The health effects of asbestos exposure among sheet-metal workers were investigated in a study prompted by the Sheet Metal Workers' International Association. The study involved 1,330 workers in seven cities in the US and Canada. A large proportion (1,016) had been employed as sheet-metal workers for 35 years or longer. Subjects underwent laboratory tests (biochemical studies and blood counts); tests of pulmonary function; X-rays; and electrocardiography (measurement of the heart's electrical activity). Medical and smoking histories were provided and subjects completed a questionnaire concerning shortness of breath (dyspnea). Results showed that X-ray abnormalities of the type associated with asbestos damage were present in just under 59 percent of the group. Sixty-three percent of the workers in the long-term group had such changes. Among this group, workers without a history of cigarette smoking (smoking interacts with asbestos exposure to produce lung damage) had fewer abnormalities than smokers. As the number of years in the trade increased, so did the prevalence of radiologic abnormalities and breathing difficulties. Eight workers had lung cancer that had not yet been diagnosed. Direct handling of asbestos materials was not associated with abnormal X-ray findings. However, subjects who reported working in areas where loose asbestos was common had a higher probability of an abnormal chest X-ray. The results, which were similar in all seven cities, suggest that all construction sheet-metal workers are likely to have been exposed to asbestos at work, placing them at risk for subsequent malignancy. Asbestos exposure and the changes it produces appear to be intrinsic to standard sheet-metal work. (Consumer Summary produced by Reliance Medical Information, Inc.)

Radiological Abnormalities among Sheet-Metal Workers in the Construction Industry in the United States and Canada: Relationship to Asbestos Exposure

THE POSSIBILITY that asbestos exposure in the sheet-metal industry might cause disease (i.e., mesothelioma) was advanced by medical literature. In 1964, Owen studied 17 individuals with mesothelioma and found strong, positive evidence of asbestos exposure in 14 (the other 3 were employed in areas where they may have handled asbestos but where there was no detailed information about their duties). Of those with a clear history, two were sheet-metal workers. [1] Similarly, there were sheet-metal workers among the 51 cases of pleural mesotheliomas in the District of Bergedorf (Germany). [2] Later, Dach et al. [3] reported a peritoneal mesothelioma in a 61-y-old sheet-metal worker.

These reports of asbestos-associated neoplasms were consistent with the growing appreciation that asbestos exposure and resulting disease had been, and was continuing to be, common in the construction industry. This was particularly worrisome to the Sheet Metal Workers' International Association and to its New York Local (Local 28). Their concern was supported by findings of radiological abnormalities consistent with asbestos in clinical examinations of 30 long-term, randomly selected volunteers at Mount Sinai in 1976. More problems were anticipated when the results of two mortality studies were published. Zoloth and Michaels, [4] who undertook a proportionate mortality study that used death certificates of members of the New York Local of the Sheet Metal Workers' Union from 1976, concluded: "The overall pattern of mortality among sheet-metal workers in the New York City Local is consistent with that found in other populations exposed to asbestos." Their observations were extended 3 y later. [5] Death certificate review and proportionate mortality analysis showed lung cancer to be significantly elevated, and an additional six deaths attributable to mesothelioma has occurred. A review of asbestos spraying in New York City buildings was published [6] and served as a background to their studies. A further valuable contribution to understanding the potential of asbestos-associated disease among sheet-metal workers was the radiological findings among 314 sheet-metal workers reported by Baker, Dagg, and Greene. [7] Pleural abnormalities were common and increased to approximately 70% in workers who had been employed more than 30 y. The pleural disease found was significantly correlated with decreased vital capacity.

Sheet-metal workers in the United States' construction industry. In 1988, there were 126 000 construction sheet-metal workers who were actively employed in the United States, which represented 2% of the total work force in the building trades. The number of retired sheet-metal workers at that time is not available.

Approximately 18 million tons of asbestos was used in the construction industry from 1900 to 1979. Unfortunately, almost no measurements of worksite exposures were made during those years. Using the very limited data available and the projections based upon the mortality experience of insulators in the building trades, Nicholson, Perkel, and Selikoff [8] calculated that construction workers' overall exposures might have been 0.2 f/ml. Whether this was specifically applicable to sheet-metal workers is not known, nor is it known whether exposures resulted from their own occasional use of asbestos materials, from repair work during which they removed asbestos, or from their merely having been in the vicinity of worksites in which others were using or removing asbestos - a common occurrence in construction work. There existed the possibility that a significant proportion of their exposure might have been derived from asbestos inhalation in other circumstances, e.g., naval service or work in other trades such as shipyards.

