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Leather facts

Essay six: Standards and use limitations for chemicals in leather production

Finding the formula

The vast majority of leather production is based on chromium salts. Chrome (III) is non-hazardous to health, and while it is possible for some chrome (VI) to form as a result of bad practice in leather manufacture, it is rare, and can be readily avoided, says Dr Kerry Senior, director of Leather UK.

Chemicals and their use touch upon every aspect of modern living. All industries make use of chemicals and the leather industry is no exception. The manufacture of leather has moved a long way from its earliest origins, to the application of a diverse range of chemistries to produce a unique and beautiful product. Modern chemicals allow tanners to manufacture leather with a huge range of applications, technical specifications and organoleptic properties.

The leather industry is frequently accused by the media, agenda groups or unwitting official organisations of using chemicals that have damaged the environment or human health. Agenda groups regularly and wrongly claim that leather manufacture involves the use of chemicals such as mercury, arsenic and selenium. Regrettably, such incorrect comments are repeated by others who have not done their own research. Even the World Health Organization continues to claim that arsenic is used in the manufacture of leather. Many of these claims may contain some historical truth but they are not relevant to the modern tanning industry.

Unrestricted and careless use of any chemical has the potential for harm to human health and to the environment. As with other industries, the use of chemicals in leather manufacture has been subject to evolving controls, largely through formal regulation such as the 2006 EC Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) regulation, and, increasingly, to meet consumer and brand requirements.

Growing awareness of risks has seen the implementation of restrictions and bans on chemicals that had previously been widely used. These requirements ensure that leather is produced without representing a risk to the environment or the consumer.

The regulations affecting the industry can be explored by reference to some of the chemicals that are often presented as causing harm to health and the environment as a result of their use in leather manufacture. These include chromium compounds, azo-dyes, formaldehyde, pentachlorophenol (PCP) and many others. Many of the regulations relating to these chemicals have been developed in Europe and the scope of restrictions will be explored by reference to certain European regulations and the leather manufacturing chemicals that they apply to. However, worldwide, the leather industry is subject to stringent regulation with regard to chemical use.

Chrome III versus Chrome VI

Approximately 80-85% of the world’s leather production is tanned with chromium salts. Chromium compounds may exist in a number of valencies; the tanning industry specifically utilises chromium III salts that are considered non-hazardous to health. The non-hazardous nature of chromium III means that there are no regulations limiting the use of chromium III salts in leather manufacture or leather products.

Owing to its strong tendency to adsorb to organic material and low toxicity, chromium III is not deemed to be hazardous to the environment. By way of illustration, the 1985 EC directive on application of sewage to land set no limit for chromium in either the soil or the sludge. In the US, the limit for chromium in bio solids for application to land was deleted as there was insufficient evidence for regulation. Solid waste from the leather industry containing chromium III is also excluded from the US EPA hazardous waste list.

Conversely, chromium VI compounds are hazardous to human health. Chromium VI can be formed by poor practice in the manufacture of leather or in leather products as a result of a number of physical and chemical processes. Chromium VI is a recognised carcinogen through inhalation, and an allergen causing contact dermatitis in sensitised individuals. Exposure via the inhalation route is not relevant to the leather industry but, given the number of leather items that an individual may regularly come into contact with, exposure by the dermal route is relevant. As a result, chromium VI that might occur in leather is subject to a range of regulations.

The 1989 EC Directive on Personal Protective Equipment required that there be no detectable chromium VI in leather work gloves. In Germany in 2010, the 18th amendment to the Regulation of the German Ordinance on Commodities extended this prohibition to all leathergoods, including clothing, furniture and bags. In 2014, the European Commission issued a draft Commission Regulation, amending Annex XVII of the REACH Regulation (EC No. 1907/2006) to include a restriction on chromium VI in leather articles coming into contact with the skin. This regulation came into force in 2015 and required that leather articles or articles containing leather parts coming into contact with the skin shall not be placed on the market if they contain chromium VI in concentrations equal to or greater than 3 mg/kg (the effective limit of detection for the test method). In 2018, ECHA put forward a proposal to further lower the limit of chromium VI in leather articles to 1 mg/kg, in line with the textiles industry. Although seen by the leather industry as not scientifically justified, the proposal went through a consultation period in 2020. Following the consultation, a recommendation was made that the 3mg/kg limit should be retained until a new analytical method is developed; it is not definite that this will be adopted in the regulation. If the 1mg/kg limit is adopted, there would be a three-year derogation of limits for which new test methods would be needed. At the time of writing, the final text has not been made public.

Outside Europe, and a situation worth keeping an eye on, is that of California Proposition 65 (Prop 65) – specifically relating to the Safe Drinking Water and Toxic Enforcement Act of 1986. This requires businesses to provide warnings to Californians about significant exposures to chemicals that cause cancer, birth defects or other reproductive harm. Since 1987, chromium VI has been on the Prop 65 list and in recent years several alleged cases of warning violations have been raised with concern about leather in gloves. 

