Tumble dryers generate even more microfiber pollution than washing machines, a new study suggests. A lot of these microfibers—tiny textile strands that can pose a threat to environmental and human health—get trapped on dryer lint filters. But even so, tumble drying a load of laundry releases roughly as many microfibers into the air as washing that load sends down the drain.
“Air pollution from vented dryers is very significant,” says study team member Neil Lant, a researcher at the consumer products corporation Procter & Gamble in Newcastle upon Tyne, UK. But the problem should be “relatively easy to fix in the longer term through advances in appliance filtration, ideally linked to a move to condenser dryers and preferably heat pump ones to reduce energy consumption,” he adds.
Lant and his colleagues at Procter & Gamble and Northumbria University washed and dried loads of 10 100% cotton plus 10 100% polyester t-shirts using both European and North American machines, laundry products, and typical machine settings—1,200 t-shirts in all. They measured the mass of microfibers released down the washing machine drain, trapped in the dryer lint filter, and released into the air from the dryer vent.
In recent years there’s been lots of concern about and research on microfiber pollution generated by washing machines, but less is known about microfibers from clothes dryers. The new study is the first to quantify microfibers from both washing and drying of the same garments and thus provide a direct comparison.
“Testing under both European and North American washing conditions found that the quantities of microfibers released to air during tumble drying were significant and comparable to levels released ‘down the drain’ during washing,” the researchers report in the journal PLoS ONE.
Dryer lint screens with finer mesh trap more microfibers: The researchers found that reducing the lint screen’s pore size from 0.2 square millimeters to 0.04 square millimeters cut the number of microfibers released into the air by more than one-third. Some tumble dryer models have lint filters with mesh as large as 1 square millimeter so these dryers may release even more microfibers to the air.
Cotton t-shirts generate more microfibers than polyester t-shirts, but dryer lint filters are more effective at trapping polyester microfibers. So, a bit of good news: most of the microfibers released into the air from the dryer vent are likely to be cotton, which is more biodegradable and therefore may cause less lasting environmental harm than polyester microfibers.
Fabric softener and dryer sheets—especially both used together—could also reduce the amount of microfiber pollution from tumble dryers. The researchers showed that adding fabric softener to the washing machine doesn’t reduce microfiber release during washing (consistent with previous studies), but it does reduce microfibers released to the air during the drying cycle by up to 14.2% in European conditions and 21.6% in American conditions.
An antiwrinkle fabric softener had even more impressive performance, reducing microfiber release from the dryer vent by 17.6-35.6%, depending on the dose. Meanwhile, dryer sheets reduced microfiber release by 14.1-34.9%, depending on the dose and product. And the combination of antiwrinkle fabric softener in the wash cycle and dryer sheets reduced microfibers in dryer exhaust by a whopping 44.9%.
The two laundry products appear to work by different mechanisms: fabric softener by increasing the accumulation of microfibers on the lint filter, and dryer sheets by trapping microfibers themselves.
Could these products trigger some kind of rebound effect that increases microfiber release at other times, such as when a garment is being worn? Lant thinks it’s unlikely. “I think the opposite will be true—more effective ‘defluffing’ should reduce subsequent fiber release. Further research will help to confirm this.”
Other ways to reduce microfiber release from clothes dryers include improving dryer lint vents with smaller mesh, and promoting a switch from tumble dryers to condenser dryers, which don’t vent to the air. “If all dryers were fitted with advanced filtration systems, for example the cyclonic separators used in modern vacuum cleaners, very few fibers would be released,” either to either the air from a tumble dryer or into the water from a condenser dryer, Lant adds.
Source: Lant N.J. et al. “The impact of fabric conditioning products and lint filter pore size on airborne microfiber pollution arising from tumble drying.” PLoS ONE 2022.