To develop exposure control and medical surveillance programs, we obtained information on asbestos exposure of sheet-metal workers in the construction industry. (Other sheet-metal workers are employed in railroads, shipyards, and fabricating shops, where work conditions are different.) Although results of asbestos air concentrations were not available for past exposures, we considered radiological findings for exposed workers a useful indication of past exposure for this population, especially because they represented results of cumulative exposure over time and reflected a biological response (pleural and/or parenchymal fibrosis).

Methods

Clinical field survey. The Sheet Metal Workers' International Association (SMWIA) was concerned about the extent of risk among construction industry sheet-metal workers. That some disease could occur was already known, but not known was what proportion of sheet-metal workers might be affected. The Association requested the assistance of the Mount Sinai School of Medicine to obtain this information. Therefore, a clinical field survey was undertaken from April, 1986, through January, 1987, in seven U.S. and Canadian cities. It was advantageous to study the status of workers in different cities located in different parts of the United States and Canada, because not only might sheet-metal work practices differ but so might the use of asbestos by other trades. The seven cities chosen were Miami, Houston, Toronto, Los Angeles, Chicago, New York, and Paterson (N.J.). The participation of sheet-metal worker from their International Association President were most valuable, as was the collaboration of his staff in Washington.

From the International Association's records, individuals who would have worked 25 + y in the trade were identified in the local unions located around the examination cities. Using a computer-derived random number sequence, 2 570 construction sheet-metal workers in the seven study cities who had been members of the union for 25 + y were listed by the Department of Statistics of the American Cancer Society); they were invited to the examination by mail. Of the 1479 who responded and were scheduled for examination, 1330 appeared for study. Their mean duration from onset of exposure was 39.51 y (SD = 7.41). There were 1016 workers who had been employed in the trade for 35 + y (Table 1). Approximately half were employed at their craft at the time of the examination.

Table : Table 1. - Work Status of 1 327 Sheet-Metal Workers in the United States and Canada (Examined 1986-1987)

Work status                      No.          Percentage 
Employed                         740             55.8 
  Sheet metal                    683             51.5 
  Other construction work          6              0.5 
  Other employment                51              3.8 
Not working                      587             44.2 
  Retired-age                    348             26.2 
  Illness/disability             172             13.0 
  Unemployed                      27              2.0 
  Other reason                    40              3.0 
    Total                      1 327(*)         100.0 

(*) Three workers were not included because of missing data.

To obtain information concerning whether the voluntary nature of participation might have led to significant selective bias (i.e., those ill not attending, or, conversely, attending disproportionately), we sought to contact 380 consecutive men who were invited but who did not come in for examination. A total of 180 had not responded to the invitations, 108 had replied and had declined to attend, and 92 had agreed to come but failed to appear. We were able to contact 248 men who did not participate. It was found that failure to attend resulted from the mailed invitation not being received (n = 47, [19%]), lack of interest (n = 61, [25%]), transportation problems (n = 24 [10%]), and family illness or other obligations (n = 20 [8%]). In 42 instances, the workers had been ill, but only 5 had pulmonary disease. Twelve had cardiac disease, 3 had cancer, 3 had acute trauma, 2 were blind, and there was a scattering of other non-work-related illnesses. Three had died, but were not so listed in the union records. Thirty seven of the 61 who did not participate because of lack of interest stated that the reason for their position was that they believed they had had little or no asbestos exposure in their work and were unlikely to have any disease. At the suggestion of legal advisors, two refused to be examined. Thirteen were under the care of their own physicians and felt no need for additional study.

Data collected included age, date of birth, lifetime occupational history, date of first employment, total employment, current employment, type of sheet-metal work, military service, and exposures other than sheet-metal employment. Lifetime smoking habits were recorded, including full smoking history (i.e., cigarettes, pipe, cigars, amount smoked, duration of smoking, current smoking, years since stopped smoking if cessation had occurred). Past medical history, family history, current medical history (including asbestos-related symptoms), respiratory status, four sets of dyspnea questions (including a standard MRC [Medical Research Council] questionnaire), and cancer history were recorded.

