Asbestos in Schools

Written evidence submitted by Prof Julian Peto DSc FMedSci, London School of Hygiene and Tropical Medicine

Asbestos in schools

Summary

This note discusses the mesothelioma risk that may be caused by the asbestos that still remains in many schools. The discussion is based largely on data for women, as so many men (including some teachers) have had some occupational asbestos exposure. The term "asbestos" should be read as "amphibole asbestos" throughout, both because the amphiboles (predominantly blue and brown asbestos) are the cause of the great majority of mesotheliomas, and because they constituted 98% of the asbestos fibres we found in British lungs.

The mesothelioma risk to female teachers is similar to that of all British women. This does not mean that no mesotheliomas are caused by asbestos exposure in schools. It means that similar exposures occurred in many offices, workplaces and homes. About 80% of mesotheliomas in women (versus 15% in men) are due to this widespread "background" exposure in various buildings. Because of the long latency, the lifetime mesothelioma risk from asbestos in schools is  probably about 3 times greater for a pupil than for a teacher. This implies that asbestos exposure is somewhat more dangerous in schools than in buildings occupied mainly by adults.

Asbestos use peaked in Britain between the 1950s and the end of the 1970s then stopped abruptly due to increasing health concerns. Men born in the 1940s were the most heavily exposed, as they worked throughout the peak. Asbestos use ceased soon after men born in 1960-64 were starting work, and their risk is 5-fold less. In contrast, childhood environmental exposure in homes and schools for women born in 1960-64 was likely to have been as high as for earlier generations, and this is confirmed by the much less rapid decline in the female mesothelioma rate. Studies of asbestos levels in lungs show the same pattern, falling sharply in men but not in women over succeeding generations up to those born in 1960-64.

The projected lifetime mesothelioma risk for people born in 1960-64 is about 1 per 1,000 in women and 2 per 1,000 in men. The risk in those born after 1965 is still too low to be studied, as the disease is so rare in young people. (Only 6 of the 1,946 male mesothelioma deaths and 3 of the 401female deaths in Britain in 2010 were aged under 45.) However, we have observed a 10-fold reduction in the average asbestos lung burden from those born in 1960-64 (~20,000 fibre/gm) to those born 1975-84 (~2,000 fibre/gm). We therefore expect the latter’s lifetime mesothelioma risk to be about 1 in 10,000. If the whole population suffered a risk of 1 in 10,000, the annual number of mesothelioma deaths (currently about 2,000 men and 400 women in Britain) would fall to about 30 of each sex. Some asbestos was still being used in 1975-84, so lung burdens are likely to be even lower in those born since 1985. We are now investigating that. We are also attempting to collect enough lung samples from female teachers to determine whether their asbestos lung burdens are higher than other women’s.

In summary, the overall current hazard from asbestos in buildings and the contribution from schools are uncertain and may be extremely low. My personal view is that the current management policy should be maintained, at least until these studies are completed. Further measures to remove asbestos could well transiently increase the low airborne levels that are generally seen in schools.

British mesothelioma rates in teachers and other occupational groups

British mesothelioma rates in various occupations for 2002-2010 are shown in table 1 (men) and table 2 (women). There were about 6 deaths a year below age 75 in female teachers, and about 8 a year in male teachers. These proportional mortality ratios (PMRs) are based on the occupation recorded on death certificates. A PMR of 100 means that the fraction of all deaths at ages 16-74 for that sex and occupation that are due to mesothelioma is the same as the national average. Mesothelioma is about 5 times commoner in men than in women, so the male PMRs of 17 in farm workers and 27 in farmers mean their risk is similar to that of the average woman with a PMR of 100, and about 20 times lower than that of carpenters and joiners (PMR 408). The PMR for male teachers may slightly exaggerate their risk, as we know from other studies that some male teachers have worked in other jobs involving asbestos exposure.

Table 1: Males: deaths aged 16-74 in 2002-2010 in Great Britain

Mesothelioma proportional mortality ratios (PMRs) for teachers, farmers, doctors and nurses.

SOC 2000	Occupation	Deaths	Expected deaths	PMR	95% confidence interval
Education teaching professionals
2314	Secondary	58	88	66	50-86
2315	Primary and nursery	10	18	56	27-103
Farming and medical (low risk)
5111	Farmers	26	97	27	18-39
9111	Farm workers	9	52	17	8-33
2211	Medical practitioners	13	27	48	25-82
Construction (high risk)
5315	Carpenters and joiners	857	210	408	381-436
5314	Plumbers; heating and ventilating engineers	414	126	329	298-362
5241	Electricians; electrical fitters	670	217	309	286-333

Table 2 shows that female rates for most occupations are close to the (female) national average, the main exception being factory workers (PMR 245). The PMR of 119 (CI 89-115) for female secondary teachers is comparable to other occupational groups, although there are too few deaths for precise comparison.

