Washing — and especially drying — the laundry can have an environmental impact that goes far beyond the amount of water and energy used.

From the air to the oceans, tiny bits of plastic — some smaller than a bit of thread — swirl through our environment. Back in 2011, scientists identified one seemingly big contributor: lint released in water used to wash laundry. A new Hong Kong study now suggests that an even bigger culprit may be your humble tumble dryer. 

For years, notes Kenneth Leung, microplastics researchers have been faced with a mystery: “Where are the atmospheric microplastic fibers coming from?” Leung studies ocean pollution at City University of Hong Kong.  

Tiny bits of plastic travel long distances on winds. They’ve been landing everywhere from the top of Mount Everest to the bottom of the ocean. Microplastic pollution is so widespread that people and animals can’t help ingesting it. That can harm wildlife and may pose risks to people, too. Yet for one in every five microplastic bits wafting through the air, Leung says, scientists “don’t have a clue” where they come from. “So now,” he says, “we’re putting the puzzle together.”

Clothing is one potentially big source. Through wear and tear, fabrics shed tiny fibers. That includes the fabric polyester. Since polyester is a type of plastic, its microfibers are microplastics. 

Scientists had seen microplastic fibers in lint coming from washing machines. Sewage-treatment plants can remove many of these fibers from water. But airborne microplastics spewed from clothes dryers rarely make it to the sewage plant.

Leung says he realized the potential role of dryers after his machine’s exhaust pipe came loose from the window. It blew lint everywhere. “It was a disaster,” he recalls — and inspired his experiments. Those tests would show that dryers can release more than a half-million microfibers every 15 minutes. That includes bits of polyester and other fabrics like cotton. These can hurt small creatures that mistake the fibers for food.

“This study is exactly what we hoped [for],” says Rachael Miller. She wasn’t part of the Hong Kong study, but does study microfiber pollution. She founded the Rozalia Project for a Clean Ocean in Burlington, Vt. Miller has also been inventing ways to capture laundry lint before it can pollute the environment.

In 2016, she noticed something weird while sampling Hudson River water in New York. She expected to find more microfibers in areas near lots of people. But microfiber levels were about the same everywhere, she says — “even where there are no people.”

She was part of a team that published those findings in the Marine Pollution Bulletin.

Miller wondered, “Could dryers be the source?” Microfibers could spread out in the air before settling into rivers. That may account for the uniform microfiber distribution. Curious, she went outside and checked her dryer’s exhaust.

The foliage nearby was covered in lint. Later, Miller teamed up with Kirsten Kapp of Central Wyoming College in Jackson. They dried fleece blankets in winter. After each load, they measured polyester microfibers on snow within nine meters (30 feet) of a dryer’s exhaust. Then they measured fibers emitted directly from the exhaust itself.

And they found plenty. But the amount varied with the type and age of a dryer. It also depended on how the dryer’s vent had been installed and differences in lint traps. (Lint traps are filters in dryers that are meant to capture lint before it escapes in exhaust.) Miller and Kapp shared their findings in 2020 in PLOS ONE.

In the latest study, Leung and his team dried polyester and cotton fabrics in household dryers. They collected the lint released in the dryer exhaust and used wax to seal the fibers in petri dishes. Fibers shorter than 5 millimeters (0.2 inch) counted as “microfibers,” notes Kai Zhang. He’s another researcher on the team. The researchers double-checked their results with a spectrophotometer (SPEK-troh-foh-TOM-eh-tur). This machine identifies substances by measuring the amount of light they absorb at different wavelengths.

And “Bingo!” says Leung. The number of microfibers they tallied “is alarming.” Dryers produced more microfibers than washing machines — up to 40 times more. Using Canadian household tumble-dryer data, his team now estimates that each year a single household dryer can spew up to 120 million microfibers into the air.

“This answered our question,” Leung says, about where airborne microfibers are coming from. His team reported its findings January 12 in Environmental Science & Technology Letters.

