An epidemiological study of the lung function of workers at a factory manufacturing polyvinylchloride

We have conducted an epidemiological study to investigate a report that some men working in a factory manufacturing polyvinylchloride (PVC) had abnormally low values of one lung function test, namely the single breath transfer factor for carbon monoxide (TLCO).We studied 265 present and past employees of the PVC factory, and 219 men from the workforce of a nearby foundry. The foundrymen were included to increase the number of men with little or no exposure to possible respiratory hazards at the PVC factory. Each man’s TLCO was measured, and smoking history and detailed occupational history obtained. More detailed lung function tests were carried out on the PVC workers only (forced expiratory flow-volume curves).The study consisted of two parts; measurement of the TLCO of current and past employees at the factory and current foundry employees and examination of the distribution of residuals after allowing for age, height, weight and smoking habit, to search for evidence of an excess of men with low values of TLCO; and a case-control study. In this, men with the lowest TLCO after allowing for age, height, weight and smoking habit were selected as cases, and their occupational history compared with that of two groups of controls; one group selected from those with near average gas transfer values, and another group from those with the highest values.The TLCO results among this combined population conformed to a Normal distribution after allowing for age, height, weight and smoking habit, and did not suggest that a substantial number of men had clinically important impairment of their Tuco.The 31 men selected as ‘cases’ included 15 men whose TLCO was abnormally low (less than 70% of published predicted values), of whom twelve were PVC workers and three were foundrymen. Among the 19 cases working at the PVC factory the pattern of lung function abnormality suggested that the low TLCO was accompanied by evidence of airflow obstruction in 11 men, suggesting the presence of emphysema, but was an isolated functional abnormality in the other eight, possibly suggesting the presence of pulmonary fibrosis or abnormalities of lung perfusion.PVC workers were slightly over-represented among the cases, although this difference could easily have arisen by chance. Men who had worked on jobs at the PVC factory which were close to the pressure vessels where exposure to vinyl chloride monomer was most likely to have occurred in the past, were also slightly over-represented among the cases, and this difference approached statistical significance at conventional levels. There was, furthermore, a statistically significant association between low TLCO and a history of having worked at the PVC factory before 1975. This date is important because it was at this time that exposure of the workforce to vinyl chloride monomer was drastically reduced, in the light of information about some of the potential hazards of this gas.The cases included slightly more smokers than the controls, and those cases who smoked, smoked slightly more heavily than controls.The relative importance of these and other factors in causing the lung functional abnormalities is not clear, but these findings give some support to the hypothesis that work in the PVC factory before 1975 involved exposure to a substance that caused impairment of lung function in a small number of men.There was no evidence of a relationship between low TLCO values and current working conditions at the PVC factory or with past or present conditions at the foundry.The results suggest that more detailed studies of the relationships with vinyl chloride monomer, polyvinylchloride, smoking habit and other causative factors would be desirable together with a clinical assessment of the lung damage in selected men.