Chrome in leather manufacture
About this essay
Dr Dietrich Tegtmeyer chairs the research commission of the International Union of Leather Technologists and Chemists Societies (IULTCS) and has written and spoken extensively about the use of chromium in leather production. Dr Tegtmeyer is vice-president for product development and application at the leather business unit of chemical manufacturer Lanxess. Before that, he worked for Bayer, the company from which Lanxess was spun off in 2004.
This essay tackles the following misrepresentation:
MYTH: The chromium salts used in leather production are toxic.
FACT: Chrome is safe; only a small proportion of chrome in use in manufacturing industries around the world makes its way into leather production. The metal is in high demand for steel production and in chrome-plating. It is also widely used in the tattoo industry. All chemicals must be treated with care but, if treated correctly, the chrome-based products supplied to tanners present no risk.
The most common method used throughout the world for tanning leather is known as chrome tannage. Approximately 85% of all leathers are manufactured using this process, and it has been established for more than 100 years. Tanning agents for this process are based on the element chromium, a metal that is naturally present in minerals, and the main use of which, after extraction, is in the manufacture of high-grade stainless steel and in chromium plating.
Chromium compounds are important in human nutrition; chromium is an essential trace element. It is also widely used as a colouring agent for tattoos, and is naturally present in many soils and woodlands.
There are two forms of chromium compounds that are taken into account within the leather industry. The first is found in chromium tanning materials that are used for tanning, where chromium is in the trivalent state, considered as non-sensitising and proven to be harmless.
The second form is the hexavalent state, which is found in chemical manufacture as an intermediate product. Hexavalent chromium is toxic to humans and animals, and so these processes are managed by the chemical manufacturers under very strict conditions. This ensures that the chromium-based tanning products received by tanners are in the trivalent state.
It is possible to convert chromium compounds from the trivalent state to the hexavalent state under extreme temperatures and oxidative conditions. Since the early 1990s, considerable studies have taken place to fully understand the detail of chrome tanning, and an indirect oxidation route has been determined under “normal” conditions. High UV exposure or oxidative agents can convert small amounts of trivalent chromium to the hexavalent state. Recommendations for avoiding these conditions are well documented, and the formation of hexavalent chromium compounds can be prevented. Moreover, in the wider environment, there is a rapid return to the harmless trivalent state.
This paper shows that, although there is confusion between these two forms of chromium, there are no reasonable issues with trivalent chromium in leather, and that the formation of hexavalent chromium in leather can be avoided.