Document a4wRaykwk22QZ9DYgo0rod82a

22636 Federal Register / Vol. 51, No. 119 / Friday, June 20, 1986 / Rules and Regulations predictor of the asbestos potency in this since Dr. Crump has suggested a value potency of exposure to asbestos in this production population. somewhat lower, OSHA believes that its population of asbestos-cement workers, The Henderson and Enterline study. estimate of 0.0tM7 for KL represents a and has lowered its original estimate of OSHA calculated the value of KL based reasonable median estimate of the Kl to reflect some reservations about the on the mortality experience of 1075 potency factor for lung cancer in this data. retirees from an asbestos products study population. As noted in Ex. 84- The Dement et al. Study. OSHA manufacturing plant [Ex. 84-48) by 392, however, "A study of a retiree calculated a lung cancer potency factor computing the slope of the dose- cohort with these characteristics would from the study of Dement and his response relationship, from the linear understate mortality by as much as 62% colleagues, who investigated the regression (KL=0.0066). Henderson and relative to the maximum observable mortality experience of 768 workers in a Enterline had presented exposure data risk" [p. 30). Thus accounting for this chrysotile textile products in terms of total dust measured in possible underestimation, and with manufacturing plant. Data from impinger millions of particles per cubic foot, and regard to the variation in possible measurements of total dust in terms of hence a factor was heeded to convert conversion factors, the range of mppcf were available since 1930 for from particles to fiber count. OSHA employed the value 1.4 f/ml/mppcf, based on the work of Hamniad in cement plants, which gives a best estimate of KL of 0.0047. Crump has pointed to what he believes to be "considerable uncertainty in the methods used by OSHA to convert from particles to fibers" [Ex. 237A, p. 14). Citing the CHAP [Ex. 04256), he recommends that a conversion factor of 2 should have been employed, giving a KL of 0.0033. He also notes that "Enterline himself employed a conversion factor of 3.0 (Enterline 1981) [Ex. 84-127)" [Ex. 237A, p. 15). However, when Or. Enterline testified before the Ontario Royal Commission in June of 1981, he expressed considerable doubt about the conversion factor of 3, noting "I don't know how anybody comes up with a number like that anyhow" [Ex. 85-2, p. 53). Enterline also noted that the conversion factor depended on the operation and that "I think, in asbestos cement, maybe that's [3's] the wrong number" [Ex. 85-2, p.,53). In addition, in the same footnote [Ex. 84-127) cited by Dr. Crump, Dr. Enterline noted that the British Advisory Committee on Asbestos used conversion factors of 1; 2, and 5 f/ cc/mppcf and that "the most conservative estimate of response at low doses in terms of protecting the public would result from assuming a low conversion factor" [p. 42). Whereas CHAP employed a slightly higher conversion factor, it also noted that-- uncertainty around this value may extend from 0.0022 to 0.0108. The Finkelstein Study. Finkelstein established a cohort of 241 production and maintenance employees from records of an Ontario asbestos cement factory. OSHA computed a KL for this cohort based on an average cumulative 18-years exposure of 112.5 f-y/ml for the production workers alone. This group had an SMR of B50, based on 17 observed lung cancer deaths versus 2 expected. These data produced a summary KL of 0.067 (Ex. 84-392, p. 33). OSHA noted some uncertainties in this estimate, particularly because the two lowest exposure categories show risk Increasing steeply with exposure, whereas the highest exposure category showed a cancer rate lower than that of the lowest exposure group. OSHA speculated in the proposal that this inconsistency may be due to the small number of deaths in each category. Several participants raised the . question of the suitability of using this value of Kl in the overall estimate of KL. In particular, Dr. Crump pointed to the lack of a dose-response relationship for lung cancer in this cohort, quoting the CHAP conclusion that "no sensible dose-response for lung cancer can be inferred from these results" [Ex. 237A, p. 28). CHAP noted that: ` * * possible explanations for these results are incorrect exposure estimates and/ or very high competing risks for the heavily exposed persons |Ex. 84-258, p. 11-111) exposures in a textile plant using chrysotile [Dement et al., 1982, Ex. 8435). Using a factor of 3 to convert from mppcf to f/ml (also used by CHAP), OSHA computed KL as the slope of the weighted regression of excess SMR on the midpoint of dust levels in f-y/ml. As noted in the November proposal, this produced a value of KL of 0.042. Participants in the hearing argued that this Kl was overestimated because Dement and his colleagues had overestimated the SMR's by using an inappropriate control group for the calculation of the expecteds. As OSHA explained in its preliminary risk assessment, Dement et al. employed U.S. national death rates rather than local county rates for computing expected values. The authors noted that: The choice of an appropriate comparison population for mortality analyses is difficult and arguments could be made for using rates for a set of counties contiguous to the county in which the plant was located. However, there are serious limitations to this approach which were considered in this study and resulted in rejecting the use of local county rate. First, the county in which the plant was located is the site of a large shipyard Industry with peak employment of approx. 29.000 persons In 1943 (Slot el al. 1978). Employees for this Industry were largely drawn from the local population. Many of these workers are thought to have been exposed to asbestos during ship construction and repair. In an ecological study Blot el al. (1978) demonstrated an association between county lung cancer rates and shipyard employment. * * since follow-up of this group began at age 65, it is essentially a study of a survivor population and as such may have underestimated the maximum relative risk actually experienced by die entire cohort. If this peak relative risk provides the best basis It should be noted that CHAP included Finkelstein's study among those categorized in the Level 1 Exposure category, that is, having job histories and industrial hygiene measurements In a more refined case-control study. Blot et al. (1979) demonstrated a summary odds ratio of 1.0 for shipyard employment and lung cancer after adjusting for smoking, other occupations, age, race, and county of residence. These data suggest that lung for predicting the long-term experience of made at the relevant exposure site. cancer deuth rales in the area in which the individuals exposed at lower.levels, then the Using the entire cohort (both production' plant was located are likely to be elevated by. fitted slope should be increased perhaps by a factor of 2.0 (Ex. 84-258,11-102). CHAP made such an adjustment in its estimate of the slope.to account for these biases (Ex. 84-256, II--100). . Therefore, given the fact that CHAP recommends a value of KL considerably and maintenance workers), CHAP computed an SMR of 608 (20 observed versus 3.3 expected): Noting reservations about the exposure levels. CHAP gave a KL of 0.048 of this cohort 1(6^06--1)/(105)). Given the same reservations as local shipyard employment. A second factor to. be considered In choosing local rates for comparison is the effect that the plant being studied might.have had on local lung cancer death rates. Because of a lack of an employment record system prior to about 1930, it is difficult to estimate the exact number of persons ever employed higher than that put forth by-OSHA in, - expressed by.CHAP, OSHA believes at this plant: however, this is likely to exceed the November.and April proposals and- 0.048 to be a valid expression of the 10,000 pnor to 1985. Thus [sic] could have a GLEASON-000884