Name: Karen
Message: I am curious. I see the designation 'dyed with low-impact dyes' frequently on goods made from organic cotton or hemp. What are these low-impact dyes, and why are they considered low-impact on the environment?

It's a good question. I doubt that there is any standard definition of this term, and certainly there is no certification in the US that a low impact dye was actually used when claims are made that it was. However, apparently there is certification in Europe as to whether dyes meet something called the Oeko-Tex Standard 100.

Dyes which contain metal ions can be assumed to be more dangerous to the environment than those which do not, and dyes which require large amounts of rinsing may be considered higher impact than dyes which use less water.

Many Procion MX dyes contain no metal ions, but some do; the very popular Procion Turquoise MX-G contains copper, perhaps 1 to 5% by weight. The MSDS (Materials Safety Data Sheets) for each dye should indicate which metal ions are present in the dye. Low impact dyeing should presumably be restricted to the use of dyes and dye mixtures which omit the ones that contain heavy metals.

The large amount of water required for washing out unattached dye makes Procion MX dyes higher-impact than other fiber reactive dye classes such as Cibacron F or Drimarene K.

Natural dyes are often not at all low-impact, depending on the specific dye and mordant used. Mordants such as chromium are very toxic and high impact, but alum is better because it is far less toxic. The extremely large quantities of natural dyestuffs required for dyeing, typically in a weight equal to or double that of the fiber itself, makes natural dyes prepared from wild plants and lichens very high impact indeed. I do not have the information necessary to compare the environmental impact of the (hypothetical) farming of renewable plants such as woad, instead of other crops, to that of chemical syntheses using natural gas or petroleum as raw material. Modern farming practices require a remarkable quantity of petroleum fuels.