Document 9JVvqxRKkagX2Zj5B61D8xxnD

Copyright 1986 British Journal of Industrial Medicine AU rights ofreproduction of this reprint are reserved in all countries of the world Radiological survey of past and present vermiculite miners exposed to tremolite JC MCDONALD, P SEBASTIEN, AND B ARMSTRONG t .3 British Medical Association, Tavistock Square, London WC1H 9JR - 10003325 British Journal of Industrial Medicine 1986;43:445-449 Radiological survey of past and present vermiculite miners exposed to tremolite JC MCDONALD, P SEBASTIEN, AND B ARMSTRONG From the School of Occupational Health, McGill University, Montreal, Quebec, Canada abstract Chest radiographs taken by a standard technique were obtained from 173 current employees (164 men, 9 women) of a vermiculite mine in Montana, from 80 of 110 past employees resident within 200 miles, and from 47 men from the same area without known exposure to dust. In 43 of the 80 and 24 of the 47 an earlier chest x ray film was retrieved from the hospital archives. All 367 films were assessed blind and independently by three experienced readers using the ILO 1980 classification. Median radiographic assessment scores were analysed in relation to estimated cumu lative exposure to the amphibole fibres that contaminate the vermiculite. Logistic regression anal yses showed independent effects of age, smoking, and exposure on the prevalence of small opacities and of age and probably of exposure on pleural thickening. Overall, the data suggest that by retirement age the increase in prevalence of small opacities (> 1/0) lies between 5% and 10% per lOOf/ml years. This gradient may be somewhat steeper than for chrysotile miners and millers, but not much so. The survey described in the present paper is one of a mining technique incorporating rubber tyre loaders series of studies undertaken to assess the health effects of work in a vermiculite mine in Libby, Montana. Two complementary programmes of research were initiated by NIOSH and ourselves, primarily because of contamination of the ore body with fibrous amphibole deposits in the tremolite series. A history and description of the mining and milling processes were given in our report on a cohort mortality study in this group of workers.1 These data showed sub stantial excess mortality compared with United States white men from respiratory cancers (SMR ** 2-45), non-malignant respiratory disease (SMR = 2-55), and malignant mesothelioma (proportional mortality = 2-4%). The NIOSH mortality study of a more broadly defined cohort obtained similar results from independently assembled data.2 Vermiculite, a micaceous mineral that expands on heat treatment has many uses in construction indus tries, agriculture, and packaging. The largest known vermiculite deposit, at Libby, Montana, has been commercially mined since 1923. At first it was on a small scale but, after 1939, when two companies merged, production increased: 20000 tons were shipped in 1940, 150000 in 1950, and, since 1972, about 200000 annually. The Libby deposit is mined using the open pit Accepted 30 September 1985 and trucks for both ore and waste removal. Waste is discharged at the perimeter of the mined area whereas the ore is hauled to a transfer point for blending and wet beneficiation. During early years of the oper ation, all functions of mining and milling were per formed in a dry state, leading to very dusty condi tions. A series of process improvements resulted in present mine personnel operating from within enclosed air controlled cabs and a totally wet beneficiation process. Vermiculite concentrate is graded into five size fractions before shipment to expansion plants in various parts of the United States. Fibrous tremolite has little commercial value and only one or two small mines in northern Italy produce it. On the other hand, it is a fairly common con taminant in various exploited minerals, notably some talc deposits of New York State and in the Quebec chrysotile mines where it is present in trace amounts. There has been no previously published radiological survey of tremolite miners as such but several studies of talc miners and millers exposed to varying concen trations of mineral fibre and silica.3 Pleural thick ening was frequently found in these workers but parenchymal opacities much less so. These obser vations are not easily interpreted in terms of tremolite fibre because of the other components in the airborne dust. 445 10003326 Radiological survey ofpast and present vermicuiite miners exposed to tremolite Table 1 Percentage ofradiographic changes by age Aft (years) Cwrent employees No Mam ammlative m 1(/1fmmin!ye)r 20-39 80 13-4 40-59 69 57-3 >60 15 103-5 AO 164 401 Stuff opacities <*tm 2-5 130 26-7 91 Hemal thickeumg (chest watt) 7-5 203 COO 15-9 Hemal ealdfieaUam Past employees No fi**y 1-3 1 60 JO 30 1602 6-7 49 961 3-7 80 H8-9 Small opacities (>IK>) _ 33-3 400 375 447 Pleural thickening (chest wall) 400 61-2 32-3 Hemal _ 16 7 367 2tO Table 2 Age standardisedprevalence ofabtusrmahlies by cumulative exposure Cumulative exposure (fjad y) Group Mem No in group Snuff opacities (>1(0) No Prevaiencr % <10 I0-<20 20-<l00 100-<200 >200 4-1 17-5 53-9 144-4 495-8 92 64 53 16 19 7 12 10 8 8 Total 65-9 244 45 *Directly age stanrianliwri, total study group taken as standard. 