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Scientific Communications AIA-53 The Health of Chrysotile Asbestos Mine and Mill Workers of Quebec J. Corbett McDonald. MD; Margaret R. BecWake, MD; Graham W. Gibbs, PhD; Alison D. McDonald, MD; Charles E. Rossiter, MA, Montreal- The results ol studies of respiratory symptoms and (unction, roentgenograph* tc changes, and mortality in relation to dust exposure in the Quebec chrysotile industry, which has employed some 28,000 workers, are brought together and their Implications lor control examined. Breathlessness on exercise, dimin ished inspiratory capacity, parenchymal and pleural changes, and respiratory dis ease mortality were related to dust expo sure and to each other. Respiratory can cer was also related to dust exposure. The overall excess ol deaths from res piratory cancers, including live with ma lignant mesothelioma, was at most 50% abova expectation, based on age-specific rates for Quebec and the mining region. If safety standards arm set, they should be based on epidemiological evidence. Prom these dels for the chrysotile produc ing Industry ol Quebec, a resonatHe fig ure, based on a 1% risk of acquiring clini cally significant disease, would lit between 2 to 4 million particles per cubic toot, calculated for a working tila of 50 years. In (he absence of epidemiological findings based on fiber counts and tack ol 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 mesotheiial 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 23,000 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 pun 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,"' international group of six readers roentgenographic change,' pulmo using the UICC/Cincinnati (now Table I .--Number of Men in Dust Exposure Analyses S-jinnitted fur publication July 2. 197(1; xr> July an. t ruai the Dn.iirnu-ni f n*t iti li:1). M.-Otli I mvi-r.ity. Muntn-a!. Mr. ii-V'.-i- u r j'-.-vntlx with the Mn'.n-al K, ..'an-}) fuin- i-:l i'n*.nr.`.,<4 I'-it. IVr.arth, S-::!h VVaioi. to Ik-partnicnt nf K;r-1--r-i; oyy at*.:! IUmIiIi. Mc'.iiii I't-ivoroty.;;7M i'nrv.'r* v;> St. M-.ntr.-J 119, Mill.. t'aa.uia (Pr Analysis .Vo-i.i:iiv stuJv nanrasMe stud-/ lyii i arKr.jr ard y Sii.Asrs -MO :.sio i iij? Dost Exposure Level, mpef-yr 13 3 1.52* ICO 1.124 1.13*1 209 I.QiJ? 912 40-1 637 717 L30i:~5 707 Tout 9.692 6.5*9 <or! $ 1 1 91 134 109 i-' 3;;i i4i 117 n.i " \ 7.; t-. 17 G7 1.015 59 80.5 0 Arcti Environ Health. Vol 28. Feb 1974 *W>1IM Ciir/sot-ia Asbestos Workers/McOon.i!2 ei ai 61 AIA-53 Tatea 2 --Roe np'v : Ch.rics Prava1 ence Percentages Roentgenographic Charge lrresular swH opacities VO 2/1 Pleural thickening Grade 1 Grade 2 Irregular small opacities 1/0 2/1 Pleural thickening Grade 1 Grade 2 -- - Dust Exposure -- Level, mpef-yr -- ------ ^ oo 10 103 230 433 JCD - Thetford Mines AverJO* 1.3 33 6 3 3.7 12 0 17.2 7.6 0 0 2 2 2 0 9 2.4 3 2 2.0 2 A 45 13 0 7 Asbestos 65 08 58 1.2 6 3 10 5 1 3 2.0 6.4 M 6.4 3.7 6.3 5.0 6.3 7 0 5.1 0 0.4 1.5 0 8 05 3 9 09 2.9 2.6 3.0 3.0 00 06 1 0 0 5 4.7 S.S 32 14 07 0 7 Rates are standardized for age and years in industry. Males were 36 to 65 years of age at time of roentgenogram. - Table 3.-- Age-Corrected Death Rates Per 1,000 Men Sorn 1891-1920: Deaths to December 1969 Dust Exposure Level, mpef-yr Cause All causes Respiratory cancers' Abdominal cancers Pneumoconiosis '<10 365 10.3 130 1.6 10 355 13.1 13.6 1.5 100 354 13.4 18.7 0.8 200 313 15.5 1 t.S 4.9 400 323 21.4 25.3 49 ' Includes malignant pleural mesothelioma. 800+ 395 32.1 28.7 23 3 Table 4.--Relative Risk of Death From Respiratory Cancer in Men by Dust Group, Estimated From Retrospective Analysis Duet Exposure Level, mpef-yr < 10 10 100 200 400 800+ Total Mo. of Cases . 