Challenges along the supply chain

In short:

  • The global leather supply chains are facing a number of sustainability challenges due to leather chemistry including impacts on environment and health, compliance issues, lack of traceability and business models.
  • The project team conducted a scenario process that yielded a number of factors that influence the use of chemicals along the supply chains – today and in 2035.

The manufacturing process of leather requires the use of chemicals. Legal requirements and specifications developed by the chemical industry on the careful use of chemicals aim to prevent harm caused by chemicals to humans and the environment. In the modern leather industry, however, global supply chains are the norm, which confronts brands and retailers with enormous challenges: in the control of processes (leather production and processing, other business processes), in compliance activities, and in the ability to actively push the implementation and development of a "more sustainable chemistry" from their suppliers.

Chemicals in tanning: Direct and indirect exposure to humans and the environment

The chemicals used throughout each production step can cause harm to humans and the environment in many ways. This applies to the entire life cycle of a leather product - starting at the slaughterhouse, where the skin is obtained as a raw material as a by-product, through the various tanning stages up to the shoe factory for instance. Many of the chemicals are problematic, e.g. labelled as hazardous based on the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) .

For further production steps after the slaughtering process, the rawhide is preserved. Problematic substances (biocides, fungicides etc.) may be used used. However, as these substances are expensive to purchase the "household chemical" salt is often used, which also poses a risk to ecosystems if wastewater is not properly disposed of. Refrigeration is often not available as a preservation method because of the technical and logistical effort and the (energy) costs involved. Preservation may also be necessary in the further life cycle during the (intermediate) storage of the processed rawhide and the end product.

In the so-called beamhouse, the hides have to be dehaired and degreased by chemical processes for the subsequent tanning process, which is usually - and to some extent necessarily - done by using "aggressive" chemicals.

With regard to the actual tanning process, three basic types - mineral, vegetable and synthetic tanning - can be distinguished, although in practice mixed forms of these methods often occur. More than 80 per cent of the leather available worldwide was processed using tanning agents, which are based entirely or partially on the mineral chemical chromium. Chromium is considered to be a comparatively efficient tanning chemical and poses, in this formulation, no significant risks to humans or the environment. However, chrome III can oxidise to the problematic substance chromium VI, which is classified as a carcinogen and may have a sensitising (allergenic) effect. Chromium VI is mainly caused by procedural errors during the tanning process, but can also be formed in the further life cycle of the leather as a result of (improper) handling. The alternative tanning chemicals can also be a hazard for humans and the environment. Thus, aldehydes which are used for synthetic tanning are also equipped with hazard labels. In addition, the production of these substances, like almost all commercially available organic chemicals, are usually based on fossil raw materials. Vegetable tanning agents have a favourable toxicological profile with regard to their intrinsic properties. However, vegetable tanning also results in a pollution of waste water, as it has a higher chemical and biological oxygen demand than e.g. chromium. Furthermore, the ecological and health-related consequences in regard to the cultivation of vegetable tanning agents must be considered (land use, monocultures lead to loss of biodiversity, competition with food supply). Consequently, all common tanning methods have specific advantages and disadvantages.

The tanning process is followed by the "finishing" of the leather, a process in which chemicals optimize the surface of the material with respect to the desired properties (protection against moisture, UV resistance, dyeing, etc.). For this purpose, the leather is for example lacquered or laminated.

Afterwards, downstream actors may process the leather into end products. Here, too, the material is often exposed to chemicals, such as adhesives (e.g. in shoes), which can cause adverse (side) reactions of the chemicals in the leather.

Compliance challenge

Legal requirements in the EU and in some cases at other locations regulate many of the problematic substances used in leather production and restrict or otherwise regulate their use (e.g. through reporting obligations). This applies, for example, to some of the per- and polyfluorinated chemicals (PFCs) used in the finish. A key issue is the restriction under the EU chemicals regulation REACH of chromium VI in leather products that may get into contact with the skin. Internal controls by - sometimes well-known - brands or by enforcement authorities show that the chromium VI limit of 3 mg/kg (0.0003 weight percent) is frequently exceeded in leather products. Many companies make considerable efforts to reduce their compliance risks, e.g. by selecting reliable suppliers and by chemical testing of products before they are placed on the market. Current control procedures can reduce the risk of product contamination with chromium VI and other regulated substances - but they cannot provide any guarantee.

Process control and Know-how

Professionalized workflows and the use of state of the art process technologies can avoid many of the hazards described. While the leather industry based in Germany obtains the relevant know-how, the capacities for waste water treatment at some locations within the EU are already reaching their limit. In addition, the situation concerning leather production in developing countries is much more problematic. Here, unskilled personnel often manages the control of the complex chemical processes of tanning; there is also a lack of investment in modern environmental technologies and of experts to operate them.

Innovations for a more sustainable leather chemistry?

Large parts of the leather industry have moved to locations in the "global south", where leather can be mass-produced in the low-wage sector. The priority here is production at low labour and investment costs. Although Europe's tanneries are investing in environmental technologies, they have reduced the amount of research and development activities considerably due to cost pressure. They mainly focus on optimising existing processes (incremental innovations). The chemical industry in Europe plays a leading role in the global market for leather chemicals. It provides the auxiliaries for the common manufacturing processes of leather and thus profits from the dominance of chromium tanning.

Lack of transparency and traceability

In today’s leather industry, global supply chains are the norm, which confronts brands and retailers with enormous challenges concerning controlling processes. A typical supply chain could look like this: Breeding and slaughter in South America, tanning to wetblue (tanned leather immediately after chrome tanning) in India, dyeing and finishing in China, manufacturing the product (e.g. shoe) in Vietnam, distribution in North America or Europe. The brand located in Europe has contact with its direct supplier, i.e. usually the importer. However, the identity of sub-suppliers regularly remains hidden to the brand. Traceability of which chemicals were used in which process and by whom (with further information on production methods, occupational health and safety, waste management, social aspects, etc.) exists – at best – only in the automotive industry. This makes the process control, compliance measures and the ability of brands to actively request "more sustainable chemistry" from their suppliers more complicated.

Business models insufficiently oriented towards sustainable development

In the light of sustainable development in relation to leather chemistry, global supply chains are based on established business models, which can impede creative thinking towards a more "sustainable" leather chemistry. New or further developed approaches are needed. Starting points for this include process and product innovations, more effective and efficient supply chain management as well as business practices such as "product-service-systems".

Problem description based on influencing factors for the use of chemicals in the leather industry

In 2019, a scenario process with actors from the leather supply chain (chemical industry, tanneries, consumer trade, automotive) and other stakeholders (NGOs, science) took place in the leather project of the Darmstadt University of Applied Sciences. One result of this process was the initial identification of factors influencing the use and handling of chemicals in the global leather value chains. For each influencing factor, there is also a brief outline of the status quo: