Document rzDxQXjRDdXdB2JxYYEGwbXG

11 red by l **tween in. Our "it 1 kg nr men ' ' ropom- clothes hat our i stand* tors for on in a ethnic owever, such as >e more ng pcougth to >v Public itml l-.SKourula- healthy cm tone* iwnmuI'nnmnn Inl pultairrclaiventa. J itelermi* -interior /v Rtp ester J: n movie Environ nc techling free. W6 " 677 :1 Mortality in the Chrysotile Asbestos Mines and Mills of Quebec J. Corbett McDonald, MD; Alison D. McDonald, MD; Graham VV. Gibbs, MSc; Jack Sicmiatycki; and Charles E. Itossiter, MA, Montreal Of 11,788 persons born between 1891 and 1920 employed In the Quebec asbestos mining Indus* try, 88.4% were traced. Of these 2,457 (23.6%) had died. Exposure Indexes for each worker were calculated from job dust levels and duration of employment. The overall mortality was lower than expected for the population of Quebec but jn the highest dust category, comprising 5% of the cohort, the age-standardized rate was 20% higher 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 15 deaths. The difference in rates tor re spiratory cancer between those maximally and minimally exposed was livefold and, though per haps exaggerated, was apparently determined by accumulated dust exposure and duration of em ployment. X HE REMARKABLE qualities of the as bestos group of fibrous minerals have been recognized since antiquity, but mining and milling on an industrial scale began only at tlic end of the 19lh century. In the Eastern Townships region of Quebec, deposits of chrysotile asbestos in serpentine rock were Submitted for publication Aug 17, 1970; accepted Nov 10. From the Department of Epidemiology and Henlth, McGill University, Montreal. Mr. Rossiler i.M presently with the Medical Itesenrch Council Pneumoconiosis Unit, Pcnarth, South Woles. Reprint requests to 377G University St, Montreal 112 (Dr. J. C. McDonnld). noted in the 1847 Canadian Geological Sur vey. The first mine was opened at Thetford in 1878, 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 1882 by one large company which also operates a small fac tory in 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 workers in the mines, mills, and primary manufe*-- ;'l Arch Environ Health--Vol 22, June 1071 1 BB 0005362 it; r.4Gi J G78 MORTALITY AN}) CHIIYSOT1EE MINES--Mcl)ONALI) ET AL luring industries arc exposed. Though the phyllite, the two textile factories referred to prevention of asbestosis is far from complete above"- used mainly chrysotiie fiber, togeth in these industries, it is still generally be er with some crocidolite, and in one of the lieved that this can be achieved by more two, some amosite. As in most industrial strict environmental control. Another aspect applications difTerent types of fibers are of the problem appeared in 1947 when mixed, the carcinogenic effects of a single ')/. Merewether* showed a link between asbes fiber type in practice can only be studied in tos exposure and lung cancer. The potential mining and milling. Chrysotiie fiber is of extent of this hazard was increased by re greatest importance because of its qualities J ports of Wagner and others1 during the last, and extensive usage. The only studies of i ton years that malignant tumors of the lung cancer in chrysotiie miners and millers - j pleura and peritoneum are related to certain were reported by Braun and Truan in j types of industrial work and perhaps also to 19581' 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 asbestos was first found in the British textile pared with six expected from provincial ; industry. Merewelher'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 (reputation the mortality from lung cancer observations among textile workers have was increased by a factor of 1.9 for miners, confirmed the association/- 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 . , I . ,, degree of exposure suggest a dose-response comprehensive epidemiological survey of thc^ -- i ; relationship. Knox et alfl found a consider entire Quebec asbestos-producing industry-.