Chromium in fabrics

28 02 2013

Art-Paints.comIn our ongoing series of looking at the different chemicals used in textile processing, we’re up to the C’s. This week’s topic is chromium.

Chromium (Cr) exists in several forms, which are described by different numbers in parentheses. The most common forms are elemental chromium (0), chromium (III), and chromium (VI). Chromium (III) occurs naturally in the environment and is an essential nutrient for the human body. Chromium (0) and chromium (VI) are generally produced by industrial processes.

Chromium VI, also called Hexavalent Chromium, is recognized as a human carcinogen by the National Toxicology Program; The International Agency for Research on Cancer (IARC) has determined that chromium VI is carcinogenic to humans. Chromium compounds are linked to lung cancer. Chromate-dyed textiles and chromate-tanned leather can cause or exacerbate contact dermatitis.

Chromium VI is used in textile manufacturing as a catalyst in the dyeing process and as a dye for wool (chrome dyes)(1). But you may know much more about it through its use in tanning leather.

Before the advent of synthetic dyes, all dyes came from natural sources such as minerals and plants. Often these dyes faded quickly if the dyed material was laundered. To fix or stabilize the color, chemical agents called mordants were used. Chemically, the mordant binds with the dye and the fibers of the material, preventing bleeding and fading. As early as 1820 the cotton and wool industries were using large amounts of chromium compounds (such as potassium bichromate) in the dyeing process. Red and green pigments developed from chromium compounds were also used for printing wallpaper during this period.

In 1822, a man named Andreas Kurtz moved to England and began producing potassium bichromate and selling it to the English textile industry at 5 shillings a pound. Competition soon drove the price down to 8 pence, about an eighth of the original price. This did not give Kurtz a satisfactory profit, so he began producing other chrome compounds, specifically chrome pigments. His chrome yellow achieved cult status when Princess Charlotte, daughter of George IV, used it to paint her carriage. This was perhaps the origin of the “yellow cab,” an idea exemplified today in New York City taxis. Kurtz left his mark on the world of color; “Kurtz yellow” is still available in British color catalogues.

In the film Erin Brockovich (2001, Universal Studios) Pacific Gas and Electric is portrayed as a corporate giant that poisoned the water of the small town of Hinkley, California. The movie, which is based on a real lawsuit, suggests that high levels of chromium-6 in the groundwater were responsible for an eclectic range of diseases among residents there, including various cancers, miscarriages, Hodgkin’s disease and nosebleeds. In 2010, the Enironmental Working Group studied the drinking water in 35 American cities. The study was the first nationwide analysis measuring the presence of the chemical in U.S. water systems. The study found measurable hexavalent chromium in the tap water of 31 of the cities sampled, with Norman, Oklahoma, at the top of list; 25 cities had levels that exceeded California’s proposed limit of Chromium VI and it’s less toxic forms.

It is leather tanning for which chromium is perhaps best known, because the animal skins are first given a chrome bath to prevent decomposition. This step is the most environmentally harmful of the entire tanning process, generating 90% of the water pollution associated with tanning leather (3). And that’s saying a lot, because tanning is an environmental nightmare: skins are transferred from vat to vat, soaked and treated and dyed. Chemicals used include alcohol, coal tar , sodium sulfate, sulfuric acid, chlorinated phenols (e.g. 3,5-dichlorophenol), chromium (trivalent and hexavalent), azo dyes, cadmium, cobalt, copper, antimony, cyanide, barium, lead, selenium, mercury, zinc, polychlorinated biphenyels (PCBs), nickel, formaldehyde and pesticide residues. At the same time, toxic gases like ammonia, hydrogen sulfide, and carcinogenic arylamines are emitted into the air(4). The smell of a tannery is the most horrifyingly putrid smell on earth.

According to the results of a three year study to address health impacts of pollution from the Blacksmith Institute, which works to solve pollution problems in the developing world, the tanning of leather is in the top 10 of the world’s worst pollution threats, at #5, directly affecting more than 1.8 million people (5).

