Asbestos-Related Diseases
1. Introduction
The fact that asbestos is a toxic material has been known for many years. The earliest recorded historical recognition of the hazards of asbestos dates from the time of Christ. Pliny, the ancient Roman historian, wrote of the "diseases of slaves" caused by injurious processes such as lead and quick-silver mining, the potters' craft, and the textile processes of preparing and weaving asbestos and flax. Observation and experience showed the Romans the effects of occupational asbestos inhalation; transparent bladder skins were used as a form of primitive respiratory protection to prolong the working lives of slaves.
Exposure to asbestos has been linked to several deadly diseases including asbestosis, lung cancer and mesothelioma; in Britain these three diseases constitute the most serious single category of occupational disease. All types of asbestos fibres are dangerous when inhaled and the dustiest processes are, in general, the most hazardous. Significant factors in the development of asbestos-related diseases are: the type of asbestos inhaled, the intensity of the exposure, the length of the exposure, the time elapsed since exposure and individual susceptibility. In 1995, a statistical analysis of epidemiological data uncovered an explosion in the number of asbestos-related deaths in Britain. The current annual mortality rate of 3000 is expected to hit 10,000 by the year 2020.
2. Evolution of Knowledge
In 1897, an Austrian physician was convinced that dust inhalation was the cause of "emaciation and pulmonary problems in asbestos weavers and their families." At about the same time, the Lady Inspector of Factories in Great Britain expressed her concern about the hazards of industrial asbestos exposure. In her annual report of 1898, she focused on asbestos manufacturing processes "on account of their easily demonstrated danger to the health of the workers...." Her report recommended the installation of "a scheme of applied ventilation" to minimise the accumulation of dust. In 1899 the annual report of H.M.Chief Inspector of Factories for the women's branch reported the presence of "injurious dust in asbestos works."
Unease continued in subsequent inspectorate reports and in submissions by British physicians. In 1906, a British factory inspector commented: "Of all injurious dusty processes of which I have again ... received complaints none I believe surpass in injuriousness to the workers the sieving, preparing, carding and spinning processes in asbestos manufacture." At this time, the inspectors noted that at every visit to asbestos plants, respiratory illnesses and in some cases deaths were reported.
In 1918, a US statistician named Hoffman wrote a monograph for the US Bureau of Labour Statistics in which he cited British asbestos research. He reported the findings of "bystander" asbestos exposure to workers in a factory manufacturing asbestos insulation mattresses. Hoffman was convinced that the "mining and dressing of asbestos unquestionably involve a considerable hazard." North American insurance companies did not take much convincing. It was not unusual for US and Canadian companies to decline life insurance to asbestos workers on account of the alleged health risks of working in the industry.
In 1928, the Factory Department commissioned a comprehensive enquiry into the risks of occupational asbestos exposure. The report by Drs. Merewether and Price was entitled: Occurrence of Pulmonary Fibrosis & Other Pulmonary Affections in Asbestos Workers; it was presented to Parliament on March 24,1930. It concluded that the development of asbestosis was irrefutably linked to the prolonged inhalation of asbestos dust. As a result of the Merewether report, the first British Asbestos Industry Regulations were formulated in 1931.
3. Asbestosis
In 1906, Dr. Montague Murray presented evidence to a government committee of a case of fatal, non-tubercular, diffuse pulmonary fibrosis in an asbestos worker. The disease was named in 1927 by Dr. Cooke who called it: asbestosis It is an irreversible and progressive lung condition which results from the inhalation of asbestos fibres over an extended period. In asbestosis, lung tissue is scarred and thickened by the action of the asbestos fibres in the alveoli, the air sacks. The latency period for asbestosis is usually at least ten years and the higher the exposure, the greater the chances of developing the disease. Asbestosis tends to be linked to heavy occupational exposure although cases of asbestosis among those not occupationally exposed have been known.
