Document bBE5BxqVOJGre330ZQ4a863jZ

- 309 Kcrs; there was a relationship not inconsistent with linearity between morta lity from respiratory cancer and cumulative asbestos exposure, except at the highest dose level (abour 1000 mppef-yr); a subdivision of the group with <125 mmpcf into three exposure levels did not yield any consistent trend; so a definite relationship for respiratory rmrcr in exposure <125 mppcf could not be established, nor ad**qv>t<:ly denied. The authors tentatively suggested a cumulative exposure level of 100-20^ rnypef-yr for workers not to be exces sive* A serious drawb.^v. of interline et el's studies is that death before 65 years of age was not tak^n into account. McDonald (1973) reported on equivalent average death rates for malignant disease for 969? workers (07% traced) in chrysotilc mines and ftiills in Quebec. Evidence for increased mortality due to cancer was clearly evident in workers exposed to >400 mppef-yr*, respiratory cancers (only a small minority were me sotheliomas) were not elevated <?00 mppef-yr, and most evidently increased >400 mppcf-yr* death duo to all ga&troi ntest i rial tumours was also higher >400 mppef-yr (suggestive trend). The lowest exposure groups had rates lower than the general population. Gher.xi et al (1971) could not find any case of mesothelioma in 90.Bt of the total population of an Italian chrysotile mine (Halangero), employed for at least one month. Recently Howard ct al (1975) reevaluated the mortality of cohorts of & Rochdale factory, U.K., particularly paying attention to the effect of a decrea sing intensity of asbestos o>:j*osure due to technical devices. In workers entering in 3933*1950 there was a decrease of mortality, and more so in those entering after 1950, i.e. the "modern period" (dust sampling was initiated, although in some areas dust levels remained high for at least 6 years after this). In this last category there still appears to be an excess death due to lung can cer (including mesothelioma) after 15 or more years of exposure (5 c'bserved, 1.86 expected, all smokers) . Dust levels had fallen in the periw^ fron><^353 to 1957 by approximately 50-BO percent throughout the factory, the largest reduction being in areas where levels were highest in 1951. A follow-up uf workers entering after 1951 may give more quantitative evidence of the doseresponse relationship. Up till now this study once more makes clear that cancer mortality is highly dependent upon intensity of exposure, but quantifi cation is still not possible. The Am. Water Works Association (3974) used the date of Enterlinc ct al Obo2 PROD! iPFr> t?v