Polyester produced more microfibers than cotton. And weirdly, cotton produced similar amounts of lint no matter how big the wash load. Both 0.5- and 2-kilogram (1.1- and 4.4-pound) loads of cotton shed similar amounts of microfibers. But with polyester clothes, large dryer loads released far more microfibers than small ones. 

The reason is that not all cotton fibers become microfibers, the Hong Kong team shows. Cotton fibers often tangle, making bigger bits of lint. These heavier fibers, Leung says, “can’t leap up into the air.” In contrast, polyester’s sleek strands don’t clump. Unprotected, they simply break into tiny bits.

“This study is a great follow-up to ours,” Miller says. “They used different materials.” And stark differences emerged between those materials. 

Knowing how microplastics get into the air is the first step to preventing this pollution — which shows up even in human poop. These bits of trash may be unhealthy for reasons besides their plastic content, too. In water, plastic wastes often become protective sites on which microbes and algae anchor themselves. Leung now wonders whether plastic lint in the air also provides an “anchoring point for microbes.” If this helps them survive, these lint bits might become home to germs with antibiotic-resistant genes.

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Several years ago, Miller invented a device that collects fibers during laundering. It tangles up lint in much the same way cotton does. When added to a washing machine, that lowers the release of lint. Researchers at the University of Plymouth, in England showed this in a 2020 study. A Canadian team has been testing another system. That one filters fibers from wash water.

Dryers already come with lint traps. But as the Hong Kong data show, these still let plenty of fibers escape. Better filtering should be possible, Leung notes. “But the engineers cannot achieve this without compromise.” Extra filters mean dryers have to work harder. And if people don’t understand the eco-friendly reasons for the extra energy and costs, they might not support it.

The real take-home message, Miller believes, is how connected we all are to the natural world. “When you pour something down your drain, it doesn’t really go away,” she says. “‘Away’ is not really away.” It comes back to you. Perhaps, one day, in your drinking water.

algae: Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.

chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

contaminant: Pollutant; a chemical, biological or other substance that is unwanted or unnatural in an environment (such as water, soil, air, the body or food). Some contaminants may be harmful in the amounts at which they occur or if they are allowed to build up in the body or environment over time.

correlation: A mutual relationship or connection between two variables. When there is a positive correlation, an increase in one variable is associated with an increase in the other. (For instance, scientists might correlate an increase in time spent watching TV with an increase in rates of obesity.) Where there is an inverse correlation, an increase in one value is associated with a drop in the other. (Scientists might correlate an increase in TV watching with a decrease in time spent exercising each week.) A correlation between two variables does not necessarily mean one is causing the other.

develop: To emerge or to make come into being, either naturally or through human intervention, such as by manufacturing.

engineer: A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need. (v.) To perform these tasks, or the name for a person who performs such tasks.

environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

exhaust: (in engineering) The plume of gases and fine particles emitted by combustion or mechanical processes.

fabric: Any flexible material that is woven, knitted or can be fused into a sheet by heat.

fiber: Something whose shape resembles a thread or filament. (in nutrition) Components of many fibrous plant-based foods. These so-called non-digestible fibers tend to come from cellulose, lignin, and pectin — all plant constituents that resist breakdown by the body’s digestive enzymes.

filter: (n.) Something that allows some materials to pass through but not others, based on their size or some other feature. (v.) The process of screening some things out on the basis of traits such as size, density, electric charge.

gene: (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

germ: Any one-celled microorganism, such as a bacterium or fungal species, or a virus particle. Some germs cause disease. Others can promote the health of more complex organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

gills: The respiratory organ of most aquatic animals that filters oxygen out of water. Fish and other water-dwelling animals use gills to breathe.

ingest: (n. ingestion) To eat or deliberately bring nutrients into the body by mouth for digestion in the gut.

microbe: Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

microplastic: A small piece of plastic, 5 millimeters (0.2 inch) or smaller in size. Microplastics may have been produced at that small size, or their size may be the result of the breakdown of water bottles, plastic bags or other things that started out larger.

physical: (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

plastic: Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.

polyester: A synthetic material used chiefly to make fabrics. The actual chemical name for the material used is polyethylene terephthalate.

sewage: Wastes — primarily urine and feces — that are mixed with water and flushed away from homes through a system of pipes for disposal in the environment (sometimes after being treated in a big water-treatment plant).

spectrophotometer: An instrument that measures the light spectrum. Typically, chemists use these instruments to measure and report the wavelengths (colors) of light that it observes. Those wavelengths can serve as a gauge to the presence of certain elements or chemicals present in some sample.

system: A network of parts that together work to achieve some function. For instance, the blood, vessels and heart are primary components of the human body's circulatory system. Similarly, trains, platforms, tracks, roadway signals and overpasses are among the potential components of a nation's railway system. System can even be applied to the processes or ideas that are part of some method or ordered set of procedures for getting a task done.

textile: Cloth or fabric that can be woven of nonwoven (such as when fibers are pressed and bonded together).

vent: (n.) An opening through which gases or liquids can escape.

waste: Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.

wastewater: Any water that has been used for some purpose (such as cleaning) and no longer is clean or safe enough for use without some type of treatment. Examples include the water that goes down the kitchen sink or bathtub or water that has been used in manufacturing some product, such as a dyed fabric.

Journal:​ ​​D. Tao​ ​et​ ​al.​​ Microfibers released into the air from a household tumble dryer.​ ​​ Environmental Science & Technology Letters.​ ​​January 12, 2022. doi:​ 10.1021/acs.estlett.1c00911.

Journal:​ ​​K. Kapp​ ​et​ ​al.​ Electric clothes dryers: An underestimated source of microfiber pollution.​ ​​PLOS ONE.​ ​​Vol.​ 15 (10),​ ​October 7, 2020​. doi:​10.1371/journal.pone.0239165.

Journal: I.E Napper, A.C. Barrett and R.C. Thompson. The efficiency of devices intended to reduce microfibre release during clothes washing. Science of the Total Environment. Vol. 738, October 2020, p. 140412.  doi: 10.1016/j.scitotenv.2020.140412.

Journal:​ ​​R.​ ​Miller​ ​et​ ​al.​ Mountains to the sea: River study of plastic and non-plastic microfiber pollution in the northeast USA.​ ​​Marine Pollution Bulletin.​ ​​Vol.​ ​124,​ July 22, 2017​ ​(web). doi:​ ​10.1016/j.marpolbul.2017.07.028.

Journal:​ A.L. Andrady. Microplastics in the marine environment. Marine Pollution Bulletin, Vol. 62, August 2011, p. 1596. doi: 10.1016/j.marpolbul.2011.05.030.

Journal:​ M.A. Browne et al. Accumulation of microplastic on shorelines worldwide: Sources and sinks. Environmental Science & Technology. Vol. 45, Sept. 6, 2011, p. 9175. doi: 10.1021/es201811s.

Journal:​ J.P.G.L. Frias, P. Sobral and A.M. Ferreira. Organic pollutants in microplastics from two beaches of the Portuguese coast. Marine Pollution Bulletin. Vol. 60, November 2010, p. 1988. doi: 10.1016/j.marpolbul.2010.07.030.

Journal:​ H. Hirai et al. Organic micropollutants in marine plastics debris from the open ocean and remote and urban beaches. Marine Pollution Bulletin, Vol. 62, August 2011, p. 1683. doi: 10.1016/j.marpolbul.2011.06.004.

Katie Grace Carpenter is a science writer and curriculum developer, with degrees in biology and biogeochemistry. She also writes science fiction and creates science videos. Katie lives in the U.S. but also spends time in Sweden with her husband, who’s a chef.

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