Is asbestos still a problem today?
Asbestos is the general name of several silicate mineral fibres. They include chrysotile with its long fibres and the more short-fibered crocidolite and amosite. They have been very popular because of their fire-resistance and have been used in all kinds of installations from private homes to ocean-going ships.
Asbestos causes three types of serious lung diseases, asbestosis, lung cancer and mesothelioma. In asbestosis, many fibres are present in the lung tissue, and abnormal connective tissue will grow around these fibres, severely damaging the ventilation capacity of the lungs. Depending on the fibre length, asbestos can cause primarily lung cancer or mesothelioma. Mesothelioma is a malignant tumour of the pleura, the fluid-lubricated bag around the lung. If there was no asbestos exposure, mesothelioma would be a very rare cancer. It is the very thin, about 5 micrometer long asbestos fibres which cause mesothelioma. The longer and thicker fibres tend to be the cause of lung cancer. Smoking adds clearly to asbestos-related cancer risk.
Mechanism of cancer causation
Cancer seems to be caused by the defence mechanisms of the body rather than by the fibre itself, although there may be several mechanisms involved. Macrophages, which are cells whose function is to “eat” and destroy foreign materials entering the body, try desperately to surround and swallow fibres that are often bigger than the cells themselves. During this process, they produce oxygen radicals to dissolve the material and they secrete different messenger compounds, e.g. cytokines, that initiate inflammation reactions and attract more inflammatory cells to the scene. This multi-faceted but useless defence activity evokes DNA-damage (mostly because of the oxygen radicals) and thus mutations, and also has a promotion effect that increases the likelihood of cancer. Thus the risk of cancer is very great after a long-term intense exposure to asbestos.
Risks at work
Those handling asbestos at work naturally experience the highest risk of cancer. Historically these were workers in asbestos mines and producers of asbestos products, and those working in shipbuilding. Since there was often inadequate, even totally absent worker protection, the exposures were massive. However, use of asbestos in new buildings was terminated in most countries in the 1980s, and all use was banned in 1990s. Therefore new cancers are only found in long-term workers. However, when old structures with asbestos are dismantled, e.g. when repairing old buildings, this can be a potential contemporary source of asbestos exposure. On the other hand, in many countries, worker protection is much improved as compared with the situation in the old asbestos mines or production of asbestos materials. Therefore the risk of new cancer is currently very low. Full protection is, however, as important as ever, and in many countries special permission and training of workers are required before they can do such risky work. Non-professional individual activities may cause risks.
Asbestos may also be transported by the wind from asbestos mines. A cancer risk due to these fibres in the environment is theoretically possible, but it is likely to be very low. There is no evidence that asbestos fibres in food would cause a risk of cancer.
Previously asbestos exposure was a major occupational cancer risk, but also the exposures were enormous in the past. Presently there is a risk associated with demolishing old structures containing asbestos. The full protection of employees doing this work is highly important.
Notes and references
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