How low can you go?

Chrome tanned leathers contain chromium in valence state III (Cr III). The amount of chrome in the leather varies due to variations in production processes but for a shoe upper leather the chromium content is typically 4%. It is, however, possible and, indeed, common practice to use chromium in conjunction with other tanning agents, referred to as combination tannages. The proportion of chromium in these leathers can vary considerably depending on whether the main tannage is based on chromium or it is used as a retannage. The Issues Whilst the use of chromium is common to varying levels within leather production, there is pressure from many industries to reduce the level of chromium used in products. BLC has carried out a life cycle analysis (LCA) to evaluate tanning chemicals. This compared chrome tanning with vegetable and aldehyde based processes. It should be noted that when considering the cradle-to-grave issues, there were no significant differences found between these technologies. However, there is one area where chromium does have a disadvantage; it is environmentally persistent. It cannot be destroyed and it will always be present in some form within the environment. Incineration, composting and gasification will not eliminate chromium. Another consideration, in terms of end-of-life leather or management of chrome tanned leather waste, is the possibility of the valency state changing from the benign Cr III to the carcinogenic Cr VI. There are also other market factors that should be considered. The automotive sector clearly dominates the chrome free market for leather. The OEMs are driving this, with Audi, VW and Volvo specifying chrome free leather. This is being transferred to other industries such as footwear. Chromium free The trend of certain brands towards a requirement for the use of chrome free leather has raised the important question of 'What is chrome free?' With any method of analysis that is intended to measure the presence or absence of a specific compound, the accuracy of the test method needs to be considered along with the presence of background interferences and contaminants. It is impossible to determine absolutely that there is 0ppm of a chemical present. This is equally applicable to the definition of chromium free leather. There are test methods in existence that are capable of measuring the concentration of chromium in leather to ppm levels. However, should leather containing 10ppm or 1000ppm of chromium be considered chromium free? There are currently no industry standards that define the limit for chromium free leather. Essentially the aim is to ensure that chromium has not been used in the tanning process, but also to detect levels that may occur from additions of potential chromium-containing processing chemicals (dyes or pigments for example). It is recognised, however, that there will be some degree of background contamination in leather. For this reason, the BLC guideline is that if chromium is detected at a level below 100ppm this should be considered appropriate for defining chrome free leather. Extractable chromium The definition of chrome free leather implies analysis of the total concentration of chromium present in the sample. There are internationally recognised methods for this and currently new methods are in progress through CEN and ISO to allow analysis with Inductively Coupled Plasma (ICP) and Atomic Absorption (AA), which are suitable for detection at ppm levels. Another area of concern for the industry is the practice of restricting the level of extractable chromium from a leather product. This is increasingly common within the various Eco-labels, especially those originally intended for application to textiles, but which have been extended to include leather. At present there is no officially recognised method for the determination of extractable chromium in leather. Generally, the approach used by many laboratories is to use an artificial perspiration solution to extract the chromium followed by analysis by AA or ICP. Currently, CEN and ISO are evaluating options for the analysis and this is the likely route to be followed. There is also one particular area of concern for the use of chrome tanned leather; this is the application of chrome tanned leather to items intended for children (particularly those under the age of 36 months). These products must conform to the Toy Safety Regulations, which includes testing according to EN71-3. EN 71-3 is a method that requires the determination of extractable metals. Chrome tanned leather will not pass the requirements of this test due to the harsh extraction conditions (dilute hydrochloric acid). There is an alternative test method in existence within the UK, which relates to the determination of extractable chromium from baby harness leather (BS 6684:1989). Leather will meet the requirements of this standard. Within the UK, therefore, compliance to this standard is often considered acceptable to allow use of chromium tanned leather and should give consumers the assurance they need over its use. However, it should be noted that there is no legal precedence for this situation and it may not be acceptable outside the UK. Conclusion The introduction of a concept such as 'chrome free' needs a similar degree of thought and research as is carried out for the introduction of a restricted substance. Whilst chromium III is not a restricted substance, it is recognised that there are certain situations where chrome tanned leather is undesirable. BLC is able to offer a full suite of tests to ensure that the appropriate technique is applied depending upon the final application and market of the product concerned. For further information contact Victoria Addy on vikki@blcleathertech.com or +44 1604 679953.