What are microplastics and where do they come from?

Microplastics are plastic fragments smaller than 5mm. Nanoplastics are smaller than 1 micrometre and are of increasing concern because they can cross biological barriers.

Two origins:

Primary microplastics are manufactured small — plastic pellets (nurdles) used as industrial feedstock, microbeads in cosmetics (now banned in many countries), and abrasives.

Secondary microplastics are fragments of larger plastic broken down by sunlight, mechanical abrasion and weathering. This is the larger source.

The dominant sources are not what most people assume. Studies of microplastic release consistently find that packaging waste is far from the biggest contributor:

Tyre wear is generally identified as the single largest source. Every vehicle sheds tyre particles continuously, washed into drains and waterways.

Synthetic textiles — polyester, acrylic and nylon shed fibres during washing and wear. A single wash can release hundreds of thousands of fibres, and wastewater treatment captures many but not all.

Road markings and paint, including marine and building paint.

Plastic litter breaking down, and lost fishing gear, which dominates in some marine environments.

Where they end up. Essentially everywhere sampled — deep ocean sediment, Arctic ice, mountain snow, soil, air, drinking water, food, and human tissue including blood, lungs and placenta.

What is known about health effects. Considerably less than the coverage implies. Exposure is established; harm at real-world exposure levels is not well characterised. Plausible mechanisms exist — physical irritation, inflammation, and transport of adsorbed chemicals and additives — and some laboratory studies show effects at high doses. The honest position is that this is an active research area with real uncertainty, and neither dismissal nor alarm is well supported yet.

Practically: tyre and textile sources dominate, so vehicle use and synthetic clothing matter more than avoiding plastic bottles — though reducing plastic overall addresses the litter pathway.