I thought we’d take a look at
the dyeing process because so many people ask if we use “natural” dyes. The
answer is no, we don’t (although we’re not entirely objecting to natural dyes),
and I hope the next two blogs will explain our position! Let’s first take a
look at what makes the dyes (and how they are applied) an area of concern.
Dyeing cloth is one of our
oldest industries; people used natural products found around them to change the
color of the fibers used to make their cloth – things like leaves, berries, or
roots. The first synthetic dye was created in 1856. Today the use of natural dyes
on a commercial scale has almost disappeared (except for a resurgence in the
craft market) in favor of the newer synthetic dyes. The production of synthetic
chemical dyestuffs has become big business, but unfortunately the production
and use of these synthetic dyes is one of the world’s most polluting
industries. Conventional synthetic dyes present health risks
to those
working with them and to those who wear them, as well as damaging the
environment in a number of ways. Why?
Dyes are compounds that can be
dissolved in solvents, usually water. The process of dyeing cloth
uses a great quantity of water – according to the United States EPA, it takes
an average of 5 – 35 gallons of water for every pound of finished fabric. That
translates into 125 – 875 gallons of water to dye 25 yards of fabric – enough
to cover one sofa![1]
The dyes in solution are
absorbed by the fibers. The process of transferring the dye from the water to
the fiber is called exhaustion or “fixation rate”, with 100% exhaustion meaning
there is no dye left in the dyebath solution. Most conventional dyes have an
exhaustion rate of 80%, meaning the dyestuff which is not affixed to the fiber
is flushed into our rivers with the spent process water. Each year the global textile industry
discharges 40,000 – 50,000 tons of dye into our rivers, and more than
200,000 tons of salt.[2]
One of the most pressing
issues today is the lack of fresh drinking water, and as one of the most polluting
industries, textiles – and especially the dyeing of textiles – is
responsible for many instances of pollution making fresh water undrinkable. In
the worst cases, communities have to use polluted water to drink, wash clothes,
bathe and irrigate crops and the toxins they’re exposed to can have
catastrophic effects. Even in those instances where water treatment is in
place, toxic
sludge is a byproduct of the process. Often sludge is sent to the
landfill, but
the toxicity of the sludge remains – containing, among others, heavy metals,
gypsum, malachite green (identified by the U.S. Food and Drug
Administration as a priority chemical for carcinogenicity testing).
The 40,000 to 50,000 tons of synthetic dyestuffs
expelled into our rivers are complex chemical formulations containing some
things that are very toxic to us, such as heavy metals (like lead, mercury,
chromium, zinc, cobalt and copper), benzene and formaldehyde. Many
certifications, such as the new Global Organic Textile Standard and Oeko-Tex, restricts the kinds
of chemicals allowed in certified products. For example, GOTS restricts amine
releasing AZO dyes and disperse dyes (must be <30 mg/kg); chromium, cobalt,
copper, nickel, mercury, lead, antimony and arsenic are all restricted
(rather than prohibited as many people believe). So the dye formulation means a
lot when you’re evaluating the eco credentials of a fabric – but almost never
will you be able to find out what dye was used in any particular fabric. Copyright:
Jucheng Hu
In addition to the
formulation, there are requirements that dyestuffs must meet regarding oral toxicity,
aquatic toxicity, biodegradability, eliminability and bi-accumulation in fatty
tissues. The GOTS details are on their website: www.global-standard.org. Some
dyestuff producers advertise that they have a dye group that meets these
standards, such as Huntsman and Clariant. So the formulation of dyes used makes
a big difference – look for dyestuffs that have been certified by a third
party, such as GOTS.
Remember
that if the average exhaustion rate is 80% for most dyes (i.e., that 20% of the
dyestuff is expelled with the wastewater) then that means that 80% of the
dyestuff remains in the fabric! In other words, those toxic
chemicals remain in the fabrics you bring into your homes. What do I
mean by “toxic” – if you can stand it, I’ll give a short synopsis of the
effects some of these chemicals found in many dyestuffs have on us:
- Mercury : Easily absorbed thru the skin or inhalation of dust which
contains residues; effects the immune system, alters genetic and enzyme
systems, damages the nervous system. Particularly damaging to developing
embryos, which are 5 to 10 times more sensitive than adults.
- Lead : Easily absorbed thru the skin or inhalation of dust which
contains residues. Impacts nervous system. Even low levels of lead can
reduce IQ, stunt growth and cause behavior problems.
- Chromium : Necessary for insulin
activity and an essential trace metal; at toxic levels it causes squamous
cell carcinoma of the lung.
- Copper : Fatigue, insomnia, osteoporosis, heart
disease, cancer, migraine headaches, seizures. Mental disorders include
depression, anxiety, mood swings, phobias, panic attacks and attention
deficit disorders.
- Cadmium : Extremely toxic to
humans because of its inhibition of various enzyme systems; primary target
organ is the kidney; but also causes lung cancer ; also causes testicular
damage and male sterility. Plants readily absorb cadmium from the soil so
it easily enters food chain. Chronic exposure is associated with renal
disease.
- Sodium chloride (salt) : not toxic in small
doses (thankfully for me and my salt addiction), but the industry uses
this in such high volumes it becomes an environmental hazard; an
organochlorine (the class of organochlorines are very stable (i.e. does
not break down into other compounds) and they bioaccumulate; 177 different
organochlorines have been found in the average population in Canada and
the US. Each person has a unique level at which this build-up becomes
critical and triggers a wide range of health problems.) Well known effects
of chronic organochlorine contamination include hormonal disruption, infertility
and lowered sperm counts, immune system suppression, learning
disabilities, behavioral changes, and damage to the skin, liver and
kidneys. Newborns, infants, children, childbearing women and the elderly
are even more vulnerable to these health impacts.
