‘Biodegradable’ textiles fail to break down in seawater, study finds

The study from the University of California, San Diego, tracked the ability of natural, synthetic and blended fabrics to biodegrade directly in the ocean.

It found that while natural and wood-based cellulose fabrics degraded within a month, synthetic textiles - including so-called compostable plastic materials like polylactic acid (PLA) and the synthetic portions of textile blends - showed no signs of degradation even after more than a year submerged in the ocean.

"This study shows the need for standardising tests to see if materials promoted as compostable or biodegradable actually do biodegrade in a natural environment," said lead author Dr Sarah-Jeanne Royer.

"What might biodegrade in an industrial setting does not necessarily biodegrade in the natural environment and can end up as marine and environmental pollutants."

An estimated 62 per cent of textiles - around 68 million tons - are now made from plastic fibres and plastic blends, which can persist in the environment for decades to centuries. Synthetic textiles also create plastic pollution from microfibres shedding during regular wearing and washing.

Most washing machines are not designed to filter for microfibres, which then end up in wastewater and ultimately the ocean.

Bio-based plastics made from renewable natural resources such as cornstarch or sugar cane have been marketed as a potential solution to the plastic problem. PLA is one such polymer in the bio-based plastics market, often labelled as biodegradable and compostable. The team chose this textile for the study given its extensive use as a replacement for oil-based materials.

For the experiment, ten different types of fabrics were used including wood-based cellulose, natural cellulose, bio-based plastic (PLA), oil-based plastic and fabric blends. All these are commonly used in the textile industry.

The textile samples were placed in flow-through containers deployed both at the sea surface and at the seafloor approximately 10 metres deep. Samples were examined every seven days, with images taken and small pieces removed from duplicate samples for further examination in the lab.

While the natural, cellulose-based textiles repeatedly disintegrated in 30-35 days, the oil-based and bio-based materials showed no sign of disintegration even after a total of 428 days.

"The natural, cellulose-based materials would disintegrate in about one month, so we would exchange for a new sample after the old one disintegrated," said Royer. "The natural samples were replicated five times, while the plastic samples remained the same for more than a year."

Under an electron microscope, it was revealed that the natural fibres became thinner with time, while the diameter of the plastic fibres remained the same showing no sign of biodegradation.

Fibre blends, which interweave natural fibre strands with bio or oil-based plastic strands, are often promoted as a more sustainable alternative to textiles made entirely from synthetic plastics. This study showed, however, that only the natural part of the fibre degraded, with the plastic portion of the blend remaining intact.

"This comparative study highlights how crucial our language is around plastics," said postdoctoral scholar Dimitri Deheyn. "Indeed, a bioplastic like PLA, commonly assumed to be biodegradable in the environment because it contains the prefix 'bio,' is actually nothing like that."