(1) Duffield, P.A., et al, “Wool dyeing with Environmentally Acceptable Levels of Chrome in Effluent”, IWS Development Centre, West Yorkshire, England
(2) “EPA’s recommendations for enhanced monitoring for Hexavalent Chromium (Chromium-6) in Drinking Water:
(3) Blackman, Allen, “Adoption of Clean Leather-Tanning Technologies in Mexico”, discussion paper, Resources for the Future, August 2005
(4) Barton, Cat, “Workers pay high price at Bangladesh tanneries”, AFP, Feb. 2011

Leather furniture – what are you buying?

22 05 2012

People like to buy leather furniture because of leather’s durability (it’s advertised to last a lifetime) – even though it demands a bit of attention to keep it looking its best.   Manufacturers also like to portray leather (perhaps because of its high price) as conveying luxury and sophistication.

Leather has been used practically forever –  ancient peoples used materials that were available, like bark and plant tannins, alum, earth minerals, fish oils, animal brains, lime and smoke to preserve animal skins.  The natural tanning process takes a long time – from 1 to 12 months.  It often also relies on physical manipulation.

Today’s leather is a far cry from  early leathers because horribly toxic synthetic chemicals have replaced the older tanning chemicals (usually in the interest of time – chrome tanning takes only a fraction of the time as does “natural” tanning); modern leather tanneries are frighteningly toxic and the animal husbandry aspect is sad and sickening. There are a very few ethical tanneries, but so far I can count them on one hand.  [1]

Let’s take a look at what that leather on your sofa means to us today.

Many people think that leather is a by-product of the meat industry, and that buying leather does not increase the number of animals slaughtered.  But in the case of some animals, the meat is the by product – on ostrich farms, the leather account for 80% of the dead animal’s value.[2]  Some leather – made from more exotic animals like kangaroos, zebras, seals, snakes, lizards and even sharks – are either raised or hunted specifically for their skins. [3] Regardless of how you define it, the skin is not a “leftover” since processing it as leather accounts for about 10% of the slaughtered animal’s overall value,[4] generating significant profits for both factory farms and the leather trade itself.  In fact, without the lucrative sale of animal skins for leather, factory farms would not even be able to turn a profit by selling meat alone. Ultimately, buying leather products subsidizes factory farms while providing financial incentive for them to produce more leather.

Most leather comes from cattle who are slaughtered for meat, worn-out dairy cows who no longer produce enough milk to be profitable, and veal calves whose soft skin is particularly valuable.  These animals often suffer in many ways that are detailed on various websites (such as Liberation BC: Speaking out for Animals and PETA) – it is such a gut wrenching, gruesome story that I can’t even bring myself to talk specifics.

Let’s face it – leather is the skin of a dead animal.  It is, by nature, meant to decompose.  What do you think has to be done to that skin so it doesn’t decompose?

After 75 years at the bottom of the Atlantic, few items aboard the R.M.S. Titanic had survived the ravages of saltwater.  But leather items hadn’t rotted away because their chrome tanning prevented their decay.[5]

The global leather industry is composed of three sectors of activity: animal husbandry and slaughter, tanning, and product manufacturing. Tanning is the stage in which raw leather is processed and made more durable so that it doesn’t decompose in your living room. Tanning consists of two major processes:

  1. Wet blue production (so called because the semi-finished hide is given a chrome bath which imparts a blusih tint).  This process involves removing unwanted substances (salt, flesh, hair, and grease) from a rawhide (by soaking in a bath of lime and sodium sulfide to dissolve hair and flesh), trimming it, treating it to impart the desired grain and stretch, and finally soaking it in a chrome bath to prevent decomposition.  This step is far more polluting than finishing, generating 90% of the water pollution associated with leather tanning.[6]
  2. Finishing – Finishing involves splitting, shaving, re-tanning, and dying the wet blue.

Often leather is advertised as being “aniline dyed”.  That means the leather is dyed for color without any pigments applied.  These dyes enhance the subtle variations of each hide and the leather does not lose any structure or grain pattern.  It is often considered to be of a higher quality than other types of dyed leather because aniline dyed leathers develop a  distinctive patina over time. Only premium hides with the most pleasing color and texture are selected for this category, less than 5% of all upholstery hides in the world.