-^' j able excess of long cancer in persons exposed since its inception. Using the considerable | before 1993 when nsltoslos control regula volume of data available, our primary aim tions were enforced, but none in persons exposed for ten years or more in the most dusty areas since then. These findings must be reviewed when a longer period of obser vation has elapsed, since Newhouse fnlso in has been to define as accurately as possible the quantitative relationship between exposure to chrysolite asbestos and the incidence of lung cancer. The results from parallel studies concerned with the relniidnshTyrof > j j fr< tier (lx rom| ing a textile factory) found an excess of lung dust exposure to radiographic appearances, j oflei cancer in persons heavily exposed 20 years pulmonary function, and respiratory symp- i men earlier for periods of less than two years. toms will be reported separately. j G.4 Workers exposed to light or moderate dust concentrations showed no excess of broncho Materials and Methods thi < m< genic cancer even after 20 years of exposure. Selikoff 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 for 20 years or more. He also found a gross Reg. istration,--A register was compiled in the personnel department of each asbestos mining rompnnv in the Eastern Townships region of Quehee listing alt persons currently or pro. viouslv employed, as of Nov 1, 10GG. A card was made out for each employee on which was reeortled his name, date of birth, address, and a 1 | I ; cot fro tio wa am vie sjin excess of pleural and peritoneal mesothe detailed work history which included Ihe de a nr] liomas. On the other hand, in a national partment .and mine, dates of starting and (tin survey of all known mesothelial tumors in Canada, 106(1 to 1068, McDonald and her colleagues1" found a history of occupational contact with asbestos in a relatively small proportion of cases. This exposure was main ly in insulation and allied trades, rather than in the aslirslos-producing industry. Of the four main types of asbestos fiber-- finishing, for every jot), and all periods of leave. Tn one of Ihe 44 mining companies represent ed in our survey, the records of at least 5G0 persons had been destroyed. These were of ex-employees and others not transferred wlirn ownership of the company changed in 10G4. The work histories of a small number of older men who had hern employed partly in this company and partly in others were also inrom- , j , one sun T17 ITS, work .since sine fact the chrysotiie, crocidolite, amosite, and antho- : ieto, imp Arch Environ Health--Vol 22. June 1071 | BB 0005363 & refen ed to ner, togethone of the industrial fibers are of a single i studied in fiber is of ts qualities studies of and millers Truan in fid.11 In the lung cancer lustry com provincial oviet Union the general lung cancer < for miners, my workers, s part of a urvey of the 1 ng industry considerable aim ' n^Jfsiblc 'twee., expo* he incidence rom parallel nlionsfiTiT of -ippca ranees. atory svmo* ds compiled in asbestos minnships region ently or pre1966. A card on which was address, and a hided the destarting and riods of leave, ales rcpresenlf at least GCO hese were of nsforred when need in lOtVi. mber of older partly in this re incom- i. ,*-. i. + ;:<r MOHTALITY AND CUUYSOTILE MINES--McDONALD ET AL Table 1.--Subjects of Study and Results ot Tracing by Age and Sex Year of Birth 1891-1895 1896-1900 1901-1905 1906-1910 1911-1915 1916-1920 All Persons M 1.553 1.982 2.027 1.897 1.837 2,027 1 1,323 F Total 14 1.567 31 2.013 50 2.077 99 1.996 117 1.954 154 2.181 465 11.788 M 1,179 1.588 1.724 1,741 1.773 1,976 9.981 Traced F 13 28 45 92 1 13 149 440 Total 1,192 1.616 1.769 1.833 1.886 2.125 10.421 % Traced 76.1 80.3 85.2 91.8 96.5 97.4 88.4 Dead 611 655 49B 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 ot Study and Results oi Tracing by Dust Index and Years of Employment Oust Index Years <1 110 30All No. % traced No, % traced No. % traced No. % traced No. % traced <10 3.043 76.6 1.025 86.3 55 100.0 0 4,123 79.9 10- 654 75.1 1,975 88,6 1.117 99.0 204 100.0 3.950 89.9 100- 38 76.3 450 89.3 566 98.9 181 100.0 1.235 94.9 200- 3 66,7 264 90.5 52? 