One tumble dryer could be responsible for releasing 120 million microplastic fibres into the air each year, new research has found.
The concerning findings follow a 2017 report that estimated by 2050, the number of microfibres released into the environment by washing textiles per year may increase to 70,000 tonnes - that's the equivalent of dumping 400 million polyester T-shirts into the sea.
The new study - led by Professor Kenneth Leung, the director of the State Key Laboratory of Marine Pollution and the Department of Chemistry at City University of Hong Kong - has found that tumble dryers are one of the primary sources of microfibre pollution in Earth's atmosphere.
But the good news is the study also appears to have found a possible solution to the problem.
According to the US Environmental Protection Agency (EPA), microfibres are the most prevalent type of microplastic (plastic pieces less than 5mm in diameter) found in the environment. Researchers have detected microfibres in a range of ecosystems, from shorelines and the seafloor to remote areas in national parks - even in snow in the Alps and the Arctic.
Scientists estimate more than 8 million tonnes of plastic enter the world's oceans each year and while bottles, bags and straws are all well-known examples of plastic pollution, another major source is what we wear on our bodies.
Most clothing is made from plastic-based materials such as polyester, rayon, nylon and acrylic. During laundering, the friction causes synthetic clothing to shed tiny plastic fragments, or microfibres. Due to their small size, many of the fibres escape through the tumble dryer's ventilation pipe and are released into the air, both indoors and outdoors - meaning humans often can be inhaling the particles directly.
It has been estimated that more than 900 microplastic particles might be ingested by a child each year through dust. In 2019, researchers at the University of Victoria in Canada found the average person consumes between 74,000 and 120,000 microplastics a year - and double if they drink bottled water regularly.
The latest research, published in the journal Environmental Science & Technology Letters on January 12, will be "essential" for managing microfibre pollution, Prof Leung, the lead author of the study, told The Guardian.
"Once we know the source, we can begin to control it using simple methods."
As part of the study, polyester and cotton clothes were tumble-dried in separate 15-minute cycles. After measuring how many microfibres were released through the vent, the researchers estimated between 90 million and 120 million microfibres are produced and emitted into the environment by each dryer, every year. The results suggested that dryers are a source of microfibre air contamination, releasing between 433,128 and 561,810 microfibres during 15 minutes of use, depending on the dryer's capacity.
To date, most published research has focused on the generation of microfibres from washing machines - for example, one pair of jeans can release around 56,000 microfibres per wash. However, the researchers' findings indicate that drying produces more airborne microfibres than washing.
"The average Canadian household washes 219 loads of laundry annually. Here, we estimated that the average Canadian household could release [90 to 120 million] microfibres from a dryer annually," the study said.
"That is, a significant number of microfibres are discharged into the atmosphere, which could be potentially inhaled and ingested by humans and animals. The microfibres released from tumble dryers are, therefore, likely to represent a substantial contribution to microplastic contamination in the environment globally.
"The microfibres might be ingested by organisms ranging from zooplankton to fish and birds and transferred into food webs."
The researchers noted that while cotton microfibres discharged into the environment can be ingested by organisms, they are not as persistent as polyester microfibres. For the same drying duration, cotton textiles produced more stable amounts of the fibres after drying, the study found, regardless of the amount of textiles in the dryer.
To minimise the release of microfibres into the air, the researchers advised that a simple, engineered filtration system could be developed and adopted as an effective way of controlling the pollution generated by household dryers.
"It is feasible to minimise the release of microfibres from tumble dryers by the installation of a simple, engineered filtration device at the end of the emission pipeline," the study said.
Prof Leung and his colleagues have already designed basic filters using 3D printing that prevent microplastics being emitted from washing machines, and are now in the process of designing a similar system for dryers, The Guardian reports.
"These [filter systems] effectively remove most of the microfibres from the laundry," he told the outlet.
However, it is unclear where these fibres will end up when the filters are cleaned.
"We suggest the particles should be collected in a bag," he added.
Regardless of whether or not the filters become widely used in the near future, the fight against microfibres largely depends on the fashion industry switching to more environmentally friendly fabrics.
"In China, the Public Environmental Audit Committee has turned its attention toward transforming the clothing industry to make it prosperous and sustainable. However, it is unrealistic for plastic microfibres to be eliminated in the short term without the substitution of more environmentally friendly textiles," the study said.
"It is essential to make better textiles and clothes with more wear resistance, longer wearing time, and enhanced environmental friendliness."
In the meantime, a simple tip to combat microplastic pollution in your household is to launder clothes with fabric softeners. A study by the Italian National Research Council in 2020 found the number of emitted microfibres can be reduced by nearly one-third when washing with softener as it reduces friction between the fibres.