compared in a consistent risk characterization," said Merel Kooi, co-author who contributed much to the development of the concepts as part of her PhD project.
An important element of the new approach is that microplastics should no longer be regarded as a material that can be characterized as separate categories of sizes, shapes or polymers. This is the traditional approach, but it takes too many parameters: dozens of polymers, about ten shape categories and also the use of ten size categories is the rule rather than the exception. Such categories are also imprecise because they lump everything together per category. Bart Koelmans: "Instead, we describe microplastics as a continuum of properties. If the particles occur in large numbers, and they do, those properties are best described with mathematical distributions. And if you know the distributions, you can align all kinds of data between studies, which is a huge improvement"
Risk assessment of microplastic
The problem of plastic pollution is high on the agenda of policymakers and the public, and society demands an assessment of the risks of plastic debris to people and the environment. Quantitative methods such as these are expected to be of great help in informing the public about where and when risks from microplastics will arise. As long as analytical methods to detect plastic particles and methods to assess impacts are all different and still under construction, the new method provides a valuable tool to assess the risk of this new contamination. Until now, the method has been used by the authors' team to assess risks for surface water and freshwater sediments on a global scale, with a risk for a few percent of the locations worldwide.
In California, the new methods have recently been applied to derive standards for microplastics in the marine environment and in drinking water in a regulatory setting. Results are expected early 2022.
At Wageningen University & Research, several new projects aim to further develop tools for the risk assessment of nano- and microplastic, further emphasising risks for human health.