99,0 250 1C0.0 1.039 97.0 400 0 122 91.0 432 99.3 303 100.0 857 98.4 8000 64 90.6 255 99.6 265 99 6 584 986 All 3.738 76,3 3.900 88.3 2.947 99 1 1,203 99.9 1 1.788 88.4 670 was of course some movornt nt of labor ic mining comjwnv to another. This necessitated bringing together and matehing 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. In all, 27,(ifi9 men and women were registered, including 6,4IS currently employed on Nov 1, 1966. Of this total, 1,039 persons had been employed by more than one company. Using the occupational histories, a list was compiled of all named jobs in each company from (he beginning of its operation. A descrip tion of each of the 13,346 jobs listed in this wav 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 5,783. For each of these and fur each vear of operation, the average dust, expo sure w.-is estimated on a 13-pnint scale. Throughout the industry in the dryers, crusliers, and mills, (he concentrations of dust at working places had been measured annually since 1949 by Maurice Lachance. Fng, and since 1946 hv various investigators in the small factory. All measurements were made wilh oi. Iher a midget impinger or C.rccnlmrc.Somth. impinger and recorded in millions of dust parti- cles per cubic foot (mpef). Levels of exposure fn 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 fo changes in operating procedure re ported hv mining and maintenance personnel. A full description of geological and environ mental features and of (lie methods and results of dust measurement arc to lie published by G. W. Gibbs, MSc, and Mr. Lachance. Before 1949, few dust measurements were recorded, and estimates of exposure for that period\ire, therefore, only approximate. Inter views wiih employees of long service enabled comparisons of dustiness to he made with con ditions since 1949. The dates of installation or modification of dust control systems were also taken into account. Duration of exposure for each person was expressed in visits or fractions of years after snhTrTiilton ot ail periods pi lc;nc. ai'TI tt"ls correetisl to a working week (jf IP hours. A dusL index was culculatixl for each emplnyec by adding together I he 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 al 40 nipcf, 15 years at 20 inpef, and 20 years at 5 mpef (ie, 200 + 300 + 100). It would lie useful if il could lie assumed Arch Environ Health--Vol 22, June 1071 n 1-- F, ti 680 MORTALITY AND CHIIYSOTILE Mlt\'ES--McDONALI) ET AL Hint an. index of GOO were also equivalent to a working lite ol !() years at iu mpcl. Gut this would entail assumptions wlneh mayurr may not hi* instilled. Selection of Cohort__ The study of mortality was based on employees in an age group thought likely to yield the most valuable infor mation. The cohort selected comprised 11,788 persons horn between 1891 and 1020 inclusive who had been employed tor one calendar month or more. Those born alter 1920 would have had periods of exposure well short of a working lifetime and would still not have reached an ago of high mortality. Those born before 1891 would have been very difficult to trace, and, as mentioned above, some of their work histories were incomplete or missing. The selected cohort comprised among others 1.203 persons who "liar! worked for .10 years or more. 3,738 who had worked for less than a year, mid 1,080 who had wr^Ji^iLIal-DllIIi.* than a year but whose job had not involved any appreciable exposure to dust. Thus, there was a substantial group with minimal exposure available for com parison witn others who had been heavily exposed. "Tracing and Ascertainment.