Document 3e2awrK8DyRbyor0ypg6rZ2D0

Scientific Communications The Health of Chrysotile Asbestos Mine and Mill Workers of Quebec J. Corbett McDonald, MD; Margaret R. Beckiake, MD; Graham W. Gibbs, PhD; Alison D. McDonald, MD; Charles E. Kossiter, MA, Montreal- The results of studies of respiratory symptoms and (unction, roentgenograph* ic changes, and mortality in relation to dust exposure in the Quebec chrysotile Industry, which has employed some 26,000 workers, are brought together and their implications lor control examined. Breathlessness on exercise, C-.mln* ished inspiratory capacity, parenchymal and pleural changes, and respiratory dis* ease mortality were related to dust expo sure and to each other. Respiratory caneer was also related to dust exposure. The overall excess of deaths (ram res piratory cancers, including five with ma lignant mesothelioma, was al most 50% above expectation, based on age-specific rates for Quebec and the mining region. If safety standards are set, they should be based on epidemiological evidence. From these data for the chrysotile produc ing Industry of Quebec, a resonabie fig ure, based on e 1% risk of ecauiring clini cally significant disease, would lie between 2 to 4 million particles per cubic foot, calculated for a working life of 50 years. In the absence of epidemiological findings based on fiber eounts and lack of a satisfactory means of conversion, par ticle counts should continue to be used for control in this Industry. In recent years, exposure to as bestos dust has been widely recog nary function.-* and respiratory symptoms." The purpose of this report nized as an important etiological fac is to bring together these and certain tor in pulmonary fibrosis, cancer of subsidiary findings and to discuss the lung, and malignant mesothelial their implications for control. tumors. The precise nature of the cau sal association has usually been ob Outline of Study* scured by exposure to more than one Records of the mining companies form of asbestos and to other mate were used to identify all persons rials in the manufacture or appli known to have worked in the industry cation of asbestos products. In the since its inception in 1STS. Earlier mining and milling industry of Que records tended to be incomplete or bec, where almost half the world's missing and certain sets had been de supply of chrysotile is produced, expo stroyed, but altogether some 28,000 sure to other types of asbestos or to employees, mostly men, were identi materials used to make asbestos prod fied and information was assembled ucts has been very slight. To assess for this group. Of these, 6,400 were the effects of pure exposure to chryso working on Nov 1,1966, the registra tile, an epidemiological study in this tion date for the study. The informa industry was started in 1966. Our tion collected for each person con aims were to relate dust exposure as sisted of date of birth and a full sessments to mortality, roentgeno- industrial history. The latest chest graphic change, pulmonary function, roentgenogram of each employee, if and respiratory symptoms. Results of available, was provided by the indus these studies have been presented in trial medical clinics and read by an separate papers on mortality,1-* international group of six readers roentgonographic change,' pulmo using the UICC/Cincinnati (now Table 1.--Number of Men in Oust Exposure Analyses Sulimiucd fur publication July 2. 1973; if, July ".i. t'rnsi the mont <f an*| M.-Oilf i'tmvmity. Montreal. Mr. R.vm* ( r i* with the Mvuw-al K* .arch 5*n.I'-it. IVr.arth. S--::tH VVaie. I'. j-r.i: r.!(."'< I}:,rtmerit *f "CV .tr.ti li.11:11. Mctii!? I't'iivrusv.aTT.*, I'm'-vp. :?> ht. Montreal UJ. QuvIxh-. t'an.i.la UV Mi l)..:..,: ' Analysis Von.iaty stujy Ui-.-tit.> nji:r;*r:h;c stud-/ luii i ;m>.r>ui' and ri!.,p;ra:'.><y Sn-Aars fvHiH-'-V.i'jrS - to 2.810 i:,? Dust Exposure Level. mpefyr 10 1.522 ICO Mp4 1.13*1 2C0 1.047 912 404 637 n COOt* :-r5 to: Total 9.692 6.529 . 91 455 isn 134 109 i 2-11 144 117 .> :> t . 17 i ' G? 1.015 53 3M 0 t-t-j Arch Environ Health. Voi 28. Feb 1974 Chryotiia Asbestos V.'orkers/McDorvii j el ai 61 Tauie 2 --Roe ip'v 2 Chance Preva ence Percenngus Roentgenographic Charge Irregular small opacities I/O 2/t Pleural thickening Grade 1 Grade 2 Irregular small opacities 1/0 2/1 Pleural thickening Grade 1 Grade 2 Dust E* posure level, mpef-yr -- -- --------- - v!0 10 100 230 i'.O vCO - ThePord Mines Averaoe 1.8 3 3 63 87 120 ! 