Semi-aniline, also referred to as “Aniline Plus”,  is also advertised.  These leathers are first dyed in the penetrating aniline dyes. Then a topcoat is applied to even out the color of the hide surface. The topcoat also serves to create fading- and soil-resistant pieces.  They retain a great amount of the softness of aniline dyed hides because the natural top grain is left intact. A much larger proportion of the worldwide hide supply is suitable for this class of leather and as a result they are more moderately priced than pure aniline dyed hides.

So now we come to the part about the problems with using leather – you knew it was coming.

According to the results of a three year study to address health impacts of pollution from the Blacksmith Institute, which works to solve pollution problems in the developing world,  the tanning of leather is in the top 10 of the world’s worst pollution threats,  at #5, directly affecting more than 1.8 milllion people.[7]

Blacksmith’s Bret Ericson, who managed the three-year project, says:  “These are not large-scale, multinational corporations that are responsible for this pollution. Typically, it’s low income, small-scale industries who have no emissions controls,” often because these outdated industries remain unregulated.

Because of the acknowledged hazards of leather production, the process is being discontinued in most European countries and the U.S., and operations are moving overseas.   Because of the relatively inexpensive cost of labor and materials, over half the world’s tanning activity occurs in low- and middle-income countries.  Leather tanneries are highly concentrated in Nepal, Bangladesh and India.  Bangladesh Tanners Association President M. Harun Chowdhury said, “Most of the European countries and USA are discontinuing leather processing, as [the] leather industry is an environmentally hazardous one.”[8]

Spurred by retailer demand in the West, leather buyers in Asia have been welcomed with open arms by governments all-too-eager for a slice of the global market, and happy to turn a blind eye to non-existent safety regulations in return. Regulations governing tannery pollution have been on the books for decades in countries such as Mexico. Among other things, they require tanneries to register with environmental authorities, install sedimentation tanks and water gauges, handle most solid wastes as hazardous materials, and— most important—pretreat wastewater so that daily concentrations of various pollutants do not exceed set standards. For the most part, however, these regulations are simply not enforced.[9]  One of the reasons mentioned for this, cited by Allen Blackman,  is that tanneries are often a mainstay of the local economy and therefore enjoy considerable political power.

So today Hazaribag, Dhaka, home to many leather tanneries,  the  once  pleasant, semi-rural district in the Bangladeshi capital, is now a wasteland of toxic swamps, garbage landfills and mountains of decomposing leather scraps, surrounded by slums where tannery workers live.  Piles of smouldering trash line the banks of the nearby Buriganga, which is classified as a “dead” river after it hits Hazaribag as pollution from the tanneries has made it impossible for any fish or plantlife to survive.

Every day, the tanneries collectively dump 22,000 cubic litres of toxic waste, including cancer-causing chromium, into the Buriganga — Dhaka’s main river and a key water supply — according to the ministry of environment.

More than 90 percent of the tannery workers suffer from some kind of disease — from asthma to cancer — due to chemical exposure, according to a 2008 survey by SEHD, a local charity, with local residents being almost as badly affected.[10]

This is The Ecologist Film Unit’s Jim Wickens take on what the situation is in Dhaka:

What chemicals are used to create such terrible pollution?

In all, around 250 chemicals are used in tanning. Skins are transferred from vat to vat, soaked and treated and dyed.   Chemicals include alcohol, coal tar , sodium sulfate, sulfuric acid, chlorinated phenols (e.g. 3,5-dichlorophenol), chromium (trivalent and hexavalent), azo dyes, cadmium, cobalt, copper, antimony, cyanide, barium, lead, selenium, mercury, zinc,  polychlorinated biphenyels (PCBs), nickel, formaldehyde and pesticide residues.[11]  At the same time, toxic gases like ammonia, hydrogen sulfide, and carcinogenic arylamines are emitted into the air. The smell of a tannery is the most horrifyingly putrid smell on earth.