--The search for ex-employees was mainly initiated in the min ing towns. Telephone or postal inquiries were made first to establish whether the person in question was alive or dead on Nov 1, 1966. If reported dead, the exact date and place was sought from relatives, friends, and parish regis ters. For those not traced by these means, a systematic search was made in the provincial death records and certificates, and about 200 persons were found in this way. In addition, a search on our hehnlf was made in the index of the Canadian Unemployment Insurance Com mission for any person not found by means of local enquiries. The names of 598 persons were found who had registered or re-registcTed be tween 19G4 and Nov 1, 19GG, and 30 more hod re-registered after that date. All 628 were pre sumed to he alive for the purpose of our study. Information was olitaiiuxl concerning 10.121 (88 41.1,,) of the 11,788 persons in the colnnt: i .iMi* were still alive iinclmlinc 2.1H1 pirrrptlv employed) and 2.157 (23.6% of tho-o t mrt`d) were reported (lead. Copies of death certificates were obtained froin Canadian Provincial and US State Registrars for 2,211 (90%) persons. For 59 more (2%), an acceptable cause of death was obtained bv other means; 30 were accidental deaths in the mines or during active service with the armed forces and 29 were caused by disease. Twenty-two of the 29 had occurred before the introduction of death regis tration in Quebec in 1920, and the cause of death was stated by relatives. In the other seven, the cause of death was obtained from a reliable source. A death certificate could not bo obtained for the remaining 187; 47 had oceurred before 1926, and 100 were deaths outside Quebec, mostly outside Canada. The cause of death was coded according to the Seventh Ri"vision of the International Classification of Disease (1CD [World Health Organization, Geneva, 19573). This was done by senior coder of the Department of Demography of Quebec who had recently retired. The proportion of subjects traced by age, sox, and category of exposure is shown in Tables 1 and 2. Success in tracing depended mainly on duration of employment; 94% of those em ployed for one year or more and over 99% of all those employed for ten years or more were (raced. Information was least satisfactory in persons horn before 1900 and in those em ployed for less than one year. The principal reasons for failure were (1) no relative or friend could he located in the neighborhood and (2) insufficient identifying information, which would have enabled us to make a request to the Unemployment Insurance Commission or to locate a death certificate in Quebec. There were no other obvious reasons for bins towards dis covering the living or the dead, but those traced dead or alive are likely to have been long-term rather than transient residents. Diagnosis of Lung Cnneer___To make our figures for lung cancer as accurate as possible, we investigated and reviewed all certified cases and searched also for eases not described as such on the death certificate. Of 95 deaths coded as due to lung cancer (ICD 162 and 163), one was certified as due to a hydronephromu and another ns due to pulmonary fibrosis, both of which had been coded incor rectly. Inquiries about the remaining 93 eases were made from hospitals, physicians, and pa thologists, and information was received in 7G, In five of these it was rcjjortod that there had been an autopsy, but we were unable to obtain pathological details. In another five, though the diagnosis had been made in the hospital, no clinical or pathological record was found. Sev enteen more had been certified by family phy sicians but wo did not succeed in finding out where and how the diagnosis had been made. In the remaining 48 cases, pathological reports were obtained, 25 at autopsy and 23 at biopsy. A diagnosis of carcinoma of the trachea was made in one, of bronchus or lung in 44, and of malignant mesothelioma of pleura in two. In one rase the histology was that of a mclnnosnreomn. and tlio pulmonary tumor was thought lo ho metastatic. Thus, of 95 certified eases, three J ! ! ' i j * I j had firmd induitzi^, to* 1st fe) lung am ployn't health,> who lad; They fe found If three tit been cat ashcatoa ease {1C autopds mentis* < irate. 1* for coai lung aa The pit cor* to" rauses o two cue third. 