We have conducted a population-based study, interviewing over 600 mesotheliomas and 1400 controls to get lifetime occupational histories (Rake et al 2009 Br J Cancer 100:1175-83). Approximately 20% of female mesotheliomas were due to occupational asbestos exposure, usually in a factory, and a further 20% were caused by domestic exposure to asbestos dust brought home by a relative who worked with asbestos. The remaining 60% were non-occupational, in the sense that they cannot be accounted for by differences in risk between occupations. Apart from factory work, there is little difference in female mesothelioma rates between occupational groups, including teachers. Average asbestos levels were always substantially higher in homes, schools and other buildings than in the outside ambient air, so this suggests (1) that about 80% of female mesotheliomas were caused by the combined effects of indoor asbestos exposure at home, at school up to school leaving age, and at work, and (2) that most women were exposed to similar amounts of asbestos irrespective of their workplace.

Table 2: Females: deaths aged 16-74 in 2002-2010 in Great Britain

Mesothelioma proportional mortality ratios (PMRs) for teachers, and all occupations with 50 or more observed or expected deaths

SOC 2000	Occupation	Deaths	Expected deaths	PMR	95% confidence interval
Education teaching professionals
2314	Secondary	4	12	34	9-88
2315	Primary and nursery	53	45	119	89-155
All occupations with 50 or more observed or expected deaths in women
9139	Labourers in process and plant operations n.e.c.	65	27	245	189-312
4150	General office assistants/clerks	68	55	124	96-157
9233	Cleaners; domestics	115	113	102	84-122
7111	Sales and retail assistants	94	84	112	91-137
6115	Care assistants and home carers	67	75	89	69-114
3211	Nurses	52	61	85	64-112
4215	Personal assistants and other secretaries	75	68	111	87-139

Latency

The mesothelioma rate rises as the third or higher power of time since first asbestos exposure. This means that children are at considerably higher risk than teachers from asbestos exposure in schools. The risk to teachers is little or no higher than to other women, but it is possible that a substantial fraction of all female mesotheliomas were caused by childhood asbestos exposure at school. This would account for the fact that the female mesothelioma death-rate in women born in 1960-64 is about half the rate of those born in 1945. Those born in 1960 started work around 1980, when asbestos use had almost ceased, but they were children during the period of maximum asbestos use.

Mesothelioma is extremely rare before middle age. In 2010, for example, only 6 of the 1,946 male mesothelioma deaths and 3 of the 401female deaths in Britain were aged under 45. This is because most mesotheliomas appear more than 40 years after the asbestos exposure that caused them.

This very long latency means that we have limited data on the death rate in Britons born in 1960-64 (67 mesothelioma deaths in men and 30 in women) and almost none on those born since 1965. We are therefore conducting a study (funded by the British Lung Foundation) to assess the risk to more recent generations, measuring asbestos levels by electron microscopy in the lungs of people of different ages, using lung samples from people who were operated for a collapsed lung or for lung cancer (fig 1). In men, the average level fell from about 80,000 fibre/gm in those born in the 1940s to less than 30,000 fibre/gm in those born 1960-64, and to 2,000 fibre/gm in men born 1975-84. In women the level remained at about 20,000 fibre/gm in those born between 1940 and 1964 before falling sharply.

Fig. 1. Average asbestos lung burdens in Britain by year of birth

(million fibres/gm longer than 5 microns)

Million fibre/gm

Year of birth

These average lung burdens correlate reasonably well with the mesothelioma risks in British men and women born between 1940 and 1964 (table 3). The lifetime mesothelioma risk in women born in 1960-64 is about 1 per 1,000, and the continuing reduction in asbestos lung burdens suggests that this may fall to about 1 per 10,000 in women (and men) born in 1975-84. We are currently obtaining lung samples from people born after 1984 to ascertain whether current exposures are even lower. The right-hand part of table 3 shows my speculative attribution of these lifetime risks.

Table 3. Lifetime mesothelioma risks and average asbestos lung burdens in British men and women born since 1940.

Year of birth Lifetime risk Average Approximate attribution of risk to exposure

per 10,000 lung burden

fibre/gm After age 20 Before age 20

(work+environment) (mainly school+home)

1940-49

Male: 100 0.07 90 10

Female: 20 0.02 10 10

1960-64

Male: 20 0.03 10 10

Female: 10 0.02 <1 10

1965-74

Male+female ? 0.006

1975-84

Male+female ? 0.002