Pulmonary function defects in nonsmoking vinyl chloride workers.

Pulmonary function was assessed by spirometry and maximum expiratory flow-volume curves to determine whether exposure to an occupational environment contaminated with vinyl chloride (VC) fumes and poly(vinyl chloride) (PVC) dust is associated with an increased risk of respiratory impairment. Data were analyzed for smoking, duration of exposure, and age. The high prevalence of impaired flow (57.5%) could not be attributed to smoking. Prevalence in nonsmokers was 36.4% when exposure was less than 10 yr, 42% when exposure was between 10 and 20 yr, and 80% when exposure exceeded 20 yr. The last is virtually the same rate as for smokers exposed more than 20 years. The same trend is shown with increasing age. Unlike younger workers, when smokers and nonsmokers more than or equal to 40 years of age are compared, prevalence rates of air flow impairment are not statistically different. The present investigation is one of the few in which the effects of occupational exposure could be separated from and were found to predominate over the effects of smoking.

In any investigation of air flow, cigarette smoking must be considered. In most previous studies, the effects of cigarette smoking predominated over any effect attributable to atmospheric pollution or occupational exposure. As stated by Ferris and Anderson in their comprehensive survey of Berlin, New Hampshire, a' city selected because its major industry is a pulp mill, "the smoking variable is so strong it overwhelms the possible effect of atmospheric pollution. Surveys of non-smokers and neversmokers may have to be undertaken to study the effect of atmospheric pollution and occupational exposure as causative factors in chronic nonspecific respiratory disease" (1). Air flow was assessed by spirometry and maximum expiratory flow volume curves in 348 workers exposed to vinyl chloride fumes and poly(vinyl chloride) dust in a polymerization plant in Niagara Falls, N. Y. The effects of exposure to this occupational environment could be separated from those attributable to smok- smoking. While prevalence of impairment is statistically different for smokers and nonsmokers -39 yr, smoking is not a significant factor beyond this age. The relationship of age and smoking to prevalence of air flow impairment, an abnormality of any of the three tests being used as the criterion, is summarized in Table 3. For all subjects, 57.59 were abnormal. For those -39 yr of age, 539 of smokers and 28%o of nonsmokers manifested reduced air flow. This difference is significant (p < 0.01). For those aged 40 yr, the prevalance of impairment in smokers (71%) is not significantly different (p > 0.5) from the prevalance in nonsmokers (64%o). In each smoking category, the prevalence of air flow impairment is significantly higher among older workers (p < 0.01).
Volume impairment was noted in only 16 or 4.6%o of the group. Prevalence was similar in smokers and nonsmokers.

Duration of Occupational Exposure
The mean age for the 265 current workers was 37.8 yr (range, 19-65 yr). Mean ventilatory values are shown in Table 4 and the prev&. lence of air flow impairment in Table 5, related to duration of exposure and smoking. On using MMF or FEF25, prevalence of impairment in both smoking categories (smokers and nonsmokers) taken together increased from 48% when exposure was less than 10 yr to 56%o when exposure was 10-20 yr, to 84%o when  exposure exceeded 20 yr. This increase in prevalence with progressive duration of exposure was true for both the smokers and the nonsmokers. The difference in prevalence between smokers and nonsmokers narrowed from 23% (p < 0.02) when exposure was less than 10 yr to 11% (p < 0.5) when exposure exceeded 10 yr. Any difference between smokers and nonsmokers cannot be attributed to age, since there is no significant difference in age at any duration of exposure. For a more conventional measurement of air flow, FEV,JFVC, the frequency of impairment ( 74%o) among all workers was also high, although 10% lower than for the MMF or FEF25. An increase in prevalence for both smokers and nonsmokers is noted when their exposures exceed 20 yr. In summary, the present investigation demonstrated a high prevalence of air flow impairment in VC-PVC workers which cannot be attributed to smoking. Prevalence in nonsmokers (past and current workers) was 36.4%o when occupational exposure to VC-PVC was less than 10 yr, 42% when exposure was between 10 and 20 yr, and 80%o when exposure exceeded 20 yr. The last is virtually the same rate as for smokers exposed more than 20 yr ( Table 5). The same trend is shown with increasing age. Unlike younger workers, when smokers and nonsmokers -40 years of age are compared, prevalence rates of air flow impairment are not statistically different (Tables 2 and 3).

Discussion
These rates of air flow impairment are higher than the rates in the literature for most other occupational groups. In a control population of farm and marble workers in Spain, 12%,o had abnormal FEV1 (15.6% of those 40 yr of age) (2), compared to 45 and 56%o of the VC-PVC workers, respectively. In a different control group, prisoners and guards (mean age about 43 yr), 7.4%o demonstrated a decreased FEVO.75 (3), while 10%o of men in rural Denmark, where cigarette smoking is relatively uncommon, had an FEVo.7s less than 2 liters (4).
The survey of Chilliwack, a small Canadian town with low levels of air pollution, showed that 12.6%o of the men had severe obstructive lung disease. About 70%o of these had an FEV1/ FVC -60% for a prevalence of severe impairment of about 99 (5). The most recent survey, of English civil servants 40 yr of age, revealed 26.4%o to have an FEV,/FVC < 75%o (6). While this figure is higher than the others cited, it is considerably lower than the 56%o for VC-PVC workers of comparable age ( Table  2). In an investigation of male bank employees 40 yr of age, Bower noted that 19%o had a diminished MMF (7), compared to 61%go of VC-PVC workers of the same age.