3. At rv malg that mi; 1G2. Or pleural < 4. W. gists in uant it I960 an worked dustry fore, ni after 6 diagn studies. Arrlt Environ Health--Vol 22, June l'J71 < Ary; t\iL ti'WsVt 'f u * tLi | BB 0005365 1 .her (from a ) not be r bad oc outside i cause of nth Rovii of DisXn. Gener coder of (Quebec who Why ago. sex. j in Tables 1 d mainly on 4 those emover 99% of r more were ^factory in those emie principal relative or Kjrhood and ition, which quest to the ssion or to There were o)waruds d< is pose sen idem. i make our is possible, rtified cases ieserihed as 95 deaths D 162 and a hydronepulmonary >dcd ineorig 93 rases is, and pa-ived in 76. there had le to obtain though the hospital, no found. Sevfumily phvfinding out en made, lological rev and 23 ,d ' the trachea ig in 44, and :a in two. In i melanosaris thought to Three MORTALITY AND CHIIYSOTILE MINES--McDONALD ET AL G81 had been included incorrectly, 47 were con firmed pathologically, 28 hospital diagnoses were presumed correct, and in 17 no further information was obtained. The following steps were taken to discover rases of lung cancer that had not been men tioned as such on the death certificate: 1. A letter was sent to the certifying physi cians whenever it was stated that an autopsy had been or would be performed. These num bered 306 in all; 33 deaths were certified as due to lung cancer and 273. as due to other causes. In 18 replies, it was stated that there had been no autopsy; in 175, that the certified diagnosis was confirmed at autopsy; and in 18, that it was incorrect. These 18 yielded five additional cases of lung cancer. The diagnoses for these had been certified as renal tumor (ICD 180), infectious hepatitis (ICD 092), pulmonary fibrosis (ICD 519), diabetes (ICD 260), and asbestosis (ICD 523). 2. We asked the physicians in charge of the industrial clinics at Thetford Mines 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 who had applied for workmen's compensation. They listed 24 of the 96 lung cancer deaths found hv the methods already described plus three additional eases. These three deaths had been certified as due to tuberculosis (ICD 019). asbestosis (ICD 523). and coronary heart dis ease (ICD 420), and though there had been autopsies for the purpose of compensation, no mention of this 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 primarv malignant mesothelial 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 I960 and 1968, and five were in men who had worked in the Quebec asbestos-producing in dustry. Two were horn in 1922 and were, there, fore, not in our cohort, and two died in 1967 after the present study had ended. A fifth case, diagnosed hy biopsy, was eligible for both studies. To summarize the results of all these inquir ies, three cases were removed from the group of 95 malignant neoplasms of the bronchus, tra chea, or lung (ICD 162 and 163) and nine were added, makinglOliy^i^^^^f^jnenjjui^nny lncludctT'in the total were the follow ing; cancer of the trachea, in one case; malig na ntineeTnt^S^Hgjor^^i^^irep; and cancer of the hronchus or lung, in 97. Results Female Mortality.--There wore only 465 women in the cohort; almost all had short exposures and all but 33 were in the two lowest dust-index categories. In all, 440 (94.6%) were traced, and of those, 45 had died. Tuberculosis (11), 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, those figures are not unusual and will not be considered fur ther. Male Mortality.--To permit comparisons of mortality hv dust index and years ol exposure, death rales'were calculated in five-year er>horls hy dale of birth. Kquivnlent average death rales11 wore I hen calculated using a standard nnrmlation 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 are shown by dust index and mam disease groupings in Table 3. In the lower five dust categories, equivalent average death rates lor "all railses" Were approximately the same, hut in I he top category, containing______ ofthe_totnl cohort, mortality wa_s_ about 20".'- In I'hpr than' cst. Malignant neoplasms, circula tory diseases, and respiratory diseases, m approximately oqual_prrvi2Qrjjrins^jmroim for the excess, 'Two groups showed the oppo site trend: "trauma," probably because rates fell with advancing age, and "unknown causes," probably because death certificates wore 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 till i ers ;ii ? '-3 - V. :5 -t. iS Arch Environ Ilrnllli--Vol 22. June 1071 s; Gf j--BB 0005366 t 1 m 682 MORTALITY AND CHIIYSOTILE MINES--McDONALD ET AL Table 3.