Answers to questions about shortness of breath were recorded. The MRC questionnaire was used despite its inherent problems. The questionnaire was designed, and is still largely used, for emphysema and bronchitis, not for occupational surveys; nevertheless, it has utility in that other groups of individuals studied elsewhere have answered questions using this format, and current results can therefore be compared with those in these other groups.

Two special 12-point scale shortness-of-breath questionnaires, developed for occupational studies at Mount Sinai (I.J.S.) (Table 2), were also administered. These had the advantage not only of greater precision and being couched in terms familiar to workers, but also that questions were asked specifically for shortness of breath at work and, separately, for shortness of breath during daily activities, which was particularly valuable for individuals who no longer work. Data in Table 1 demonstrate that more than 40% of the men examined were not working at the time of the survey.

Table : Table 2. - Two-Part Mount Sinai Dypsnea Scale

a. Shortness of Breath at Work (check one):

* 1. Not at all, ordinarily. Of course, if strenuous exertion

as anyone would be.

* 2. With strenuous work, that didn't trouble me before.

But I can do it.

* 3. With strenuous work, that didn't trouble me before.

I avoid such work.

* 4. With moderate work. But, no real trouble if I can

pace myself.

* 5. With moderate work. I try to avoid such work.

* 6. With moderate work. Had to change job.

* 7. With lighter work. OK, if I pace myself.

* 8. With lighter work. I try to avoid such work and, if it

worsens, will have to change jobs.

* 9. With lighter work. Can do sedentary work only.

*10. With lighter work. Can't go to and from work. OK

around house, minor jobs.

*11. With lighter work. Can't work around house, even

on easy jobs.

*12. Other problem doesn't allow activity; therefore,

cannot judge shortness of breath.

b. Shortness of Breath Away from Work (check one):

* 1. Not at all, unless strenuous exertion, as always.

* 2. Only with sports or strenuous work, that didn't

bother me before. But I can do it.

* 3. Only with sport or strenuous work, that didn't

bother me before. I avoid them.

* 4. Only with moderate exertion. No trouble if I pace

myself.

* 5. Only with moderate exertion. I try to avoid it. No

trouble with one flight of stairs.

* 6. Only with moderate exertion. One flight of stairs

gives me trouble.

* 7. With ordinary activity, as carrying bundles. Slow up

stairs. Fairly good on level ground.

* 8. With ordinary activity, can't keep up with others on

level ground.

* 9. Yes, if walking around house. I avoid stairs if at all

possible.

*10. If walking on flat ground, even at my own pace.

*11. Virtually sendentary. I'm short of breath walking

across room.

*12. Other problem doesn't allow activity, therefore cannot

judge shortness of breath.

Notes: Twelve-point scales are used to increase sensitivity. The approach was developed (IJS) for investigation of occupational diseases. It does not include questions concerning cough and sputum. In surveys, both questionnaires are utilized.

Laboratory tests included biochemical studies (SMA-18), complete blood count with differential, urinalysis (including microscopic examination), ventilatory pulmonary function test, electrocardiogram, posteroanterior and lateral chest x-ray films with oblique films as needed. All x-rays were read at the examination sites and were subsequently re-read at The Mount Sinai Hospital, New York. The ILO Classification (1980) was used for categorization.

Each worker was sent a confidential report of findings. Copies were also sent to his physician and to any other person so requested by the worker.

Results

Radiological findings. Chest x-ray changes consistent with effects of asbestos, i.e., parenchymal and/or pleural abnormalities, were found frequently among the sheet-metal workers examined. Radiologic changes were seen in 58.99% of the 1 330 men. These changes occurred more frequently in the subgroup of 1 016 workers who had been in the trade for at least 35 years (63.3%). Chest x-rays showing parenchymal abnormalities only represented 16.3%; most were grade 1 (1/0, 1/1, 1/2) according to the ILO Classification. In 27.8% of the cases, only pleural abnormalities were found (both circumscribed and diffuse, as defined in the ILO Classification), and in 19.2% of the cases, both parenchymal and pleural changes were present (Table 2).

Radiological findings in relation to cigarette smoking. Because cigarette smoking influences the likelihood of finding asbestos-related small opacities on the chest x-ray,[9] we analyzed the prevalence of abnormal chest x-rays among the 1 016 men who had been in the trade for at least 35 y in light of their smoking histories. Those who had no history of regular cigarette smoking had fewer radiologic abnormalities than those who currently smoked or who were ex-smokers (Table 3). [Tabular Data Omitted]

The most important influence on the proportion of individuals with abnormal films was the duration from onset of work experience (Fig. 1). Twenty-three men had less than 25 y trade experience. As occurs in most surveys, a few workers were advised by their union officials to appear for examination (although not invited by us). We did not object, for both practical and theoretical reasons: the former, because union officials viewed the studies to be a diagnostic service to their members and, for the latter, it gave us some (sparce) data concerning radiological appearance among workers who had less than 25 y trade experience.

Dyspnea. Shortness of breath, the major symptom of asbestosis, received special attention; however, other symptoms and signs were considered (Table 4). [Tabular Data Omitted]

Figures 2a and b show the results for the three separate sets of dyspnea questions, which accounted for cigarette smoking and duration from onset of work. The presence of radiological abnormalities on chest x-rays was accompanied by an increased prevalence of dyspnea. There was fairly good agreement among the three different dyspnea questionnaires.

The prevalence of dyspnea was highest when the Mount Sinai questionnaire was used, intermediate with the patient's assessment, and lowest with the MRC questionnaire.

Cancer. Although most cross-sectional studies of asbestos-exposed workers are not directed to the detection of cancer, in this study lung cancer was found in six individuals, and pleural mesothelioma was found in two. Those findings are consistent with the experience of many investigators in studies of this type, i.e., that previously undiagnosed lung cancers are discovered in 1-2% of cases.

Asbestos exposure. of the 1 330 workers, 64.2% had, at some time, installed asbestos; 80.8% had removed it; 53.2% had undertaken repairs; and 43.1% had mixed asbestos cement (Table 5).

Table : Table 5. - Asbestos Exposure during Sheet-Metal Work Reported by 1 330 Workers in the United States and Canada (Examined 1986-1987)

                                       Direct asbestos 
                                      exposure reported 
                                           Yes    No   Uncertain 
Activity                          No.       %     %       % 
Installed asbestos               1 319*   64.2   34.0    1.8 
Removed asbestos                 1 320+   80.8   17.9    1.3 
Repaired asbestos insulation     1 319*   53.2   45.8    1.0 
Mixed asbestos cement            1 315++  43.1   55.9    1.0 

* Data incomplete for 11 workers. + Data incomplete for 10 workers. ++ Data incomplete for 15 workers.

The probability of an abnormal x-ray was not significantly affected by a positive history of directly handling asbestos materials; 63.2% of the longer-term men who had reported such asbestos exposure as part of their work had abnormal films compared with 64.3% of those who did not.

Many of the men had worked in other asbestos-exposure trades from time to time. There were 265 sheet-metal workers who had been employed in shipyards, 714 in insulation work, and 95 had done brake repair and brake maintenance. Analyses showed that this could not explain the prevalence of abnormal x-rays. Of men with 35 y or more from onset of work, 62.4% who had shipyard, brake repair, or insulation exposures at work had abnormal x-rays, whereas 63.4% of those who did not have such additional work also showed abnormalities on x-ray consistent with the effects of asbestos.

Each man was questioned with regard to his military service. Of the 885 men who had been in the Armed Forces, asbestos exposure was believed to have occurred in only 67 and was uncertain in 10. In 64 additional instances, asbestos had been present but it was indicated by the examinees that exposure had been minimal.

Only 3.9% of the total group thought that they had not worked in areas with loose asbestos (Table 6). The importance of the standard sheet-metal work environment was emphasized when we correlated the workers' estimates of the percentage of time worked in areas that contained loose asbestos with the presence or absence of chest x-ray findings consistent with the effects of asbestos exposure. For example, among the 39 individuals who had not thought that they had been in such contaminated areas, 51.3% of the x-rays were abnormal. Conversely, for those who reported that 1-20% of their work was done in such areas, 62.7% were abnormal, whereas 72% were abnormal among those who considered that more than half of their work had occurred in areas contaminated by loose asbestos. It is interesting that workers' perceptions concerning asbestos exposure correlated well with the likelihood of chest x-ray abnormality.

Table : Table 6. - Estimated Indirect Asbestos Exposure in Sheet-Metal Workers, Reported During Examinations of Sheet-Metal Workers in the United States and Canada, 1986-1987

Percentage of work done in areas at     No. of 
work having loose asbestos              workers          % 
None                                         50         3.9 
[is less than] 20                           830        64.1 
21-50                                       279        21.6 
50+                                         136        10.5 
                                          1 295* 

* Missing data in 35 cases.

Discussion

There were no significant geographic variations in radiographic or clinical findings. Disease was detected in similar proportions in each of the seven cities in which the survey occurred when analyzed by duration from onset of employment.

Sheet-metal workers were not greatly different from other construction workers; in general, they did not have planned regular medical care at the time of our survey, and they did not have any extensive information about asbestos health hazards (1 195/1 318 had brought work clothes home from construction sites, and 1 269/1 320 had them washed there).

Radiological abnormalities consistent with asbestosis provided clear evidence of fibrogenic effects resulting from asbestos exposure and warn of an increased risk of other asbestos-induced disease (i.e., cancer). Radiological abnormalities provide conservative estimates; standard x-rays are somewhat insensitive because interstitial pulmonary fibrosis can be present without being detected on radiographs.[10] Other changes were also sought, e.g., abnormalities on physical examination, pulmonary function tests decrements, presence of lung cancer or mesothelioma, but asbestotic x-ray abnormalities were the key changes analyzed.

Approximately 60% of the sheet-metal workers had x-ray abnormalities consistent with the effects of asbestos. Those who had been in the trade the longest time had a greater percentage of abnormal films. The first conclusion, therefore, is that asbestos exposure of construction sheet-metal workers had commonly occurred in the past.

However, the fibrosis did not induce seriously debilitating shortness of breath, at least among those who were examined, although decrement of pulmonary function detected by ventilatory tests was by no means rare (to be reported by A. Miller and colleagues).

With few exceptions, all construction sheet-metal workers should be considered to have been exposed to asbestos at their work. This places them at risk of suffering asbestos-associated neoplasms in the future, whether or not they currently have significant pulmonary and/or pleural fibrosis on x-rays.[11]

There have been occasional reports of workers exposed to asbestos who have no x-ray abnormalities and who claim to be short of breath.[12-17] Our observations are consistent with these reports. Some shortness of breath was seen in one-third of 102 sheet-metal workers (primarily among the longer-term men) who had normal x-rays, no history of cigarette smoking, and no cough nor sputum.

Clearly, only a few men who had been examined showed marked respiratory impairment, although some abnormalities were seen. It is well known that during clinical field surveys, the severely disabled may not come, and functional impairment can therefore be underestimated. Moreover, asbestosis progresses with or without further work exposure;[18,19] therefore, pulmonary insufficiency may become a future problem for some sheet-metal workers because of progression of shortness of breath and because it may be exacerbated by other medical conditions as the men age.

Cancer is the chief concern in a group with such asbestos exposure. When the survey was initiated, we were aware that projections would depend upon how much asbestosis was seen on x-ray for the group as a whole. Future risk would then be a function of the prevalence of x-ray abnormality: the more x-ray asbestotic change, the more cancer would be expected. However, 8 cases of previously undiagnosed cancer were detected (6 lung cancers, 2 mesothelioma), among the 1 330 examined.

Analysis of the data on past work conditions, provided by the men examined, indicated that asbestos exposure was primarily experienced during standard sheet-metal work. The radiologic findings were not explained by asbestos exposure while in service, as in U.S. Navy vessels, including engine rooms. The data were inconsistent in this regard; only 8% of 1 330 men had so served. Work in other asbestos exposure trades (insulation work, shipbuilding, etc.), did not provide an explanation for the radiographic abnormalities. A similar prevalence of radiologic abnormalities was seen among those with and without such work. The direct use of asbestos materials during sheet-metal work (mixing cement, applying insulation, etc.) was not found to be a decisive factor in providing radiographic changes; similar proportions of sheet-metal workers had abnormal x-rays with and without such history.

Duration from onset of sheet-metal work was the single most salient factor.

