Jeans are bad for the environment

but a new discovery may help

by Olivia Ferrari

27 February 2024

National Geographic

https://www.nationalgeographic.com/environment/article/blue-jeans-indigo-indican-enzyme

A worker unloads jeans from a fabric dyeing machine at a jeans factory in India. Manufacturing jeans comes at a steep cost to the environment, and the toxic byproducts of producing jeans endanger the health of people who make them.

Photograph by Dhiraj Singh, Bloomberg/Getty Images

Blue jeans, one of fashion’s most classic wardrobe staples, also happen to have one of fashion’s biggest environmental footprints.

Billions of denim garments are produced each year, with the global denim market valued at $63.5 billion in 2020. To produce this classic garment, producers rely on indigo dye, the only molecule known to provide jeans’ unique, beloved color. While indigo itself is naturally derived from a plant, growing demand for blue jeans throughout the 20th century gave rise to synthetic indigo, which is now more commonly used.

But indigo, whether natural or synthetic, does not dissolve in water to become liquid dye. Instead, it must be altered using harsh chemicals that bind the dye to clothing fibers.

Researchers in Denmark have engineered an improved dyeing method that eliminates the need for harsh chemicals, instead using an enzyme for dyeing. This technology, outlined in a study published today in Nature Communications, could enable large-scale production and application of indican, a molecule related to indigo, without toxic chemicals.

Eliminating those chemicals from denim manufacturing would mean healthier conditions for textile workers and less dangerous wastewater leakage.

A greener way to go blue

Indican, a precursor to indigo found in the same plants of the Indigofera genus, is the key to this dyeing alternative. Indican is a compound that turns indigo plant leaves blue when mashed up, and it can be converted into indigo.

This was not the first study to use indican as a dye alternative—scientists have even engineered bacteria to secrete indican—but a major challenge has been finding a way to efficiently use indican dye at the scale necessary to supply the global blue denim market.

According to Ditte Hededam Welner, biologist at the Novo Nordisk Foundation Center for Biosustainability and lead researcher on the new study, their newly engineered enzyme is extremely stable, so it can withstand the industrial manufacturing process better that previous methods for using indican.

To test other sustainable approaches to indican dyeing, the research team also used light, from sunshine to household light bulbs, to dye denim. Their results show that leaving fabric with indican and water on a windowsill converts indican to indigo without even adding the enzyme.

“This was a really surprising observation,” says Welner. “It may be viable, but it’s too early to really compare them; the enzymatic route is much more mature, it’s been known for years.

How does dyeing jeans impact the environment?

The chemical process for dyeing blue jeans has persisted for the last century. The denim industry uses about 50,000 tons of synthetic indigo a year, along with over 84,000 tons of sodium hydrosulfite as a reducing agent. Textile workers are exposed to these chemicals, which can be poisonous and carcinogenic.

Toxic chemicals also pollute the environment near factories. Dyeing just one pair of jeans uses can require nearly 30 gallons of water, and chemical additives used with the water are highly alkaline and corrosive—so containing wastewater can be difficult. Chemical-contaminated water often ends up in waterways near factories, decimating local ecosystems and even dyeing rivers blue.

Welner’s team’s new methods would replace these dyes. The researchers looked at 18 impact categories, including fossil fuel use, human exposure to carcinogens, and water pollution. Using the engineered enzyme to dye with indican cuts environmental impacts by 92 percent compared with conventional dyeing, and using light to dye with indican cuts environmental impacts by 73 percent.

“There is basically nothing that can pollute in either enzymatic or photolytic [light] dyeing,” says Welner.

Just reducing those chemical additives massively cuts carbon emissions. Welner’s team estimates replacing indigo with indican would decrease blue jeans’ annual carbon dioxide emission by over three million tons, based on an estimated four billion pairs of jeans traded per year.

“It is difficult to predict what kind of niche it can find at this stage,” says Sergiy Minko, chemist at the University of Georgia, “but general directions to replace aggressive chemistry with green processes is the right direction, even if only some steps can be done initially.”

More sustainability hurdles

But the technology doesn’t solve all of the denim industry’s environmental issues.

A single pair of jeans is estimated to consume over 790 gallons of water throughout the supply chain, from growing cotton, to dyeing, to washes to achieve desired colors and patterns.

Adam Taubenfligel, co-founder of sustainable denim company Triarchy, calls conventional methods for producing jeans “horribly consumptive.” That’s why Triarchy manufactures their jeans using new technologies not traditionally used in the denim industry, creating the vintage denim look without as much water use or chemical discharge.

Because they have successfully learned to recycle factory water, Triarchy has pivoted from focusing primarily on water reduction, to reducing plastic. Synthetic fibers used to make stretch jeans typically contain plastic and are a major source of microplastics.

Yet implementing sustainable practices is not always easy or cheap.

Welner says it’s still not clear if her team’s new dyeing methods would be logistically and financially viable for the average manufacturer. The overall cost to switch from conventional dyeing to this costs about seven cents more per pair of jeans for enzymatic dyeing, or a fraction of a cent more per pair of jeans for LED light dyeing. But Welner says it’s worth it for the environmental benefits.

If larger clothing companies adopted more responsible practices, says Taubenfligel, the environmental effect of blue jeans would improve.

In light of new advances in technology for every step in the denim production process, Taubenfligel is hopeful. “My hope is that as time goes by… we will get to a point where all these technologies hopefully will be adopted, and we’ll have a much cleaner industry for everybody.”