Understanding Microplastics and Human Health

Henry Lee
Technical Manager

3rd July 2025

What are microplastics?

When I first started exploring microplastics, I was surprised by how misunderstood they are. At their simplest, microplastics are tiny plastic particles less than 5 millimetres in size(1) — about the size of a sesame seed or smaller. They can come from products that are manufactured to be that small, like microbeads in cosmetics, or they can result from larger plastic items breaking down through wear and exposure to the elements.

These particles are typically made from plastics we’re already familiar with — polyethylene (PE), polypropylene (PP), PET, and PVC. What’s important to understand is that even though these plastics are small, they still behave chemically like the larger versions we use every day. They’re generally inert, stable, and non-reactive.

I often hear people express concern at the mere presence of microplastics in the environment — in water, soil, even the air. But just because we find them doesn’t mean they’re automatically harmful. Like any material, their impact depends on how much we’re exposed to, their size, their chemical composition, and how they enter our bodies (through the skin, airways, or digestion).

Personally, I think it’s worth reminding ourselves that many of these same plastic materials are used safely in food packaging, drinking water systems, and medical devices. The risks, if any, need to be evaluated with context and credible science — not just headlines.

How toxic are microplastics?

Toxicity is often thrown around in discussions about microplastics, but it’s important to understand what that actually means. When we talk about acute toxicity, scientists use something called the LD₅₀ — the dose needed to cause death in 50% of a population(2). Chronic toxicity, on the other hand, looks at long-term exposure and uses something called NOAEL — the No-Observed-Adverse-Effect Level(3). To put things in perspective, here’s a simplified comparison using data based on a 70kg person:

I find this table incredibly helpful when explaining the actual risks. For example, caffeine — something most of us consume daily — has a far lower threshold for toxicity than common plastics. This isn’t to say plastics are harmless, but it does show that not everything small and synthetic is inherently dangerous.

How prevalent are microplastics?

It’s easy to assume microplastics are everywhere, but when we look at the data more closely, the actual exposure levels are surprisingly low. One study estimates the average person ingests just 184 nanograms of microplastics per day(5). To put that into perspective, a single grain of salt weighs about 60,000 nanograms.

Even in the air we breathe, microplastics make up only a tiny fraction of what’s considered respirable dust — so much so that they aren’t even mentioned in most indoor or outdoor air quality studies.

That’s not to dismiss concerns altogether — I just believe we need to focus on evidence-based discussions, not assumptions.

Do microplastics degrade?

One of the most common misconceptions I hear is that plastics never break down. But that’s not entirely true. Microplastics do degrade over time, through mechanical wear, sunlight (especially UV radiation), and even microbes.

Some organisms can actually break down parts of plastic materials. Over time — and with the right conditions — plastics can degrade into water, carbon dioxide, and other simpler compounds(8,9).

Of course, this process isn’t always quick, and degradation rates vary by material and environment. But to call plastics “forever materials” ignores the growing body of research showing that they do degrade — just at different rates.

Final Thoughts

From what I’ve seen, there’s a lot of fear around microplastics, much of it driven by uncertainty and media headlines. But when we take a step back and look at the science — both in terms of toxicity and actual exposure — the picture becomes more nuanced.

This isn’t about dismissing concerns, but about approaching the topic rationally and with context. After all, many of the materials that make up microplastics are the same ones we trust in life-critical applications every day.

Acknowledgements

I would like to thank Dr. Chris DeArmitt for his review on the subject of microplastics and would strongly advise anyone interested in this subject or the matter of plastics and the environment in general to read ‘The Plastics Paradox’ and ‘Shattering The Plastics Illusion’.

References

1. Microplastics | Definition, Properties, & Plastic Pollution | Britannica
2. Median lethal dose - Wikipedia
3. No-observed-adverse-effect level - Wikipedia
4. J. A. Styles & J. Wilson, Comparison between in vitro toxicity of polymer and mineral dusts and their fibrogenicity, The Annals of Occupational Hygiene, 16 (3), pp. 241–250, November 1973
5. Nur Hazimah and Mohamed Nor, Lifetime Accumulation of Microplastic in Children and Adults, Environmental Science & Technology Journal, 55 (8), pp. 5084–5096, 2021
6. L. Wallace, Indoor Sources of Ultrafine and Accumulation Mode Particles: Size Distributions, Size-Resolved Concentrations, and Source Strengths, Aerosol Science & Technology, 40, pp. 348–360, 2006
7. A. Mukherjee & M. Agrawal, World air particulate matter: sources, distribution and health effects, Environmental Chemistry Letters, 15, pp. 283–309, 2017
8. J.C. Prata in T. Rocha-Santos, M. Costa, C. Mouneyrac (eds), Handbook of Microplastics in the Environment, Springer Switzerland, pp. 531–542, 2022
9. A. Delre et al., Plastic photodegradation under simulated marine conditions, Marine Pollution

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