Clothes dryers are an underappreciated source of airborne microfibers

Microfibers can come from natural fabrics, such as cotton, or synthetic ones, such as polyester -- which are also considered to be microplastics. Releasing microfibers into the environment is a concern because they can adsorb and transport pollutants long distances. And the fibers themselves can be irritants if they are ingested or inhaled. Previous studies have shown that microfibers are released from clothes washers into laundry water, but this waste is treated, removing some or most of the fibers before the water is discharged into rivers or streams. However, there's very little information about whether dryers, whose air passes through a duct and is vented directly to the outdoors, are an important source of airborne microfibers and microplastic contamination in nature. So, Kai Zhang, Kenneth Leung, and colleagues wanted to count the microfibers generated by cotton and polyester clothing in a dryer to estimate the amount released into the outdoor air from a household's laundry each year.

The researchers separately dried clothing items made of polyester and those made of cotton in a tumble dryer that had a vent pipe to the outdoors. As the machine ran for 15 minutes, they collected and counted the airborne particles that exited the vent. The results showed that both types of clothing produced microfibers, which the team suggests comes from the friction of clothes rubbing together as they tumbled around. For both fabrics, the dryer released between 1.4 and 40 times more microscopic fragments than were generated by washing machines in previous studies for the same amount of clothing. They also found that the release of polyester microfibers increases with more clothes in the dryer, whereas the release of cotton microfibers remains constant regardless of the load size. The researchers suggest this occurs because some cotton microfibers aggregate and cannot stay airborne, a process that doesn't happen for polyester. Finally, the team estimated that between 90 and 120 million microfibers are produced and released into the air outside by the average single Canadian household's dryer every year. To control the release of these airborne microfibers, additional filtration systems should be adapted for dryer vents, the researchers say.

The authors acknowledge funding from the State Key Laboratory of Marine Pollution; the Innovation and Technology Commission of the Hong Kong Special Administrative Region of the People's Republic of China; a Discovery Grant from the Natural Science and Engineering Research Council of Canada; Western Economic Diversification Canada; the Canada Foundation for Infrastructure; the Canada Research Chair program of the Natural Science and Engineering Council of Canada; and one of the authors was supported by a Distinguished Visiting Professorship at Baylor University.