--Equivalent Average Death Rates per 1,000 Men by Dust Index Oust Index No. of men Tuberculosis (ICD 001-019) Malignant neoplasms (ICD 140-209) Circulatory diseases (ICD 400-469) Respiratory diseases (ICD 470-529) Trauma (ICD 800-999) Other causes Unknown causes All causes <10 3.006 18.8 38.8 65.0 9.5 34.7 46.8 30.6 264.1 103,408 19.9 39.3 80.8 15.3 30.8 52.9 21.4 260.4 1001.148 31.6 32-2 82.5 19.5 36.3 39.0 16.5 257.6 2001.002 23.8 27.5 83.5 16.7 35.2 47.7 6.2 240.6 400842 28.5 45.1 94.8 15.3 33.8 38.3 7.2 262.9 800575 25.8 61.8 107.3 41.6 13.7 58.9 3.4 312.5 All 9,981 72.5 38.6 85.8 15.6 31.5 48 4 20.8 263.1 Table 4.--Equivalent Average Death Rates per 1,000 Men lor Malignent Neoplasms (ICD 140-209) by Dust Index Dust Index Location Esophagus & stomach (ICO 150151) Intestine & rectum (ICD 152-154) Other abdominal areas (ICD 155-15*) Bronchus, trachea & lung (ICD 162-163) Other malignant neoplasms Alt malignant neoplasms (ICD 140-209) <10 10.2 (32) 2.5 (8) 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 (1) 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 (M) 13.5 (8) 61.8 (36) AH 7.5 (68) 4.0 (38) 2.9 (27) 9.9 (94) 14.4 (131) 38,6 (358) (ICD 162 and 163). In tins group there was little difference between ratesthe four lower dust r,-itor-q]-'^g <1TM nftV. ciwl-. groups showed an linwnrd trend. A similar trend with years of exposure was found (Table a), hut the figures within the hodvoT thelable suggest a closer relationship with dust than wiili" 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 clast and longest exposure, but did not materially change the picture (Ta bic CO. FnrlhoE_nnnlvscs tn distinguish licLtcr the relative importance of years of expo sure and dust index are described as follows. 'Hairs- lor ameer ol the intestine were about one third of those for cancers nrlhe bronclnis, trachea, and lung, hut showed a very similar trend.-Hates lor 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. Mast of the rvi-rcc mnrir|H(v from resnirntnrv disease was nsejihefLtn nnenmn. coniosis < Table 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 ns nnlhracosis, four as silico sis, and the remaining 23 as aslicstosis. Tlte greatest excess mortality from pneumocon iosis wTnrrnrmng persons m 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 lughest two dust categories, mainly id |>MmiriK tllftploycd Arch Environ Health--Vol 22, June 1971 C/, between equally1 ative he f which all circv "other 419 and Comp The nui would 1 rates he lowing ' provine 1966. tr in 1950 started ber of r wherem was 1,6' cancer r wherea this can ing erre tion wa for the . In jh include Boauce, and Wc about t_ ex node inelv 1were no died, ar gone to were hi deaths 61, den from th over ex) lies son most pr> Facto bers of same, tl ment ar circums rates co reviews lyxing t tables a which h of the n I 1* iA.L Oj*. - t ' QB 0005367 | Mji' U ! , i ' i .i it 'ij . : t iilld All '.981 22.5 18.6 85.8 15.6 31.5 I8~4~ '0.8 i3.1 All 7.5 < 68^ 40 .38) 29 27) I 4 81 131) <8.6 358) n any consisd neoplasms unrelated to it might be Itoneal meson this group. tv from ro- -tnpnf'rnnn. ttle evidence e included in Of the 28 conioses, one nir ns silicolicstosis. Tlio pneumoconhighest dust l>etwccn ten group, there ; highest two TOTmployed MORTALITY AND CHRYSOTILE MINES--McDONALl) ET AL 683 between ten and 20 years. It was present equally in me 1 'arteriosclerotic and degener ative heart disease" group (ICD 420 to 422 [which included more than three quarters of all circulatory deaths)) and in the group of "other circulatory diseases" (ICD 400 to 410 and 423 to 469), 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 the fol lowing way. Age-specific death rales for the province were applied for each year, 1950 to 1966, to all the men traced who were alive in 1950, with an adjustment for those who started work after 1950. The expected number of deaths among men, thus, was 1,824, whereas the observed ndh_iUTiM_N^ yonnrt was 1,674. A similar calculation was made for lung cancer