A single clothes dryer could discharge up to 120 million microfibres every year according to estimates from a new study published in Environmental Science & Technology.
This is considerably more than the volumes released from washing machines and is of concern as in some countries, dryer air is vented directly to the outdoors.
Machine washing clothes releases microfibres into wastewater, which can be treated to remove some or most of them. But little has been previously known about the impact of tumble drying as a source of microfibre contamination in nature.
Microfibres can form from natural fabrics – such as cotton – or synthetic ones like polyester (which are also considered to be microplastics) and are of particular concern because they absorb and transport pollutants across long distances and can act as irritants if ingested or inhaled by animals and humans.
The researchers collected and counted the microfibres generated by clothing made from the two most common textile fibres – cotton and polyester – and found that they release roughly 430,000–560,000 microfibres during just 15 minutes of machine drying.
Why 15 minutes? Well, they found no significant difference in the number of released microfibres in increments from 10 to 50 minutes, so drying time didn’t seem to have an impact.
Clothes dryers released between 1.4 and 40 times more microfibres than had been generated by washing machines in previous studies for the same amount of clothing. Both types of textile produced microfibres; the researchers suggest that this is caused by the friction of clothes rubbing together as they tumble.
Interestingly, the release of polyester microfibres increased with more clothes in the dryer, whereas the release of cotton microfibres remained the same regardless of load size – a worrying finding as polyester microfibres are more persistent in the environment than cotton.
The researchers think this could be occurring because some cotton microfibres aggregate and cannot remain airborne. Polyester microfibres don’t behave the same way.
Based on the study’s numbers, it’s estimated the total amount of microfibres released from a Canadian household’s laundry each year is between 90 and 120 million.
The researchers suggest the release of these airborne microfibres could be controlled by additional filtration systems adapted to dryer vents.
The study was conducted on a dryer with a vent that discharges the air to the outdoors directly, common in Canada and the US but not necessarily the rest of the world.
The researchers acknowledge that in the case of dryers that aren’t vented, the released microfibres could be inhaled directly from indoor air by humans, and that more research is needed in this area.