To chrome or not to chrome?

The manufacture of leather does have an environmental impact, in as much as in the manufacturing process not all the inputs end up in the leather. Also when leather is disposed of the product becomes a waste material. What seems to have happened is that the gauge of a leather’s ‘eco-ness’ is measured by the absence of certain restricted chemicals or the method of tannage rather than any consideration of the real environmental impact. This push is fuelled by legislation and risk assessment processes but also more recently by environmental pressure groups, eco labels, high street retailers and brands or those seeking to gain competitive advantage through product positioning.
Whilst by no means the only consideration in defining or measuring an eco-leather, the type of tannage does have an influence on the environmental footprint. In a study commissioned by BLC, using a specialist company Ecobilan S.A1, there was no significant difference between the overall environmental life cycle between chromium, vegetable and aldehyde tannages. This said, chromium is still very much in the spotlight in terms of its suitability as a green tannage.
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 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. 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 form 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.
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.
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.

Further information on this can be found at www.leatherworkinggroup.com