32 41 13 14 t5 19 134 No. of Controls 186 188 39 61 40 22 S36 Relative Risk 1.0 1.3 1.9 1.3 2.2 5.0 Table 5.--Age-Corrected Mortality Per 1.COO Men From Respiratory Cancer and Pneumoconiosis at Thetford Mines and Asbestos Respiratory cancer Thetford Minas Asbestns Pneumoconiosis Thetford Mines Asbestos <10 9 It 4 0 Duit Exposure Level, mpef-yr 10 100 200 400 12 18 15 24 13 6 18 13 1 1 76 00 53 100+ 31 43 24 24 GC/ILUi I'ljviSa: ten.- a f^W-,.;. of c.vu'mplnyivs -a .vs su', up .lnri death Certilicitl'1.* an.I anl-ji'^y rt ; rtn u t .-a O' .iminni Tit ( ho~-.' win. |:.;,i ;;K,; Q-e sivlii'it of tite- artivte d-.ds t'h re sults in worni<n; the rust i'>::evrnivl with men only. Oust H\pviri.\--Dust exposure lev els were determined i'oreuoh recorded joh within the industry, and 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 (mpefj. 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 partides, it has been recommended that standards for occupational exposure be based on fiber counts obtained by the membrane filter technique," 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 ilu* Qt.vbcc chrysolite indus try. The correlation between the two type's of measurement was too poor to justify the use of any single conver sion factor. Rocntgcnocraphic Chances.--The two main rnentgenngniphic indices of re sponse to asliestns exposure are ir regular small opacities and pleural t hit-koning. The prevalences of the-' and of all other roentgenograp 62 Arch Environ Health/Vol 28, Feb 1974 Chrysolite Asbestos Workers-'McOona'd et a AIA-53 r ?:; t; t lT-.^ u r- '.< r if; \ :u* l h,-t i 1 nl .M iiit'a .uv t ' i i. i: i ! j. :;.r A a:rva o' o.. - riv '-I k;yi , . i \1; O \ Vs 11 ;ti tl ; thu a M 1 1 i.n !:i:rvl _v`h1 **_TT t',.l;!v similar TfU1 ;l>- >oL*:;itinu >i. x Hl` ril, withi ilu^L <i*\> pnMi.'V V. ,;,N a!,-*' > foi: al TliulA jrd Mineo t;i,,n LiL Am v- !tii Tabic 2 r-hov.'-x lliat ul Mines the \o\-\ a U'lH'i' jtJ u,- small opacit,lr> nt catI. tin >r- rose siendib; uilh ' if USt, 1d\- posure win T'/.i' : 2 or in-ire the 1 rkw ;.qi l *> vlu M t L" was less marked, except for the con siderable rise ir, the most exposed workers. Ever, with allowance lor dif ferences in dust exposure, the pre'a- lenee of category 1 or more was markedly age-roiated. rising to 14.8rc for those 61 to 65 years old. This age effect 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 1 or more rose to 9.2'i 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 miivn lower and preva lence increased among those with the highest dust exposure. * For pleural thickening, the effect of age was slightly greater than 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 0.4% at Asbestos and 5.2'.t 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 areas were not surpris ing. as overall dust exposure levels at Asbestos were considerably tower than at Thcttord Minos, bstt others cannot yet be explained in terms of dti'*. exposure or geology, If variation in fiber content "f di:.-t wi-r*- an im portant factor, Ike result' iu mine workers, for whom the fiber propor tion \x i ns it i be low, 'hindd differ from for mil! u.,ikiT'. in `about the fiber prcporiior! w.b-- higher. Al together. -'IX as p. . w...cki r.s u ho had worked lor ten or more y ears en tirely in mining or e::'.:r>.