A single tumble dryer could be responsible for releasing 120m micro plastic fibres into the air each year, a study has found.

Tumble dryers are one of the main sources of microfibre pollution in the atmosphere, according to research by Prof Kenneth Leung, director of the State Key Laboratory of Marine Pollution (SKLMP) and department of chemistry at City University of Hong Kong.

He described the findings as “essential” for managing microfibre emissions, which are known to damage human health and the environment.

“Once we know the source, we can begin to control it using simple methods,” said Leung, the lead author of the study published in the journal Environmental Science & Technology Letters.

Microfibres are a common group of microplastics – plastic pieces less than 5mm in length. During washing and drying, friction causes materials to shed these fibres. Because of their small size, many slip through the filters in tumble dryers and are released into the environment, where they have been found in water, food and even the placentas of unborn babies.

These tiny plastic particles have been found in even the most remote regions, from the Arctic to high up in the Earth’s troposphere.

Researchers tumble dried polyester and cotton clothes in separate 15-minute cycles and measured how many microfibres were released through the vent. While natural materials such as cotton shed fibres too, they can be digested by animals and “decompose in the environment relatively quickly”, said Leung.

The team estimated that between 90m and 120m microfibres are produced and released into the air outside by each dryer annually.

Using 3D printing, Leung and colleagues have designed simple filters that prevent microplastics being dispersed from washing machines, and are in the process of designing a similar system for tumble dryers.

“These [filter systems] effectively remove most of the microfibres from the laundry,” he said. However, it is still unclear where these microplastics would end up when the filters were cleaned.

“If people just put these [fibres] in the dustbin, some of the fibres will be released back into the air,” he said. “We suggest the particles should be collected in a bag.”

Even if fitting these filters is “possible, as Leung says, microfibres will still be pervasive until the clothing industry uses more environmentally friendly fabrics.

“Manufacturers need to make textiles and clothing that are more resistant to wear,” Danyang Tao, a PhD student at SKLMP, said.

Microfibres are inhaled and ingested by humans and animals each day. These plastics are known to harm wildlife, and studies are beginning to uncover the damaging health consequences they have on humans. In 2021, scientists found microplastics caused damage to human cells in the laboratory. These tiny fibres have also been linked to intestinal inflammation and other gut problems.

Leung said he hoped the research would help “raise the alarm and trigger more innovation” to tackle the problem.