What are microplastics?

What people ask us next.

What exactly is a microplastic?

NOAA defines microplastics as plastic fragments smaller than 5 millimeters (about the size of a sesame seed) down to about 1 micrometer. Below 1 micrometer, they're called nanoplastics. They come in two forms: primary microplastics are manufactured small (microbeads in old exfoliants, pre-production pellets, microfibers from synthetic clothing), and secondary microplastics are fragments that break off from larger plastic items as they degrade.

Where do microplastics come from?

Four main sources. Synthetic textiles shed microfibers during washing and wear (a 2020 study in Environmental Science & Technology found 400-600 fibers per garment per wash). Tire wear releases rubber particles that qualify as microplastics. Packaging and consumer plastics fragment over time in sun, heat, and mechanical stress. And primary microplastics from industrial pellet spills and (historically) cosmetic microbeads. In the US, microbeads in rinse-off cosmetics were banned by the Microbead-Free Waters Act of 2015.

How small are nanoplastics?

Nanoplastics are below 1 micrometer. For scale: a human hair is roughly 75 micrometers wide, a red blood cell is about 7 micrometers, and nanoplastics get down to the size of viruses. Qian et al. 2024 (PNAS) developed a new imaging technique and found that nanoplastics in bottled water outnumbered microplastics by an order of magnitude; previous studies had simply been unable to detect them.

Are microplastics proven to be harmful to humans?

Here's the honest answer: they're confirmed to be present in human tissue (placenta, blood, stool, arterial plaque) and documented to cause inflammation in cell and animal studies. The direct epidemiological link between microplastic exposure and specific disease outcomes in humans is newer and less settled. Marfella et al. 2024 in the New England Journal of Medicine documented a 4.5x higher cardiovascular event rate in patients with microplastics in carotid plaque, the first major causal-looking finding. Treating exposure reduction as precaution is the defensible stance.

What's the biggest source of daily microplastic exposure?

Probably plastic food contact materials, particularly heated. Hussain et al. 2023 found microwaving food in plastic containers released up to 4.22 million microplastic particles per square centimeter in three minutes. Bottled water is another large one (Qian et al. 2024). Airborne microplastics from household dust, synthetic carpets, and textiles contribute at lower per-exposure levels but constantly. Tea bags with polypropylene mesh release billions of particles per cup per Hernandez et al. 2019.

How can I actually reduce my exposure?

The evidence-based interventions, roughly in order of impact: stop microwaving food in plastic, filter drinking water with a unit rated for microplastic reduction, switch hot and acidic food storage to glass or stainless, replace non-stick cookware, choose loose-leaf tea over bagged tea, and reduce synthetic clothing where practical (especially underwear and anything worn against skin). Perfect elimination isn't possible; the particles are in rainwater. Reasonable reduction is.

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