The Restricted Chlorophenols

The International Agency for the Research of Cancer (IARC) is a powerful body that passes judgements on the nature of hazards posed to humans. The Agency has had several criticisms levelled at it in recent years, but one that seems to stick is that the Agency tends to find potentially hazardous chemicals that can cause a risk to human health, but it cannot seem to find the likelihood that they cause cancer. In other words, they identify the hazard that red meat can cause cancer, but they cannot definitively risk assess the likelihood of getting it. Some have argued that too many high-profile decisions on use/disuse of chemicals have been based on this hazard-linked approach rather than a risk-linked approach.

To put it another way everyone knows that eating too much salt, sodium chloride, is hazardous to a person’s health – that you could possibly develop high blood pressure. However, it is known that stress is probably a higher indicator of getting blood pressure. So, a risk assessment exercise for determining what factors would be greatest for giving you high blood pressure would have to give work stress as a higher factor than eating too much salt.

The IARC is funded by member states who contribute differing amounts of funding to an intergovernmental organisation. The IARC is answerable to the United Nations World Health Organisation who are given a mandate to compile compendiums on various chemicals. The Agency then prepares monographs - and as a conclusion uses an unknown assessment methodology (it is kept secret by the Agency). The chemicals are then classified using the following categories, see Table 1.

Table 1. Categorisations of carcinogens by the IARC.

The IARC strongly maps onto the various international classification structures, e.g., the REACH classification, labelling, packaging (CLP) guidance; and the US Environmental Protection Agency (EPA). To give you a flavour of these classifications, processed meat is classified as Group 1 (same as tobacco smoke) and red meat is classified as a Group 2a. The strongest reaction to the IARC conclusions have come from the classification of glyphosates (the herbicide called Roundup) as a Group 2A, which has not been classified anywhere near that level by any other organisation.

2,4,6-Trichlorophenol (2,4,6-TriCP)

A Group 2B carcinogen, lumped together in a monograph prepared by the IARC on the use of “polychlorophenols and their salts.” An example of bad science, where different chemicals are compared for their ability to cause cancer using typical IARC methodology: introduction, chemistry, broad (tenuous) links to disease in the workplace, known effects on animals, known effects on human cells, and a conclusion. The conclusion in this case takes all the listed chlorophenols and uses the strictest effect (pentachlorophenol) and uses that category to make a broad judgement on all polychlorophenols, despite strong evidence that 2,4-dichlorophenol is not cancerous in experimental animals (IARC, 1999).

Figure 1 shows the chemical structure and some useful classification information on a fungicide that used to be commonly used in the tanning industry.

Figure 1. A chemical information card showing basic information on 2,4,6-trichlorophenol. Source: Authenticae drawn and researched.

2,4,6-Trichlorophenol (2,4,6-TriCP) has been used in the tanning industry for well over 60 years. It should not be confused with the common antiseptic trichlorophenylmethyliodosalicyl (TCP) which is much safer for human health. The EPA have classified 2,4,6-TriCP as a Class B2, possible carcinogen. The EU has placed the risk phrase as H351, i.e., suspected of causing cancer. Note the other risk phrases, including harmful if swallowed or touched, and it is damaging to the natural environment.

2,4,6-TriCP is commonly a chemical that will contaminate tanning equipment. This means that if a single batch of wet-blue is processed in the tannery it will contaminate that equipment for a very long time. A single use of a cheap fungicide containing 2,4,6-TriCP will contaminate all batches of leather using that equipment until the it is cleaned or is eventually decontaminated through attrition. 2,4,6-TriCP is very soluble in alcohols, so contaminated drums or sammying machines are decontaminated using methylated spirits or another form of ethanol.

2,4,6-TriCP is commonly restricted in leathers across the EU at 0.2-0.5 ppm with the detection method, by high performance liquid chromatography (HPLC), currently set at 0.00064 ppm. Even trace quantities of contamination can be found in fungicides, bactericides, retanning, and even in finishing products. More on this below.

Pentachlorophenol (PCP)

A fungicide well known by tanners, especially those at the height of their game in the 1970s. PCP was a commonly used fungicide and pesticide. Compared to 2,4,6-TriCP, PCP is considered worse, see Figure 2. It was highly regulated and restricted since the 1980s and leathers has been tested for PCP since then.

Chemicals are generally carefully screened for PCP, and more lately for 2,4,6 TriCP as to avoid problems later with the importing/exporting of leather into sensitive markets. As a duty-of-care, a tannery at the very least should be concerned about using these products in leathers they supply to any market.

Figure 2. A chemical information card showing basic information on pentachlorophenol. Source: Authenticae drawn and researched.

PCP is limited in products in the EU at around 0.05 ppm and it can be detected at levels as low as 0.0074 ppm using HPLC. The total amount of 2,4,6-TriCP and PCP are normally totalled and a further restriction on total chlorophenols is usually applied.

Other than the obvious use of these products to prevent mould and bacterial growth, these fungicides are often included in protein based retanning/finishing chemicals. These can include protein containing pigments, fillers. It is not uncommon for a biocide to be included in any chemical that can rot while sitting on a shelf so chemical companies include a biocide. For cheap chemicals these could include PCP or 2,4,6-TriCP so it is advised to be cautious of these types of products. If in doubt, have them screened for these chemicals.

To say these chemicals are banned is difficult, as chemicals are very rarely outright banned due to the difficulty of detecting 0 ppm. It is easier to say the amount of chemical included is limited at XYZ ppm and amounts above that means the leather is restricted. Get used to testing (and paying for that testing) of the leather product, as consumer safety product testing is on the rise.


International Agency for the Research on Cancer, IARC (1999) Polychlorophenols and its salts. IARC Monographs 71: 770-815,

The author of this article are providing this article for information only. It must be clear that this article cannot be taken as legal advice, nor can it be taken as an absolute interpretation of the legislation. Restriction amounts are given as a guide and a reader should seek further guidance by their customers or a professional consultant.

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