CWC professor Kirsten Kapp and co-author Rachael Miller published a ground-breaking study identifying dryer vents as a significant source of microfiber pollution. Photo: Kirsten Kapp and

RIVERTON, Wyo. — It is well-known that washing machines contribute to microfiber pollution, when tiny fibers shed from clothing and home textiles during the wash and enter the wastewater treatment system. However, until recent research conducted by Central Wyoming College professor Kirsten Kapp and co-author Rachael Z. Miller, little was known about the contribution electric clothes dryers make to this environmental problem.

The first-of-its-kind study was funded in part by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institute of Health, and the journal article was recently featured in Forbes Magazine.

In the study, Kapp and Miller found “that electric clothes dryers emit masses of microfiber directly into the environment. Microfiber emissions vary based on dryer type, age, vent installation and lint trap characteristics.”

Kapp and Miller concluded that “dryers should be included in discussions when considering strategies, policies and innovations to prevent and mitigate microfiber pollution”.

Miller has been working on microplastic pollution since 2011, but it was in 2016 when she honed in on dryers as a source. “I remember the day in October of 2016 that I went outside to where my dryer exhaust vent is located and saw fibers all over the foliage.”

“While chatting about this (with Kirsten Kapp), we realized that while sampling sediment and soil for microfibers is quite difficult, we could use the fact that we both lived in places with significant snowfall and let snow simplify the process to understand how much microfiber dryers might be emitting.”

Snow plots used during the dryer study on microfiber pollution. Photo: Rachael Miller

The study, which used bright pink polyester fleece blankets in two different household dryers, found that microfibers that flow out the dryer air vent land beyond the area directly under the vent. While the majority of fibers from the blanket fell within five feet of the vent, fibers were observed in five test plots 30 feet from the vent. Results suggest that wind may be a factor.

Heat map showing distribution and concentration of fibers from the test blanket in the 14 plots that were sampled. The bigger and darker the circle, the more fibers were found at that test location. An important note, the extent of this study was 30’ from the vent, we do not know exactly how far these fibers travel, and how much they contribute to atmospheric microfiber pollution during transport. Photo: Kirsten Kapp and Rachael Miller

In terms of the amount of microfiber released by dryers, this study found that a total of 105-209 milligrams of lint, including fibers, is released from one polyester fleece blanket into the environment (outdoor air) via electric clothes dryer exhaust after three dryer cycles.

Because this is one of the first studies to investigate dryer emissions into the air and surrounding ground, it was done without pre-washing with washing machines in order to reduce the variables washing machines would have introduced. Rather, the blankets were soaked before drying. Accordingly, this paper does not make an estimate about the total amount of fiber dryers might be contributing to the environment.

Variations in dryer design, age and/or installation are factors in determining the amount of fibers emitted into the environment. There were several differences in the dryers used in this study, most notably: age, length of ducting and size of lint trap screen.

The older dryer with longer ducting produced less microfiber emissions. The researchers suspect that is due to fiber buildup in the walls of the ducting. The dryer with the larger lint trap screen (approximately three times greater, and also the older model) caught more lint than the dryer with the smaller lint trap screen.

The authors hope that these initial findings encourage additional studies investigating fiber buildup in ducting, and identifying characteristics that make lint trap assemblies most effective as well as how dryer settings, fill levels, in-drum devices and other design parameters affect both shedding rates and volume of fibers that are emitted with the dryer exhaust.

Fiber captured from dryer exhaust vents. Each petri dish shows the fiber emitted into the air by one polyester fleece blanket that was soaked and then dried in an electric clothes dryer for one complete dry cycle (low heat). A-C represent location 1, and D-F represent location 2. The amount of fibers emitted decreased with each cycle. This is a similar pattern seen with microfiber emissions in washing machines and something that needs further investigation to best estimate total emissions from electric clothes dryers. Photo: Kirsten Kapp and Rachael Miller

“This research suggests that clothes dryers are another potential and important source of microfibers into the environment,” says Kapp. “While the study only looked at surface snow after single dryer events, it will be important to quantify the cumulative effect of fibers emitted from dryers and how or if they accumulate in the soil over time, potentially altering soil properties and biota.”

“The potential impact of this research spans multiple scientific disciplines and industries,” says Miller, “The goal of this study was to break the story about dryers and microfiber emissions, rather than answer all the questions.”

“Our intent is that these data now inspire researchers to investigate exactly what factors concerning dryer design, installation and settings increase or reduce shedding, inspire the white goods industry to include dryers in their discussions about microfiber pollution and educate consumers about the potential effects that dryer use has on our environment.”