1.Hexavalent chromium

chromium plays an important role in the tanning of leather and is an essential tanning agent as it makes the leather soft and supple. Chromium exists in two valence states, trivalent chromium and hexavalent chromium. Trivalent chromium is not harmful to humans, but hexavalent chromium, which is produced by oxidation under specific circumstances, is a carcinogen. The production of hexavalent chromium is related to process technology. Leather manufacturers in some European countries (e.g. Italy, Spain) do a better job of treating chromium, and although they also use tanning agents containing chromium, they have relatively good control over the operation of the process and can achieve almost undetectable hexavalent chromium. The amount of metal in some dyes varies, some metals are essential but can be harmful at certain levels, for example nickel can cause lung cancer. Excess hexavalent chromium can destroy the blood in the body.

2.Banned azo dyes

There are currently more than two thousand azo dyes, of which more than 150 are listed as banned. The current international regulations list more than 20 types of azo dyes that can be detected, most of which are present in dyes. On 11 September 2002, the European Union issued a total ban on azo dyes, with a deadline of 11 September 2003. Products found to contain banned azo in the European market will later be returned to the market and may even be subject to anti-dumping. Azo is a synthetic dye that is widely used in leather and textiles. Azo produces an aromatic amine through contact with the skin, which can cause cancer when absorbed by the skin.

3. PCP

PCP is an invisible and intangible substance that is added as an ingredient in tanning to prevent corrosion and can be left in the product after the preservative process if it is not treated completely, causing harm to people’s health. PCP is a preservative that is very toxic to living things and can deform or cause cancer.

4. Formaldehyde

Formaldehyde is widely used as a preservative and tanning additive. If not completely removed, free formaldehyde can cause a variety of diseases, such as irritation of the eyes, affecting the nasal mucosa when the concentration exceeds the limit, and long-term contact with formaldehyde can easily lead to blindness and even throat cancer. So it is not only in Europe that there are strict legal restrictions, but since 1st January 2003, China has also banned formaldehyde in excess of the standard.