117

Asbestos Disease-1990-2020: The Risks of Asbestos Risk Assessment

Irving J. Selikoff Mt. Sinai School of Medicine New York, New York 10027

The first recorded case of asbestosis when a patient treated by Dr. Montague Murray of the Cross Hospital in London. The man died in 1990, following 14 years of work in an asbestos factory. Interstitial fibrosis was seen (Murray, 1907). Since that time, a great deal of additional information has accumulated. In 1924 Dr. W.E. Cooke reported a case of a young woman who died with extensive scarring of the lung (Cooke, 1924). The report, when republished three years later, gave the disease its name, pulmonary asbestosis (Cooke, 1927). Almost at once (indeed, even in Cooke’s case) it was found that, unlike other dusts, such as silica and coal, the mesothelial lining of the chest (the pleura), frequently became scarred (pleural fibrosis). In 1935 a man with asbestosis, who also had lung cancer, was reported by Lynch and Smith (1935). In 1953 a man who had worked with asbestos died of a neoplasm of the pleura, a pleural mesothelioma (Weiss, 1953). This disease is still very much with us and still incurable. Also in the 1950, several men who had worked with asbestos developed tumors of the mesothelial lining of the abdomen (the peritoneum), peritoneal mesothelioma. Thus, by the early 1960s we had a variety of diseases that had been found among people exposed to asbestos.

Charing

1.

would

Constraints in Risk Assessment

First, a natural question, How much exposure produces such disease? Evaluation of hazard depend upon such information. Next, the effects of exposure, Who suffers these effects, and what are the constraints in health control, with risk assess-

making evaluations? This would be useful as we consider public ment becoming a guide to public policy. Measurements

of Exposures

Risk assessment began in 1930. Asbestos industry officials and the British Factory Inspectorate met to consider what to do about disease being seen in asbestos factories (Merewether and Price, 1933-34). There was little information; very few dust measurements had been made, although it was evident that there had been considerable intensity of exposure. Among the first sets of data to be reported were records of measurements that had been made in Quebec mines and mills and retrieved by Dr. Graham Gibbs and his colleagues. On the average, there had been only 10 counts per year per mill or mine, although these facilities contained dozens of different worksites with many exposure variables. They were made with an instrument we no longer use and were reported in million particles (both fibrous and non-fibrous) per cubic foot, which is not the current designation of choice, with an optical microscope at 100X magnification (grossly inadequate power of resolution). Fiber-years were calculated in an admittedly unsatisfactory and uncertain mathematical construct. This improved in 1968 when a British Occupational Hygiene Society Committee undertook a risk assessment based upon counts made with improved collection and counting techniques in an asbestos products factory. Evaluation was restricted to projected incidence of asbestosis because, it was noted, there was not enough information to warrant making an assessment of cancer risks (British Occupational Hygiene Society, 1968).* Assessments have been undertaken ever since. In

* Unfortunately, this risk assessment for asbestosis became known as risk assessment for asbestos, despite the specific warning of the Committee that risk of asbestos-induced cancer was not included in its evaluation and despite the fact that most excess deaths among asbestos workers

were

due to cancer and not asbestosis.

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118 1988 OSHA undertook risk assessment, recommending a level about 1/20th of the 1968 British estimate. A number of problems existed in these risk assessments. The first was the difficulty that few measurements had been made in an industry with hundreds of product uses. Duration of Exposure as a Surrogate In the absence of exposure measurements, duration of employment is frequently used as a surrogate. In one factory we studied (where no counts had been reported), the duration of employment of the 933 men in that plant, for the years 1941-1945, was utilized. There was a gradient for asbestos-associated disease in relation to duration of exposure. Those who worked more than two years had considerably more risk of lung cancer than those who worked less than a month; but even less than a month was more than enough, in this factory, to double the lung cancer risk, when observation was continued for 35 years (see Figure 1) (Seidman et al., 1986).

Variability Further, most asbestos used (and most exposure) was in the construction industry. Here, work experiences were far more complicated than in factories, and far more difficult to evaluate. In shipbuilding, for example, opportunity for exposure was largely indirect. Therefore, the question was not only how many counts but the number of measurements in relation to the extensive and difficult problem of variability. ,

FIGURE 1. Deaths of

varying periods of time,

lung cancer among amosite asbestos factory workers 1941-1945 and observed subsequently for 35 years.

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employed

for

119 Disease Consequences of Exposure What were the effects of exposures? To answer this question, analysis of the experience of asbestos insulation workers is useful. In 1963, 1,117 men were examined. Of the 725 men with less than 20 years from onset of their work, most had normal x-rays. It was only after the 20-year point that most x-rays became abnormal (Selikoff et al., 1965). This was a small group. It was considered important to study a much larger group and to evaluate its mortality experience as well. For that reason, on January 1, 1967, all 17,800 members of the Insulation Workers Union in the United States and Canada were registered. Most were young; 10,101 (57%) were under age 40. Most (12,683 or 71%) were less than 20 years from onset of exposure (Selikoff et al., 1979). TABLE 1 Deaths among

17,800 Asbestos Insulation Workers in the United States and Canada January 1, 1967 - December 31, 1986

Principal

Causes of Death

1967-1986 of the U.S. National Center for Health Statistics, for white males. data were available, 2. Ascertained after review of autopsy, surgical, and clinical material. Where no such were accepted for this diagnostic Cases mesothelioma. for was utilized except death certificate diagnosis category only after Mount Sinai’s histopathology review and confirmation. not 3. Calculated for information only, since it utilized &dquo;best evidence&dquo; vs. &dquo;death certificate&dquo; diagnoses, verification. and ascertainment of strictly comparable due to different quality 4. Rates are not available since these have been rare causes of death in the general population. 5. Includes cancer of stomach, esophagus, and colon/rectum. 6. Includes cancer of stomach, esophagus, colon/rectum, liver, gallbladder, and bile ducts. 1.

Expected deaths based upon death rates

Probability levels: -p

bp cp

< .05.

Asbestos disease-1990-2020: the risks of asbestos risk assessment.

117 Asbestos Disease-1990-2020: The Risks of Asbestos Risk Assessment Irving J. Selikoff Mt. Sinai School of Medicine New York, New York 10027 The...
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