The Cost of Colour

Dyeing fibre, by any method, requires two things: water and chemicals. As you’re also no doubt aware, combining these two things doesn’t always end happily.

Readers interested in practicing dyeing on a small scale as hobbyists or artisans can reduce the ecological consequences of their art by using recycled tools and containers, being conscious of the sources and quantities of energy and water they’re using and finding ways to avoid wasting either such as by reusing pre-soak or mordanting water and dye-baths, and by making sure that dye solution is “exhausted”: the dye is all taken into fibre leaving as little as possible in the leftover water, and the pH level returned to the neutral range (6-8.5) before disposal. Note that with dyes, there’s no such thing as “all-purpose”; commercial “union dyes” such as RIT contain different dyes for both protein and cellulosic fibres. If used to dye only wool the plant-fibre dye will remain in the dye bath and vice versa, so these are best used to dye different fibre types together or back-to-back.

For hobbyists practicing dyeing, making sure dye solutions are 'exhausted' can prevent harmful chemicals from entering wastewater.
For hobbyists practicing dyeing, making sure dye solutions are ‘exhausted’ can prevent harmful chemicals from entering wastewater.

But what happens further up the chain, where the dye and fibre are produced? And what about buying thread, yarn, fabric, or finished garments that are already dyed? While it depends some on the type and origin of the fibre and on the dyeing method employed, the sad fact is that the dyeing and printing phase accounts for over 50% of the chemical and water consumption and pollution generated in textile production, making it the most ecologically destructive segment of the most ecologically destructive industry on the planet today. The real kicker lies in the historical view that, because the study of dyeing sparked the evolution of organic chemistry as a discipline and of chemical synthesis as an industry, it was the quest for colour in textiles that caused all of our current pollution problems. The industrial revolution was a chemical revolution.

Thousands of different chemicals are used in textile production, and it’s common for traces to remain in the garments and other items that reach the end consumers, where they can be inhaled or absorbed through skin contact—bad news if the substance in question is toxic or carcinogenic. The situation is even worse for factory workers who are exposed to the chemicals in much larger doses and more volatile states. For example, azo dyes, a class of compounds containing the molecular group (-N=N-), add up to 60-70% of dyes in use today. Of these azo dyes, a small subset metabolize into aromatic amines known to cause bladder cancer when they enter a human body. The EU forbids the use of any azo dyes in textiles that will come into close contact with human bodies, while other regions navigate between health risks posed by azo dyes and economic dependence on them.

The chemicals that do wash out during production are no less dangerous, because polluted wastewater poisons ecosystems from the bottom up. Dyeing demands enormous quantities of water, contributing to aridification, and later expels it as effluent loaded with heat, heavy metals, ammonia, alkali salts, colourants, and other compounds which can be toxic and cause cancer and mutations. The specific ingredients of effluent change along with the colour demands of fashion designers and consumers.

Waterways near textile dyeing plants are especially threatened.
Waterways near textile dying plants are especially threatened.

This issue is of particular concern in India, where textiles comprise roughly 14% of all industrial production, and in other developing countries. Local residents rely on bodies of water that are already badly contaminated. These countries may have environmental legislation but it is not consistently enforced, and where new oversight is applied textile producers may simply move shop to areas with less regulation. The Board of the Ecological and Toxicological Association of Dyes and Organic Pigment Manufacturers tries to regulate chemical content of dyes but has no power to enforce these rules on non-members.

Any amount of colourant in wastewater is too much: matter has colour because its molecules reflect wavelengths within the visible light spectrum while absorbing all others, so colourants reflecting back light that would otherwise penetrate the water interfere with photosynthesis which kills algae and aquatic plant life, causing ripple effects throughout the food chain. The textile industry today uses 1.3 million tons of dyes and pigments annually, of which 10-50% are not exhausted by fibre and 2-20% are discharged in wastewater—up to 200,000 tons of dye. Most of these dyes escape traditional water treatment and, because being engineered to withstand washing out makes them frustratingly stubborn, refuse to degrade naturally.

As scientists, government agencies, and textile buyers and manufacturers learn more about the extent of the damage caused by polluted wastewater, they’re also looking for ways to reduce and repair it.

Silk-worms fed with a mulberry mixture containing dye naturally produce permanently coloured silk.
Silk-worms fed with a mulberry mixture containing dye naturally produce coloured silk.

Tactics for improving environmental friendliness of textile production include tailoring effluent treatment to the processes that generated it, identifying opportunities to reduce total water usage and waste and finding ways to reuse water, selecting dyes and other products without toxic ingredients such as heavy metals, reducing overall chemical use and recapturing chemicals for reuse, and finding other ways to contain and neutralize contaminants. Technologies with the potential to transform the dyeing process include air dyeing, dye-feeding silkworms, drastically lowering the temperature requirements and improving overall textile feel by using liposomes to deliver dye, saving time and energy by improving dye uptake with renewable ultrasonic energy, and pretreating cotton to dye significantly faster and with better exhaustion, using less water and energy, and zero toxic discharge. We, as fashion professionals and consumers, can support these efforts by exercising choice wherever possible, choosing dyes and overseeing dyeing processes to ensure products are dyed in the most ethical and ecologically friendly way possible, as well as choosing ethical producers and more sustainable fibres.

Written by Claire Dalmyn.

Photo credits:
Dye containers: UK Parliamentary Office of Science and Technology
Red dyed river: Zhang Xiaoli for ChinaFotoPress reproduced in
Silk-worm cocoons: