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Health risks from asbestos

Part of "Information on asbestos in schools"

Chrysotile dangerous
Amosite 100 times more so
Crocidolite 500 times more dangerous
Chrysotile is dangerous however amosite is 100 times more dangerous and crocidolite is 500 times more dangerous. As has been seen considerable quantities of ACMs have been used in schools whether in the structure of the buildings or used in the laboratories and workshops. Large quantities of chrysotile have been used which if released and breathed in can be dangerous 44, however much of the asbestos is amosite which is 100 times more dangerous than chrysotile and other ACMs contain crocidolite which is 500 times more dangerous 45. All the ceilings in one of my wife’s schools contained amosite and they were regularly damaged.
Susceptibility to mesothelioma varies.
School Governors have expressed the opinion that the kind of exposures suffered by my wife could not cause mesothelioma otherwise most primary teachers would suffer the same disease 46. They are wrong. That is a false premise. Even among asbestos workers with a heavy exposure only a small percentage of them develop mesothelioma 47, because each individual’s susceptibility to the disease is different 48, and only relatively few people will develop the disease. Regretably however it is not known which people are amongst the most vulnerable 49.
Cumulative small exposures
Since 1960 experts have concluded that even the smallest exposure to asbestos can cause mesothelioma 50, and most studies consider that there is no minimum threshold exposure for mesothelioma 51. However the risk is greatly increased with either a large exposure over a relatively short time or else repeated small exposures 52. Some studies have agreed that a relatively brief exposure can cause mesothelioma, although they consider that the risk is low 53. An eminent Chest Physician explained the process that takes place when an asbestos fibre enters the pleura, and how subsequent exposures have a cumulative effect until mesothelioma develops. A single asbestos fibre can in theory cause a mutation of a single cell from which a malignant tumour can develop. Each additional exposure can therefore cause cell mutation, and each exposure lowers the body’s natural ability to combat mutating and mutated cells. This lowering of the body’s defensive system is dose related and the effects are cumulative 54. Consequently the greater the dose and the greater the number of times that exposure takes place then the greater the risk of developing a tumour.
Low level exposure to crocidolite and amosite can cause mesothelioma. No threshold for Chrysotile
In 1960 a paper was first published that gave examples of mesothelioma being caused by environmental, or low level, exposures to crocidolite 55. The 1964 Working Group on Asbestos concluded that crocidolite definitely caused mesothelioma but they stated that “It cannot be concluded that only this type of fibre is concerned with the tumours.”56 In the 1964 the Chief Inspector of Factories report acknowledged that mesothelioma had occurred in non-occupationally exposed people, and that it was likely that in the past mesothelioma had incorrectly been diagnosed as lung cancer 57. Their report in 1965 acknowledged that mesothelioma had occurred after low levels of asbestos exposure “At astonishingly low degrees.”58 This was backed up by a report which cited exposures in the home being associated with mesothelioma 59. In 1967 the Factories Inspectorate concluded that it was most probable that amosite could also cause the disease 60This was confirmed by studies of asbestos related deaths among shipbuilders in WWII which were published in 1972 and 1979 61. Later studies concluded that even low levels of amosite were capable of causing mesothelioma 62. In 1998 the World Health Organisation stated in relation to the levels of chrysotile needed to cause cancer “No threshold value has been identified for carcinogen risks.63
Cumulative low level exposure in a school
The investigation discovered evidence of my wife’s exposure to asbestos at school and, although perhaps no large exposures took place, there were at times constant small exposures for every working day for years. Over the course of her thirty year teaching career these exposures gradually had a cumulative effect with the result that mesothelioma developed. It is known that her exposure was typical of other teachers.
Long latency of mesothelioma
Mesothelioma has a long latency from the first exposure to the disease developing, therefore the deaths happening now are the result of asbestos exposures that happened some years ago. An initial exposure from some years before could initiate the process, and then subsequent exposures would have a cumulative effect, as each exposure happened the chances of a tumour developing would increase. The causative potency of each exposure is considered by some to have an equal effect and the earlier exposures are no more or less causative than later exposures. Others consider that earlier exposures have a greater effect 64. All are agreed that the greater the intensity and longer the duration of exposure then the greater contribution it makes. This cumulative process has been assessed as continuing to have an effect on tumour growth until about ten years before the onset of symptoms 65. Consequently any investigation has to look back over the whole of a person’s life to identify any likely occasions when exposure could have occurred.
Latency periods vary considerably
Each individual is different and their susceptibility to developing mesothelioma varies significantly as does their individual period of latency66, for instance my wife’s mesothelioma developed rapidly 67, and such increases in tumour doubling can indicate a comparatively short latency68. It is also considered likely that the larger the exposure then the shorter the latency69, and that environmental exposures, which tend to be lower, will cause a longer latency than occupational exposures. 70
Latencies from 10 to 60 years after first exposure
The latency from first exposure to the symptoms of mesothelioma has been recorded in a few cases as being from less than 10 years 71 to over 60, but opinion on the average latency varies considerably between different studies and experts. This variation depends on the quality of the patients history of exposure, the sample of those people studied, the size of the study, the type of asbestos inhaled and the expert’s experience and the weight he places on the available data to make his conclusions. A leading British doctor considers that the average range in latencies is from 20 to 35 years and he readily accepts latencies of ten years 72 as does the leading British cancer advice body Cancerbacup 73.Whereas a study of Turkish villagers gave a mean latency of 59.2 years 74.The people in this Turkish study had inhaled mainly tremolite and some chrysotile, which would inevitably explain the longer latencies as the fibres are less potent than amosite or crocidolite. In a separate paper the same authors quote an average latency for occupational exposure of 30-40 years derived from three other studies, and that gives a more balanced picture 75. The HSE consider that the average latency is between 35-41 years 76.
First exposure in a school may be overlooked
It must therefore be borne in mind that in the case of multiple exposures, the first exposure, and perhaps the one that initiated the process, could have happened many years before and passed unnoticed. A heavy exposure some years later might therefore be blamed in isolation and the earlier exposure might be overlooked. This is particularly applicable to childhood exposures. Therefore one has to take into account all these factors when determining the likely latency and the occasions that the exposures occurred
Latency depends on the individual and the type of exposure

