What are microplastics, and where do they come from?

In brief

• Microplastics are plastic pieces generally smaller than 5 mm [1][2].
• Some are added to products on purpose. Much larger amounts are released unintentionally, through tyre wear, synthetic textile fibres, lost plastic pellets and the breakdown of larger plastic items [2].
• Definitions and size classes vary between studies, so take care when comparing numbers [3].

The word “microplastics” turns up in the news almost every week, but what it actually means, where these particles come from and why they are so widespread often goes unexplained. This post covers those basics.

The definition: plastic smaller than 5 millimetres

The most common definition is simple: microplastics are pieces of plastic smaller than 5 millimetres. Both the US National Oceanic and Atmospheric Administration (NOAA) and the European Commission use this cut-off [1][2]. That covers a lot of ground, from a fragment you can see with the naked eye to a fibre you can only make out under a microscope.

There is no agreed lower limit, and that is where things get messy. Researchers do not all draw the same size lines for “microplastics” and for the even smaller “nanoplastics”. According to the abstract of a 2019 paper, the lack of a shared definition and classification for plastic debris can cause confusion in both research and mitigation, and this shows especially in the inconsistent size classes used for microplastics [3]. The World Health Organization’s 2022 report names the two together in its title: “nano- and microplastic particles” [6].

In practice, this means that when two studies report “microplastic” counts, the first thing to check is which size range each of them counted.

Two main routes: added on purpose, or released by accident

Added to products on purpose

Some microplastics are made small deliberately. The best-known example is the tiny polyethylene beads (microbeads) once used as scrubbing agents in face cleansers and some toothpastes [1]. The resin pellets that serve as raw material for plastic products are also in this size range [1].

These uses are now restricted in many places. The United States banned plastic microbeads in cosmetics and personal care products in 2015 [1], and the European Union restricts microplastics intentionally added to products [2].

Released by accident

According to the European Commission, much larger amounts end up in the environment unintentionally. It highlights three sources [2]:

• Lost plastic pellets: raw material spilled during production and transport. The Commission estimates that more than 2,100 truckloads of pellets were lost to the environment in 2019 [2].
• Synthetic textile fibres: fibres shed from fabrics such as polyester.
• Tyre wear: particles worn off vehicle tyres on the road.

The Commission puts the volume of microplastics released unintentionally each year at somewhere between 200 and 600 Olympic-size swimming pools [2].

Larger plastics breaking down

Then there is plastic that gets smaller over time. Bags, bottles and packaging break into ever smaller pieces once they are in the environment. Particles formed this way are called secondary microplastics [1][2]. Those that enter the environment already small are called primary microplastics; according to the International Union for Conservation of Nature’s (IUCN) description of a 2017 report, they are a major global source of ocean plastics [4].

Which plastics turn up most often?

A review of 50 studies on freshwater and drinking water found polyethylene (PE) and polypropylene (PP) to be the most common polymers, followed by polystyrene (PS), PVC and PET [10]. The shapes reported most often were fragments, fibres, films, foams and pellets [10]. The authors link this ranking partly to how much of each plastic the world uses [10].

Why it matters

In the European Commission’s words, microplastics do not biodegrade and cannot be removed once they are in the environment [12]. That is why most of the debate is about two things: how to cut releases at source, and what the effects are on health and ecosystems. I cover these in separate posts:

• Microplastics and health: what we know and what we don’t
• How are microplastics measured?

References

1. [1]NOAA National Ocean Service. What are microplastics? https://oceanservice.noaa.gov/facts/microplastics.html
2. [2]European Commission, Directorate-General for Environment. Microplastics. https://environment.ec.europa.eu/topics/plastics/microplastics_en
3. [3]Hartmann, N. B. et al. (2019). Are We Speaking the Same Language? Recommendations for a Definition and Categorization Framework for Plastic Debris. Environmental Science & Technology, 53(3), 1039–1047. https://doi.org/10.1021/acs.est.8b05297 (Full text not read; cited from the abstract on Europe PMC.)
4. [4]Boucher, J. and Friot, D. (2017). Primary microplastics in the oceans: a global evaluation of sources. IUCN. https://doi.org/10.2305/IUCN.CH.2017.01.en (The report itself was not read; cited from the description on the IUCN library page: https://portals.iucn.org/library/node/46622)
5. [6]World Health Organization (2022). Dietary and inhalation exposure to nano- and microplastic particles and potential implications for human health. https://www.who.int/publications/i/item/9789240054608 (The full report was not read; cited from the WHO’s publication page.)
6. [10]Koelmans, A. A. et al. (2019). Microplastics in freshwaters and drinking water: Critical review and assessment of data quality. Water Research, 155, 410–422. https://doi.org/10.1016/j.watres.2019.02.054
7. [12]European Commission (25 September 2023). Commission protects environment and health by restricting intentionally added microplastics. https://commission.europa.eu/news-and-media/news/commission-protects-environment-and-health-restricting-intentionally-added-microplastics-2023-09-25_en

How to cite this post

Mikroplastikveri. (2026, November 2). What are microplastics, and where do they come from? https://mikroplastikveri.com/en/posts/what-are-microplastics/

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