Groundwater near tanneries has been found with highly elevated levels of a variety of toxic substances. The Regis Tanning Co., Inc., operated a tanning facility from the early 1950s until 1972 in New Hampshire. But more than 20 years after it closed down, groundwater samples collected in the area revealed that arsenic, chromium, lead, and zinc were all still present—likely because of wastes disposed of on the property—while samples taken from nearby Lamprey River and its wetlands indicated the presence of cyanide, chromium, and polychlorinated biphenyls (PCBs).[12]

The U.S. Centers for Disease Control and Prevention (CDC) found that the incidence of leukemia among residents near one tannery in Kentucky was five times the national average.[13]

Arsenic, a common tannery chemical, has long been associated with lung cancer in workers who are exposed to it on a regular basis. Several studies have established links between sinus and lung cancer and the chromium used in tanning. [14] Studies of leather-tannery workers in Sweden and Italy found cancer risks “between 20% and 50% above [those] expected.” [15]

And that aniline dye that is often advertised as non toxic:  not according to these sources:  Aniline is toxic by inhalation of the vapour.   [16] The International Agency for Research on Cancer(IARC) lists it in Group 3  (not classifiable as to its carcinogenicity to humans) due to the limited and contradictory data available.  It is linked to bladder cancer.[17]

What about vegetable-tanning, which is sometimes touted as an environmentally-friendly alternative to chrome-tanning? Vegetable-tanning is actually only different from chrome-based in one way: it uses vegetable dyes rather than, perhaps, aniline dyes, to give the leather a “more subtle, muted colour.”[18]The preparation of the skin for tanning is the same, and though vegetable-tanning eliminates the toxins produced during the process of chrome-tanning, it also has its limits: being stiffer and firmer than chrome-tanned leather, it can be used for saddles, belts,  and leather carving, but often not for shoes, coats, or anything that requires much flexibility. Additionally, when exposed to water and allowed to dry, it can discolour and shrink, becoming brittle.

As mentioned in the first footnote above, there are a few companies that are trying to transform the industry and to educate consumers about leather, such as Organic Leather in California.  They seek to “return reverence to the practice of working with leather…to pay homage to the tribal peoples of our world and to encourage respect for the quality of the animals’ lives, from the way they are raised to the way they die…(and) to make sure that no part of the animal already being harvested goes to waste.  Moreover, we are strongly concerned with the chemicals used in the tanning and dyeing process and their effects on the natural environment and the health of both workers and customers.”

[1] Organic Leather, in California,  is trying to create high-quality and stylish leather while working to transform the industry and educate consumers.  See their white paper:

[2] Kate Carter, Don’t Hide from the Truth,, 27 Aug. 2008

[3] Leather Made From different animals, Leather Supreme, May 13, 2008 AND “Animals Abused and Killed for their Skins”, PETA media center, 2010.

[5] Davis, John, “Method for safer leather tanning published by Texas Tech researchers”, Texas Tech Today, November 2007.

[6] Blackman, Allen, “Adoption of Clean Leather-Tanning Technologies in Mexico”, discussion paper, Resources for the Future, August 2005

[8] Jasim Uddin Khan, “Local Tanners Eye Bright Prospect as US, EU Quit Leather Processing,” The Daily Star 20 Dec 2007.

[9] Blackman, Allen, “Adoption of Clean Leather-Tanning Technologies in Mexico”, discussion paper, Resrouces for the Future, August 2005

[10] Barton, Cat, “Workers pay high price at Bangladesh tanneries”, AFP, Feb. 2011

[11] Ibid.

[12] U.S. Environmental Protection Agency, “Regis Tannery,” Waste Site Cleanup and Reuse in New England 9 Aug. 2006.

[13] Richard E. Sclove et al., Community-Based Research in the United States (Amherst: The Loka Institute, 1998) 52.

[14] Richard B. Hayes, “The Carcinogenicity of Metals in Humans,” Cancer Causes and Control 8 (1997): 371-85.

[15] France Labrèche, Occupations and Breast Cancer: Evaluation of Associations Between Breast Cancer and Workplace Exposures (Montréal: McGill University, 1997).

[16] Muir, GD (ed.) 1971, Hazards in the Chemical Laboratory, The Royal Institute of Chemistry, London.

[17]  AND Carreon, Tania, et al, “Increased bladder cancer risk among workers exposed to o-toluidine and aniline: a reanalysis”, Occupational and Environmental Medicine, 2010; 67:348-350

[18] Elizabeth Olsen, Can Leather Be Eco-Friendly…Ever?, Ecouterre, 19 Oct. 2009