-!y in mill ing- Analysis of roentgenographic changes in these men showed that mill vvorkeis had a slightly higher prevalence of irregular small opac ifies, hut the differences between Thetford Mines and Asbestos re mained. Xu 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 analysis1 was limited to deaths before Nov 1,1966, but the fol low-up will continue until at least 1974. By the end of December 1969, S7.5% of the 11,572 persons in the cohort and .99% of those who had worked ten years or more had been traced.1 Of these, 3.270 had died, com prising 65.4r5 of those born 1S91 to 1895 but only 9.8% 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 rates, the ex pected number of respiratory cancer deaths in the cohort was 139. or al>ut i' "< on the basis of estimated rates in the mining riginr:. This suggests that mortality from respiratory cancer in the Quebec chryvt ilv ir.bi-.trv a, u wiiole lij-. been at mi s', m - abovr- , pectation am! probably ah ,,'V; The primary me1 hod .m.Lb. , , Used in our report 011 deaths i:>. I,, 196G' had two main weaknesses. The first was that length of expo-cre might well have been related to length of survival and thus might tend to obscure differences in mor tality between exposure 'gnuij s. We looked for evidence of such an inter action using the parametric approach of Berry." and though we failed to find a significant effect, 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,- which dealt with death* 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 oniy estimates of relative rather than alv 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 ease, se lected at random among persons liv ing at the time of the death of the respiratory cancer case and l>orn in the same year. The distribution of eases and controls by dust exposure category is presented in Table 4 It can he seen that the pattern of rela tive risk obtained by this approach iquite similar to that for respirator* Aten Erw.ron Hvoilh vol 23. Feb 197..J Chryua'ile Asbestos Workers-McDonald et ai 63 AIA-53 Tao o G.-- Morichly From All Causes urd =.c; t,i- -s,n. Changed at 7ne Vi 1091 1 SOS Roentgencrrrjphjc , Changes Obs Us. cr C-. c.-ved and t O-: c J O .Vjis by Year or *rt*l Cchyrt* tOCMih-'O 1901 i*:05 I9uo-I9:0 Obs Exp Obs Exp Obs Zxv Obs Eid cn.Vfi-.-S n*Vy 17 13 6 7 7S 4 pieur.il ch*rncs only 11 10 3 15 1C 3 10 Both parenchymal and olpural changes U 11.4 17 10.7 8 39 92 65 M 45 5 52 6 22 7 2 3 * Expected number was catctdated from aeath rates in men without roentgancg.-dphic change. 16 34 06 191C 1920 Q`js Exp ' Total 0!i5 E ip 2 : s 43 33 0 2 2 4 <5 47 3 t 0 2 43 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 12*1, 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 respiratory 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 Roentgenographic Changes.--Of 10,120 persons traced in the mortality stud}*, 9.692 were men and of these 5.0S2 had chest roent genograms and 7S5 had died. At Thetford Mines, there were 354 deaths in 2,448 men traced. Death rates were calculated by date of birth, dust exposure, ar.d the presence or absence of parenchymal or pieural roentgenographic changes. The rate from all 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 roent genographic changes (131/1,000) or with pleural cliKtges only (125/1.C00). In Table 6, the observed number of deaths by year of birth and roentgen ographic change is compared with the expected number based on those without roentgenographic change. Of 97 deaths in those with parenchymal changes, 33 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 chyma! 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 Op to 100 cigarette- - years 100-439 500-999 .1.009 Never smoked Up lo ICO cigarette* Breathlessness years 100 499 500-999 1.000 Oust Exposure Level, mpef-yr <10 10 too 223 433 e:j1C 19 19 4fi 21 43 18 0 12 0 43 0 41 23 21 33 42 43 32 39 44 23 47 S3 109 47 45 55 54 35 0 14 '24 31 13 44 0 t2 39 21 41 43 to 14 8 33 42 1? 