A CASE-CONTROL STUDY OF MALIGNANT AND NONMALIGNANT RESPIRATORY-DISEASE AMONG EMPLOYEES OF A FIBERGLASS MANUFACTURING FACILITY .2. EXPOSURE ASSESSMENT

A case-control study of malignant and non-malignant respiratory diseas e among employees of the Owens-Corning Fiberglas Corporation's Newark, Ohio plant was undertaken. The aim was to determine the extent to whi ch exposures to substances in the Newark plant environment, to non-wor kplace factors, or to a combination may play a part in the risk of mor tality from respiratory disease among workers in this plant. A histori cal environmental reconstruction of the plant was undertaken to charac terise the exposure profile for workers in this plant from its beginni ngs in 1934 to the end of 1987. The exposure profile provided estimate s of cumulative exposure to respirable fibres, fine fibres, asbestos, talc, formaldehyde, silica, and asphalt fumes. Employment histories fr om Owens-Corning Fiberglas provided information on employment characte ristics (duration of employment, year of hire, age at first hire) and an interview survey obtained information on demographic characteristic s (birthdate, race, education, marital state, parent's ethnic backgrou nd, and place of birth), lifetime residence, occupational and smoking histories, hobbies, and personal and family medical history. Matched, unadjusted odds ratios (ORs) were used to assess the association betwe en lung cancer or non-malignant respiratory disease and the cumulative exposure history, demographic characteristics, and employment variabl es. Only the smoking variables and employment characteristics (year of hire and age at first hire) were statistically significant for lung c ancer. For non-malignant respiratory disease, only the smoking variabl es were statistically significant in the univariate analysis. Of the v ariables entered into a conditional logistic regression model for lung cancer, only smoking (smoked for six months or more v never smoked: O R = 26.17, 95% confidence interval (95% CI) 3.316-206-5) and age at fi rst hire (35 and over v less than 35: OR = 0.244, 95% CI 0-083-0.717) were statistically significant. There were, however, increased ORs for year of employment (first hired before 1945 v first hired after 1945: OR = 1-944, 95% CI 0.850-4.445), talc (cumulative exposure >1000 fibr es/ml days v never exposed: OR = 1.355, 95% CI 0.407-4.515), and aspha lt fumes (cumulative exposure >0.01 mg/ml days v never exposed: OR = 1 .131, 95% CI 0.468-2.730). For non-malignant respiratory disease, only the smoking variable was significant in the conditional logistic regr ession analysis (OR = 2-637, 95% CI 1.146-6.069). There were raised OR s for the higher cumulative exposure categories for respirable fibres, asbestos, silica, and asphalt fumes. For both silica and asphalt fume s, ORs were more than double the reference groups for all exposure cat egories. A limited number of subjects were exposed to fine fibres. The scarcity of cases and controls limits the extent to which analyses fo r fine fibre may be carried out. Within those limitations, among those who had worked with fine fibre, the unadjusted, unmatched OR for lung cancer was 1.0 (95% CI 0-229-4.373) and for non-malignant respiratory disease, the OR was 1.5 (95% CI 0.336-6.702). The unadjusted OR for l ung cancer for exposure to fine fibre was consistent with that for all respirable fibres and does not suggest an association. For non-malign ant respiratory disease, the unadjusted OR for fine fibre was opposite in direction from that for all respirable fibres. Within the limitati ons of the available data on fine fibre, there is no suggestion that e xposure to fine fibre has resulted in an increase in risk of lung canc er. The increased OR for non-malignant respiratory disease is inconclu sive. The results of this investigation clearly indicate that for this population, in this place and time, neither respirable fibres nor any of the substances investigated as part of the plant environment are s tatistically significant factors for lung cancer risk although there a re increased ORs for exposure to talc and asphalt fumes. Smoking is th e most important factor in risk for lung cancer in this population. Th e situation is less clear for non-malignant respiratory disease. Unlik e lung cancer, non-malignant respiratory disease represents a constell ation of outcomes and not a single well defined end point. Although sm oking was the only statistically significant risk factor for non-malig nant respiratory disease in this analysis, the ORs for respirable fibr es, asbestos, silica, and asphalt fumes were greater than unity for th e highest exposure categories. Although the raised ORs for these subst ances may represent the results of a random process, they may be sugge stive of an increased risk and require further investigation.