Most of the microfibres polluting our oceans – which have long been assumed to be plastic – are actually natural fibres like cotton and wool. But we don’t yet know whether these fibres pose the same health risks to marine organisms.
Textile microfibres are major contributors to marine pollution because they are readily shed from clothes during general wear and tear and laundering, and drift through the air or wash down drains into waterways. A single machine wash of polyester clothing, for example, releases half a million textile microfibres.
Previous ocean surveys have tended to count all microfibres as plastic, based on the assumption that natural fibres like cotton and wool biodegrade too quickly to persist in marine environments.
However, when Peter Ryan at the University of Cape Town in South Africa and his colleagues analysed 2000 microfibres drawn from several oceans, they found that only 8 per cent were plastic fibres like polyester or nylon. The rest were natural fibres including cotton, which made up 50 per cent of the total, and wool, which made up 12 per cent, and others like silk, hemp and linen.
The team used a technique called infrared spectroscopy to analyse microfibres, which were 1 millimetre long on average, in 916 seawater samples collected from the Atlantic, Indian and Southern oceans and the Mediterranean Sea.
The finding is surprising because almost two-thirds of textiles manufactured today are synthetic. It is possible that natural fibres degrade more slowly than previously thought, and that most of the cotton and wool fibres currently floating in oceans are pollution from previous decades when they were the most common textiles used in clothing, says Ryan.
Natural fibres are often dyed and coated in chemicals like flame retardants when they are used to make clothes, which may reduce their biodegradability, says Ryan. An intact dyed cotton waistcoat has previously been discovered in a 133-year-old shipwreck, for example.
Even though the study found fewer plastic microfibres than expected, natural microfibres may carry the same health risks to marine creatures, says Ryan. There is some evidence that crabs and zooplankton are harmed by ingesting plastic microfibres, but the impact of natural microfibre pollution on ocean wildlife hasn’t been investigated.
“We should be trying to reduce the numbers of microfibres from clothing getting into the environment, irrespective of whether they are plastic or not, because it appears they are likely to last a long time in the environment,” says Ryan.