Abstract

BACKGROUND
By 1970 Britain led the world in asbestos regulation, yet the British mesothelioma death-rate is now the highest in the world, with 1740 deaths in men (1 in 40 of all male cancer deaths below age 80) and 316 in women in 2006. According to the latest HSE projection about 1 in 170 of all British men born in the 1940s will die of mesothelioma. The increase in mesothelioma mortality in Britain over the last 40 years is the legacy of widespread use of asbestos. Substantial exposures continued until about 1970 in parts of the asbestos industry, and until the early 1980s in the much larger workforce in construction and other occupations where asbestos lagging was
applied or AIB (asbestos insulation board) was sawn. Most mesotheliomas now occurring are due to exposures prior to 1980, and analyses of British mesothelioma deaths based on last recorded occupation suggest that former construction workers, particularly plumbers, electricians and carpenters, constitute the main high risk group, together with insulation workers, shipbuilders and locomotive engineers. However, until now, no representative study to quantify the relationship between mesothelioma risk and lifetime occupational and residential history has been carried out in Britain. A separate scientific publication of the results set out in this report is also available(Rake et al., 2009).

METHODS
Lifetime occupational and residential histories were obtained by telephone interview with 622 mesothelioma patients (512 men, 110 women) and 1420 population controls. Lifetime risks (LR) were estimated for British men and women born in the 1940s. Occupations other than construction were classified as high, medium or low risk, and proportions of mesotheliomas attributable to these groups, including construction, and to domestic exposures (living with an exposed worker) were also estimated.

RESULTS
Men: Relative to low-risk occupations, risks (odds ratios) for men with more than 10 years of exposure before age 30 were 50.0(95%CI 25.8-96.8; LR = 1 in 17) for carpenters, 17.1(95%CI 10.3-28.3; LR = 1 in 50) for plumbers, electricians and painters, 7.0(95%CI 3.2-15.2; LR = 1 in 125) for other construction workers, 15.3(95%CI 9.0-26.2; LR = 1 in 55) for other recognised high-risk occupations, and 5.2(95%CI 3.1-8.5; LR = 1 in 170) in other ‘medium risk’ industries where asbestos may be encountered. The risk in men who had worked only in industrial occupations that we classified as low-risk was no higher than in white-collar workers; only 8%
(13/153) of male mesothelioma cases who had worked in ‘low-risk’ industrial occupations had never worked in a higher risk occupation. Among men, 46% of mesotheliomas were attributable to construction, 39% to other occupations and 1.3% to domestic exposures, with 14% of cases not attributable to any known occupational or domestic asbestos exposure. Over a fifth (21%) of male cases had worked as carpenters. Only 4 cases (<1%) had worked for 5 or more years in asbestos product manufacturing. Women: Only 5 of the 110 women with mesothelioma had worked in high-risk occupations (odds ratio (OR) 4.8, 95%CI 1.3-17.7), and a further 32 had worked in industrial jobs classified as medium risk, often as assemblers (OR 2.4, 95%CI 1.3-4.3). Among women 22% of mesotheliomas were attributable to occupational exposures and 16% to domestic exposures, with 62% not attributable to occupational or domestic asbestos exposure.
Unexposed cases: The LR was similar in apparently unexposed men and women (less than 1 in 1000). This ‘background’ risk was approximately doubled in exposed workers’ relatives (OR 2.0, CI 1.3-3.2). No other specific environmental hazards were identified.

CONCLUSIONS
1. Mesothelioma risk is determined largely by asbestos exposure before age 30, and ranges from a lifetime risk of 1 in 17 for ten or more years of carpentry before age 30 to less than 1 in 1,000 in apparently unexposed men and women. Our results suggest that the predicted total of 90,000 mesotheliomas in Britain between 1970 and 2050 will include approximately 15,000 carpenters.
2. The risk of lung cancer caused by asbestos is likely to be of the same order as the
mesothelioma risk. This would imply that more than 1 in 10 of British carpenters born in the 1940s with more than 10 years of employment in carpentry before age 30 will die of a cancer caused by asbestos.
3. Asbestos exposure was widespread, with 65% of male and 23% of female controls having
worked in occupations that were classified as medium or higher risk.
4. Britain was the largest importer of amosite (brown asbestos), and there is strong although indirect evidence that this was a major cause of the uniquely high mesothelioma rate. The US imported far less amosite than Britain but used similar amounts of chrysotile (white asbestos) and more crocidolite (blue asbestos), and US mesothelioma death-rates in middle age are now 3 to 5 times less than British rates. British carpenters frequently worked with asbestos insulation board containing amosite.
5. We found no evidence of increased risk associated with non-industrial workplaces or those that were classified as ‘low risk’, including motor mechanics and workers handling gaskets and mats that may have contained asbestos.
6. The only potential non-occupational exposure associated with increased risk was living with an exposed worker.
7. The increasing trend in female rates in Britain and a comparison between British and US female rates both suggest that a substantial proportion of mesotheliomas with no known occupational or domestic exposure were probably caused by environmental asbestos exposure. The sources of this presumably included construction, building maintenance and industrial activities but may also include release of asbestos from buildings due to normal occupation and weathering.

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