4. Lung Cancer
An article in The Lancet in 1934 presented evidence of a link between asbestos and lung cancer. Dr. Richard Doll's landmark paper: Mortality from Lung Cancer in Asbestos Workers (1955) found that the incidence of lung cancer among men at a Turner & Newall asbestos factory in Rochdale was ten times the national norm. An article in the Journal of the American Medical Association estimated that an asbestos insulation worker who smoked had 92 times the chance of dying from lung cancer as a non-smoking, non-asbestos worker.
Asbestos-related lung cancer is a prescribed disease provided the patient exhibits another clinical sign of asbestos exposure such as asbestosis, or pleural thickening and evidence of occupational asbestos exposure. Studies of particular groups of asbestos exposed workers suggest that the number of excess lung cancers produced is - roughly and with considerable variation from study to study - double the number of mesotheliomas. This means that the number of lung cancer cases currently attributable to asbestos exposure in the UK may be estimated at about 1800 per year. Many of these go unrecognised by doctors and patients and remain uncompensated by former employers or government agencies. Asbestos-related lung cancer can occur from occupational or environmental exposure: it is virtually incurable. The latency period for lung cancer associated with asbestos exposure is usually between fifteen and thirty-five years.
5. Mesothelioma
Mesothelioma is a very rare cancer of the lung or the abdominal cavity, the only known cause of which is exposure to asbestos. Malignant mesothelioma can be contracted from low exposures to asbestos and accounts for the majority of victims who contract an asbestos-related disease through environmental exposure. The latency period for mesothelioma is generally between thirty to fifty years although British courts have accepted a latency period as short as ten years. The prognosis for mesothelioma patients is affected by the cell type and the size, stage, extent and susceptibility of the tumour to treatment. On average, mesothelioma patients survive for eighteen months to two years following diagnosis. Currently, there is no known cure for malignant mesothelioma.
The annual number of mesothelioma deaths increased from 153 in 1968 to 1,628 in 2000. According to a paper published in January, 2004:
"One in every hundred men born in the 1940s will die of malignant pleural mesothelioma… For a man first exposed as a teenager, who remained in a high risk occupation, such as insulation, throughout his working life, the lifetime risk of mesothelioma can be as high as one in five...The disease is increasing in frequency…we will be seeing many more mesotheliomas in the next 25 years. In the developed world alone 100,000 people alive now will die from it."
British mesothelioma deaths are expected to peak by 2020 at 2,000 cases a year. Occupations with the highest risk of contracting this disease (for males) are: metal plate workers (including shipyard workers), vehicle body builders (including rail vehicles), plumbers and gas fitters, carpenters and electricians.
6. Other Asbestos-Related Diseases
6.1. Bilateral Diffuse Pleural Thickening
This prescribed asbestos-related disease can produce serious impairment of lung function. Thickening of the pleura may reduce lung function and victims can experience severe shortness of breath. Diffuse pleural thickening can occur on one side of the lungs or on both sides (bilateral). H&SE statistics show 172 cases of bilateral diffuse pleural thickening in 1993.
6.2. Pleural Plaques
While not classed as a disease, the occurrence of pleural plaques (dense bands of scar tissue) is usually regarded as a marker of past asbestos exposure. One study found that the lung cancer rate in a group of shipyard workers with plaques was double that of shipyard workers without plaques.
7. Deaths
Figures for asbestos-related deaths have traditionally been under-reported in Britain. Statistics derived from death certificates include only deaths from asbestosis and mesothelioma and ignore lung cancer even though there are at least two cases of asbestos-induced lung cancer for each case of mesothelioma. One conservative estimate puts the number of British asbestos deaths over the next thirty years at 90,000. While a more recent British epidemiological study forecasts a mortality rate of around 200,000 for this period, an extrapolation from US statistics would give a figure of 500,000. Although there are reasons to question all three predictions, the fact of the matter is that over the next three decades tens of thousands will die in Britain from exposure to asbestos.
September 2, 2004