deaths. The expected number was 91, wherenc 03 'p^le rlnnO.c rnrlilirri rts fine to this cause were observed. Correction for cod ing errors and additional autopsy informa tion was not appropriate, since certificates for the general population were uncorrected. In the six counties of the province which inchide the mining region t frrtJmbaska, Beauce, Drummond Mewnim TtiVb.iimw-l. and Wolfe), the, 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 pm-tad deaths probably lies between the nmnhers 6], 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. Berry14 recently reviewed some of the methods used for ana lyzing the importance of factors in multiway tables and described a parametric approach which has the advantage that the adequacy of the model may be checked and statistical Table 5.--Equivalent Average Death Rates per 1,000 Men lor Cancer ot Bronchus, Trachea, and Lung* Oust index Years <10 10* 100- 200- 400- 800' All As certified <i 6.4 (16) 11.7 1.7 27.8 (1) (1) 9.5 11.3 0.0 (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) All 7.6 8.6 1 1.2 8.9 (25) (26) (10) (8) Using all available i nformation <i 6.7 1.7 0.0 0,0 (17) (1) (0) (0) i- 12.0 10.1 9.4 11.5 (9) (16) (3) (2) 10- 0.0 12.8 7.6 9 2 (0) (8) (A) (4) 30- 12.5 14.7 13 9 (-3) (2) (4) All 7.8 9.1 10.1 10 6 (26) (28) (9) (10) 7.6 (1) 19.9 (6) 16.1 (4) 15.8 (in 7.6 (1) 19.9 (6) 16.1 (4) 15 8 an 0.0 (0) 23.6 (6) 27.9 (8) 24.2 (14) 5.9 (18) 9.6 (30) 13.C (25)-17.2 (21) 99 (94) 0.0 (0) 23 6 (6) 35.3 (10) 27,7 (16) 5.9 (18) 10.1 (31 T 14.3 (28) 19.1 (23) 10. tr (100) * By dust index and years of employment. Diagnosis was ICO 162 and 163. significance evaluated. From the number Of deatlis from any particular cause in grouty* 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.'-'* 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 respiratory 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 difTer significantly but those for the first four are significantly different from the highest exposure group. There are, however, also differences between the rales 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 mcxlcl 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 E/wiron Health--Vol 22. June 1971 mm 684 MORTALITY AND CHRYSOTILE MINES--McDONALD ET AL Table 6.--Equivalent Average Death Rates per 1,000 Men tor Respiratory Diseases (ICO 470-529} by Dust index and Years of Employment Dust Index Year* <10 10- 100- 200- 400- Pneumonia and bronchitis (ICD 490-509) <1 2.6(7) 8.7(4) 0 (0) 1- 7.1(5) 3.7(6) 2-5(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 3.8(12) 4.7(14) 4.2(4) 6-6(6) 5.6(5) Pneumoconioses (ICD 523 end 524) <1 1.4(3) 4.5(2) 0 1- 1.4(1) 1.5(2) 0 10- 0 2.3(1) 0 30- 0 0 AH 1,5(4) 2.0(5) 0(u) 0 5.8(1) 1-2(1) 3.6(1) 3.7(3) 0 1-6(1) 7.1(2) 3.9(3) Other respiratory diseases (ICD 470-489, 510-522, 525-529) <1 4.5(10) 5.7(3) 0 00 ]- 3.8(3) 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 4.2(13) H.6(25) 15.3(11) 6.3(4) 5.9(4) All respiratory diseases (iCD 470-529) <1 8,6(20) 18.8(9) 0 1- 12.2(9) 18.4(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) Ail 9.5(29) 15.3(44) 19.5(15) 16.7(13) 15.3(12) 800* 16.7(1) 9.5(2) 3.4(1) 6.9(4) 0 34.3(8) 17.9(5) 22.6(131 0 13.9(1) 7.8(2) 13.5(4) 12.1(7) 30.6(2) 51.6(12) 34.7(10) 41.6(24) All 4.0(12) 5.2(16) 6.3(14) 2.9(3) 4.9(45) 1-9(5) 1-5(4) 6.3(11) 6.9(8) 3.2(28) 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) ratio test, 88.9 and y2, 90.4, each with 95 degrees of freedom; and P > 0.5. Comment table 7.--Age-Corrected Death Rates per 1,000 Men lor Cancer of the Bronchus, Trachea, and Lung by Dust Index and Years of Employment' Dust Index At face value, the findings suggest that our cohort of workers in the chrysotile 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 tional hazard sufficient to offset the con siderable selective advantage of being and remaining fit for work. This advantage was clearly lost by the men in the highest dustindex category whose standardized mortali ty was about 20% above that of the rest. Two thirds of the excess mortality in this group was probably due to pulmonary fibro sis, shown