BLC News
About chromium and leather
23rd May, 2011
Most leather processed throughout the world is tanned using chromium (approx 80%). Correctly processed, leather should only contain the safe trivalent form of chromium. However, the use of inappropriate chemicals, processing conditions or treatments, such as washing finished leathers, may result in the hexavalent form being detected in leather.
Frequent chemical testing and control of processing can ensure that chrome tanned leather remains a safe, high performance product with an environmental impact on a par with other tanning systems.
Chromium remains a vitally important chemical in the global production of leather with at least 80% of global leather production being tanned with safe chromium III salts. It is a highly effective tanning agent producing leather with a flexible range of properties making it suitable for many end uses.
The safety of chromium salts has become a fiercely debated subject and as a result there is much inaccurate information in circulation regarding the use of chromium salts and their associated safety for the tanning of leather. In addition there is pressure within the supply chain to investigate alternatives to chromium based on the fact that the chrome salts used in tanning do have a propensity under very specific conditions to convert to hexavalent chromium.
Chromium is a mineral that humans require in trace amounts, although its mechanisms of action in the body and the amounts needed for optimal health are not well defined. It is found primarily in two forms: trivalent (CrIII), which is biologically active and found in food, and hexavalent (CrVI), a toxic form that results from industrial pollution. Chromium is widely distributed in the food supply, but most foods provide only small amounts (less than 2 micrograms [mcg] per serving). Meat and whole-grain products, as well as some fruits, vegetables, and spices are relatively good sources. In contrast, foods high in simple sugars (like sucrose and fructose) are low in chromium.
Chromium is a transition metal that can exist in a number of different oxidation states each with distinctive properties.
Metallic chromium
This is a steel grey, hard metal found as chromite ore (it does not occur in the metallic state naturally). It is used to harden steel, to manufacture stainless steel, and to form alloys. It is also used in plating to produce a hard corrosion resistant surface.
Trivalent chromium (Cr III)
Trivalent chromium compounds occur naturally in the environment and are also the most abundant from of chromium highlighting that nature favours the formation of low toxicity salts. They are found in rocks, soil, plants and volcanic emissions. Chromium salts are present in foodstuffs and are a necessary nutrient for the human body as trivalent chromium is required for the normal metabolism of fats and sugars. Nutritional supplements are currently on sale containing chromium picolinate. Chromium (III) sulphate is considered safe to use in leather manufacture.
Hexavalent chromium (Cr VI)
Hexavalent chromium is the hazardous form of this element. It can be formed when trivalent chromium is oxidised. This usually occurs in the presence of oxygen combined with other factors such as extremes in pH. The salts have a characteristic yellow colour and are classified as carcinogens. Chromium VI is not used in the tanning of leather.
In its hexavalent form chromium is hazardous. Breathing high levels of chromium (VI) can cause irritation to the nose, nosebleeds, and ulcers and holes in the nasal septum. Ingesting large amounts of chromium (VI) can cause stomach upsets and ulcers, convulsions, kidney and liver damage, ultimately death. Skin contact with certain chromium (VI) compounds can cause skin ulcers. Some people are extremely sensitive to chromium (VI). Allergic reactions consisting of severe redness and swelling of the skin have been noted.
Despite the overwhelming body of evidence to support the safety of trivalent chromium, the potential for the conversion to the less stable chrome VI remains. Leather is a reductive matrix which naturally supports the more stable trivalent form. If manufactured in a responsible way using appropriate process control and using chemicals from reputable sources then the chance of chrome VI being detected is negligible.
It is known that certain process chemicals, process conditions and other factors have the potential to result in the formation of CrVI in leather. It is also known that there are process modifications, alternative chemicals and stabilisers that can be used to avoid the potential formation of CrVI. By means of a thorough appreciation of the process chemicals used, frequent testing (ie at intervals required for BLC's ConsumerSure, EcoSure and MetalSure standards) and control of processing, tanners can ensure that chrome tanned leather remains a safe, high performance product.
There is a recognised test method for assessing the amount of chrome VI present in leather (EN ISO 17075). This method has a current detection limit of 3ppm and leathers should have no detectable chrome VI present within them. It is the view of BLC that this test method is a suitable test to determine risk to consumer health.
Aside from safety considerations, there has been much debate over the environmental credentials of chromium as a tanning material. Work carried out previously at BLC investigating the life cycle of three tanning materials, (chromium, aldehyde based tanning materials and vegetable tanning systems) determined that each of these materials has specific advantages and disadvantages in terms of their life cycle and were comparable in terms of environmental profile. In view of this, recent work has focused on the management of these tanning materials within the leather production process as a key measure of environmental performance.
For further information on the safe use of chromium and appropriate testing protocols, please contact info@blcleathertech.com . LCA data is also available to BLC members.
BLC members receive 30% discount on testing, training and consultancy.