9 19 21 O 14 0 23 27 31 34 4 .* respiratory causes. At Asbestos, the difference be tween the mortality of those with ar.d without roentgenographic changes was less. Calculations similar to those used for Table 6 showed that only 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 roentgenogran had len performed and who haa been subsequently traced. Though the excess death rate in this highest ex posure group was about 9fe 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.11 Pulmonary Function.--A total of 1,015 current employees underwent pulmonary function studies during the summers of 1967 and 196S.` 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 chxugvs in fumti-in. Th.w tv>ted comprised s::'. of the sample selected. The variation in .-cm* of the lung function indice* by dust level in smokers and tto::..::iiikers is shown in Fig l. 2, and 3. The results of each lest were standardized to age 50 years, hidgli; I To cm. and weight 7' kg. Total lung v->!urne fill .-dight!} aith increasing d.:-t i-.vp.i.'Lirc.\|*stire had little effect cr. y r $4 Aren Environ Health. Vol 28. Feb 1974 rn - n 1 _ r -w - CnrySvJMe Asbestos W-V^-.-rs AIA-53 CIO 10 100 200 400 800* Dust Group. mpd->r Fig 2.--Variation in forced expiratory volumes with dust group, standardized for age. height, and weight. the same age and year of death bat who had never been employed in the industry. There was a higher propor tion of nonsmoken in patients titan controls, which suggests that pulm> nary cancer may be caused by as bestos exposure in the absence of smoking. The controls were on aver age heavier smokers, which reinforces the point but does not rule out the possibility of synergism between as bestos exposure and cigarette smok ing. Clear cvideniu was obtained from a survey of all known cases of malignant mesothelioma in Canada that this disease was not related to smoking. ** Women.--The number of women ev.-r employed in the Quebec chryso lite industry is small. In the mortality study, 42$ of 463 women in the cohort were traced and of these o4 had died. Only 79 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 yean 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 most and serious manifestation of oX|>sure to usitestos, it is not the most sensitive. Excess dent Its related to ex posure altogether were probably in total no more than 2I7 of the 3.270 deaths in the'cohort study. Most of these were attributed to respiratory cancer or pneumoconiosis and almost all Were in tlie two highest duM evposure categories. Thus, excess mortal ity ten- vir; ti.tlly ae'llni. J to m-.a u rh c\|Hure ctptivaletU to at iva.-t nipcl'-yr. Detailed examination nf mortality slioaed m> particular ca.;:e. except pneumneoni"':'. with a rate abinv that of the general popuht inn of Quebec. An investigation was made of the 220 known cases of malignant meso thelioma in Canada. In to through 1970. The manner of death certi.'icaturns o; these patients were exam ined. ' and the pathological ftnr.ings reviewed in detail In the Mesothe lioma Panel of the Canadian Tumour Reference Centre."' Epidemiologi cal inquiries showed that 23C7. of men and 1M- of women had definite or probable occupational exposure to as bestos, and a further l'e 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 h`ad worked in the industry. These cancer rates are very low in comparison with the studies of New York insulation workers-` 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 Union1" and Italy-7 support the view that only high levels of exposure to chrysotiie during mining and milling have an appreciable efTcct on mortality. Although roentgcnogmphic 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.