A team at Plymouth University in the UK spent 12 months analysing what happened when a number of synthetic materials were washed at different temperatures in domestic washing machines, using different combinations of detergents, to quantify the microfibres shed.

They found that acrylic was the worst offender, releasing nearly 730,000 tiny synthetic particles per wash, five times more than polyester-cotton blend fabric, and nearly 1.5 times as many as polyester.

“Different types of fabrics can have very different levels of emissions,” said Richard Thompson, professor of marine biology at Plymouth University, who conducted the investigation with a PhD student, Imogen Napper. “We need to understand why is it that some types of [fabric] are releasing substantially more fibres[ than others].”

These microfibres track through domestic wastewater into sewage treatment plants where some of the tiny plastic fragments are captured as part of sewage sludge. The rest pass through into rivers and eventually, oceans. A paper published in 2011 found that microfibres made up 85% of human-made debris on shorelines around the world.

The impact of microplastic pollution is not fully understood but studies have suggested that it has the potential to poison the food chain, build up in animals’ digestive tracts, reduce the ability of some organisms to absorb energy from foods in the normal way and even to change the behaviour of crabs.

Clothes washing has been widely reported as a contributor to microplastics pollution. A study released in June by the University of California Santa Barbara, in partnership with a clothes company Patagonia, found that each wash of a synthetic fleece jacket released an average of 1.7g of microfibres.

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There has been little quantitative research on the contribution that fibres from synthetic clothing make to other sources of microplastics pollution, according to Thompson. It is too soon to reach firm conclusions, he said, but “our research shows it’s likely to be an important source”.

“More work is needed to understand other factors [that] affect emissions,” he said. He pointed to wash duration, washing machine filter designs and spin speeds as potential factors in the quantity of microfibres released.

“These tiny plastics are just the tip of the iceberg of the estimated 12m tonnes of plastic [that] enters the sea every year,” said Louise Edge, oceans campaigner at Greenpeace UK. “From bottles to packaging to microplastics, companies need to take responsibility for what they produce; governments need to legislate for change – and all of us need to change how we think about plastic.”

Governments are already acting on plastic pollution. The UK has announced a ban on microbeads to come into effect by the end of 2017, while in the US they will be banned by mid-2017. “We are not advocating that this research should trigger something similar,” said Thompson. But “industry needs to think about the design of fabrics to ensure their environmental emissions are minimised”.