6. Mesothelioma
This is a malignant, incurable cancer of the outside lining of the lungs (called 'the pleura') or the lining of the bowels ('the peritoneum'). When it affects the pleura it causes pain in the chest and breathlessness, and the chest X-ray shows signs of fluid and tumour inside the chest wall. It progresses slowly over 1 to 2 years, making the patient suffer more and more pain and malaise, lose weight and eventually die. A similar course is followed with peritoneal disease, though here there is pain and swelling in the abdomen.
Figure 5 Mesothelioma
The disease is clearly associated with exposure to crocidolite and amosite, but the association with exposure to chrysotile (white asbestos) is much less obvious. Although there is evidence that risk of development of mesothelioma is related to intensity of exposure, many cases have occurred after relatively short (around 6 months) exposure to amphiboles. This is historically why different hygiene standards were applied to these minerals.
John Hodgson and Andrew Darnton published an important paper investigating the risk of mesothelioma (and lung cancer) in 2000 3. The concluded that for historical exposure levels the risk of mesothelioma from the three main commercial asbestos types was roughly in the ratio 1:100:500 for chrysotile, amosite and crocidolite respectively. So from this analysis for the same fibre exposure crocidolite is 500 times more likely to cause mesothelioma than chrysotile.
Mesothelioma usually develops between 20 and 50 years after exposure to asbestos first took place. This explains why the occurrence of the disease has been steadily rising in Britain over the last 20 years (the current yearly total has now reached more than 2,000 deaths), since the peak use of amosite and crocidolite in Britain occurred during and after the last war. Restrictions on the use of asbestos in Britain over the last 40 years should eventually result in a reduction in the numbers of new victims of this disease.
Figure 6 Annual deaths from mesothelioma in Britain
1
Latest estimates from the Professor Julian Peto and colleagues from Cancer Research UK4 indicate that men born in the 1940's who worked as carpenters for more than 10 years before they reached age 30 have a lifetime risk for dying from mesothelioma of about one in 17. For plumbers, electricians and decorators born in the same decade who worked in their trade for more than 10 years before they were 30, the risk is one in 50 and for other construction workers one in 125. The risk is particularly marked for carpenters because they were more likely to have worked cutting asbestos insulation boards (AIB).
These researchers also showed that for every case of mesothelioma, asbestos also causes a case of lung cancer and so the overall risk of asbestos-related cancer for carpenters is about one in 10.
The risk was also increased in other industries and the study showed that two-thirds of all British men and one quarter of women had worked in jobs involving potential asbestos exposure at some time in their lives. There was also a small increased risk in those who had lived with someone who had been exposed to asbestos.
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