The conclusion from these data seems clear. In the past, construction sheet-metal workers were significantly exposed to asbestos on the job. The majority of individuals who have been employed 30 or more y now have abnormal chest x-rays that resulted from exposure, and the less experienced men face the likelihood of developing similar changes over time. Every effort should be made to minimize the serious health consequences that can be anticipated in the next decades, and asbestos exposure to those who continue to work in this trade should be avoided.

References

(1.) Owen WG. Diffuse mesothelioma and exposure to asbestos dust

in the Merseyside area. Br Med J 1964;2:214-18. (2.) Dalquen P, Dabbert AF, Hinz I. Mesothelioma of the pleura. An

analysis of 119 cases. Prax Pneumonol 1969;28:547-58. (3.) Dach J, Patel M, Patel S, Petasnick J. Peritoneal mesothelioma:

CT, sonography, and gallium-67 scan. Am J Roentgenol 1980;

135:164-66. (4.) Zoloth S, Michaels D. Asbestos disease in sheet metal workers:

the results of a proportional mortality analysis. Am J Ind Med

1985;7:315-21. (5.) Michaels D, Zoloth S. Asbestos disease in sheet metal workers:

proportional mortality update. Am J Ind Med 1988;13:731-34. (6.) Drucker E, Nagin D, Michaels D, Lacher M, Zoloth S. Exposure of

sheet-metal workers to asbestos during the construction and

renovation of commercial buildings in New York City. A case

study in social medicine. Ann NY Acad Sci 1987;502:230-44. (7.) Baker EL, Dagg T, Greene RE. Respiratory illness in the construction

trades. I. The significance of asbestos-associated pleural

disease among sheet metal workers. J Occup Med 1985;27:

483-89. (8.) Nicholson WJ, Perkel G, Selikoff IJ. Occupational exposure to

asbestos: population at risk and projected mortality - 1980-2020.

Am J Ind Med 1982;3:259-311. (9.) Lilis R, Selikoff IJ, Lerman Y, Seidman H, Gelb SK. Asbestosis: interstitial

pulmonary fibrosis and pleural fibrosis in a cohort of

asbestos insulation workers: influence of cigarette smoking. Am J

Ind Med 1986;10:459-70. (10.) Gamsu G. High resolution CT in the diagnosis of asbestos-related

pleuroparenchymal disease. Am J Ind Med 1989;16:115-117. (11.) Coutts II, Gilson JC, Kerr IH, Parkes WR, Turner-Warwick M.

Mortality in asbestosis in relation to initial radiographic appearance.

Thorax 1980;35:235-36. (12.) Jodoin G, Gibbs GW, Macklem PT, McDonald JC, Becklake MR.

Early effects of asbestos exposure on lung function. Am Rev

Respir Dis 1971;104;525-35. (13.) Bristol LJ. Pneumoconiosis caused by asbestos and by other

siliceous and nonsiliceous dusts. Sem Roentgen 1967;2:283-305. (14.) Langlands JHM, Wallace WFM, Simpson MJC. Insulation workers

in Belfast. II. Morbidity in men still at work. Br J Ind Med 1971;

28:217-25. (15.) Mai-Ling W, Pei-Lien L. Lung function studies of asbestos

workers. Scand J Work Environ Health 1985;11:34-42. (16.) Scott JK, Hunt R. The diagnosis of asbestosis. Br J Dis Chest 1975;

69:51-56. (17.) Thomson ML, McGrath MW, Smither WJ, Shepard JM. Some

anomalies in the measurement of pulmonary diffusion in

asbestosis and chronic bronchitis with emphysema. Clin Sci

1961;21:1-13. (18.) Sluis-Cremer GK, Hnizdo E. Progression of irregular opacities in

asbestos miners. Br J Ind Med 1989;46:846-52. (19.) Barnes R. Progression of radiographic changes in asbestos

workers and ex-workers. J Soc Occup Med 1986;36:9-12.

PHOTO : Fig. 1. Chest x-ray abnormalities consistent with effects of asbestos exposure among 1 328 sheet-metal workers in the United States and Canada relative to years from onset of work in the construction industry.

PHOTO : Fig. 2a. Dyspnea on exertion among 1 330 sheet-metal workers with long-term employment. Comparative prevalence rates were derived using three different questionnaires.

PHOTO : Fig. 2b. Dyspnea on exertion among 1 330 sheet-metal workers with long-term employment and radiographic changes consistent with effects of asbestos exposure.