-idered of clir.ii-al impor tance, ami these were much less inlltienccd lit age. Changes of this order occurred in I.OQ and 0.7'r of the en tire working population. In men aged tti to tio. employed an average of 20 years in the industry, the rates were .7.11'( and 2..V< at an average exposure level of 1-i nipef. These rales arc M-r;. 66 Arch Environ Health/Vol 28. Feb 1074 Chrysotiie Asbestos Woikers McDonald a; AIA-53 fani.-1i..n;11 rapacity (FUC) >ir rcii'lu.t! \o!i;inVj. Tiius 1`Xj'o.siiro to affected only the inspira tor, v.ip.ui'v p- 'ti'in of tile total 1 '.jrs volum- iTLV). Forced vital capacity (F\'C) a-.;! forced expiratory volume ir. nr- si-n>!'<! (FEV ) both deciir'.cI with increasing exposure, the FVC vi tal capacity tailin'' by about 1^'< its tiic highest dust group and the FES' rather less. Neither steady state nor single-breath diffusing capacities showed any effect of c.xp-'siru at rest; on exercise, tno 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 2Q% in three indices: FRC, RV, and single-breath 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 parenchyma! 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.* 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 flow rates less than ex pected, had had heavier dust expo sure, more symptoms of bronchitis, and more irregular' small opacities than those with normai or restrictive patterns of pulmonary function.'* Respiratory Symptoms.--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. Relit persistent cough and phlegm (bronchitis) and breathlessness on exercise were re lated to exitosure." Table 7 shows, however, that after standardizing for age, the prevalence of bronchitis rose o" u. n 5 "!. c Oust Group, mpcf-yr Pig 1 .--Variation in lung 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 Smoking-Smoking habits were originally determined only for employees in the pulmonary function survey. Figures 1. 2. and 3 show that, with many of th-.- physiological in dices, the effect "i smoking was greater than the off* it of exposure to aslk-stos dust. This was most obvious in FRC. IIV, and perhaps in the si.ydy-state dir'.'u-ing capacity at re.-t. Forced vital capacity am! FKV, 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 asbestos exposure. A controlled retrospective study-'- has lieon made based on deaths from lung cancer in the cohort study. Each pa tient was matched wiLh a death from lung cancer from the same hospital records in a man of approximately Aren Environ Hca'in.Vcl 23. FeO 1974 CUrysotile AsSentos VVorXers.'McDnnc'd ct at 55 AIA-53 -3 -:r;:i!.ir ;.i ;ln--e f-.und ii; the chn.-o- tili- ..!111 nliii:i-T imiu.-lry in ( > fi'i;-. *mt .ire much hover than t1'-- n ihi- New York insulation a I--!., r-. 1 nr in the British Koval Na- l ai I - al'iis.' " fi-r pulmonary function and resi.r-:stn'y -ymptoms. the clToct of wi.-kmg \\a generally greater than cdVet of exposure to asi-e-tos. However. for inspiratory capacity, foivi-'l tU-w rat-'?, and breathlessness on exercise. relationships to dust ex posure were found. With respect to these indices, a 107 reduction in non smokers occurred after a total expo sure in excess of 100 mpcf-yr. This is dose to the lower limit of the dust category at which 17 of subjects had grade 2 roentgenographic changes. In the Quebec studies, information on dust exposure was obtained, where as in most other studies quantitative information was not available. Mur phy et ai ' found 11 cases of ashestosis in 101 Sew 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 chrysotile production. However, the main constituent of the insulating materials used was amosite, with some chrysotile and no crocidolite. Dust 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 hy Enterline and Weill, ' where the main exposure has been to chrysotile and silica, but the results ure not yet available. The limit standards for occupa tional exposure to asbestos are based solely on the airborne concentration of dust nr fiber, averaged over a life time's '.Mirk, and the results in this re port haw in-on presented from this point of *. i.