About Asbestos

There are different forms of asbestos, broadly divided into the amphibole (actinolite, amosite, anthophyllite, crocidolite, and tremolite) and serpentine (chrysotile) groups. Chrysotile is the most used form of asbestos worldwide and the only one that is commercially mined today.

All forms of asbestos are known to cause cancer in humans (as concluded in the IARC Monographs (1)). The most recent IARC Monograph on this topic concluded that there is sufficient evidence that asbestos causes cancers of the lung, larynx, and ovary as well as mesothelioma (1). The Monograph also reported that positive associations have been observed between asbestos and cancers of the stomach, pharynx, and colorectum. The World Health Assembly, in Resolution WHA 60.26, requested the World Health Organization (WHO) to conduct global campaigns for the elimination of asbestos-related diseases. WHO, in collaboration with the International Labour Organization and other intergovernmental organizations and civil society, has recognized that stopping the use of all forms of asbestos is the most efficient way to eliminate asbestos-related diseases (WHO Fact Sheet No. 343).

As with most identified carcinogens, there are still unanswered questions to be addressed about chrysotile. Because chrysotile has different chemical and physical properties to other asbestos fibres, it is important to conduct studies specifically of chrysotile to improve knowledge about its carcinogenicity, as distinct from that of amphibole asbestos or mixtures of chrysotile and amphiboles.

The current study seeks to contribute to filling the gaps in understanding about chrysotile with continued research, needed to obtain:

• More precise quantification of the risks of lung cancer and mesothelioma associated with exposure to chrysotile asbestos, e.g. in terms of duration and intensity of exposure
• Estimation of the risk of cancers of the ovary and larynx (recently classified as asbestos-related cancers) and other cancers, especially those for which there is some evidence of an association with chrysotile (cancers of the pharynx, stomach, and colorectum).

Answers to these questions have implications for cancer prevention and early detection, cancer services planning, compensation, and estimation of the cancer burden due to the effects of chrysotile exposure worldwide. This is particularly important given the prolonged disease burden from chrysotile, which arises for two reasons:

• First, asbestos-related cancers typically arise several decades after first exposure. This is evidenced in countries that now have the highest mesothelioma mortality rates worldwide, such as Australia, the Netherlands, and the United Kingdom, all of which have long banned the use of all forms of asbestos (bans were extended to include chrysotile in 1989 in Australia, in 1993 in the Netherlands, and in 1999 in the United Kingdom).
• Second, even in the absence of continued mining and use of chrysotile, exposure to chrysotile would be expected to continue worldwide due to persistence of this mineral fibre in the environment and ongoing occupational exposures such as those arising from repair work.