7.2 7 5 0 0 2 22 0 9 2.4 9 2 2 0 24 4 5 6 5 58 8 3 105 6.4 1 3 0 7 0 8 1.2 13 2.0 1.1 Asbestos 6.4 3.7 6.3 SO 6.8 7 0 5.1 0 0.4 1.5 0 8 06 39 09 2.9 2.6 3.0 3.0 00 06 1 0 0 5 4.7 S.8 32 14 0 7 0 7 Rates are standardized for age and years in industry. Males were 36 to G5 years of age at time of roentgenogram. - Table 3.-- Ace-Corrected Death Rates Per 1,000 Men Born 1891-1920: Deaths to December 1969 Dust Exposure Level, mpef-yr Cause All causes Respiratory cancers* Abdominal cancers Pneumoconiosis `do 365 10.3 18.0 1.6 to 35S 13.1 13.6 1.5 100 3S4 13.4 18.7 0.8 200 313 15.5 11.6 4.9 400 323 21.4 26.3 4.9 Includes malignant pleural mesothelioma. 800+ 395 32.1 28.7 23 -3 Table 4.--Relative Bisk of Qeath From Respiratory Cancer in Men by Oust Group, Estimated From Retrospective Analysis Oust Exposure Level, mpef-yr < 10 to 100 200 400 800+ Total No. of Cases . 32 41 13 14 15 19 134 No. of Controls 186 188 39 61 40 22 S36 Relative Risk 1.0 1.3 1.9 1.3 2.2 SO Table S.--Age-Corrected Mortality Per 1.000 Men From Respiratory Cancer and Pneumoconiosis at Thetford Mines and Asbestos Respiratory cancer Thefferd Mines Asbestos Pneumoconiosis Thetford Mints Ashnstos <10 9 11 4 0 Oust Exposure Level, mpef-yr 10 100 2C0 400 12 18 15 24 13 6 18 13 1 1 76 00 53 600+ 31 43 24 24 LC/lLui 'A of c.\-ciu;>!nyiv$ w.'.s set up ui\d .'.e.-.th ' aiul :ui'.-ji'$v !\;>->r;.x u C' .in:iin ri fi r ! ho-v u lu- i_v ;iu ; Qr.e section of ih!> artiv!^ ,, r.h re sults in 'vomon: the rust i> o>:;oernod w iih men only. DmJ K\|ji<jrv.~Diist expo-uro lev els worn determined lore.tod recorded job within the industry. r.n<! for each year of employment. These levels were used to calculate a total dust ex posure index for each worker. Gibbs and Lachance" described the tech niques used and Gibbs'- dealt further with certain qualitative aspects. The main index was based on particle counts from midget impinger sam ples, expressed as millions of particles per cubic foot (mpef). A total dust ex posure index was calculated for each worker by multiplying the measure ment of dust exposure by the number of years of exposure at that level, and was expressed as mpef-years. ` The results which follow are pre sented in terms of range of total dust exposure based on particle counts (Tabe 1). Table 1 also lists the number of men included in the main analyses considered in this report. Since disease is probably caused bv asbestos fibers rather than dust par- tides, it has been recommended that standards for occupational exposure be based on fiber counts obtained by the membrane filter technique.1' If there were a reasonably consistent relationship between particle counts by midget impinger and fiber counts by membrane filter, the results of our surveys could also be presented and interpreted in terms of fiber counts. A study was carried out by Gibbs and Lachance'* in which 87 side-by-side midget impinger and membrane fil ter measurements were made at nine locations in each of five mines and mills of tin* Qtu-bec chrysolite indus try. The correlation between the two types of measurement was too poor to justify the use of any single conver sion factor. Roemgenocritphic Chance**---The two main rrvntgnnngniphu* indices of re sponse to aslK'stns exjwsure are ir regular small opacities and pleural thickening. The prevalences of the*" and of all other roentgvnograp 62 Arch Environ HeaUft/Voi 28. Feb 1974 Chrysotite Asbestos Workers-'McDonaic et a < ii.utLf'' u, !' i'i'.'Mi r it; '.:u- l1 < > r< I Mini.-.' .ii' i ;i.t*i :i. l:.c A i-.'l"' x:v.i 0 . Q'.n T. ,! ; I |t . I l!;c V .lIV.l.' >11 l` ') k;:i ./o| the ,t'b<.-.-!".> !Ti::ivl in .similar Tin- a.'- >.)c:::l a'n .i; the (h..!!go> wi! h du^t rx- p"-iire v..;.n .i!.n > ''.ivcufr at ThcUord Mines th-n -l .'i.'ii'.---'.os. Tahii. 2 >how- '.`Kit at Thctfor.l Mint's till- piv\ a!e:u-i- of irregular small opacitii-N o' c::t--g'-rv I or mor- ro?e stvndib. with mctv.iMUg dust ex posure whor-a- tvirt*r\ 2 or more the ivia'-.'m in au't ixposau; was less marked, except for the eon* siderablo rise ir. the most exposed workers. Even, with allowance for dif ferences in dust exposure, the preva lence of category 1 or more was markedly age-related, rising to 14.63 for those 61 to 65 years old. This age efTect was much lower for category 2 or more, and amounted to only about one third of the change associated with dust exposure. At Asbestos, the prevalence of ir regular small opacities of category l or more rose to 9.23 for those aged 61 to 65, and there