New studies warn of denim’s lasting impact through wastewater

Introduced to municipal treatment systems through the laundry, the researchers found that one pair of used jeans could release approximately 50,000 microfibres per wash cycle. Photo credit: Tommy Lee Walker / Adobe Stock.

Two new studies with connections to the University of Toronto have detailed the troublesome environmental footprints that blue jeans — one of the most popular and durable garments on Earth — have been leaving behind for decades.

The researchers used a combination of microscopy and Raman spectroscopy to identify and count indigo denim microfibres in various water samples collected in Canada.

One of the new studies, published this month in Environmental Science and Technology Letters, found that microfibres comprise as much as 90% of the anthropogenic particles found in sediments from the Canadian Arctic Archipelago, Laurentian Great Lakes, and shallow suburban lakes in southern Ontario. Of those particles, as much as 23% were found to be indigo (a type of blue dye) denim microfibres.

The researchers also noted that of the microfibres found in wastewater treatment plant material collected from southern Ontario, 13% was dyed with indigo. Introduced to municipal treatment systems through the laundry, the researchers found that one pair of used jeans could release approximately 56,000 microfibres per wash cycle.

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Based on the levels of microfibres found in wastewater effluent, the researchers estimated that the wastewater treatment plants in the study discharge about 1 billion indigo denim microfibres per day.

“We conclude that blue jeans, the world’s single most popular garment, are an indicator of the widespread burden of anthropogenic pollution by adding significantly to the environmental accumulation of microfibres from temperate to Arctic regions,” states the study by co-author Sam Athey, a doctoral candidate in the University of Toronto’s department of earth sciences.Following publication of the study, Athey recommended on social media that people should consider washing their denim products significantly less often to reduce the burden on the environment.

Of the microfibres studied, indigo denim microfibres comprised 12% of those collected from the Toronto Lakes; 20% from the Arctic Archipelago; and 23% from the Great Lakes.

“Despite a high abundance of denim microfibres in Great Lake sediments, the team detected only a single denim microfibre in the digestive tract of a type of fish called rainbow smelt,” researchers said in a statement about the study, although they did not extensively examine the effects microfibres have on aquatic life.

In another recent study, published in June in the journal Facets, a research team with University of Toronto scientist Chelsea Rochman found a surprising number of tiny blue fibres during microfibre and microplastic analysis in Canada’s eastern Arctic.

Laundry machines in Canada and the U.S can release upwards of 878 tonnes of microfibres to the aquatic environment each year following wastewater treatment, according to research by the Ocean Wise Plastics Lab in Vancouver.

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