It should always be remembered that if a person has been exposed to asbestos it is unlikely that they will develop mesothelioma at all. Amongst groups of asbestos workers who have been highly exposed only about 5% develop mesothelioma 77. However if a person is susceptible to developing the disease then if they were exposed in 1966 they will have either died by now or, as the latency can be so long, the mesothelioma has yet to developed. A person dying in 2005 could have been first exposed in childhood and a process initiated which was regularly added to by subsequent low level exposures, and until about 1995 each exposure contributed towards the development of the tumour. It is also possible that a person dying from mesothelioma in 2005 could have been first exposed as late as 1995. It purely depends on that individual and the type of exposures they have experienced. It must be remembered that 1966 is the year that the DES were made aware of the dangers of asbestos, and hence measures could have been taken from that date to prevent subsequent exposures in schools.

Other cancers caused by asbestos
Mesothelioma is the only cancer specifically associated with asbestos, however asbestos can cause other cancers such as lung cancer and it is thought cancer of the larynx, gastro-intestinal tract and kidney 78. In 1947 substantial evidence was available that asbestos causes lung cancer 79 and by 1964 this was confirmed beyond doubt 80. Views about how many lung cancers are caused by asbestos vary, although the number is thought to be at least on par with the number of mesotheliomas 81. The incidence varies with the type of asbestos, the length and duration of exposure, and the person’s age and smoking habits, with an excess of lung cancers being recorded of up to five times. The HSE’s best estimate is that asbestos probably causes one or two lung cancers for each current mesothelioma 82. Although it is generally considered that the exposure levels have to be greater to cause lung cancer than they have with mesothelioma 83, small exposures may cause the disease 84. The HSE used to state that bronchial carcinoma is linked to high exposure for a long period of time 85, however they have updated their view by stating that studies suggest that very small exposures can cause lung cancer 86. Such studies generally agree that large levels of chrysotile are required, but demonstrate that the level of exposure from amphiboles (mainly amosite, crocidolite, tremolite) can be very low and still cause the disease 87. The Scottish Executive state that lung cancer can only occur after heavy occupational exposures, however they have not stated the study on which they have based their conclusion 88. It is generally acknowledged that the latency periods can be less than those of mesothelioma and symptoms can occur as little as five years after exposure, although longer latencies are more usual, with an average of perhaps 20 years. 89
Lung cancer risks increased by smoking

It is considered that smoking does not increase the chances of developing mesothelioma, however it can greatly increase the chances of developing lung cancer after an asbestos exposure 90. The US Government state in an EPA schools’ publication:

“The risk of contracting lung cancer as a result of exposure to asbestos increases if the worker is a cigarette smoker. Cigarette smokers are 50 times more likely to develop lung cancer than the normal, non smoking population.” 91

This increase in risk has been assessed by an acknowledged leading expert as 30-50 times greater when associated with an exposure sufficient to cause lung cancer, and with a heavy exposure sufficient to cause asbestosis the risk is increased to 75-100 times.92 The HSE agree that smoking interacts with asbestos to cause lung cancer 93, although they state that the risk only exists after high exposure levels and that if a person stopped smoking the synergistic effects would be tiny.94


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