- Toluene: affects the central nervous system; symptoms range from slight
drowsiness, fatigue and headaches, to irritation of the respiratory tract,
mental confusion and incoordination; higher concentrations can result in
unconsciousness and death. Prolonged contact can cause dermatitis.
Teratogenic, embryotoxic.
- Benzene: Highly carcinogenic, linked to all types of leukemia but believed
to cause the rarer forms (acute myelogenous leukemis (AML) and acute
lymphocytic leukemia (ALL); effects the bone marrow and decrease of red
blood cells, leading to anemia, excessive bleeding and/or immune system
disfunction. Low levels cause rapid heart rate, dizziness, headaches,
tremors, confusion. Easily absorbed by skin
Better Thinking Ltd., a UK based organization, took a look at the dyes
used in the industry and what they do to us and our environment. They published
their findings in a paper called “Dyeing for a Change” which explains the
various synthetic dyes available and how they’re used. (Click here
to read about it.)
There are several classes of dyes:
1. Direct dyes: given this
name because they color the fibers “directly” and eliminates the need for a
mordant (the chemical fixing agent lots of dyes need). Azo dyes are a type of
direct dye made from a nitrogen compound; azo dyes are known to give off a
range of carcinogenic particles and have been banned in many places, including
the EU. Effluent contains 5 – 20% of original dyestuff, plus salt and dye
fixing agents.
2. Vat dyes: these dyes
need a powerful reducing agent, such as alkali, to make them soluble. Expensive
and complicated to use, effluent contains 5 – 20% of residual dyestuffs, plus
reducing agents, oxidizing agents, detergents and salts.
3. Sulphur dyes: 90% of all
sulphur dyes contain sodium sulphide, which endangers life and alters DNA,
corrodes sewage systems, damages treatment works and leads to high pH and
unpleasant odors. Effluent contains 30 – 40% of the dyestuff plus alkalis and
salt.
4. Reactive dyes: these dyes
bond directly with the fibers, rather than merely remaining as an independent
chemical entity within the fiber. Applied with relatively cool water (saving
energy) and
Of all the classes of synthetic dyes, a subset of “reactive” dyes
(called “low impact fiber reactive”) seems to be the best environmental choice.
As “Dyeing for a Change” explains:
Low-impact reactive dyes are
usually defined as “low impact” because of the supposed lower fixation rate –
however, these dyes have a fixation rate of at least 70%, which still leaves
much room for improvement. What does make them “low impact” and classified by
the EU as eco-friendly: they have been formulated to contain no heavy metals or
other known toxic substances, and do not need mordants. The high cost of this
dye becomes an environmental advantage, as it is cheaper to reclaim dye from
the effluent rather than discharge it all and start from scratch. The water can
also be recycled. The dye cycle is shorter than it is for other dye processes,
meaning less water, salt and chemicals are needed. The entire process normally
occurs at a pH of around 7.0, meaning no acids or alkalis need to be added to
the water.
However, there are still
disadvantages: like other environmentally damaging dyes, these dyes are made from
synthetic petrochemicals. The process requires very high concentrations of salt (20%-80%
of the weight of the goods dyed), alkali and water. Even if the
unfixed dye is reclaimed, the effluent from this process can still contain high
concentrations of salts, surfactants and defoamers, and is strongly
alkaline. It’s also quite expensive, whereas conventional dye is
cheap. This process’ effluent normally contains salt, alkali, detergent and
between 20% to 50% of dye used. As reactive dyes currently make up 50% of world
dye consumption, more knowledge on how to improve upon this method is needed.
Fortunately, research is being
undertaken in this area, and a number of companies have produced products that
improve on its impacts. It’s been found that, by pre-treating cotton with 120g
of phosphate buffer per kg of fabric, no salt or alkali is needed in the dyeing
process as the process can occur at a neutral pH. It also means the amount of
water required can be halved and the whole dyeing process can be significantly
reduced, presenting additional benefits in the form of cost savings. Compared
to the other chemicals used to dye fabric the conventional way, this is a
relatively low concentration, and its high exhaustion value means the effluent
would only contain it in small proportions, making it a greener alternative.
And British scientists have developed a way to use algae (called diatoms) to
color the fabric – eliminating dyes entirely![3]
So you see why water treatment
is critical – even if a dyestuff has a rather benign chemical formulation, the associated
salts, defoamers and fixing agents must be dealt with. We chose low
impact fiber reactive GOTS approved dyestuffs for our fabrics – and we made
sure that all wastewater is treated adequately before release. But that’s not
good enough – partly because there is still the question of the sludge created
during the process and partly because we need to make sure that ALL process
inputs have a benign chemical profile.
Tune in next week, when the
subject will be “natural” dyes – hopefully the discussion will clear up our
thinking on synthetic vs. natural dyes.
[1]“Analysis
of the Potential Benefits of Recycled Water Use in Dye Houses”, Water 3
Engineering, Inc., April 2005.
[2]
Dyeing for a Change, page 4
[3]
Madrigal, Alexis, “How Pond Scum Could Lead to Eco-Friendly Fabric and Paint”,
Wired magazine, 10.11.07
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Tags: chemical-laden, fabric, Global Organic Textile Standard, GOTS, healthy, heavy metals, natural dyes, natural fibers, sustainable, synthetic dyes, Textile, textiles, water
Categories : dyes, processing and manufacturing, Textile
Tags: chemical-laden, fabric, Global Organic Textile Standard, GOTS, healthy, heavy metals, natural dyes, natural fibers, sustainable, synthetic dyes, Textile, textiles, water
Categories : dyes, processing and manufacturing, Textile
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