Denim blue jeans are arguably the most popular clothing item in the world, with many wearing them daily for work, school, social engagements, and everything in between. However, their fashion versatility comes at a cost to the environment. Not only is manufacturing blue jeans carbon and water-intensive, but every time you wash a pair of jeans, microscopic fibers are shed and end up in the waterways. According to a new study, blue jeans microfibers are common across the world, reaching lakes and even remote Arctic marine sediment.

Blue denim is made from natural cotton cellulose fibers, which are processed with synthetic indigo dye and other additives in order to improve performance and durability. According to the UN, it takes roughly 3,780 liters of water to manufacture a single pair of jeans, from growing cotton to the fashion store’s shelf. What’s worrisome is that most jeans are made in water-scarce areas of the world, including Pakistan, Mexico, China and India, and also parts of California.

Around 20% of wastewater worldwide comes from fabric dyeing and treatment, according to the UN. On the consumers’ side, blue jeans laundering produces microfibers that not only end up in wastewater effluent but also in all sorts of marine and freshwater environments.

In a new study, researchers at the University of Toronto investigated the distribution of denim indigo microfibers in aquatic environments across Canada, from urban Toronto to remote Arctic regions. The idea and motivations behind the study came about serendipitously.

“We were all finding these cotton fibers dyed with indigo in high numbers across all our samples, but we didn’t know what they were or where they were coming from. Then someone said “Blue Jeans! What if they’re coming from blue jeans?!”. And so, from there we all set out to investigate the distribution of these indigo fibers across Canada and trace them back to their source – blue jeans!” Samantha Athey, a Ph.D. candidate at the University of Toronto’s Department of Earth Sciences and author of the new study, told ZME Science.

Despite the fact that wastewater treatment plants remove some of the fibers, the results show that denim microfibers still enter the environment.

“In doing this, we aimed to trace the pathways and identify a source of these fibers to the environment. We found that most microfibers found in sediments and fish were not actually plastic microfibers but were anthropogenically-modified cellulose (or cellulose fibers with associated chemical additives, such as dyes), most of which were indigo denim fibers. We then identified these indigo denim fibers in WWTP final effluent and from there through controlled washing experiments were able to demonstrate that blue jeans are a source of these fibers to the aquatic environment via wastewater,” Athey said.

“Most strikingly, this study really reveals to us the widespread environmental footprint of the clothing we wear and wash every day (blue jeans being just a prime and personal example from our wardrobes). These fibers act as a potent symbol of the remnants of our clothing reaching far beyond our closets, from our washing machines to the fish we consume to the remote Arctic Ocean, which hopefully encourages us to reflect on the impact of their clothing,” she added.

According to the results, indigo denim comprises up to 20% of all microfibers found in sediments from the Great Lakes to the Canadian Arctic Archipelago. Athey says that, based on evidence gathered so far, cotton fibers dyed with indigo undergo long-range transport through atmospheric and oceanic circulation, which means they can easily end up anywhere, even in places as remote as Arctic sediments.

Based on wastewater denim microfiber levels, the researchers estimate that all of the wastewater treatment plants in Canada included in this study discharge about 1 billion indigo denim fibers daily. One single pair of jeans could release about 50,000 microfibers per wash cycle, the authors added in their paper published in the journal Environmental Science & Technology Letters.

Although blue jeans microfibers were found to be abundant across all sediments they sampled, the researchers were able to find only one denim microfiber in the digestive tract of a type of fish known as the rainbow smelt. But since the aim of this study was to quantify denim microfibers in the environment rather than their impact on wildlife, it’s yet unclear what the short-term or long-term implications are.

One thing’s for sure, though: the impact isn’t positive — at best denim microfibers have a neutral effect on the wellbeing of wildlife and the environment at large. But aside from not buying jeans anymore, the best thing consumers can do is wash their pair of denims less frequently, the researchers say.

More research in the future might determine just how impactful these denim microfibers are to the environment.

​”Although the cotton used in denim fabrics is a natural material, during production many chemical additives are incorporated into the material to give it the characteristics we like our clothing to have (stain/water resistance, anti-microbial properties, etc.). Past work in our group has also shown our cotton clothing can accumulate chemicals from our homes and offices as well – so the cotton textile fibers that make their way to the environment are not just cotton, they are cotton fibers that may contain a mixture of chemicals. Building on this work, we are currently looking into the effects, release pathways, and diversion of chemical additives associated with microfibers,” Athey concluded.