By Mette Oorthuijs
The fashion industry is one of the most polluting industries in the world1. This is not that surprising if you take into account that it requires more than 7 thousand liters of water and 2kg of carbon dioxide (CO2) to make a single pair of jeans2. To keep up with our increasing demand for clothing3,4 120 million trees are logged yearly, 79 billion cubic meters of water are used and a significant volume of greenhouse gasses is emitted (estimates ranging from 3% to 10% of global emissions)5. Moreover, throughout the fashion industry supply chain, a staggering amount of 15,000 chemicals is used. These chemicals impact the environment all over the world and are even found in remote places such as the Arctic6.
The growing share of sustainable fashion on the market shows an increase in consumer demand7, but more change is needed. In combination with altering our behavior, smart biotechnological innovations can mitigate the impact of the fashion industry. And that’s where we come in! Solutions for reducing this environmental impact start in a petri-dish.
An unsustainable rainbow
Synthetic alternatives to natural dyes are much cheaper and available in more colors8. Unfortunately, this means that many more chemicals are involved that impact our health and the environment. One example of a synthetic dye is indigo. This dark blue pigment is used to dye one of the most popular fashion items out there: blue jeans.
Indigo used to be derived from the leaves of the indigo plant for thousands of years. Synthetic versions, however, have replaced the plant version in 1900, and with that came many problems…
Synthetic indigo is currently derived from petroleum. And, to make indigo water-soluble (which is necessary for the dyeing process), a reducing agent is needed: sodium dithionite. This reducing agent is cheap and fast but damaging to the environment.
Making blue greener
In the search for a cleaner dyeing process, Hsu and colleagues9 from the University of California, Berkeley turned to the Japanese indigo plant. This is one of the plant species that was used to derive indigo throughout history. Its green leaves turn blue when they are damaged because of a special biochemical mechanism that involves a sugar similar to the type that you use to bake cakes or sweeten your coffee.
In this case, a sugar group is added to the colorless molecule indican, a precursor of indigo (see figure on the right). Because of this modification, the molecule cannot transform into indigo, and so remains colorless.
The sugar group can be removed again using β-glucosidase (BGL), an enzyme that is present in the chloroplasts of the leaf. When the leaves are damaged, BGL leaks out of the chloroplasts and transforms indican to another intermediate, indoxyl, which spontaneously forms indigo when it comes into contact with oxygen
Surprisingly, the fact that indican is colorless makes it a very interesting dye. It can be kept colorless and used to dye exactly when and where the manufacturer wants it. So, the Berkeley group came up with an alternative dyeing process, inspired by the biochemical process in the plant (shown schematically in the figure below).
The use of petroleum is environmentally unsustainable, but on the other hand, getting all the necessary indigo out of plant leaves remains too expensive, so E. coli bacteria were used as a vector to generate the indigo precursors. First, the Berkeley group identified the enzyme responsible for adding the sugar group in Japanese indigo. Next, they expressed this enzyme in E. coli, generating a culture of bacteria that can transform indoxyl to indican. When it’s time to dye, the sugar group can be removed by adding another enzyme (like BGL) to transform indican back to indoxyl, preventing the need for damaging reducing agents. Finally, indoxyl turns into indigo when in contact with the air and dyes the fabric a vibrant blue!
No green light yet
As always, there are challenges to overcome before this process can be used for the commercial production of indigo. The indican, for example, can be transformed using a strong acid or an enzyme. However, both of these options are not ideal. The use of an acid is counteractive to the dyeing process as the properties of indigo are better under basic conditions. Using an enzyme, like BGL, would increase the cost and the time needed to dye the fabric. Before our jeans can be dyed with this new process these challenges need to be overcome to make it commercially viable.
Fortunately, many other research groups are also working on sustainable dyeing, as well as trying to mitigate other environmental pressures caused by fashion production. Fabrics are being made of the most surprising sources, from wood pulp to food waste. For example, the start-up Algiknit is making fabric using kelp. This sea plant is one of the fastest-growing organisms in the world. As it grows, it absorbs the CO2 of its surroundings through photosynthesis, capturing carbon in our oceans and decreasing acidification. To make it into fabric, they mix the extracted alginate from kelp and combine this with other biopolymers and water to form a paste, which can be turned into fibers to be used for knitting.
New materials and new methods for dyeing can mitigate some of the impacts of fashion, but if we really want to tackle the environmental problems that the fashion industry causes we need to work together; companies and individual consumers alike. We, as consumers, can make more conscious choices about what we purchase. However, to change the whole industry we need innovative ideas first that improve long-established supply chain processes. Biotechnological solutions can help to make the fashion industry more sustainable, from the fibers to the dye we use to color these. The challenge lies in scaling it up, so we can all wear blue jeans with a hint of green!
Want to learn more?
- Get inspired by projects of the TextileLab.
- Visit the Textielmuseum for exhibitions on textile & innovations.
- Look for interesting companies on Fashion for Good’s innovation platform & museum.
About the writer
Mette is a student of the Environment & Resource master at the VU with a background in biomolecular sciences. She is interested in many different aspects of sustainability, from changing our consumption patterns to the uneven distribution of climate change effects. However, cell biology and biochemistry will always remain two of her big interests, especially when they intersect with or facilitate sustainability.
- UN Environment Programme. (November 12, 2018). Putting the brakes on fast fashion. Retrieved from https://www.unenvironment.org/news-and-stories/story/putting-brakes- fast-fashion#:~:text=The%20fashion%20industry%20produces%2020,a%20typical%20pair %20of%20jeans.
- Karthik, T., & Murugan, R. (2017). Carbon footprint in denim manufacturing. In Sustainability in Denim (pp. 125-159). Woodhead Publishing
- Remy, N., Speelman, E., & Swartz, S (2016). Style that is sustainable: A new fast-fashion formula. McKinsey & Company. https://www.mckinsey.com/business- functions/sustainability/our-insights/style-thats-sustainable-a-new-fast-fashion-formula
- Ellen MacArthur Foundation. (2017). A new textiles economy: Redesigning fashion’s future. Retrieved from: https://www.ellenmacarthurfoundation.org/assets/downloads/publications/A-New- Textiles-Economy_Full-Report.pdf
- McKinsey & Global Fashion Agenda. (2020). Fashion on climate. https://www.mckinsey.com/~/media/McKinsey/Industries/Retail/Our%20Insights/Fashi on%20on%20climate/Fashion-on-climate-Full-report.pdf
- Niinimäki, K., Peters, G., Dahlbo, H., Perry, P., Rissanen, T., & Gwilt, A. (2020). The environmental price of fast fashion. Nature Reviews Earth & Environment, 1(4), 189- 200.
- Kaucic, N., & Lu, S. (2019, May 28). A deep dive into the global market for sustainable apparel. https://www.just-style.com/analysis/a-deep-dive-into-the-global-market-for- sustainable-apparel_id136210.aspx
- Saxena, S., & Raja, A. S. M. (2014). Natural dyes: sources, chemistry, application and sustainability issues. In Roadmap to sustainable textiles and clothing (pp. 37-80). Springer, Singapore.
- Hsu, T. M., Welner, D. H., Russ, Z. N., Cervantes, B., Prathuri, R. L., Adams, P. D., & Dueber, J. E. (2018). Employing a biochemical protecting group for a sustainable indigo dyeing strategy. Nature chemical biology, 14(3), 256.
Image credits: cover photo by IMMATTERS Studio via Scientific American