Katherine Martinko is an expert in sustainable living. She holds a degree in English Literature and History from the University of Toronto.

There has been a great deal of talk in recent years about the link between washing machines and microfiber pollution. People have learned that the agitation of clothes in water loosens minuscule fibers (less than 5 mm in length) and releases them into the soapy water. Once there, some are captured by wastewater treatment facilities, but most end up entering the natural environment.

What many people have not considered, however, is what happens when they transfer clothes from a washing machine to a dryer. And yet, it stands to reason that the process of tumble-drying would have a similar effect on microfiber release that washing machines do—and potentially worse, as the contaminated air is emitted from the machine throughout the cycle.

Now a group of researchers from the State Key Laboratory of Marine Pollution and Department of Chemistry, at the City University of Hong Kong, has delved deeper into this question of tumble dryers and made some alarming discoveries. 

Their study, titled "Microfibers Released into the Air from a Household Tumble Dryer," was published in the journal Environmental Science & Technology Letters in early January 2022. It confirms that tumble dryers do play a major role in releasing textile microfibers into the ambient atmosphere, particularly when clothes are dried at high temperatures.  

The authors write, "Because vented air is usually not treated, microfibers are emitted directly through a ventilation pipe connected to the dryer to ambient air, either indoor or outdoor ... If dryers are not connected to a ventilation system, the released microfibers could be inhaled directly from the indoor air by humans."

We know that humans do inhale microplastic particles, as they've been found in human stools and even in the placentas of unborn babies, as direct evidence of exposure. The study cites research that estimates more than 900 microplastic particles might be ingested by a child each year through dust. A separate 2019 study found that people ingest, on average, the equivalent of a credit card's weight in microplastics weekly.

For the study, the researchers used 12 clothing items made from 100% polyester fabric and 10 items made from pure cotton. These were dried separately in several 15-minute cycles in a standard household tumble dryer. A "high-volume, total suspended particle air sampler" was placed at the end of the duct to collect all airborne particles, regardless of size. The collected fibers were transferred to sealed Petri dishes for subsequent examination.  

The researchers estimated that over 110,000 microfibers are released from just one kilogram (2.2 pounds) of polyester clothing in a 15-minute dryer cycle. Since a dryer's average capacity is 6-7 kilograms (13-15 pounds), the total number of polyester microfibers released in 15 minutes of drying a full load could be around 561,810 ± 102,156. That number is only slightly lower for cotton clothes, at 433,128 ± 70,878 microfibers per full load.

These high numbers reveal that dryers are worse than washing machines: "Regardless of whether the textiles are cotton or polyester, for 1 kg of textiles, a dryer can generate more microfibers than that generated by a washing machine."

Professor Kenneth M. Y. Leung, one of the study authors, told Treehugger,

While cotton microfibers still raise some concerns due to the residual chemicals they may contain from processing (such as fluorescent whitening agents and azo dyes), they eventually break down in the natural environment, unlike synthetic microfibers, which are known to persist and contribute to bioaccumulation in animals that inadvertently consume them.  

Leung thinks that a filtration system, with filters of various mesh sizes, could be effective at removing microfibers from tumble dryers. "We believe it will work, provided that the user regularly cleans the filters carefully." 

It matters how they're cleaned, though. As Leung told the Guardian, "If people just put these [fibres] in the dustbin, some of the fibres will be released back into the air. We suggest the particles should be collected in a bag." 

Lower temperatures could help reduce the quantity of fibers released, as would hang-drying clothes—a solution that's far more environmentally-friendly for more than this reason alone. Reducing washing frequency could help, too. Try airing clothes out or spot-washing as needed.

Of course, opting to buy clothes made from natural, biodegradable materials is preferable to synthetics, no matter what promises of technical grandeur a brand or designer may make. A return to basic cotton, wool, linen, hemp, etc. would reduce plastic microfiber pollution, while providing garments that last and age well. 

In the meantime, this gives dryer manufacturers something else to ponder. Hopefully they can come up with designs that feature better filtration systems, as well as options for retrofitting dryers that lack them.

Cai, Yaping, et al. "Formation of Fiber Fragments During Abrasion of Polyester Textiles." Environmental Science & Technology, vol. 55, no. 12, 2021, pp. 8001-8009., doi:10.1021/acs.est.1c00650

Tao, Danyang, et al. "Microfibers Released Into the Air From a Household Tumble Dryer." Environmental Science & Technology Letters, 2022, doi:10.1021/acs.estlett.1c00911

Tao, Danyang et al. "Microfibers Released Into The Air From A Household Tumble Dryer." Environmental Science & Technology Letters, 2022. doi:10.1021/acs.estlett.1c00911

Ragusa, Antonio, et al. "Plasticenta: First evidence of microplastics in human placenta." Environment International, vol. 146, 2021. doi:10.1016/j.envint.2020.106274

Abbasi, Sajjad, et al. "Distribution and potential health impacts of microplastics and microrubbers in air and street dusts from Asaluyeh County, Iran." Environmental Pollution, vol. 244, 2019, pp. 153-164. doi: 10.1016/j.envpol.2018.10.039

Dalberg for WWF. "No Plastic in Nature: Assessing Plastic Ingestion From Nature to People." University of Newcastle, Australia, 2019.

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