Document 7OVMbba23RLB01jg44EMb7Jd6

I 574 J. T. Hodgson uml A. Darnion and 1.3 respectively) but both confidence intervals are very wide. Even if the mines cohorts are excluded there is still very clear statistical inconsistency between the Carolina results and those from Con necticut and New Orleans (/,=0.00l 3). The Carolina results are also out of line with the two other (mixed fibre) textile cohorts--Rochdale and Pennsylvania-- whose 93% confidence intervals for RL have no over lap with those for Carolina. mineral oil (slight, moderate, high). The coefficients for these categories in the joint model were not reported, but were as follows, expressed as odds ratios relative to 'slight' exposure: Mineral oil exposure Odds ratio Moderate 1.12 High 1.47 (Dement, personal communication) 95% Confidence interval 0.57-2.21 0.3-2.75 RISK ASSESSMENT AT MODERATE AND HIGHER CUMULATIVE EXPOSURES Mesothelioma The quantified risk for mesothelioma at the kinds of cumulative exposure levels recorded in the reviewed cohorts--say. from 10 f/mt.yr upwards-- presents a reasonably coherent picture, with values of Rm, in round figures, of 0.S, 0.1 and 0.001 (at most 0.003) for crocidoliie, amosite and chrysotile respect ively (see Fig. 2). Lung cancer It is more difficult to come to a clear view of the quantified risks of lung cancer, because of the incon sistency of the results especially for the chrysotile cohorts (see Fig. 3). The omphibole estimates ore reasonably consistent In round figures the estimates fall in the range 2-10% per f/ml.yr. The mean for the crocidolite group is rather lower (4.2) than that for the amosite group (3.2), though their confidence lim its overlap substantially. The mean risk for all amphibole cohorts is 4.8% per f/ml.yr (95%Cl 3.9-5.8), but with some evidence of heterogeneity (P=0.027). If the SA amosite cohort data ore set aside, the remaining data are reasonably consistent (P=O.Q72), and the mean estimate becomes 3.1 (93%CI 4.1-6.2). In round figures, a value of 3% per f/ml.yr would rep resent a reasonable risk estimate for both omphibole fibre types. The pure chrysotile cohorts produce estimates of Rl spanning two orders of magnitude, from a value of 6.7 for the* Carolina women to 0.03 for Balengero mine. How should this very wide range of est>* mates be interpreted? As far as evidence, from 'pure' exposure goes there are only two strongly informative cohorts: Quebec and Carolina. The differences between these two has been studied and discussed extensively but, finally, inconclusively. The hypoth esis that mineral oil used to suppress dust in the Caro lina plant may have contributed to the lung cancer excess has been addressed by an internal case-control analysis of this factor reported by Dement el al. (1994) and Dement (1991)). The most recent report (Dement et al., 1994), shows that the odds ratios for different cumulative asbestos exposure categories are essentially unchanged by the addition of a variable representing subjects' typical level of exposure to Although these ORs are not statistically significant (and do not form a statistically significant trend), there is some suggestion that mineral oil may have a role in enhancing the asbestos effect, particularly since all the effect of exposure duration is absorbed in the asbestos measure (workers were assigned to oil exposure categories according to the assessed oil exposure level at which they had spent the longest proportion of their employment in the plant). Early results from this cose control study showed a cross tabulation of cases and controls by asbestos exposure and mineral oil category (Dement, 1991), without for mal modelling. Crude odds ratios on (his data suggest that the asbestos response is progressfrely steeper with increasing mineral oil category. If mineral oil does have an enhancing effect, (he anomalous increase in estimated exposure specific lung cancer risk for men in the Rochdale cohort first exposed after (930 could be explained, since dust suppression using mineral oil was introduced from that date (Peto et al.. 1983). The regression slope estimate of /?L for the men first exposed after 1950 is 1.3 (95%CI 0.37-2.6). three times the value for men first exposed between 1930 and 1950. The plausible suggestion that the longer fibre used in textile processes are responsible seems to be con tradicted by the comparative analyses of lung fibre burdens in Quebec and Carolina cohorts reported by Sebastien et al. (1989). They found that the projtortionate distribution of fibres by length' was very similar in Quebec and Carolina lungs. Nevertheless, (he notion that the longer fibres used in textile pro cesses do represent a higher risk, is consistent with experimental evidence that longer fibres are more car cinogenic (Meldrum. 1996; Stanton et al., 1981; Miller et al., 1999). Green et al. (1997) have shown that the mean length and aspect ratio of chrysotile fibres in the lungs of Carolina workers are greater than in a local population control series: and than in the lungs of workers from the Albin cohort (Albin et al.. 1990o.b). Both studies on (he lung content of Carolina work ers have found omphibole (crocidolite or. amosite) fibres in an appreciable proportion of them, (hough at much lower levels than for chrysotile and its associa ted tremolite. Sebastien etal. (1989 report that amphibole fibres at concentrations >0.1 f/pg (fibres >5 microns long) were only found in the lungs of work- M i