-w. There was some evi dence in our studies that longer expo sures for the same total dust levels are'assiK'iated with slightly higher pri-Mib rve rates of ro.-tiigi-!:.gr,iiihic Oust Group, mpcf-yr Pig 3.--Variation in diffusing capacity with dust group, standardized for age. height and weight. change. However, the roentgen ograms were all 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 tewl. Therefore, in assessing the overall died of as bestos exposure, duration of exposure should n -t really In.- ignored.'For this reason, it would k* unwise to apply the results of this or other de. eriptive epidemiological studies to widely dif ferent exs'osu'v patterns. The Kriti.-h do-! standard for hr',.-utile of 2 pper iri"iiiu r. averaged over three months, is based on the concept that a 17 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 symp toms-the 17 risk is reached by men in our third dust exposure category (100 to 200 mtK-f-yr). The relationships that exist be tween measurements of total dust ami ri!>er exposure are thus of critical im;>rtuRv if standards are to be set fur as!e#tos production and other asbi-stos industries. Such standards should be based on do*-response re lationships established by sound epi demiological inquiries. To date, ver\ few of th.-se have imJuded any qua: - Aren Eiw-ron Health Vot ?S. r=> ;074 Or,;ot*ie Asbe-O-ii Workers McDonald et ar S7 _AiA-53 _ illative u.'Sc'.'incnts of duit. let alone of (i tier exposure. Tiiouph safety stan dard# expressed in filler coneentrations have theoretical and conceptual attractions, there is as yet little or no direct cpidemiulotrica! evidence on which to base them. Our studies ap pear to provide a reasonable basis for e-.-7:11'!: ,'iiiyr s.iK'ty .-1 ;t :. il:: rtis for chrysotih' ninini: ;imi tuiliitv,' in ti-r.v's of dii.'.t comcntr.tiion. Wuivmt ftt-uv i-yt-i'-nv'.' on the oi'nwrvion f.ivtor thui jhoulti be ;tpj>iii'ti in d.'li'oivnt purls of '.hi- in.hi-try, iv\- cannot cxpr'i#.# uiir rcsuUs contider.tly in fiber count#. Further efFc.rta to find a ?;itis- factory mi'.ms of yonviTtin-.r ivtii? impiiitfvr lo ihivr amii's tiro nuriui! 11U t. llllli! TyW Vpil!-.*Pi i >il'y iy1 Vy,. lii'flcv l;t>vii on i;tU'f v'liril# h;t- Un " .'i.-soiiibiyil, il npiv.tr.- mnvixe tr> ,i;*. coiuimif tt#o "f j'.trtivlo vour.;: for control in thi# in-histry. Refer#nces 1. McDonald JC, et al; Mortality in the chrvsotile asbestos mines and mills of Quetx-e. Arch Ertnrsm Health J-S77-tSS, 1971. 2. McDonald JC, et *1: Mortality in the ehryto pic producing industry of Quebec; A progress re port. Scad before the Fourth International Pneumoconiosis Conference, Bucharest. Hun gary. 1971. 3. McDonald AD, et si: Epidemiology of pri mary malignant mesothelial tumours in Canada. Cancer 26:914-919. 1979. 4. McDonald AD, McDonald JC: Epidemiologic surveillance of malignant mesothelioma in Can ada. Can Med As.**e J 109:359-362, 1973. 5. Kossiter CE, et a!: Radiographic changes in chrysotiie asbestos mine and milt workers of Quebec. Arch Enrirm Health 24:333-400, 1972. 