Not washing your denims is not a question of look and lifestyle any more: it also helps to stop pouring microfibers into our oceans. That's what scientists of the University of Toronto* found out when they examined the footprint of jeans by investigating the environmental distribution, pathways, and sources of indigo denim microfibers shed by denim clothing. To anticipate: the results give reason to worry.
Indigo denim microfibers: a source of pollution
To date, most environmental microfiber research has focused on synthetic microfibers. However, recent studies have reported AC microfibers, including indigo denim, in environmental compartments and ingestion by biota.
The Toronto team hypothesized that blue jeans are a major source of introduction of AC microfibers into aquatic environments and serve as a tangible and potent indicator of anthropogenic pollution. They present evidence in support of this hypothesis assembled from controlled washing trials and identification of AC microfibers from WWTP effluent, sediments, and fish from the Laurentian Great Lakes basin, shallow suburban lake sediments, and remote Arctic marine sediments.
The study shows that blue jeans do have a widespread geographic footprint in the form of microfibers in aquatic environments from temperate to Arctic regions. In fact, these “natural” microfibers are often more abundant than synthetic microfibers in environmental samples. Thus, the findings expose a new front in the challenge of microfiber pollution, “natural” fibers.
21% to 51% of all microfibers in sediments were anthropogenically modified cellulose (AC), of which 40−57% were indigo denim microfibers (12−23% of all microfibers analyzed). AC microfibers were also found in rainbow smelt from the Great Lakes.
Denim microfibers are a form of “natural” microfiber; however, they are chemically processed and are sufficiently persistent to undergo long-range transport and accumulate in environmental compartments, where they could be of concern for biota.
Microfibers: how they get into the oceans
As a source for introduction into wastewater, the scientists found that one pair of used jeans can release 56,000 ± 4,100 microfibers per wash. Microfibers from jean laundering were consistent in chemical composition and morphology with those found in the environment.
In Canada alone, recent surveys estimate that 46−56% of Canadians wear jeans almost every day–and wash their jeans after wearing a pair twice. While most microfibers that enter wastewater treatment plants (WWTPs) are retained, final effluent offers a direct pathway for indigo denim microfibers, as well as other microfibers and contaminants, to enter the aquatic environment.
The presence of indigo-dyed microfibers has been recently documented in marine, freshwater, and terrestrial ecosystems, where they are relatively persistent. The conclusion is that blue jeans are an indicator of the widespread burden of anthropogenic pollution by adding significantly to the environmental accumulation of microfibers from temperate to Arctic regions.
All these findings support the hypothesis of diffuse emission pathways and long-range transport of microfibers to aquatic ecosystems. While washing clothes is likely a significant source of introduction of microfibers into the aquatic environment via WWTP effluent discharge, more than 83% of microfibers in WWTPs are incorporated into sewage sludge, which may be subsequently applied to agricultural fields. Runoff or wind entrainment from sludge-applied fields may offer an additional pathway for microfibers to enter the aquatic environment. In addition, recent studies suggest textile production, electric drying, and wearing clothes are additional sources of introduction of microfibers from clothing into the environment.
Washing Blue Jeans is a source of denim microfibers: To investigate laundering as a source of AC microfibers, the scientists measured the release of microfibers from blue jeans during washing. New jeans released significantly greater numbers of microfibers than used jeans. This finding is consistent with previous studies showing that significantly more microfibers are released from garments in initial washes, with the amounts released decreasing throughout their lifetime. New distressed jeans released fewer microfibers than new nondistressed jeans.
Microfibers released from jeans were blue (94%) or clear (6%) and all were identified as cotton. In addition, 82% of blue cotton microfibers analyzed were confirmed as indigo denim microfibers due to the presence of an indigo dye. Clear cotton microfibers released from jeans showed no evidence of anthropogenic modification, like “cellulose fibers of unknown origin” found in all environmental samples.
While wash conditions in this study were representative of a North American, domestic, cold-water wash cycle, past studies have found greater microfiber release from cotton fabrics during warm- and hot-water cycles.
Brands and retailers should use this to ’educate’ consumers about how often it is really necessary to wash denim pieces and what alternatives could work. Washing instructions on hangtags and also informing consumers when they purchase an item are no-brainers to bring the message across.
*Source: The Widespread Environmental Footprint of Indigo Denim Microfibers from Blue Jeans by Samantha N. Athey, Jennifer K. Adams, Lisa M. Erdle, Liisa M. Jantunen, Paul A. Helm, Sarah A. Finkelstein, and Miriam L. Diamond;
published in: Environmental Science & Technology Letters/ACS American Chemical Society, Sep 2, 2020