was virtually no rela tion to dust exposure. With respect to only category 2 or more* the relation to age was muen lower and preva lence increased among those with the highest dust exposure. * For pleural thickening, the effect of age was slightly greater titan the ef fect of exposure on the prevalences of grade 1 or more, and of grade 2 or more, for both mining areas. ' The biggest difference among all the roentgenographic features was in pleural calcification, for which the prevalence of grade 1 or more was 0.43 at Asbestos and 5.23 at Thetford Mines. In spite of the relationship to dust exposure, no correlation ex ceeded 0.3. This is largely a reflec tion of the very high proportion of men who showed no roentgenographic change. Some of the differences be tween the two area' were not surpris ing. as overall dU'i exposure levels at Asbestos were considerably tower than at Thetford Mines, hut other.-. cannot yet be explained in terms of d;i'*. exjs.sure or geology. If variation in fiber content of di:.-t wer- an im portant factor, the result' in mine workers, for whom the fiber propor- linn womb ' low. 'hoi: d ridler from l:;< -e |.r riibl w..;mT-. ;r, whom the fiber pr.-;.o!t:o[i uvb-- higher. Ai- '.ogeirv:', tm-im w, r- ' . wm-ro who had work'-d lor t-n ur more years en tire!)' in mining or entirely in null ing. A nab. >i' of roe.n tgermgraphic changes in these men showed that mill workcis h.id n slightly higher prevalence of irregular small opac ities. but the ddl'erenees between Theiford Mines and Asbestos re mained. No other consistent differ ences could be detected between the mine and mill workers. Mortality.-This study was limited to those who had worked for one month or more, and who were born 1S91 to 1920. This age group was se lected because the records of older persons were frequently incomplete and few of the youngerones had died. An initial analysis* was limited to deaths before Nov 1,1968, but the fol low-up will continue until at least 1974. By the end of December 1969, $7.53 of the 11,572 persons in thecohort and .993 of those who had worked ten years or more had been traced/ Of these, 3.270 had died, com prising 65.43 of those born 1SD1 to 1S95 but only 9.83 of those born 1916 to 1920. The age-standardized mortality per 1,000 men for certain causes of death are given in Table 3. Cancer of the lung showed a rising rate with in creasing dust exposure, particularly in the two highest dust exposure groups. Cancers of the gastrointesti nal tract also showed a rise in the two highest, and pneumoconiosis in the highest categories of dust exposure. Of 134 deaths in men from respira tory cancer, five were from pleural mesothelioma. These cases showed no clear relationship with dust exposure. There were no peritoneal mesothe liomas. Mortality from all causes fell with increasing dust exposure up to the highest dust group, probably be cause those who died young could not attain a high dust exposure. On the basis of Quebec death rales, the ex pected number of respiratory cancer deaths in the cohort was 139. or al>out on the luifis of estimated rales in the mining rig in::. This suggests that mortality from iv'piratury cancer in the Quebec chrtvtile ir.'n'trv a whole ha' been a: m< - ;i;m\ r- ,.v pcetution ant! probably ai' _'V; The primary me'h-t.l , f ,, used in our report on ile./h' ip. t,, 10'G' had two main. \ieakne"i.- The first was that length of e\pM-,,r<_. might well have been related to length of survival and thus ought tend to obscure differences m mor tality between exposure grniij s. Wo looked for evidence of Mwh an inter action using the parametric apon-aMi of Berry,'' and though we failed to find a significant efTect. the possi bility remained. The second weakness lay in the fact that deaths accumu lated over many years were used in a single calculation of mortality. It is reassuring that our subsequent anal ysis,5 which dealt with deaths over a three-year period, 1967 through 1969, gave essentially the same results. To some extent these problems are some what academic, since the total excess mortality in the industry from res piratory cancer, compared with mor tality of the general population, was so small. The data are of practical im portance nevertheless in defining the form of the dose-response relation ship, essential for the setting of safety standards. For this reasoson, when the follow up is eventually completed, an analy sis based on man-years of exposure" is planned to minimize