Minimising the Risk of Chromium VI Formation in Leather

Guest Contributor: Georgina Mawer, Eurofins BLC Leather Technology Centre 

The presence of Chromium VI in leather goods remains under the supply chain spotlight. It is mentioned in weekly RAPEX reports (EU), ongoing discussions under the proposed EU sensitizer regulations and in recent 60-day notices under the California Proposition 65 law (US). Products containing excessive levels of Chromium VI continue to be withdrawn from the market, recalled from end users, and rejected at borders, impacting manufacturers and retailers in terms of cost and reputation. 

Chromium – The Facts 

Chromium is a naturally occurring element found in rocks, animals, plants, food and soil. It can exist in several different forms. The most common forms are chromium (0) and chromium (III).  Chromium (VI), also known as hexavalent chromium, is a rarer form that can be formed from the oxidation of Chromium III.  

Trivalent chromium – Chromium 3 – Cr 3 - Cr III 

Trivalent chromium III compounds occur naturally in the environment and can be found in rocks, soil, plants, and volcanic emissions. Chromium salts are present in foodstuffs and are a necessary nutrient for the human body - Chromium III is required for human metabolism of sugars and some nutritional supplements contain chromium picolinate.  

Chromium III sulphate is safe to use in leather manufacture and, when sourced from reputable companies and used appropriately in accordance with best practices, produces a leather with a low risk of Chrome VI content. 

Hexavalent chromium – Chromium 6 - Cr 6 - Cr VI 

Hexavalent chromium VI is the hazardous form of chromium. It can be formed when trivalent chromium is oxidized. This usually occurs in the presence of oxygen combined with other factors such as extremes in pH. The salts have a characteristic yellow color and are classified as carcinogens. Chromium VI is not used for tanning leather, but chromium III can potentially convert to chromium VI under very specific conditions. 

Why do some leathers contain Chromium VI? 

Chromium III salts are used during the tanning process for most leather that is produced around the world. Chromium III tanned leather can generate traces of Chromium VI when exposed to certain environmental conditions (heat, UV radiation, changes in pH) or in the presence of unsaturated organic compounds and oxidizing agents. Often several of these factors need to be present at the same time in order to generate Chromium VI.  

The formation of Chromium VI from Chromium III can take place over time, which means that leather that is free of Chromium VI when it is manufactured may develop traces of Chromium VI later in its life, though this is only likely when the product is exposed to the harsh conditions described above. 

Under well managed production conditions, chrome tanned leather poses a low risk for Chromium VI formation. Tight process control, high quality raw material and the correct storage conditions can ensure that the risk of hexavalent chromium formation in leather is extremely low. 

Why is Chromium VI a problem for consumers? 

Chromium VI is classified as a skin sensitizer and can cause allergic contact dermatitis. EU REACH Regulations state that leather articles, and articles containing leather parts, that come into contact with the skin cannot contain 3 mg/kg or more of Chromium VI, by weight of the total dry weight of that leather part.? Further details can be found here

What can the tannery do to avoid the formation of chromium VI in leather during the processing? 

The following list of items is intended to show the tannery what to do to avoid the possible formation of Chromium VI in leather. It must be noted that there is no single item or step that will avoid the formation of Chromium VI in leather, but the factors listed below give the highest level of assurance that leathers will not form in situ Chromium VI. A brief summary is as follows: 

  • Purchase high quality raw material from reputable suppliers 
  • Monitor the fat content of leathers and the type of fat liquors used 
  • Control process pH levels 
  • Manage the free-chrome content 
  • Avoid oxidizing chemicals 
  • Use chemicals that minimize the risk of Chromium VI 
  • Understand the risks associated with transportation 
  • Include anti oxidizing chemicals in the process 

Please join us for our next webinar on Chromium, which will include information on the LWG guidelines for Chromium VI formation prevention – register via the links below: