Document KG8n29Nw8BXBRXjeDd52wz4VN

JUL l 2 v m INTERNATIONAL C 0 fi H E SP Q N D EH C E ' C.S. Tennesson, Jr. Cincinnati, Ohio date: June 17, 1971- R.J. Merrill, Fidi-ve dali-e, P.Q. cc: E.W. Swain Bacenstose A.R. Korean CT: The Mc.Dcrc.iri1 s su: f!-.* relatione!".! r af Ch: ` .* *. ^' 'rrri J.'j'i" Cancer At long last the Toy'..:i. dr 2: tiir `\r-stuur of the aabest industry has been yx' d in Archiv f Environmental Health - & Canadian Pubiicat: , : thiv: h it :r.a):cc especially tho abst-i ac ) the #*' * ,* 4> C-Ct*r;s- ' worth -while- reading the underlined sections' on pages 684 and 635. .torc nr.y i to reproduce t!iis further for the nrmy distributors and cust *s wro u asked for information on this subject. R.J. Merrill RJM/br M 5 3 3 9--A REV. Mortality in the Chrysotile Asbestos Mines and Mills of Quebec J. Corbett McDonald. MD; Alison D. McDonald, MD: Graham U'. MSc; -Jar!; Sirin!atycl:i; and Charles A*. Hr.-tiler, MA, Montreal Of 11,788 persons born belv/een 1891 and 1. 20 employed In the Quebec asbestos mining ir.J 3Iry, 88.4e,S> were traced. Of these 2,457 (23.Cs) had died. Exposure indexes for each worker v. jre calculated from job dust levels and duration ol employment. The overall mortality was lower than expected for the popup,tion of Quebec but in the highest dust category, comprising 5% ol the cohort, the age-standardized rale was 20% hlnlicr than in the other groups. Respiratory, cardiovas cular, and malignant disease in equal proportions accounted for the excess. There were 101 deaths from respiratory cancer including three from ma lignant mesothelioma, an estimated excess of about IS deaths. The difference in rates for re spiratory cancer between those maximally and minimally exposed was fivefold and, though per haps exaggerated, was apparently determined by accumulated dust exposure and duration of em ployment. ThE REMARKABLE qualities of the as bestos group of fibrous minerals have, been recognized since antiquity, but mining land milling on an industrial scale began only at the end of the 19th century. In the Eastern Townships region of Quebec, deposits of chrysotile asbestos in serpentine rock were Submitted for publication Aug 17, 1970; aoccptcd Nov 10. Krom the Department of Epidemiology and Health, McGill University, Montreal. Mr. Itossiler id presently with the Medical ltcscaivh 'Council Pneumoconiu-is Unit, l'enaith. South Wales. . Reprint requests to 3T7.7 University St, Jffnnliral 112 tDr: J. C. MvDonnbl). noted in the IS 17 Canadian Geological Sur vey. The first mine was opened at Thetford in 1S7S, and within 30 years the region was producing most of the world's asbestos. The proportion fell as Russian, South African,, and Italian mines came into operation, but Quebec still produces about 40% of the world's supply, now estimated at about 4 million tons a year.1 There are two main mining areas, one at Thetford Mines and neighboring towns of Black Lake and Broughton, and the other at Asbestos. The Thetford area was devel oped by many different companies, but with amalgamation the number has now been re duced to six. At Asbestos, the mining has been carried .out since 18S2 'by one large company which also operates a small fac tory hi the town for the manufacture of mixed asbestos products. There is a small mine owned .by another company a few miles away. Concern for the health effects of asbestos has paralleled growth in its production, and the. main available evidence was reviewed fully by Wright2 in 1969. The-first cases of diffuse pulmonary fibrosis after prolonged exposure were noted by Murray in 1907, and by 1930 asbestosis was recognized as an important occupational hazard. Controls in troduced since then have reduced consider ably the dust concentration to which wc'kers iii the ini ties, mills, and primary manufne- Arclt Fni'inm Health--Vol `22, June 1971 XT I >r:v,1*: \v ./. * hiring industries arc exposed. Though the phvllitc; the two textile factories referred to prevention of nsbcstcisis is far from complete above-8 used mainly chrysotilc fiber, togeth- \. in these, industries, it is still generally be or with some crocidolite, and in one of the I."- lieved that this can be achieved by more two, some amosile. As in most industrial strict environmental control. Another aspect applications different types of fibers are of the problem appeared in 39-17 when mixed, tire carcinogenic effects of a single \~ Mcrewolhor3 showed a linl: between asbes fiber type in practice can only be studied in tos exposure and lung cancer. The potential mining and milling. Chrysotile fiber is of >_ extent of this hazard was increased by re greatest importance because of its qualities *'' ports of Wagner and others' during the last and extensive usage. The only studies of. ten years that malignant tumors of the lung cancer in chrysotile miners and millers }. pleura and peritoneum rue related to certain were reported by Braun and Truan in types of Industrie.! work and perhaps also to 195S11 and by Kogan et al in 1966.12 In the ; neighborhood exposure. first of these, nine deaths from lung cancer | The association between lung cancer and were observed in the Quebec industry com- k- asbestos v.as first found in the British textile pared with six expected from provincial J t industry. Meiowcthor's inquiry showed an rates. The second was in the Soviet Union unduly high proportion of lung cancers at and showed that compared with the general autopsy in cases of asbestosis, and other population the mortality from lung cancer observations among textile workers have was increased-by a factor of 1.9 for miners, confirmed the association/"8 Two studies in 3.1 for millers, and 2.3 for factory workers.' particular which take some account of the The present investigation forms part of a t* degree of exposure suggest a dose-response comprehensive epidemiological survey of the relationship. Knox et al" found a consider- , entire Quebec asbestos-producing industry !' able excess of lung cancer in persons exposed since its inception. Using the considerable ' before 3933 when asbestos control regula volume of data available, our primary aim f tions were enforced, but none in persons has been to define as accurately as possible exposed for ten years or more in the most the quantitative relationship between expo- dusty areas since then. These findings must sure to chrysotile asbestos and the incidence . be reviewed when a longer period of obser of lung cancer. The results ftom parallel ( vation has elapsed, since Ncwhouse8 (also in studies concerned with the relationship of ' ` a textile factory) found an excess of lung dust exposure to radiographic.appearances, cancer in persons heavily exposed 20 years pulmonary function, and respiratory symp- earlier for periods of less than Two years. toiys will be reported separately. f Workers exposed to light or moderate dust concentrations showed no excess of broncho Materials and Methods genic cancer even after 20 years of exposure. SelikofT and his colleagues'* found an eightfold increase in lung cancer compared with national figures in a cohort study among the members of an American insula tion workers union who had been exposed . Registration.--A register was compiled in the personnel deportment of each asbestos min ing compa'ny in the Eastern Townships region ' / of Quebec listing all persons currently or pre- / > viously employed, as of Nov 1, 1968. A card f was made out for each employee on which was ` for 20 years or more. He also found a gross recorded his name, date of birth, address, and a excess of pleural and peritoneal mesothe detailed work history which included the de- 1 p liomas. On the' other hand, in a national partnient and mine, dates of starting and survey of all known mesothelial tumors in finishing, for every job, and all periods of leave. Canada, 1960 to 1968, McDonald and her colleagues' found a history of occupational contact with asbestos in a relatively small proportion of cases. This exposure was main- ' In one of the 44 mining companies representcd in our survey, the records of at least 660 persons had been destroyed. These were of ex-cmployees and others not transferred when ownership of the company changed in 1964. - ly in insulation and allied trades, rather The work histories of a small number of older than in the asbestos-producing industry. men who had been employed partly in this Of the four main types of asbestos filer-- company and partly in others were also incom- j' i' ^ Jj- ; S | ' chrysolile, crocidolilc, ninosilc, and antho- plcfe. , Arch Environ Health--Vol 22. June 1971 Table 1.--Subjects of Study end Results of Tracing by Ago and Sex Yea'- o( Sirtli 1891-1895 1896-1900 1901-1905 1906 1910 1911-1915 1916-1920 ai: M 1.55.1 I.'JS? 2.027 1.R97 1.837 2 0.>7 11.>23 Pcrssns F 14 31 50 99 117 1 4 65 Total 1.567 2.013 2.077 1.996 1.954 2.181 1 1.78-< Traced M 1.179 1.588 1.724 1.741 1.773 1.976 9.9SI F 13 28 45 92 113 149 4.10 Total 1.192 1.616 1.769 1.833 1.836 2.125 10.421 % Traced 76.1 80.3 85.2 91.8 96.5 97.4 88.4 Dead 611 655 498 330 221 142 2.457 % of Persons Traced 51.3 40.5 28.2 18.0 11.7 6.7 23.6- Table 2.--Subjects ol Study and Results of Tracing by Dust Index and Years ol Employment Dust Index Yeai s <1 11030All No. To traced No. % traced No. To traced No. % traced No. To traced <10 3.043 76.6 1.025 86.3 55 100.0 ... 0 4.123 79.9 10654 75.1 1.975 88.6 1.117 99.0 204 100 0 3.950 69.9 100- 38 76.3 450 89.3 566 98.9 181 100.0 1.23S 94.9 200- 3 66.7 264 90.5 522 99.0 250 1C0.0 1.039 97.0 4000 122 91.0 432 99.3 303 100.0 857 98.4 800- 0 ... 64 .90.6 255 99.6 265 99.6 584 98.6 All 3.738 76.3 3,900 88.3 2.947 99.1 1.203 99.9 11.788 88.4 There was of course sortie movement of labor from one. mining company to another. This necessitated bringing together and matching the records of all the companies, to obtain complete work histories. In the course of trac ing ex-employees, the matching process could often he confirmed or amended. Jn nil, 27,609 men and women were registered, including 6.415 currently employed on Nov 1, 1966. Of `this total, 1,039 persons had been employer] by more than one company. Using the occupational histories, a list was compiled of all named jobs in each company from the beginning of its operation. A descrip tion of each of the 13,346 jobs listed in this way was obtained from existing evaluation systems and by interviewing employees with long ser vice. Jobs with several names but involving the same work and dust exposure were combined and the codes finally needed for classification thus reduced to 5.7S3. For each of these and for each year of operation, (he average dust expo sure was estimated on a 13-point scale. Throughout the industry in the dryers, crush ers, and mitls, the concentrations of dust at working places had been measured annually since 1949 by Maurice Lachance. Eng, and since 1946 by various investigators in the small factory. All measurements were made with ei ther a midget impingi-r or Grcenhurg-Smitli, impinger and recorded in millions of dust parti cles per cubic foot (mpef). Levels of exposure in mining and maintenance jobs and in other operations where no dust measurements had been made were estimated by investigating present-day dust levels and adjusting these ac cording to changes in operating procedure re ported by mining and maintenance personnel. A full description of geological and environ mental features and of the methods and results of dust measurement are to be published by G. W. Gibbs, MSc, and Mr. Lachance. Before. 1949, few dust measurements were recorded, and. estimates of exposure for that period are, therefore, only approximate. Inter: views with employees of long service enabled comparisons of dustiness to be made with con ditions since 1949. The dates of installation or modification of dust control systems .wore also taken into account. Duration of exposure for each person was expressed in years or fractions of years after subtraction of all periods of leave, and was corrected to a working week of- 40 hours. A dust index was calculated for each employee by adding together the products of time spent on each job and estimated average dust concentra tion. For example, suppose the dust index for a man was 600; this might mean that he had worked for five years at 40 mpef, 15 years at 20 mpef. and 20 yi-nrs at 5 mpef (ie, 200 + 300 + 100). It would be useful if ft could lie assumed Arch Environ Health--Vol 22, June 3971 i i J that an index of (500 were also equivalent to a death was stated by relatives. In the other working life of 40 years at 15 mpof. but this seven, the cause of death was obtained from a would entail assumption-* which may or may reliable source. A death certificate could not be not be- justified. obtained for the remaining 187; 47 had oc Selection of Cohort.--The study of mortality curred before 1926, and 100 were deaths outside was based on employees in an age group Quebec, mostly outside Canada. The cause of thought likely to yield (lie mod valuable infor death was coded according to the Seventh Revi mation. The cohort selected comprised 11,783 sion of the International Classification of Dis persons horn between 18m and 1930 inclusive ease (ICD [World Health Organization, Gene who had been employed for one calendar va, 1957]). This was done by senior coder of month or more. Thov bum after 1920 would the Department of Demography of Quebec who have had periods of exjre well short of a had recently retired. working lifetime and would still not have The proportion of subjects traced by age. sex, reached an age of high mortality. Those born and category of exposure is shown in Tables 1 before 1891 would have been very difficult to and 2. Success in tracing depended mainly on trace, and, as mentioned above, some of their duration of- employment; 94% of those em work histories were incomplete or mi.-sing. The ployed for one year or more and over 99% of selected cohort comprised among others 1,203 all those employed for ten years or more were persons who had worked for 30 years or more, traced. Information was least satisfactory in 3,738 who had worked t'oi less than a year, person? born before 1900 and in those em and 1,080 who had worked for more than a year ployed for less than one year. The principal but whose job had not involved any appreciable reasons for failure were (1) no relative or exposure to dust. Thus, there was a substantial friend could be located in the neighborhood and group with minimal exposure available for com (2) insufficient identifying information, which parison with others who had heen heavily ex would have enabled us to make a request to the posed. Unemployment Insurance Commission or to Tracing and Ascertainment.--The search for locate a death certificate in Quebec. There were ox-employees was mainly initiated in the min no other obvious reasons for bias towards dis ing towns. Telephone or postal inquiries were covering the living or the dead, but those made first to establish whether the person in traced dead or alive are likely to have been question was alive or dead on Nov 1, 19GG. If long-term rather than transient residents. reported dead, the exact date and place was Diagnosis of Lung Cancer.--rTo make our sought from relatives, friends, and parish regis figures for lung cancer as accurate as possible, ters. For those not trad'd by thcc means, a we investigated arid reviewed all certified cases systematic search was made in the provincial and searched also for cases not described as death records and certificates, and about 200 such on the death certificate. Of 95 deaths persons were found in this way. In addition, a coded as due to lung cancer (ICD 162 and search on our behalf was made in the index of 163). one was certified as due to a hydrone- the Canadian Unemployment Insurance Com phronta and another as due to pulmonary mission for any person not found by means of fibrosis, both of which had been coded incor- local enquiries. The names of 598 persons were rectly. 'Inquiries about the remaining 93 cases found who bad registered or re-registered be were ma^e from hospitals, physicians, and pa tween 196-1 and Nov 1, 1966, and 30 more had thologists; and information was received in 76. re-registered after that date. All G28 were pre In five of these it was reported that there had sumed to be alive for the purpose of our study. been an. autopsy, but we were unable to obtain Information was obtained concerning 10,421 pathological details. In another five, though the (88.4%) of the 11,788 persons in the cohort: diagnosis had been made in the hospital, no 7,965 were still alive (including 2,434 currently clinical or pathological record was found. Sev employed) and 2,457 (23.6% of those traced) enteen more had been certified by family phy were reported dead. Copies of death certificates sicians but we did not sucoeed in finding out were obtained from Canadian Provincial and where and how the diagnosis had been made. US State Registrars for 2,211 (90%) persons. In the remaining 48 cases,.pathological re For 59 more (2%), an acceptable cause of ports were obtained, 25 at autopsy and 23 at death was obtained by other means; 30 were biopsy. A diagnosis of carcinoma of the trachea . i- accidental deaths in the mines or during active was made in one, of bronchus or lung in 44, and " * * service with the armed forces and 29 were of malignant mesothelioma of pleura in two. In j -caused by disease. Twenty-two of the 29 had one case the histology was that of n melanosar- ! occurred before the introduction of death regis- coma, and the pulmonary tumor was thought to t '(ration in Quebec in 1926, arid the cause of be metastatic. Thus,-of 95 certified cnscs, three { r Arch Km-iron Health--Vol 22. Jane 197] MUlll Ai.l 1 ) A.\U l II/i 1 AVI I L.r. .I//.W..X--.<tCUU.\ALJJ f. L AL. 08 X !md been included incorru-tly, -17 wi re con firmed pathologically, 28 hospital diagno><-< were presumed correct, and in 17 no further information was obtained. The following steps weir- taken to di-covi r eases of lung cancer that had not been men tioned as su< h on the death eel tifieate: 1. A letter was sent In tin- certifying physi cians whenever it wa.- stated that an aulop-y had been or would hi pcif. ::ocd. Tin- e minibored 30G in all; 3d doaT.~ were certified as due to lung cancer and 273. a- due to other cau-is. In 18 replies, it was statid that tin re hail been no autopsy; in 175, (hat the certilnd diagnosis was confirmed at autopsy; and in 18. that it was incorrect. These 18 yielded five addition..1 cases of lung cancer. The diagnoses for these had been certified as renal tumor (IC'D 18tJ), infectious hepatitis fICD 002). pulmonary fibrosis (ICD 519), diabetes (IC'D 2<'>0t. and asbestosis {ICD 523). 2. We asked the physicians in charge of the industrial clinics at Thetford Minis and Asbes tos for lists of all deaths known to be due to lung cancer. Their records included only em ployees who. had given up work because of ill health, those who were pensioned, and those whq, had applied for workmen's compensation. They listed 2-1 of the 96 lung cancer deaths found by the methods already described plus three additional cases. These three deaths had been certified as duo to tuberculosis (ICD 019). asbestosis (ICD 523), and coronary heart dis.ease (ICD 420), and though there had been autopsies for (he purpose of compensation, no mention.of (his was made on the death certif icate. In addition, there were three autopsies for compensation purposes in which a small lung-cancer was noted as an incidental finding. The pathologist had not considered these can cers to have contributed to death and the causes certified were asbestosis (ICD 523) in two cases and cardiac infarction (ICD 420) in a third. 3. A search was made for any case of prima ry malignant mesothclial tumor of the pleura that might have been given a code other than 162. One additional case coded as a - benign pleural tumor was found. 4. We reviewed cases reported by patholo gists in the national survey of primary malig nant mesothelial tumors in Canada between 1960 and 1968, and five were in men who had worked in the Quebec asbestos-producing in dustry. Two were born in 1922 and were, there fore, not in our cohort, and two died in 1937 after the present study had ended. A fifth case, diagnosed by biopsy, was eligible- for borl: ' ftudies. To summarize the results of all these inquir ies, thire eases were removed from the group of 95 malignant neoplasms of the hrohehus, tra chea, or lung (ICD 162 and 163) and nine were added, making 101 in all (100 men and one woman). 1Deluded in (he total were the follow ing: eanerr of the tiaehea, in one ease; malig nant nie.aithelial tumor, in three; and cancer of the bronchus or lung, in 97. Results Female Mortality.--There were only 465 women in (he cohort; almost all had short exposures .and all but 33 were in the two lowest dust-index categories. In all, 440 t94.6%) were traced, and of those, 45 had died. Tuberculosis (II), malignant neo plasms (12), circulatory (nine) and re spiratory (one) diseases, and trauma (one) were the causes of death in 34. Death was due to other causes in eight cases, and the cause of death was unknown in two; there was one death from lung cancer. Apart, perhaps, from tuberculosis, these figures are not unusual and will not be considered fur ther. Male Mortality.--To permit comparisons of mortality by dust index and years of expo sure, death rates were calculated in five-year cohorts by date of birth. Equivalent average death rates1-1 were then calculated using a standard population with equal numbers in each age group. Since the actual number at risk in each cohort was similar, this method of age standardization was particularly ap propriate. The standardized rates arc shown by dust index and main disease groupings in Table 3. In the lower five dust categories, equivalent average death rates for "all caus es" were approximately the same, but in the top category, containing 5% of the total cohort, mortality was about 20% higher than the rest. Malignant neoplasms, circula tory diseases, and respiratory diseases, in approximately equal proportions, accounted for the excess. Two groups showed the opi>osite trend; "trauma," probably because rates fell with advancing age, and "unknown causes," probably because death certificates were difficult to find for older men with short periods of employment. Table 4 shows that the main contribution to the excess in malignant disease was from cancer of the bronchus, trachea, and lung Arch Environ Health--Vot 22. June 1971 {- S* r ) i'I'C >* - Table 3.--Equivalent Average Death Rates per 1,000 Men by Dust Index Oust InrliSI No. of moo 1 uberculosis (ICO 001-019) Mol^rtani noop!jvu> (ICO 1 40-209) Circulatory diseases (ICD 400 4(39) Respiratory diseases (ICO 470-52*1) Trauma (ICD 800-999) Other causes Unknown causes Alt causes <10 3.006 18.8 38.8 85.0 9.5 34.7 46.8 30.6 264.1 103.408 19.9 3C.*.3 80.8 15.3 30.8 52.9 21.4 2 60.4 1001.148 31.6 32.2 82.5 19.5 36.3 39.0 16.5 257.6 2001.002 23.8 83.5 16.7 35.2 47.7 6.2 240.6 m 400842 28.5 45.1 94.8 15.3 33.3 38.3 7.2 262.9 800575 25.8 61.8 107.3 41.6 13.7 58.9 3.4 312.5 AM 9.981- 22.5 38.6 85.8 15.6 31.5 48.4 20.8 263.1 Table 4.--Equivalent Average Death Rates per 1,000 Men for Malignant Neoplasms (ICO 140-209) by Dust Index Oust Index Location Esophagus & stomach (ICO 150-151) Intestine & rectum (ICO 152-154) Otncr abdominal areas (ICO 155-159) Bronchus, trachea A lung (ICD 162-163) Other malignant neoplasms All malignant neoplasms (ICD 140-209) <10 10.2 (32) 2.5 (S) 4.0 (13) 7.6 (25) 14.4 (47) 38.8 (125) 10- 4.5 (13) 4.9 (15) 3.0 (9) 8.6 (26) 18.6 (54) 39.3 (117) 100- 1.7 (2) 3.2 (3) 1.7 0) 11.2 (10) 14.5 (11) 32.2 (27) 200- 7.0 (5) 3.9 (3) 1.3 (1) 8.9 (8) 6.4 (5) 27.5 (22) 400- 11.3 (8) 5.6 (4) 2.8 (2) 15.8 (11) 9.5 (6) 45.1 (31) 800- 13.7 (8) 8.7 (5) 1.7 (1) 24.2 (14) 13.5 (8) 61.8 (36) All 7.5 (68) 4.0 (38) 2.9 (2?) 9.9 (94) 14.4 (131) 38.6 (358) (ICD 162 and 163). In this group there was little difference between rites in the four lower dust categories, but the fifth and sixth groups showed an upward trend. A similar trend with years of exposure was found (Table 5), but the figures within the body of the table suggest a closer relationship with dust than with years. Subtraction of the three incorrectly coded cases and addition of the nine lung cancer cases found at autopsy increased slightly the rate among persons with highest dust and longest exposure, but did not materially change the picture (Ta ble 5). Further analyses to distinguish bet ter the relative importance of years of expo sure and dust index are described as follows. Rates for cancer of the intestine were about one third of those for cancers of the bronchus, trachea, and lung, but showed a very similar trend. Rates for cancer of the esophagus and stomach, on the other hand, did not appear related to dust in any consis tent manner. Other abdominal neoplasms were less frequent still and also unrelated to dust. This is important since it might be expected that unrecognized peritoneal meso theliomas would be found within this group. - Most of the excess mortality from re spiratory disease was ascribed to pneumoconiosis.fTable 6). There was little evidence that dust-associated deaths were included in other respiratory categories. Of the 28 deaths coded under the pneumoconioses, one was described as anthracosis, four as silico sis, and the' remaining 23 as asbestosis. The greatest excess mortality from pneumocon iosis was among persons in the highest dust group who had been employed between ten and 29 years. In the circulatory diseases group, there was also excess mortality in the highest two dust categories, mainly in persons employed Arrh Environ Health--Vol 22. June 1971 i tr V* \r I ! K' . between tin and 20 years. It was present equally in the "artcriii'-vlcrcitir and degener ative heart disease" group . 1('D 420 to 4:22 [which included more than three quarters of all circulatory deaths]) and in the group of "other circulatory diseases" -ICD 400 (o 419 and 423 to 409). Comparison 'With Quebec Mortality.-- The number of deaths from all causes which would have been expected if Quebec death rates had applied was calculated in 1 Iso fol lowing way. Age-specific death rates fur the province were applied for each year, 1950 to 1966, to all the men traced who were alixe in 1950, with an adjustment for those who started work after 1950. The expected num ber of deaths among men, thus, was 1,824, whereas the ob-erved number in the cohort was 1,674. A similar calculation was made for lung cancer deaths. The expected number was 91, whereas 94 male deaths certified ns due to this cause wore observed. Correction for cod ing errors and additional autopsy informa tion was not appropriate, since certificates for the general population were uncorreefed. In the six counties of the pro\ ince which include the mining region fArthahaskn, Beauce, Drummond, Megantic, Richmond, and Wolfe), (he lung cancer death rate was about two-thirds the provincial rate and the expected number of deaths was correspond ingly lower. However, many ex-employees were no longer living in this area when they died, and most of those who had moved had gone to cities where lung cancer death rates were higher. The best estimate of expected deaths probably lies between the numbers 61, derived from the mining region, and 91, from the province. The excess of observed over expected lung cancer deaths, therefore, lies somewhere, between zero and 30 and is most probably between ten and 20. Factor Evaluation.--Although the num bers of men in each' cohort were about the same, their distribution by years of employ ment and dust index was uneven. In these circumstances, equivalent average death rates could be misleading. Berry1-* recently reviewed some of the methods used for ana lyzing the importance of factors in multiway tables and described a paramo! ric. approach which has the advantage that (ho adequacy of the model may be checked and .statistical Table 5.--Equivalent Average Death Rales per 1,000 Men tor Cancer of Bronchus, Trachea, and Lung* Dust Index Years <10 10- 100- 200- 400- 800- All As certified <i 6.4 1.7 27.8 0.0 (16) i- 11.7 (1) (1) 9.5 11.3 (0) 5.8 (9) (15) (4) (1) 10- 0.0 12.4 6.7 5.3 (0) (7) (3) (3) 30- ... 12.5 14.7 13.9 (3) (2) (4) Alt 7.6 8.6 11.2 8.9 (25) (26) (10) (8) Using ell available unformation <1 6.7 1.7 0.0 0.0 (17) (1) 1- 12.0 10.1 (0) (0) 9.4 11.5 (9) (16) (3) (2) 10- 0.0 12.S 7.6 9.2 (0) (8) (4) (4) 30- ... 12.5 14.7 13.9 (3) (2) (4) AH 7.8 9.1 10.1 10.6 (26) (28) (9) (10) ... 7.6 (1) 19.9 (6) 16.1 (4) 15.8 (ID 7.6 (1) 19.9 (6) 16.1 (4) 15.8 (11) ... 0.0 (0) 23.6 (6) 27.9 (8) 24.2 (14) 5.9 OB) 9.6 (30) 13.1 (25) 17.2 (21) 9.9 (94) ... 0.0 (0) 23.6 (6) 35.3 (10) 27.7 (16) 5.9 (18) 10.1 (31) 14.3 (28) 19.1 (23) 10.6 (100) By dust index and years of employment. Diagnosis was ICO 162 and 163. significance, evaluated. From the number of deaths from any particular cause in groups subdivided by date of birth and year of employment or dust index, expected rates may be calculated assuming no interaction between age and the other two factors. For this analysis, the complementary log log transformation was used.13 This transforma tion is appropriate when increasing expo- ' sure is associated with proportional in creases in the age-specific death rates. The results of this parametric analysis for respiraton.' cancer (Table 7) agree remark ably closely. with the equivalent average death rates shown in the lower half of Table 5. The rates for the first five dust index levels do not differ significantly but those for the' first four are significantly different from the highest exposure group. There are, however, also differences between the rates by years of employment, those for the lower two categories being significantly less than that for men with the longest exposure. The general fit of the complementary log log model is very good. In no cell of the 24 does the observed number of deaths differ significantly from expectation. Tests for in teraction between the 24 cells and the six cohorts gave the following results: likelihood Arch Encirnn I[culth--Vol 22. June 1971 Tabic 6.--Equivalent Average Death Hates per 1,000 Men lor Respiratory Diseases (ICD 470-523) by Dust Index and Years ol Employment Dust ImJe* - Years <10 10- 100- 200- 400- Pneumonia and tiri nchitis (1CU 490-509) <1 2.6(7) 8.7(4) 0 (0) 1- 7.1(b) 3.7(0) 2.b(1) 10- 0 6.3(4) 5.9(2) 30- 0 4.9(1) 166.7(1) 4.4(1) 5.3(3) 5.8(1) ... 15.5(2) 5.6(3) 0 (0) All 3.6(1?) 4.7(14) 4.2(4) 6.6(6} 5.6(5) Pneumocoit'O'-M (l CD b73 ami b?4) <1 1.4(3) 6(2) 0 1- 1.4(1) l.b(?) 0 10- 0 7.3(1) 6 30- 0 0 0 5.8(1) 1.7(1) 3.6(1) 0 1-6(0 7.1(2) Ail l.b(l) 7.0(b) D(0) 3.7(3) 3.0(3) Otner respiratory diseases (ICD 470-489, 510-522. 525-529) <i 4.50 0) 5.7(3) 0 00 i- 3.8(2) 13.2(20) 29.0(9) 9.8(2) 7.9(1) 10- 0 2.7(2) 9.2(2) 7.9(2) 11.0(3) 30- 0 0 0 0 All 4,20 3) { .6(25) 15.2(11) 6 3(4) 5.9(4) All respirotoiy clseases (ICD 4 70 529; <1 8.6(20) 18.8(9) 0 1- 12.2(9) )S.4(28) 31.5(10) 10- 0 11.2(7) 15.1(4) 30- 0 4.9(1) 166.7(1) 20.0(4) 14.4(6) 9.3(2) 23.5(3) 18.2(7) 7.1(2) All 9.5(29) 15.3(4 4) 19.5(15) 16.7(13) 15.3(12) 800- ..4 16.7(1) 9.5(2) 3.4(1) 6.9(4) .44 0 34.3(8) 17.9(b) 22.6(13) 0 13.9(1) 7.8(2) 13.5(4) 12.1(7) *4. 30.6(2) 51.6(12) 34.7(10) 41.6(24) All 4.0(12) 5.7(16) 6.3(14) 2.9(3) 4.9(45) 1.9(5) 1-5(4) 6.3(11) 6.9(8) 3.2(26) . 4.6(13) 12.5(36) 7.3(11) 3.6(4) 7.5(64) 10.5(30) 19.2(56) 19.9(36) 13.4(15) 15.6(137) 4 ; * T r I ratio lost, SS.9 and x' 90.1, each with 95 degrees of freedom; and /' > 0.5. Comment Table 7.--Age-Corrected Death Rates per 1,000 Men for Cancer ol the Bronchus, Trachea, and Lung by Dust Index and Years ol Employment'" Dust Index At face value, the findings suggest that our cohort of workers in the chrysotilo min ing industry had a lower mortality than the population of Quebec of the same age. This is generally true of employed persons, pro-' vided they are not subjected to an occupa Years <1 1- 1030All <10 6.3 11.4 0.0 . 7.5 102.0 9.4 10.4 13.3 8.7 1000.0 8.1 9.8 9.9 8.9 2000.0 8.3 10.3 i4.e 11.0 400- 444 9.6 16.8 13.7 14.6 800- ,,, 0.0 23.4 34.4 26.3 All 5.5 9.5 12.8 17.9 10.0 A complementary log log model was used, and diag nosis was based on all available information. tional hazard sufficient to offset the con siderable selective advantage of being and finely recorded by the companies or the remaining fit for work. This advantage was medical clinics. However, in a survey of a clearly lost by the men in the highest dust- selected, random sample of over 1,000 cur index category whose standardized mortali rent employees there was little or no rela ty was about 20% above that of the rest. tionship, after allowing for age, between Two thirds of the excess mortality in this smoking habits and either dust exposure or group was probably due to pulmonary fibro duration of employment. sis, shown on the death certificate as either Our attempts to assess separately the asbestosis or in the guise of various respira importance of cumulative dust exposure and tory or cardiovascular diagnoses, and the duration of exposure in relation to lung remaining third to cancer, mainly of the cancer are capable of more than one inter respiratory tract. pretation. As shown in Table 5, there is a The high rate of lung cancoc_in_mcn fivefold difference between the mortality for heavily _exposed_to ashestos_ njieht be ex- those with the lowest amount and duration plained if such men jilso. tended to smoke of exposure, 6.7, and that for those with the more heavilythanplhers. We have no direct highest, 35.3. This is confirmed by the para evidence on thi_. pfiiuL..-for _ ex-.employaes*. metric analysis (Tnble 7) which 'urther sug sincejnformation on smoking.was not rou- gests that accumulated dust exposure and tL Arch Fstuirott Health--Vol 22, June 1971 T* mohtaijty a.\u cuiiYsoriLK mixks--McDonald et al G85 Table 8.--Comparison al Mesothelial Tumor Findings in Tvto Previous Studies and the Present Study No. ol men studic-.l No. of deaths All causes luri cancer McsothctMl tumoi> at16 ( 632 J V--- 380 72 22 Newhouse*.*7 4.806 436 42 20 Present Study ------ (-"-9--.9--8-1---)------ 2,413 97 3 duration of employment are about equally ly dust-related and partly time-related. We important in (k-iennining I ho difference. Un propose in future analyses; when a longer fortunately, there are possible sources of period of observation will have yielded more bias and error which may have contributed data, to use an exposure index based on the to both (hose effects. concept of amount of dust inhaled and the In Tabic 5. the rates for men with less time that it remains in the lung. Our than one. year of employment seem remark findings so far appear compatible with such ably low; IP deaths were observed, whereas a model. 29 would have been expected on the basis of In the Canadian survey mentioned ear Quebec rates. It was in this group that lier.10 primary malignant mesothelial tumors tracing was least satisfactory (Table 2). were rarely associated with chrvsotile asbes Failure to ascertain even a small number of tos production In Qnehec and I he prespnt lung cancer deaths would have made an survey bears this out. Three deaths from appreciable dill'eronce in the rates. Short this cause were found among nearly 2,500 term employees who were traced tended to deaths from all causes in the cohort. This is be those who had stayed in the neighbor probably more than would be expected in a hoods where, in any case, lung cancer rates comparable number of deaths in the general were much lower than in the urban areas of population, but Quite out of line with the the province and elsewhere, to which those findings of Selikoff ct al1'8 in insulation untraced may well have gone. Whatever the workers and these of Newhouse*-17 in'a Lon-. explanation, it is difficult to accept, without don asbestos factory. The magnitude of the reserve, the low rate of lung cancer in this .difference can be inferred from the figures in group. Table S. Though these figures are not entire .A second source of error is related to the ly comparable, because of age, methods of ascertainment of lung cancer as a cause of ascertainment, or other factors, they suggest death. It is generally believed that this diag that the results of Newhouse3-17 are similar nosis is greatly.aidcdJw-gnstmnrtem exami- to those of Selikoff et allB for mesothelial nption- In our study. <34?;. of the cases be tumors nnd, perhaps, lung cancer. It is clear fore correction ancl(40% after correction had that the Quebec chrysotile workers have had, had an autopsy, compared with of all nothing like this experiences of the America-', deaths. This might not matter nautopsies insulation workers or the London factory were evenly distributed in relation to expo workers with respect to malignant mesothe sure, but this was not so. The autopsy rates lioma, and it seems unlikely that they are in ascending order of dust-index group were compatible with respect to lung cancer. 1.1%'. 11%'.'iQ^JG^lnnd ?_2S'o,. nnd 'Fhese findings strongly suggest either that by years _of_ employment. 12?;,. 9?,',, 17%. chrysotile is less likely to cause malignant and 21%. ?his trend is ailso likely to have disease of the lung and pleura 'than other exaggerated the difference in lung cancer forms of asbestos, such as crocidolite, or that raTcs"ffTTcTaTTon to exnnsiirrv hut hv how workers engaged in insulation and process- much if is impossible to sav. ing are exposed to additional factors which Taking all these considerations into ac explain the difference. count we are inclined to conclude that the true difference between those maximally am. minimally exposed may well be closer to threefold than fivefold and that tins is part This work was undertaken with the assistance ol a grant from the Institute of Qxupntion..i and Environmental Health of the Quebec Asbestos Min ing Association. I'aul M. Cartier, MO. mriluu! diitvtor of the I \' GtiG MOh'TALITY AM) CHHISU1 ILL M {.\KS-~ McJJUSAUJ Jr.'l' Al. Thetfuid lndii-Jiiul Clinic. and T. Roger (haing. i. Ml), nicdieul diix-etnr of the Canadian .li.lni--Manvillo Company .i.--i.-iletl nil c rU-i! in this study. Mcnilx.-1's of unions and management [ crsotmel of the Quebec AsU-.ni; Mining Industiy gave their support. 'Ilie Department of l'1' mumaphy, Qu-her, and otlicr deportments of vital statistics helped us oli(.-iin death cettificales. The Depatliuent of Xatiunal Health mul Welfare, Oltnw'u, and the- Canadi an Unemployment Insin.uiee Coiiiini.- ion n;.-is|ed in the follow-up. Julnnnc- Hoy, Ft-m.uide lV.i'.lx, mid Joseph-Albert Cairur, and others trawl ox-cmployets, and Gcrahlitic Jacobs and Jean Peabody hclix-d with the data processing. r V k' V lU'fCTClKt'.S 1. A'U-slos; A tceiew of the- Canadian industry. Minin-; in Canaan, O-'t IS'tC, pp 17-3-x. 2. Wright C1W: AsK-dus and health in JOtiO. Amrr /{cr liesp DU lit!): |.",'-17:\ lpi*`\ 3. Merer, el her I'.ltA: A-be.-to-i-and em. inoinu of the lung, in Annual Hcpi'i: of 7 Chief Inspector nf I'ach-ries for tin- Y<r;r 1917. l.ondiai. Her Majc-ty's Stationery' Oili-'e, IfM'J, pp 7P-S7. 1. Wagner JC, Sle:;.t-i CA, Man-hand 1': Piifu-e pleural m-.-;otheUuma and a-!., -to.. expo-utc in the Notlh Wi-.-leru Oa|je J'loeinee. Brit -J Imhislr Med 17:2W)-271. lynO. 5. Doll It: Mortality fiotn lung eaneer in asbestos workcis. Bril ) Intluslr Med 12:Xl-&, lf'-Vi. G. Knox J)-\ Holmes S, lloll 11, ct al: Mortality from lung eaneer and other cau-es among workers in mi asbestos textile faetorv. Bril ) hultislr Mnl 24:2)13-31)3, JCtaS. 7. Enterline PI-:, Kendrick MA: A-h.stos-dust cx|)osurcs at various levels .and mortalitv. Arch Knrirnn Health lmlSt-ltfi, lSviV. . 8. Newhouse MI.: A study of the mortality of x wothers in an R.sbe~tos faetorv. Brit J Imluslr Med : 2G:201-301, 1909. ' 9. SelikofT JJ, Hammond KC. Cnurg J: Asbestos exposure, smoking and neoplasia. -JAMA itllilrtG- 112, 19GS. 10. MeDunald AD, H.u|vr A, K1 Attar C)A. el al: Epidemiology of primary malignant nu ,-uthclial tu- - J1 linns in Canada. Cancer 2.J:0J 1-010, 1070. `* , )!. Ilraim DC. Trtwn TD: An epidemiological studv of lung cancer in asliostns minets. Arch Indihtr Health l7a-U-r03, lf*08. "i i: f 12. Kogan,I'M, Troitsky SY, Cuh-vskaya Mil: On the ci-ictnogonic effect of asbestos (hot. C7,j Tr )'ruf /.nbol 8:-.:j.t>3, 1WG. Ut. llill All: Blindpits of Meilirnl Statistics, eel 8. J-oiiduti, Lancet Ltd, IV-'-C, p 2f>9. M. Horry G: Parmnelv'e analysis of di-ra.-c inei- eir-iuv.j in mnlliwav lahles. Biometrics 2GgJ72-o7)i, llCD. 15. Yaic-s F: The use of transformation-, and maximum likelihood in the analyses of tp.ianlnl f expriimenU involving two irentments. Bioinetriha 12:382-103. 1CC-3. l : 10. Selikotl I-T, Hammond ICC, Cliurg 0: Mf-rtali- ! ty expci infe-s of asbestos insulation woikcis, in Proceeding* of the International Confcrmcc on Vneuinneuniosis Johannesburg, J9$9, to lie pub- ` j. lished. ; 17. Newhouse MI- Wagner JC: Validation of death et-rtilie-ates in asbestos workers. Brit J Iniliistr Med 23:302-307, 1900. . ! f ; f ( r` ^: - M ' Arch Environ Health--Yul 22, June 1071 Tf WTT1