these possible errors. Meantime, another method of analysis (G. Eyssen, MSc, and F. D. K. Liddell, MA, unpublished data) has been employed that, we believe, elim inates certain of these problems, though it does not make full use of the data available and provides only estimates of relative rather than ab solute risk. For this analysis, the dust exposures of the 134 men included in the 1969 analysis of respiratory can cer mortality were compared with a sample of men. four for each ca>e. se lected at random among persons liv ing at the time of the death of the respiratory cancer case and )>orn in the same year. The distribution of cases and controls by dust exposure category is presented in Table 4 H can he seen that tho pattern of rela tive risk obtained by this approach b quite similar to that for rospiraton Arch Esv.ron Hv.am Vol 23. Feb 197.., Chryuotiic Asbestos Workers-McDonald et ai 63 Tao 0 6.-- Mortality rrom Al Causes opfi.c Change 3 a: 7n* 'c.'d Roentge nenrjphic Changes PO'tf'iC'yMiai ch.vn._-s m'y PiSor.il Ch.mncs only Both ojrenciiymal and o'.eural changes 1891 1SSS Obs 17 13 6 11 10 3 14 11.4 Mi. ci 0- e.-ved and fc >:r!<_d O J.V.ns by Year ct O.rtn Ccf yrt* 1J2M90-) ISCit v;c5 1930-1910 19H 1915 Obs Exp ' Obs Exp Obs Exp Obs Exa ` 7 7 S 4 39 11 4 5 7 1 6 15 1C 8 10 9 7 5 5 2 2 34 17 1C.7 8 68 6 22 3 06 * Expected number was calculated from ceath r?:es tn men without rocntgancg.-aphic change. 1010-1920 Obs Exp 2 16 2 24 1 02 Total Obs 43 33 0 45 47 3 49 33.7 cancer mortality shown in Table 3. It seemed possible that the roent- genographic differences between Thetford Mines and Asbestos might also be reflected in mortality. There was little evidence of this. The agestandardized mortality per 1,000 pop ulation, for all causes, all malignant neoplasms, all respiratory diseases, and all circulatory diseases were 342, 54, 20, and 120, respectively, at As bestos and 362,61,22. and 121, respec tively, at Thetford Mines. All detailed comparisons showed the same sim ilarity. For example, in Table 5, the age-standardized mortality by dust exposure is presented for respirator}* cancer and pneumoconiosis. The only apparent difference is that the res piratory cancer rate rose in relation to dust slightly earlier but to a less extent at Thetford Mines. Mortality and Roentgenognphic Changes.--Of 10,120 persons traced in the mortality study, 9.692 were men and of these 5.0S2 had chest roent genograms and 785 had died. At Thetford Mines, there were 354 deaths in 2,448 men traced. Death rates wore calou'-au-d by date of birth, dust exposure, and the presence or absence of parenchymal or pieural roentgenographic changes. The rate from ail causes combined was in creased in the highest dust exposure group but, with allowance for expo sure and date- of birth, those whose roentgenograms showed parenchymal changes had a higher mortality (220/1,000) than those without roentgonographic changes (131/1,000) or with pleura! clwmres only (125/1,COO). In Table 6, the observed number of deaths by year of birth and roer.tgenographic change is compared with the expected number based on those without roentgenographic change. Of 97 deaths in those with parenchymal changes, S3 were in excess of the expected figure. Considering only deaths from respiratory disease, in cluding tuberculosis and cancer, we calculated in a similar way that there were 32 deaths in those with paren chymal change compared with eight expected, an excess of 24. Thus of the 33 excess deaths in this group at Thetford Mines, 24 were attributed to Table 7.--Age-Corrected Prevalence Percentages by Oust Exposure and Cumulative Smoking Habits Bronchitis Never smoked Up to 103 ciparette- - years 100-439 500-999 1.009 Never smoked Up to ICO cigarette- Breathlessness- years 100 499 500-999 1.000 Oust Exposure level, mpef-vr <J0 10 1C 19 100 205 403 t 19 4 lit Y8 0 12 0 45 0 41 28 21 33 42 43 32 38 44 23 47 58 too 47 45 55 54 35 0 14 ' 24 31 13 44 0 12 15 14 39 8 22jt 4t >2 13 1? 9 19 21 13 14 2 Q 23 27 31 34 respirator}' causes. At Asbestos, the difference be tween the mortality of those with 2nd without roentgenographic changes was less. Calculations similar to those used for Table 6 showed that oniy seven of the 431 total deaths were as sociated with parenchymal change, and of these 2.4 were attributable to respiratory causes. Dust exposure levels at Thetford Mines were much higher than at As bestos; thus, in the highest exposure group there were 356 and 69 men, re spectively, on whom roentgonogran had Iwen performed and who hau been subsequently traced. Though the excess death rate in this highest ex posure group was about 95 at both places, the numbers of excess deaths were therefore 35 and 6 respectively. Calcified pleural plaques were not related to mortality as there were 60 deaths in persons with pleural plaques compared with an expected 59 deaths.15 Pulmonary Function.