Your Cotton T-Shirt Sheds Pollution Too

Pull a sweater over your head, tug a cotton shirt from the dryer, and you release a small cloud of fibres too fine to see. If the garment is polyester, we have learned to worry about that cloud: those are microplastics, and they end up in rivers, oceans, soil and lungs. If the garment is cotton or viscose, most people assume the opposite: that natural means benign, that a cellulose fibre will quietly rot away and do no harm.

A new systematic review in Environmental Research Letters, which pulls together the scattered evidence on textile-fibre pollution, argues that this assumption deserves far more scepticism than it usually gets. Its case, drawn from the existing literature rather than from a single new experiment, is blunt: "natural" fibres are not the clean choice we take them to be, and by treating them as harmless we may be missing a large share of the fibre pollution actually accumulating in the environment.

"Natural" is not the same as "unprocessed"

The first problem is the word itself. A cotton boll or a stand of bamboo begins as a plant, but the fibre that reaches a garment has usually been through an industrial gauntlet. Cotton is bleached, dyed and treated with finishes for softness, wrinkle-resistance and colour-fastness. Viscose (marketed as a natural or "regenerated" fibre because it starts from wood cellulose) is manufactured by dissolving that cellulose in a harsh chemical bath, including compounds such as carbon disulfide and caustic soda, then reconstituting it as a filament.

By the time it is woven into cloth, a "natural" fibre is a heavily engineered material carrying dyes, finishes and processing residues. That matters for what happens when it sheds. The review's argument is that these chemical treatments change how the fibre behaves in the environment (what it carries with it and how slowly it breaks down), so that the reassuring intuition of a leaf quietly composting does not straightforwardly apply.

The shedding does not stop at the factory

Every wash sends fibres down the drain, and natural garments shed just as synthetic ones do. The comfortable assumption has been that cellulosic microfibres, unlike plastic, biodegrade quickly enough to pose little lasting problem. The review pushes back on how firmly that is actually established. Degradation in the real environment (cold water, low oxygen, deep sediment) can be far slower than a laboratory or a compost heap suggests, and a treated, dyed fibre is not the same as a clean strand of cellulose.

The evidence the review assembles points to a striking mismatch. Natural and regenerated cellulosic fibres made up only a small slice of the fibres tested in controlled shedding experiments, on the order of a fifth. Yet when scientists go out and sample the actual environment, cellulosic microfibres often dominate the count. Studies measuring what is really out there have reported cellulosic microfibres at concentrations well above those of synthetic ones, by some accounts several times greater. They turn up in deep-sea sediment, in seawater and freshwater, and in samples of the air.

A monitoring blind spot

That gap points to the review's most consequential claim: our picture of fibre pollution may be systematically skewed. Much environmental monitoring is built around microplastics: the search is for synthetic polymers, and the methods and headlines follow. Cellulosic microfibres, precisely because they are assumed to be harmless and are harder to classify, are often undercounted or set aside.

If natural fibres are shedding in comparable or greater numbers and persisting longer than assumed, then a monitoring regime focused on plastics is measuring only part of the problem. The reviewers frame this as partially supported rather than settled. The exact degree of undercounting is uncertain, and it varies by study and method, but the direction is consistent across the literature they surveyed. We have been looking hard for one kind of fibre while a large population of another kind drifts past the net.

The practical upshot is not that cotton is secretly as bad as plastic, nor a reason to abandon natural fibres for synthetics. It is narrower and more useful: "natural" is a marketing category, not an environmental guarantee. The processing a fibre undergoes, and the persistence of what it sheds, deserve scrutiny regardless of whether it began as oil or as a plant. And if we want an honest accounting of textile pollution, the monitoring has to count all the fibres in the water, not just the ones we already decided to fear.