Press Release WHO/51
26 July 1996
The group concluded that the industrial production of chrysotile has become generally safer for all those involved in the process, but further use of products, especially the handling of building materials during alterations, maintenance and demolition, may pose health risks. Therefore, where available, safe substitute materials for chrysotile asbestos should be considered.
The commercial term "asbestos" refers to a group of fibrous minerals that have extraordinary tensile strength, conduct heat poorly, and are relatively resistant to chemical attack. The other two widely used principal varieties of asbestos include crocidolite and amosite.
Asbestos is ubiquitous in the environment because of its extensive industrial use and the dissemination of fibres from natural sources. The asbestos minerals occur naturally as fibre bundles that may be several centimetres long. However, when manipulated, they break down into smaller units which may have dimensions in the submicron range. It is the small fibres that penetrate the human bodyconveyed by air and water which pose health risks.
Epidemiological studies, mainly on occupational groups, have established that human exposure to all types of asbestos fibres, measured in a number of fibres per one litre of dust or water, is associated with such diseases as diffuse pulmonary fibrosis (asbestosis), bronchial carcinoma, and primary malignant tumours of the pleura and peritoneum (mesothelioma).
The evaluation of chrysotile was specifically requested by several governments after the International Labour Organization (ILO) had recommanded the discontinuation of crocidolite, while chrysotile asbestos was still widely used throughout the world, especially in construction. Today, it accounts for over 95% of the world asbestos trade, and chrysotile deposits are exploited in more than 40 countries. Most of these reserves are found in southern Africa, Canada, China, and the Russian Federation.
The group met in the Geneva headquarters of the World Health Orgnization (WHO) within the framework of the International Programme of Chemical Safety (IPCS) co-sponsored by WHO, ILO and the United Nations Environment Programme (UNEP).
According to the experts, the available published data showed that in general the production of chrysotile has become considerably safer for all those involved. The exposure levels which were very high in the past dropped significantly in the late 1970's and have continued to decline to present day low levels. However, in production facilities without adequate dust control, the exposures are still high.
Data on exposure levels during installation and use of chrysotile products were very limited but showed that such levels my be high, especially for building maintenance personnel due to large quantities of friable mixed asbestos fibres in place.
Exposure of the general population to adverse effects of chrysotile was considered to be "generally low".
The experts stressed that appropriate control measures should considerably reduce risks of developing asbestosis, lung cancer and mesothelioma. Data from industries where such measures have been introduced demonstrates the feasilibity of keeping exposure at levels generally below 0.5 fibres/ml. Clinical manifestations of asbestosis, they said, were unlikely to develop under well controlled conditions while the risk of lung cancer depended on exposure. Today, this risk is the highest in the chrysotile textile production, and considerably lower in chrysotile cement production, in the production of friction products, and in mining.
The question of the extent to which the mesotheliomas may be attributed to chrysotile versus other accompanying asbestos fibres has not been resolved by the group. Proportional deaths which could be attributed to mesothelioma in various mining and production sectors range from 0 to 0.8%. However, the participants thought that by far the greater proportion of mesotheliomas was likely to occur in workers-users of asbestos containing products, such as in the construction industry, rather than among those involved in production.
The use of friable products has high exposure potential. Construction materials are of particular concern because the workforce involved is large and control measures are difficult to institute. In place, it was stressed, building materials may pose risk to those doing alterations, maintenance and demolition.
The chrysotile evaluation once again confirmed that asbestos exposure and cigarette smoking interacted greatly to increase the risk of lung cancer. Those who have been exposed to asbestos can substantially reduce this risk if they stop smoking.
More than 140 IPCS contact points - collaborating centres, institutions and individuals both in developed and developing countries - were involved in the preparation of the evaluation of chrysotile, which was reviewed by 17 experts from 10 countries: Austria, Canada, China, Croatia, Finland, Germany, Italy, Japan, the UK and the USA.
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For further information, please contact Igor Rozov, Health Communications and Public Relations, WHO, Geneva. Tel (41.22) 791.2532 or Fax (41.22) 791.4858.
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