-A total of 1,015 current employees underwent pulmonary function studies during the summers of 1967 and 1968/-T The sample chosen for study was strati fied to include a higher proportion of older than younger workers, as the former were more likely to show i-hungi* in fum:t'n. Th<w t<->ted comprised s::', of th-.- .simple selected. The variation in of the lung function indices by dust level in smokers and tt<'r..-::>"k**rs is shown in Fig l. 2, and 3. The results of each test wore standardised to age 50 y< ars. hidglit |7o cm. and weicht kg. Total lung '!u:ne Ml sV'h:!j with ir.ereasm!.' (i.i.-t ,:t e.\|s*sure had little effect cr. r $4 Aren Environ Health. Vol 28. Feb 1974 fl 1 _r> Chrysolite Asbestos Wo^-.rs <10 10 100 200 400 800* Dust Group. mpct->r Fig 2.--'Variation in forced expiratory volumes with dust group, standardized for age. height, and weight the same age and year of death but who had never been employed in the industry* There was a higher propor tion of nonsmokers in patients titan controls, which suggests that pulm> nary cancer may be caused by as bestos exposure in the absence of smoking. The controls were on aver age heavier smokers, which reinforces the point but does not rale out the possibility of synergism between as bestos exposure and cigarette smok ing. Clear ovideniv was obtained from a survey of all known cases of malignant mesothelioma in Canada that this disease was not related to smoking.*-4 Women.--The number of women ev.*r employed in the Quebec chryso lite industry is small. In the mortality study. 428 of 465 women in the cohort were traced and of these 54 had died. Only T9 women had worked for more than ten years, and few had been ex posed heavily to asbestos dust One death was ascribed to lung cancer and none to pneumoconiosis. Chest roentgenograms were avail able for 294 women, most of whom were 30 years old or less. The only roentgenographic changes recorded were one subcategory 0/1 rounded small opacities, one subcategory 0/1 irregular small opacities, and one grade 1 ill-defined cardiac outline. Comment Although death is the m>>' -finite and scrinus manifestation of cX|k>sure tu asbestos, it is not the most sensitive. Excess deaths related to ex posure altogether were probably in total no more than 2Tt of the 3.270 deaths in the' cohort study. Most of these were attributed to respiratory cancer or pncdinocomoMs and almost all were in the two highest dust evisure categories. Thus, excess mortal ity wa- \ irtu.'.liv co.':!iri ii to ::v,^ u *- exposure equivalent to ;>.* iea.-.;. ;;v-o mper-yr. I Vt ailed examination <: mortality >!io.u-d m* particular ca.0>?. except wish * rate abuw Uuil of the general population of Quebec. An investigation was mr.de of the 220 known casus of malignant meso thelioma in Canada. through 1970. The manner of death eertihea* lions of these patients were exam ined.-' and the pathological findings reviewed in detail In the .Mesothe lioma Panel of the Canadian Tumour Reference Centre."-- Epidemiologi cal inquiries showed that 23To of men and Vi of women had definite or probable occupational exposure to as bestos, and a further 1^ of men and 6% of women had lived in the home of an asbestos worker. In the remaining cases, none had ever lived within 32 km of an asbestos mine or mill. Of all known cases of mesothelioma in Can ada, only nine have been associated in any way with the Quebec chrysotiie mining and milling industry. Seven (five in the cohort) had been employed and two were women whose fathers had worked in the industry. These cancer rates are very low in comparison with the studies of New York insulation workers*1 and the London crocidolite factory workers,*- in both of which there were much higher rates of malignant neoplasms, particularly of mesothelioma. Other studies in the Soviet Union** and Italy-7 support the view that only high levels of exposure to chrysotiie during mining and milling have an appreciable effect on mortality. Although roentgenographic changes had some relationships to dust expo sure, the clinical significance of the minor changes which were also re lated strongly to age is uncertain. Ir regular small opacities of category 2 and pleural thickening of grade 2 are usually con.