6. Becklake MR. et al: Lung function in rela tion to chest radiographic changes in Quebec a*, bestos workers. Suil Phytiopathol Rctp 6:637 659. 1970. 7. Becklake MR. et al: Lung function in chrysotiie asbestos mine and mill workers of Quebec. Arch Enrtren Health 24:401-409, 1972. S. Jodoin G. et ai Early efftets of asbestos ex posure on lung function. Am Rcc Re/p Di* 104:525-53.5. 1971. 9. McDonald JC, et al: Respiratory symptoms in chrysotiie asbestos mine and mill worker* of Quebec. Arch Enciron Health 24353-363.1972. 10. L'ICC Cincinnati dasaifteetion of the radiographie appearance* of pneumoconiosis. Chest 5057-67. 1,974 1L Gibbs GW, Lachance >fc Dust exposure to the chrysotiie asbestos mines and mill* fOo* bee. Arek Environ Health 24:129-197,1972 12 Gibbs GW; Qualitative aspects of dust *x- posurc in the Quebec usbi-'tos mining and mill ing industry, in W.iiton UH (i-ill; Inhaled Par- tie'- ' !U taumiy, England. Unwin Bros Ltd. 1971, vol 2. pp 7# 3-799. 13. J'andnrd fur AsUnton Dnnt Coiicinlrcilurit for L'se Il'ii/i A.ihrsr.,s Refutations techm-. cal note 13. Department of Employment and Productivity. Her Majestv's Factory Inspector ate. 1970. '` 14. Gibbs GW, Lachance M: Dust fibre rela tionship.* in the Quebec chrysotiie industry. Arch Ei' imit Health, to be published. 15. Berry G: Parametric analysis of disease in cidences in multiway tables. Biometric* 26:572 579. 1970. 16. Hill ID: Computing man years at risk. Br J Her Sc Med 26:133-134. 1972 17. Gibbs GW: EpitUmioheig af Pleural Calci fication, thesis. McGill University,' Montreal, 1973. IS. Foumier-Massey G: Pulmonary Function in Quebec Albertos ll'orfrers, thesis. McGill Uni versity. Montreal. 1973. 19. Gilson JC: Occupational bronchitis. Pro- R Sjt Med 63:357-864. 1970. 20. Manfreds J. Evssen G: Lung cancer and smoking in chrysotiie asbestos workers. Arch Environ Health, to be published. 2L Dude S: L'Exactitude drs causes de dikes. ' Cun J PuNic Hcabk 62394-402 197L 22 Report by Mesothelioma Panel of tho Ca nadian Tumour Reference Centre Primary ma lignant mesolhelial turnouts in Canada. I960- 1963: A pathological review. Cancer 3L369-676, 1972 22 Mxgner D, McDonald AD: Malignant meso- tbelial tumours; Histological type and asbestos exposure. .S' E-,-il J M, J 2v7'S7f!.57t, !3T.l 24. St-lik.ifT U. EC. Churg J Mor tality c.iperivnccs of .ivb-.'-tuS insulation work- ore, 1(1 PCuC-lil i /I IS ./ /-Il rn''*K*nit/ If retire on Pne-i moe-uintus. J>ha" < r--I,. r,j. Ca.H'toxn. South Africa, Oxford University Pr-sS, I97u, pp 180-1 #6. 25. Newhuuse ML: A study of the mortality of workers in an asliestos factory. Er J l,id Med 26:294-301. 1969. 26. Kogan FM. Gitselnikova NA. Gtilcvskav* MR: The cancer mortality rate among workers in the asbestos industry of the Urals Gig Samt 3729-32 1972 27. Vigiiani EC: Asbestos exposure and its re sults in Italy, in Preoceding* of International Conference nit PnC'ini'-vn I'l-ts. Johannesburg. Capetown, South Africa, Oxford University Press. 1970. pp 192-195. 23. McDonald JC: Asbestos in chrysotiie mines and mills. Read before the IARC Conference on the Biological Etfects of Asbestos; Lvon. France, 1972 29. Harries PC: The Em els and Control ofDis eases Askoria/fif H'i'fi Er'lire tn .4'ietf'L- in a Afaral Dni./ard. thesis. University of London, London 1970. pp 141-273. 30. Harries FG. et aI; Radiological survey of men exposed to asbestos in Naval dockyard*. Br J M Met! 29274*279. 1972 31. Murphy RLH. et at: Effects of low concen trations of asbostot. Af Engl J Med 265:1271 1276.1971. 32 Efltorlia* P. Weill H: Asbestosis in as bestos cement workers. Read before the IARC Conference on the Biological Effects of Asbestos, Lyon, Franco. 1972 i\i Ii 001322 ssstf*''-' 01-0201547