Restriction of azo dyes

Chromium is not the only chemical used in leather manufacture that is subject to regulation. Azo dyes account for 60-80% of all dyes and most coloured leathers are treated with azo dyes and pigments. However, a small number of these dyestuffs may be reductively cleaved to form carcinogenic aromatic amines. 
As such, in 1994, the German Consumer Goods Ordinance was amended to restrict the use of certain azo dyes that may give rise to the restricted aromatic amines in consumer goods, including leather. Several other EU member states introduced similar regulations and, in 2002, the 19th amendment of the Council Directive 76/769/EEC, prohibiting the use of those azo dyes in consumer goods that are considered to have regular skin contact, was approved.
Similar legislation exists outside Europe. In 2010, the US EPA added benzidine-based and benzidine congener-based dyestuffs, specifying 48 dyes, to the EPA List of Chemicals of Concern, on the basis of their potential to form carcinogenic aromatic amines. India has published legislation prohibiting the handling of 112 azo- and benzidine-based dyes. “Handling”, as defined under the Environment (Protection) Act, 1986, includes manufacture, processing, treatment, package, storage, transportation, use, collection, destruction, conversion, offering for sale, transfer or the like of such substances. Other countries, such as China, Syria and Turkey, have enacted or are in the process of enacting legislation or other risk management actions on certain azo- and benzidine-based substances.

EU rules have global reach

In the past, legislation has been developed on a compound-specific basis in response to an identified risk in use. However, regulations such as the 2006 EC REACH regulation and 2012 EC Biocidal Products Regulation take a much more proactive approach. This requires chemical suppliers to identify and understand the risks posed by their products in order for them to put be on the market.

The REACH regulation requires chemical substances manufactured or imported into the EU in quantities of greater than one tonne are registered with the European Chemicals Agency (ECHA) with a dossier of information on that substance. Failure to do so will mean that the substance cannot be manufactured, imported or sold in the EU. The dossiers will be evaluated and those substances considered to be of ‘very high concern’ will require an authorisation for use. Manufacturers, importers and users seeking an authorisation will have to demonstrate that risks associated with uses of these substances are adequately controlled or that the socio-economic benefits of their use outweigh the risks. They will also be required to analyse whether there are safer suitable alternatives or technologies. If there are, then they must prepare substitution plans and, if not, then they should provide information on research and development activities if appropriate.

REACH also restricts the sale or manufacture within the EU of product formulations containing more than certain amounts of chemical substances or the presence of certain chemical substances in consumer goods, e.g. chromium VI in leather. This means that, while REACH has no force outside of the EU, any product imported into the EU will have to comply with its requirements, such as the proposed restriction on chromium VI, and the limits on substances of very high concern. As the EU is the biggest import market in the world, this gives the regulation truly global reach and requires all manufacturers, including tanners, wishing to sell their products to the EU to be very careful in their choice of process chemicals.

Regional regulations can rapidly become global phenomena, as has been the case with EU restrictions on azo dyes and the REACH regulation, which has led to the development of similar legislation in other countries. Additionally, international agreements, such as the Stockholm Convention on Persistent Organic Pollutants, have impacted the use of chemicals that have been used in the manufacture of leather, such as brominated organic flame retardants and perfluoroctane sulfonates. Clearly, the constant evolution of legislation and its rapid adoption around the world means that the tanning industry, like other industries, is subject to numerous and increasingly stringent controls governing the use of chemicals in the manufacturing process.

Restricted substance lists

In recent years, however, a significant driver for the restriction and control of chemicals in leather manufacture has been the development of Restricted Substance Lists (RSL) by major users of leather, such as Nike, adidas, Marks & Spencer and Ikea. These RSLs normally repeat existing legislative standards but have global application. Any company wishing to supply leather to these brands must comply with the RSL regardless of their geographical location.

As RSLs are developed without the need for the same, and often extended, legislative process as regulations, they can be developed much more quickly and require considerably more stringent limits than might be required by ‘local’ regulation, e.g. there is no EU restriction on the formaldehyde content of leather yet the Nike RSL sets a limit of 75 mg/kg (16 mg/kg for products for infants) as defined in Japanese Law 112. The formaldehyde limit applied by Jaguar Land Rover for interior trim components is just 10 mg/kg. As such, for tanners needing to meet the RSL of their customers, these become the de facto standard regardless of local regulation.

The development of RSLs is driven by a number of factors, including a desire for an attractive corporate social responsibility profile, consumer demands and pressure from environmental groups. The Roadmap to Zero Discharge of Hazardous Chemicals, now managed by the ZDHC Foundation, attracted commitment from a number of major footwear and apparel brands, including Nike, adidas and Puma, to work towards eliminating the discharge of hazardous chemicals from their production processes by 2020. By the end of 2015, the ZDHC had compiled its Manufacturing Restricted Substances List (MRSL) to include for the first-time chemical formulations and substances that it wanted companies involved in leather production to be aware of and avoid. Currently the ZDHC has over 160 contributors, covering chemical suppliers, solution providers, associations, and brands plus an increasing number of tanneries.

The legislation governing the use of chemicals in industry, including the manufacture of leather, is in a constant state of evolution and, for the most part, each iteration or version increases the stringency and demands placed upon tanners. In addition to the requirements of legislation, tanners find themselves under increasing scrutiny by their customers and are required to comply with increasingly stringent product specifications. The combination of regulatory compliance and the commercial necessity of RSLs and MRSLs mean that tanners must be mindful of the chemicals used in the manufacture of their products. It would be disingenuous to claim that all leather (as with all other industries) is entirely compliant with the relevant legislation. However, the majority is and is manufactured by companies that not only rise to meet the demands of legislation and customers but are also driven by their own desire to produce a desirable, beautiful and safe product.

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