106 18-4 13-4 31-3 27-9 184 Heueal tUdcesthtt ofchest wall No AnalwrK* 15 23-3 14 21-7 22 38-7 6 22-2 11 38-3 68 27-9 Table 3 Prevalence ofabnormalities m men aged 60 or more by aomdative exposure Cumulative exposure (f}ml y) Group Mem <10 l0-<20 20-000 I00-<200 >200 65 1941 567 153-4 463-4 Total 97*9 No in group 15 17 16 8 8 64 Small opacities (> I/O) No Prevalence % 2 13-3 6 35-3 6 37-3 6 73-0 4 300 24 37-5 Pineal thicker** of chest waU No Prevalence % 7 46-7 9 529 10 625 s 625 5 62-5 36 56-3 Table 4 Logistic regression analysis ofexposure response relations Test for hi the presence of Small opacities (^IjO) Pleural thickening ofchest wall I2 <df) p x1 (<&> P Cumulative exposure Smoking Age Fatimaled coefficients: Age, smoking Age, cumulative exposure Cumulative exposure smoking 10-9(1) 8-2(2) 27-2(1) p < 0-001 p < 0-025 p < 0001 3-9(1) 4-6(2) 28-1(1) p < 0025 p ~ 0-10 p < OOOt Small opacities: Log --- -7-27 + 04)035 (cum exp) + 0084 (age) + (0-82 if ex-smoker r {1.72 if current smoker Pleura) thickening: Log j--g- -J-62 + 00024 (cum exp) + 0088 (age) + {-041 if ex-smoker {042 if current smoker______________________ 10003328 Radiological survey ofpast and present vermiculite miners exposed to tremolite 449 01 f/ml, no excess of radiological change should be detectable after a working life of 40 years. The imprecision associated with radiological technique and reading error would be far greater than the expected level of risk. Theft are few other data sets against which these findings may be compared. Our original studies of Quebec chrysolite miners* gave a slope of about 0-6% per 100 fibre years and a later analysis,7 confined to men aged 60-69 with an average gross service of 42-3 years, gave a lower estimate (0-2%). Both these esti mates were based on men still at work and it was concluded that the true gradients were probably steeper. A more recent study of the Quebec workers (JC McDonald et al, paper presented at XXI inter national congress on occupational help, Dublin, 1984) was based on current and past employees, used x ray films taken with a similar technique to that at Libby, and one of the three readers took part in both studies. That study gave a slope of 4% per 100 fibre years, about half that in the present survey. The radiographic study by NIOSH was based on the most recent chest xray films (188 in all) available in the local hospital for men employed five or more years and at some time since 1974.2 These men were all current employees at the time of the x ray exam ination, were somewhat younger than those in our sample, but had been employed nearly four years longer and at a slightly higher average level of exposure. Despite this, and the fact that one of the readers was common to both studies, the prevalence rates of both parenchymal and pleural changes were substantially higher in our study than theirs. The slope of the logistic regression line for small opacities 01/0) and cumulative exposure was also somewhat steeper in our data. We believe that these differences were due to better film quality and perhaps to the inclusion of ex-employees in our survey. This under lines the problems and imprecision of radiographic estimates of exposure response in dust exposed workers. This research was supported by a grant to McGill University from WR Grace and Co. The chest x ray films were taken at St John's Lutheran Hospital. Libby, Montana, under the supervision of Dr T Gill and read by Dr J Gilson, Dr R Jones, and Dr G Sheers. The active participation of past and present employees and the company is gratefully acknowl edged. References 1 McDonald JC, McDonald AD, Armstrong B, Sebastien P. Cohort study of mortality of vermiculite miners exposed to tremolite. BrJlnd Med 1986;43:436-44. 3 Amandus HE, Wheeler R. Morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite. Part II: Mortality. Am J lad Med (in press). 3Dement JM, Zumwalde RD, Gamble JF, era/. Occupational exposure to talc containing asbestos. Washington. DC: US Government Printing Office, 1980. (National Institute (or Occupational Safety and Health technical report.) 4 International Labour Office. Guidelines for the use of ILO inter national classification ofradiographs ofpneumoconioses. Geneva: ILO, 1980. (Occupational Safety and Health series 22 Rev 80.) 3 Baker RJ, Nelder JA. The GLIM System.- release 3. Oxford: Numerical Algorithm Group, 1978. `Rossiter CE. Bristol LJ, Cartier PH. era/. Radiographic changes in chrysolite mine and mill workers of Quebec. Arch Environ Health 1972;14:388-400. 7 Liddell FDK. Gibbs GW, McDonald JC. Radiological changes and fibre exposure in chrysolite workers aged 60-69 years at Thetford Mines. Ann Occup Hyg 1982;26:889-98. 10003330 Published by British Medical Association, Tavistock Square, London WCIH 9JR, and primed in England by Eyre < Spottiswoode Ltd, Thanet Press, Margate 10003331