Asbestos-associated lung effects in car mechanics

S. Asbestos-associated lung effects in car mechanics. Scand J Work Environ Health 13 (1987) 252-254. In a study of the possible impact of asbestos exposure on car mechanics, 925 car mechanics and 109 referents (office workers in car-repair firms) were examined. They took part in a health screening in 1977-1981. The forced expiratory volumes in I s and the forced vital capacities of the car mechanics were close to the predicted valuesand did not differ from the findings of the referents. Pleural plaques were found in 41 of the mechanics but in none of the referents. Only minor changes were detected in the chest radiographs ie, 1/ 1or less according to the ILO-U/C classifica tion. It is concluded that asbestos exposure can generally cause pleural plaques in car mechanics but no substantial impairment of lung function.

The health effects of hea vy expo sure to asbestos are well known. A rather large number of worker s is exposed to asbe stos during the repair of cars . Asbestos is used in friction materials such as brake lining s. The clean blow ing of brake drums and the smoothing of the brake linings cause peak exposures to asbestos. As these periods of exposure are very short, the cumulative dose of asbe stos expo sure is rather low for mechanics when compared, for example, with that of insulation workers. Little is known about the health effects of such relati vely low exposure.
In th e late 1970s a health screen ing was offered to mechanics in Goteborg. Thi s study describes the findings of that sur vey. The objective of the an alysis was to determine whether asbestos exposure during car repair impairs respiratory function or cau ses pleural plaques or asbestosis in the mechanics performing the job.

Subjects and methods
Between 1977 and 1980 a free health examination was offered in Sweden to person s who had been exposed to asbestos at work. In Goteborg most car repair firms are associated with the same occupational health center that organized the health screening.
Participation in the screen ing was volunta ry, but all persons who were or who had been exposed to asbestos were actively encouraged to participate. Th e response rate is not exactly known , but from the number of Reprint requ ests to: Dr BG Jarvholm , Departm ent of Occupational Medicine, St Sigfridsgatan 85, S-412 66 Goteborg, Sweden .
252 mechanics associated with the health center, we estimate th at the surv ey covered more th an 90 % of the mechan ics emplo yed at the time . We restricted the analysis to men, as very few women had such jobs.
During the analysis we found that some office workers had also been examined. Their exposure to asbestos was negligible, and we therefore analyzed their data separately to provide information on a reference group . A total of 925 mechanics and 109 offi ce workers were examined (table I). Thirty-four per cent of the mechanic s and 32 010 o f the offi ce workers were life-lon g nonsmokers .
Every man answered a questionnaire about his occupational background, first exposure to asbestos, and total workt ime in asbestos exposure. In almost all cases the worktime in asbestos expo sure was found to be equi valent to the time from the start of asbe stos exposure to the time of the examination , ie, the laten cy time. We therefore o nly anal yzed th e data stratifying for time since on set of exposure. The qu estionnaires were checked by nurses in th e presence of the patients. After the questionnaires had been answered, all the men und erwent spirometry on a calibrated dry bellow spirometer (Yitalogra ph). At least three technically acceptable recordings were made , and the best forced vital capacity (FYC) and for ced expiratory volume in I s (FEY 1.0) were selected from the cur ves. Trained nur ses assisted with the spiro metry .
A full-size chest radiograph (posterior-anterior and lateral views) was taken and read by one of three trained physicians . Pleural plaques were defined according to Thiringer et al (8). Their defin ition requires that the chan ge be at least 5-mm th ick on th e chest wall or 3-mm th ick on the diaphragm to be called a pleural plaqu e. Persons whose radiog ra phs sho wed a suspiciou sly increased number of opacities and/ or irr egularities in the lung parenchyma and persons with a pathological spirometry of unknown origin were referred for further exa mina tion , ie, other lung ph ysiological tests, a lung biopsy, etc.   For a diagnosis of asbestosis we required at least two of the following criteria : (i) pathologic al chest radiogra ph, ie, I/O or more , (ii) findi ngs in the lung ph ysiology in ag reement with fibrosis, or (iii) inspiratory rales on au scult ation .
The differences between the mean values were tested with a two-t ailed t-t est, and onl y P-valu es of less than 0.0 5 were noted .

Results
The results of the spiro metry indicated no changes in the lung fun ction of the mechani cs when comp ared to that of the office wo rkers; the mechanics had , in fact, slightly better values . Neither were an y chang es indicated in comparison to th e reference material (2), ie, the FEVl.o and FVC were close to 100 0,70 of the predicted values (table 2). A multivariate an alysis on smoking , age, and latency time did not indica te th at an impaired respiratory function was associated with lat ency time (not sho wn in the tables).
Forty-one of th e mechanics but none o f the o ffice workers were found to have pleural plaqu es (ta ble 3). The frequency of plaques was highly depend ent on the time since the onset of asbestos exposure . In mechanics with at least 40 years since the onset of expo sure, 57 % had pleural plaques (N = 35), while the corresponding figures were 14 % for mechanics with 30-39 year s a One man had paresis of the right diap hragm. b This man had bronch iec tasi s.
Twenty -four mechanics were referred for further exam inat ion: seven because of abnormal spirometrie s, nine becau se of abno rma l chest radi ograph s, two because of symptoms, and six because of two or more of the a forementioned reason s. Six were nonsmokers, six ex-smokers, and 12 cur ren t smo kers. Th e rad iogra phs of these 24 men were reviewed blindly in 1986 by a chest physician (SL) and classified according to the ILO -U/C system (4). Non e of the se radi ograph s indicated pro fusion s of mo re tha n III (ta ble 4). No diagno sis of asbest osis was made a fter the se thorough clinical exami natio ns. In two cases tran sbro nchial lung biopsies were taken , but both were found to be no rma l.

Respiratory fun ction
Concentratio ns of asbestos of up to 72 fibers/ ml have been repo rted for the repair of brak es wit h asbestos linings (6). Ho wever , th e per iods of du st exposure are sho rt, mo stly about I min or less, a nd therefore the cumulative do se is low. The risk of contracting asbestosis is highly dependent on the cumula tive dose (3). As mechanics ar e exposed to low doses , an y po ssible impairment of the respiratory function should be very low, and such was the case in our investigation (table  2). It may be argued that more sophisticated tests might have revealed impairment of the respiratory function. However, deteriorations of clinical importance are usually detected by simple spirometry. Furthermore, a decrease in vital capacity can be detected in persons exposed to asbestos without changes on chest radiographs (9). Because the results of spirometry were nearly normal, we have concluded that the asbestos exposure of mechanics generally does not impair respiratory function substantially.

Pleural plaques
Even low exposure to asbestos may cause pleural plaques if the latency time is long enough (1, 7). The dose required can be rather low, and environmental exposure to asbestos in the soil seems to be sufficient (5). It is therefore not surprising that the asbestos exposure during brake maintenance seems to be sufficient to cause pleural plaques in mechanics.

Considerations of validity
The data used in this study were primarily collected by means of a general health survey. However, the examinations were highly standardized and performed by highly qualified physicians and nurses. The referral to further examinations was liberal, and it is improbable that a person with substantial fibrosis remained undiagnosed. The review of 24 radiographs did not indicate any substantial risk of clinically important fibrosis. (See table 4.) This study was cross-sectional, which may mean underestimated risks. However, a slight impairment of the respiratory function or occurrence of pleural plaques does not normally lead to a change of jobs.

Conclusion
The asbestos exposure generally experienced by car mechanics may lead to an increased incidence of pleural plaques but does not generally lead to substantial impairment of respiratory function.