-idi-n-d of clinical impor tance, ami these were much less inllu- enei-d h\ age. Changes of this order occurred in Ufr and 0.7'r of the en tire working imputation. In men aged f*| to tin, employed an average of 20 years in the industry, the rates were 5.U\ and 2.5'< at an average exposure level of 13 mpef. These fates are \ er, 66 Arch Environ Hcalth/Vol 28. Feb 1974 Chrysotiie Asbestos Workers WcDonaJd a: functional inpacity (FUC) or rc'i'iu.-.! \o!u::iv iilVj. Ti;u> rxp<ure to <-hrv-.it 11- f<.ctcd only the inspira tor. i-.ij'.u-ity p-nion of the total tar-j vot-jrrv iTLV}. Forced vital eapacit.v (FV('t an;! forced expiratory volume ir. or-- s<find (FEV.) both decline! with increasing exposure, the FVC vi tal capacity failing by about ltFr tn tile highest dust group and the FES' rather loss. Neither steady state nor single-breath di (Fusing capacities showed any effect of e.xp-'siro at rest; on exercise, tne steady state diffusion declined slightly. Analysis of the relation between lung function and roentgenographic changes' showed that in those with small opacities of category 2 or more there was an average reduction of 20*0 in three indices: FRC, RV, and singlebreath diffusing capacity at rest. Most indices showed a progres sive reduction with increasing cate gory' of small opacities, but only VC and FVC showed significant reduc tions in association with the earliest roentgenographic changes. Pleural changes were also associated with re ductions in pulmonary function, which ranged from about 3% in those without parenchymal change to about 6% in those with advanced.parenchy mal change. An additional small sur vey showed that changes in pulmo nary mechanics possibly precede roentgenographic and other function changes.1 Detailed analysis of those aged 61 to 65 showed that those with an obstructive lung function profile, ie, RV and TLC greater than ex pected and fiow rates less than ex pected. had had heavier dust expo sure, more symptoms of bronchitis, and more irregular small opacities than those with normal or restrictive patterns of pulmonary function.1* Respirator) Symptom*.--Each of the 1,015 workers in the function survey answered a slightly modified version of the Medical Research Council (MRC) respiratory questionnaire given in French or English by a bi lingual interviewer. Ib-th persistent cough and phlegm (bronchitis) anti breathlessness on exercise were re lated to exjosuro.' Table 7 shows, however, that after standardizing for age, the prevalence of bronchitis rose <10 10 100 200 400 800' Oust Group, mpcf-yr Fig 1 .--Variation in iung volumes with dust group, standardized for age. height, and weight. to about 50% in both the highest dust and highest smoking categories. Thus, the effect of heavy exposure and heavy smoking together were the same as that of either separately. The same relationships have been ob served in other dusty trades.'* In con trast, the prevalence of breath lessness on exercise was unaffected by smoking, but increased steadily with dust exposure. Effect of Smokiug.-Sinoking habits wore originally determined only for employees in the pulmonary function survey. Figures 1. 2. and 3 show that, with many of t:;. physiological in dices, the effect m smoking was greater than the !' vt of exposure to ask-stos du<t. This was most olnious in FRC. UV, and perhaps in the st.'iuly-state dii'.u-iu.r capacity at re.-t. Forced vital rapacity am! FEV, were both decreased to a similar ex tent with increasing dust exposure, but only FEV was lower in smokers. As mentioned above, smoking and dust exposure were both related to the prevalence of bronchitis, but smoking was not associated with breathlessness. Attempts are now being made to collect smoking histories in the cohort study of mortality, both for those who are still alive and for those who are dead. This may eventually provide prospective and retrospective evi dence on the interrelationship . of snicking and asb.*s'<s exposure. A controlled retrospective study'* has Ivcn made based on deaths from lung cancer in the cohort study. Each pa tient was matched with a death from lung cancer from the same hospital records in a man of approximately Arch Environ Hea'trvVcl 23. FeO 1974 Chrysotile Aspestos VYorkers.-McDona'd ct at S5 'ifi'.h.ir l" ill"-*.' r*'un<l :i'. the ihr\><>- till- :n;.;..'"1 nd;i:ng iniiu.