Document Rp3Be5R7aZw4BRevZO2g0gXmE

I 600 1. T. Hodgson and A. Damion, slope for (hose cohorts with clearly positive results. This might be predicted from the flattening of regression slopes by inaccuracies in exposure esti mates. But it can also reflect inadequacies in baseline rates. For example, (he two-fold difference between the cohon average and regression slope measures for the Quebec cohort reflects the SMR of about 1.3 seen in all the low dose subgroups, and which the authors interpret as non-asbestos related. Nevertheless, the broad agreement between the two measures across studies suggests that valid conclusions can be drawn from the cohon average measure. ably present assuming some exhaust control on (hr bag opening, carding and mixing areas. Unfortunately no mention of the control system is made. Also it is probably an average value that has been given for both the wet and dry methods as both were in use. It is probable given that the sampling locations are unknown that higher concentrations occurred in the dry areas: around 100 f/ml as measured by the current method. Of course this is very approximate, but 100 f/ml looks to be a good maximum exposure with TVVA of 60 f/ml. Appendix B Apfwndlx c FIBRE-PARTICLEJ20NVERSION FOR CROCIDOLITE CIGARETTE FILTER COHORT NOTE BY DR G. BURDETT The measurements in 1932 which gave an average of 80 particles per ml, within the Massachusetts stan dard of 173 particles per ml, almost certainly refer to impinger measurements, which were frequently made for insurance company purposes. The normal units are millions of panicles per cubic foot (mppcf). As one cubic foot is equivalent to 28 316.8 ml the value of 80 panicles per ml is equiv alent to 2.263 mppcf and 173 panicles per ml is equi valent to 5 mppcf. Five mppcf was the threshold value in force from the 1930s to the 1960s (maybe even until 1972) when it was replaced by a membrane Alter limit of 10 f/ml, which has been falling ever since. As the units suggest, the method only counted par ticles using relatively low powered microscopy and would overlook many of the respirable fibres and is a very indirect measurement of the fibre level. It should also be remembered that impingers have poor capture efficiency below 1 pin. It is also noted that cotton and acetate fibres were mixed, carded and deposited on crepe paper under dry conditions. This would suggest that fibres made up many of the particles but I have not referred to the patent to work out quantities used to estimate the fibre percentage. My best guesstimate is that 30% of the particles were fibres but only about 10% of the fibres seen would be crocidolite (it is more dusty, but has very few >1 pm fibres compared to the other dusts). This would mean about 3% of the count was cro cidolite. fibres or about 2.3 f/ml>l pm wide. To con vert to the current index we generally find one can assume only some 4% of the >3 pm long crocidolite fibres were visible os compared with the current index. This is equivalent to a concentration of about 60 crocidolite fibres per ml using a modem version of the membrane filter method. This is several times higher than the better factories at (his time but not too far away from what was prob- DEVELOPMENT OF ADJUSTMENTS TO THE ... SOUTH AFRICAN MINES COHORT DATA ' The starting point for the adjustment of the reported results from this cohort is the data given in Tables 1 and 2 of the published paper, which give illustrative data on exposure levels in different per iods (Table 1) and a breakdown of the whole cohort by year of birth and date of first exposure (Table 2). The average age at first exposure'of the groups rep resented by the cells of Table 2 con be estimated using the mid points of the year of birth and year of first employment categories (1900 and 1933 were assumed for the earliest birth and employment categ ories respectively). Age specific all cause and lung cancer rates for white South African men in 1933. 1965 and 1975 were then used to calculate the distri bution of expected lung cancer deaths by time since first exposure in each cell. The rates for 1955 were also used for (he cells relating to first employment between 1941 and 1950, but the expected number was reduced by a factor of 0.64 to allow for the fact that cause specific follow up was only recorded from 1949. The total expected lung cancers calculated in (his way (39.3) agrees quite closely to the value reported in the paper (36.6) and the proportion of expected lung cancer deaths arising from follow up less than 10 yr from first exposure is 0.23. The reported observed and expected tung cancers in the two pure fibre subcohorts have therefore been reduced by 0.23 times the expected numbers given. The data reported in Table 1 was used to estimate approximate relative exposure levels at ten year inter vals from 1943. Taking 1943 as 1, the numbers used were 1, 0.6, 0.35, 0.23 for amosite; and 1, 0.5, 0.23, 0.15 for crocidolite. Exposures in the 1930s were assumed to be the same as in the 1940$. To derive an expected lung cancer weighting for this relative exposure pattern, the expected lung cancers in each birth-start cell from the 10th anniversary of first employment to the end of follow up in 1980 was cal v culated in a similar way to that described for the first 10 yr of follow up. The resulting distribution, of