Are natural fabric dyes best for the environment?

The answer to this question is not as obvious as many people think! Natural dyes carry their own hazards, and are not necessarily kinder to the environment than a dye factory which is run with proper environmental controls. Note that dye plants in some countries such as China are poorly run without proper environmental regulation, but other dye companies such as Dystar have earned eco certification for their factories (the EU label [PDF link] and Oeko-Tex Standard 100 certification [PDF link]).

Most natural dyes require the use of a mordant, which is a metal ion used to pretreat the fabric so that the natural dye will stick to it. Unlike synthetic dyes, most natural dyes will not bond to the fiber without a mordant. The mordant potassium dichromate produces beautiful colors with natural dyes, but it is a known human carcinogen and a dangerous environmental contaminant. (It's the chemical that was in the Erin Brockovitch movie.) The safest mordant, and therefore the most popular for home dyeing, is alum, but alum has been fatal to adults in some cases, and it is much more dangerous for children than the synthetic dyes in a tie-dye kit. Other mordants, such as iron, copper, and tin, have caused many more deaths than alum.

A major cause of environmental damage is the use of pesticides and fertilizers to grow crops such as cotton. Anything which encourages garments to last longer before being replaced is kinder to the environment; anything which encourages people to discard clothing because it looks old and faded is bad for the environment. Natural dyes tend to fade after only a few washings, in contrast to fiber reactive dyes which stay bright for years. Long-lasting permanent dyes probably do less harm to the environment than the frequent diposal and replacement of clothing that has been dyed with less permanent dyes.

Even the production of natural dyes can be bad for the environment. Unlike synthetic dyes, which can be used in tiny quantities, most natural dyes must be used in immense volumes. A pound of fabric that can be dyed with a small spoonful of synthetic dye requires two to three pounds of a natural dyestuff to dye it. This means that converting from synthetic dyes to natural dyes will require that a great deal of land now wild be switched to use in farming. The land required to grow the dyestuffs must be cleared, killing the eco-system that originally occupied the land. The animals and plants that belong to the eco-system are destroyed. Fertilizers are often applied, creating run-off that causes dead zones in the ocean, and pesticides are used that kill birds and other animals, as well as harmless butterflies and other beneficial insects. There are serious economical problems that will result from adding new farm crops, as well; consider how food prices went up around the world this last year, dooming many poor people to starvation, at least partly as the result of the diversion of corn from food for ethanol fuel production. Farming is not harmless to the environment.

In order to be kinder to the environment, you cannot simply substitute natural dyes for synthetic dyes, because in many ways they are just as bad or worse. Instead, you can wear clothing that is made from naturally colored cotton or wool. Cotton can be grown with a range of natural colors in the fiber; instead of fading as they are washed, these naturally colored undyed cottons become more intense in color. Colored cotton fibers were grown in the Americas before the time of Columbus, and in recent years their breeding has been revived by Sally Vreseis Fox. Unfortunately, textile industry forces have tended to suppress the production and sale of naturally colorful undyed cotton. More importantly, you should reduce the amount of clothing that you buy and throw away. Don't buy "disposable" clothes; buy clothes that will last and that you will like for a long time.

For more information, see:
Are Reactive Dyes eco-friendly?
and
Aren't natural dyes safer than synthetic dyes?


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[A version of this answer was first posted, by me, on Yahoo answers, on August 14, 2008.]