-try tn }i-u. !>ut .rv much lower than t1,-- \\\ th,'- N'v-v York inhibition w nr in the British Koval Nu- \ ,il ! arils.-' " Ki-r pulmonary function and res* ;i.:-:Uo-y 'ymptoms. tho etfcct of >:::--kinir v.aa generally greater than eil'ect ot exposure to asi.c'tos. Hoiuu.-r. for inspiratory capacity, forced tUw rut--. and brenthU-ssne-s on exercise, rvlationships to dust ex posure were found. With respect to these indices, a lO'r reduction in non smokers occurred after a total expo sure in excess of 100 mpef-vr. This is dose to the lower limit of the dust category at which of subjects had grade 2 roentgenographic changes. In tho Quebec studies, information on dust exposure was obtained, where as in most other studies quantitative information was not available. Mur phy et al 1 found 11 cases of ashestosis in 101 N'ew England shipyard workers with an average exposure of 120 mpef-years, compared with one in a nonexposed control series. These workers appear to show a larger ef fect of asbestos exposure than those engaged in chrvsotile production. However, the main constituent of the insulating materials used was amosite, with some chrysotile and no crocidolite. Oust exposure assessments were also made for the Cyprus mining and milling industry.** and the rates of roentgenographic change for the same exposure levels were quite sim ilar to those in Quebec. Exposure in dices have also been assessed in a study of two asbestos-cement plants in the United States by Enterline and Weill, ' where the main exposure has been to chrysolite and silica, but the results are not yet available. Tho limit standards for occupa tional exposure to asbestos arc based solely <n the airborne concentration of dust or fiber, averaged over a life times v.ork. ami the results in this re port ha\e ln-cn presented from this point of \ie\i. There was some evi dence in our studies that longer ex|**sures for the same total dust levels are`associated with slightly higher ptvi ah rve fates ,.f ro.iiig>-m*gr:iphie Aren Ewron Health Voi ?2. rt> :;< Oust Group, mpef-yr Pig 3.--Variation in diffusing capacity with dust group, standardized for aga. height, and weight change. However, the roentgen ograms were alt taken during work ing life, so the correlation between total dust and years of exposure or years since first exposure is high, and the separation of the contributions from these two factors, duration and concentration, would be very diffi cult. The cohort study also showed that respiratory cancer mortality was greater in those who took more years to reach a given dust level. Therefore, in assessing the overall elVevt of ns- bestf>s i x|x>.sure. duration of exp. sure should in -t really lv ignored.'F.f this rca<'n. it ui.tsld Ik* unwise to .. poly the results of thts or other de.-eri::ive epidetn iul.'gical r(Indies to wbUiy dif :Vre:it ii*Xp*'St.*V patterns. Yl.e Briti.-h tiii'l standard fer hr. sol ile ,.f 2 p-.-r i- i:;; iiu r. Civ,- averaged over three months, is based on the concept that a risk of ac quiring clinically significant disease in a 50-year working lifetime of expo sure is acceptable. Considering all facets of disease-death, roentgenographic changes, pulmonary func tion changes, and respiratory syrup* toms-thc I'c risk is reached by men in our third dust exposure category (100 to 200 mj>cf-yr). The relationships that exist be tween measurements of total dust and tilier exposure are thus of critical tmiirtumv if standard-*-are to be sot for aslvstos production and other as bestos industries. Such standards should be based on d.isorosponso re lationships established by sound epi demiological inquiries. To date. vor\ lYw of th-'se have itujudcd anv qua: ./V; la Asboi^i Workers McOona'O et al 57 r- u'.aiivc a.'St <sincrits of dust, let alone of liber exposure. Though safety stan dards evprc.sseii in fiber eoruvniralions have theoretical and conceptual attractions, there i? as yet little or no direct epidemiological cadence on which to base them. Our studies ap pear to provide a reasonable basts for c-.-r :t d; .-Ti i safety for chrys-ude mining am) :?!.;diay m U-r:MS of conu-ntrai ion. Wilivmt to id'-n-.-' on the conversion fac tor that :>lunjld be applied in different parts of the in.la-try. u\- cannot e\- pr<\-> uur results contidcn.tly in fiber counts. Further efforts to find a sutis- fat-lory moans of vonwrii'p'.: m,)--,.; imp.ayrr ti< iiiar ;,rc nu liut. until1 nv'V vpill-.'IM'nil'-^iv;'.! 'c\ lilnruv lia> vti '*n iukt cunts iu- nivr. a.-svnibivi 1, it aptv.tr.- unwise t- oontimio .<*' >`f pariidc cow.-.; - for control in this in-lastrv. Refertnces 1. McDonald JC. et al; Mortality in the chrysotile asl'Oiios mints and mill# of Quebec. Arch Ennmii Health 22:677-din, 1971. 2. McDonald JC. et al: Mortality in the chryjc* tile producing industry of Quebec A progress re port. Road before the Fourth International Pneumoconiosis Conference, Bucharest. Hun gary. 1971. 3. McDonald AD, et l: Epidemiology of pnmart- malignant mesotheltal tumours in Canada. Cancer 26:914-319. 1970. 4. McDonald AD, McDonald JC: Epidemiologic surveillance o! malignant mesothelioma in Can ada. Can Med As.< J 109:359-362.1973. 5. Kosstter CE, et al; Radiographic changes in chrysotile asbestos mine and milt workers of Quebec. Arch Enrim Health 24:353-400, 1972. 6. Becklak* MR. et al: Lung function in rela tion to chest radiographic changes in Quebec a*bestos workers. Bull Physiopathol Retp 6:637 659. 1970. 7. Becklake MR. et ah Lung function in chrysotile asbestos mine and mill workers of Quebec. Arch Enrinn Health 24:401-409, 1972. 8. Jodoin G. et al Early effects of asbestos ex posure on lung function. /1m See http Die 104:523-53$. 1971. 9. McDonald JC. et al: Respiratory symptoms in chrysotile asbestos mint and mill workers of Quebec. A reA jEnrtrea Health 24:333*363.1972. 10. UICC Cincinnati ciawiftation of the ra diographic appearances of pneumocontosia. Chat 5&S7-67. 1.97a IL Gibbs GW. Lachance it Dust exposure is the chrysotile asbestos mines and milla of Qs bee Are* fneiroe Health 24:139-197.1971 12. Gibbs GW: Qualitative aspects at dust e* posurc ir. the Quebec asb.'-:os mining ar.-i mill ing industry. in W.iiton H M ill. Inhalol far. ft. '- ' III durrey. England. Unwin Bros Ltd. 1971, v(.l 2. pp 7S3-799. 13. `'ni</'trri fur Atlxsto* Dn*t Concentration for L'se With Aahmt.'* hryulatiom techni cal note I V Department of Employment snd Productivity. Her Majesty's Factory Inspector ate. 1970. 14. Gibbs GW, Lachance M: Dust fibre rela tionship.* in the Quebec chrysotile industry. Arch Health, to be published.. 15. Berry G: Parametric analysis of disease in cidences in multiway tables, Biometrics 26:572* 579. 1970. 16. Kill ID: Computing man yean at risk. Sr J he- >< Med 26:132-134. 1972. 17. Gibbs GW: Epidemiolijy of Pleural Calci fication, thesis. McGill Universitv, Montreal, 1973. 18. Fournter-Massey G: Pulmonary Funetion in Quebec Asbestos Workers, thesis McGill Uni versity. Montreal. 1973. 19. Gilson JC: Occupational bronchitis. Pro- Ft Sr Ue.1 63:837-864. 1970. . 2a Manfreds J, Eyssen G: Lung cancer and smoking in chrysotile asbestos workers. Arch Enriron Health, to be published, 2L Ducic S: L'Exactitude ds eausts de dices. Cun J Public Health 393-402.197L 22. Report by Mesothelioma Panel of the Ca nadian Tumour Reference Centre: Primary ma lignant mesoUielial tumour* in Canada. I960- 1961 A pathological revie*. Cancer 3LS69-876, 1972. 23. Magner D, McDonald AD: Malignant mteo- tbriial tumours; Histological type and asbestos exposure. S' J J 2-7 57<:-57t. i'l72. 24. 6r'.ikofT 1J. Kom~or..l FU. Ch-.irg J Mor tality CNp/rivnres of a*b\Moi insumOo? work ers. in pruc-t,/</!/. l"f, rn-ru.nnl Conien.-nce on Pnfimocii'HHS. r-h,ir\j. CuiV.own. South Africa, Oxford University ?.-<.*$. I07u, pp 190-156. 25. Newhvuse ML; A study of the mortality of workers in an asiiestcs factory. Dr J Ind Mtd 26:294-301. 1PS9. 26. Kogan FM. Guelnikova NA. Gulosskayi MR: The cancer mortality rate am-mg workers io the asbestos industry of the Urals. Gig 5a>u; 3759-32. 1972. ` 27. Vigliani EC: Asbestos exposure and its re sults in Italy, in Proceedmys of international Conference on Pnenmocom^tis. Johannesburg. Capetown. South Africa. Oxford University Press. 1970. pp 192-195. 2d. McDonald JC: Asbestos in chrysolite mines and mills. Read before the IARC Conference on the Biological Erfects of Asbestos; Lvon. France. 1972- ' 29. Harries PC: The Efictsand Content ofDis eases Asroriatid li'/'A Ej`;-ure to Asi**t-yi in a Haval &nk;ford. thesis. University of London. London 1970. pp 141-275. * 30. Harries PG. et ah Radiological survey of men exposed to asbestos in Naval dockyard*. Br J lad Med 29574-279, 1972. 31. Murphy KLH. et al: Effects of low concen trations of aibctos. A* E*gt J Med 285:1271 1278.1971. 32. Enteriiae P. Weill H; Asbestosis in as bestos cement worker*. Read before the IARC Conference on the Biological Effect* of Asbestos. Lyon. Franco. 1971 001322 01-020154 7