Historical cohort study of US man-made vitreous fiber production workers: I. 1992 Fiberglass cohort follow-up: Initial findings

This 1986 to 1992 update and expansion of an earlier historical cohort stud y examined the 1946 to 1992 mortality experience of 32,110 workers employed for 1 year or more during 1945 to 1978 at any of 10 US fiberglass (FG) man ufacturing plants, Included are (1) a new historical exposure reconstructio n for respirable glass fibers and several co-exposures (arsenic, asbestos, asp, epoxy, formaldehyde, polycyclic aromatic hydrocarbons, phenolics, sili ca, styrene, and urea); and (2) a nested, matched case-control study of 631 respiratory system cancer (RSC) deaths in male workers during 1970 to 1992 with interview data on tobacco smoking history. Our findings to date from, external comparisons based on standardized mortality ratios (SMRs) in the cohort study provide no evidence of excess mortality risk from all causes c ombined, all cancers combined, and non-malignant respiratory disease. Also, excluding RSC, we observed no evidence of excess mortality risk from any o f the other cause-of-death categories considered. For RSC among the total c ohort, we observed a 6% excess (P=0.05) based on 874 deaths. Among long-ter m workers (5 or more years of employment) we observed a not statistically s ignificant 3% excess based on 496 deaths. Among the total cohort, we observ ed increases in RSC SMRs with calendar time and time since first employment , but these were less pronounced among long-term, workers. RSC SMRs were no t related to duration of employment among the total cohort or long-term wor kers. In an externally controlled analysis of male workers at risk between 1970 and 1992, we observed no association between RSC SMR and increasing ex posure to respirable FG. Our findings to date from, internal comparisons ba sed on rate ratios in the case-control study of RSC were limited to analyse s of categorized study variables with and without adjustment for smoking. O n the basis of these analyses, the duration of exposure and cumulative expo sure to respirable FG at the levels encountered at the study plants did not appear to be associated with an increased risk of RSC RSC risk also did no t seem to increase with time since first employment. There is some evidence of elevated RSC risk associated with non-baseline Levels Of average intens ity of exposure to respirable glass, but when adjusted for smoking this was not statistically significant, and there was no apparent trend with increa sing exposure. This same pattern of findings was observed for duration of e xposure, cumulative exposure, and average intensity of exposure to formalde hyde. None of the other individual co-exposures encountered in the study pl ants appeared to be associated with an increased risk of RSC The primary fo cus of ongoing analyses is to determine the extent to which our present fin dings are robust to alternative characterizations of exposure.