on the death certificate as either nsbestosis or in the guise of various respira tory or cardiovascular diagnoses, and the remaining third to cancer, mainly of the respiratory tract. The high rate of lung cancer in men heavily exposed to nslx\stos might be ex plained if such men also tended to smoke more heavily than others. Wo have no direct evidence on this point for ex-employecs, since information on smoking was not rou Years <1 1* 1030All <10 6.3 1 1.4 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 14.6 11.0 400- 9.6 16.8 13.7 14.6 800- 0.0 23 4 34.4 26.3 All 55 9.5 12.8 17.9 10.0 A complementary log log model was used, and diag nosis was based on all available information. tinely recorded by the companies or the medical clinics. However, in a survey of a selected random sample of over 1,000 cur rent employees there was little or no rela tionship, after allowing for age, between smoking habits and cither dust exposure or duration of employment. Our attempts to assess separately the importance of cumulative dust exposure and duration of exposure in relation to lung cancer are capable of more than one inter pretation. As shown in Tnhlc 5, there is a fivefold difference between the mortality for those with the lowest amount and duration of exposure, 6.7, and that for those with the highest, 35.3. This is confirmed by the para metric analysis (Table 7) which further sug gests that accumulated dust exposure and Arch Environ Health--Vol 22, June 1971 C 4 duration important fortunatel bias and to both th InTab than one ablylowT 29 wouTcT Quebec r tracing v. Failure to lung cam appreciab term emp be those hoods wh were muci the provii untraced i cxplanatii reserve, tl group. A secon ascertainn death. It i nosis is gr nation. In fore correr had an an deaths. Tl were even; sure, but t in ascendi nor 11 <7* by years and 21%. exfiggerati rates in r much it i^ Taking count we true differ' minimally threefold i I SB 0005369 j (30) (56) '(36) 1(15) 5(137) Iales per 1,000 , Trachea, and Ers^^ment* '0- 800- as used, and diag- metion. ipanies or the a survey of a over 1,000 curttle or no relar age, between iust exposure or separately the Lst exposure and. elation to lung than one interble 5, there is a (he mortality for mt and duration or those with the med by the paravhich further sugist osure and MOHTALITY AND CHliYSOTILE MINES--McDONALD ET AL 685 Table 8.--Comparison of Masothelial Tumor Findings in Two Prarioua Studies and the Present Study No. ot men studied No. of deaths All causes Lung cancer Mesothelial tumors Sehkolf et al'* 632 380 72 22 Newhouse*.** 4.806 436 42 20 Present Study 9.961 2.413 97 3 duration of employment are about equally important in determining the difference. Un fortunately, there are possible sources of bias and error which may have contributed to both these effects. In Tahlo 5.-the rates for mcr) w;<K than one year of employment seem remark ably low; 18 deaths were observed, whnrnag 29 would have been expected on the basis of Quebec rates. It was in tnm group that tracing was least satisfactory (Table 2). Failure to ascertain even a small number of lung cancer deaths would have made an appreciable difference in the rates. Short term employees who were traced tended to be those who had stayed in the neighbor hoods where, in any case, lung cancer rates were much lower than in the urban areas of the province and elsewhere, to which those untraced may well have gone. Whatever the explanation, it is difficult to accept, without reserve, the low rate of lung cancer in this group. A second source of error is related to the ascertainment of lung cancer as a cause of death. It is generally believed that this diag nosis is greatly aided by postmortem exami nation. In our study, 34% of the cases be fore correction and 40% after correction had had an autopsy, compared with 12% of all deaths. This might not matter if autopsies were evenly distributed in relation to expo sure, but this was not so. The autopsy rates in ascending order of dust-index group were '11%, 11%, 9%, 10%, 16%, and 22%, and by years of employment, 12%, 9%, 17%, and 21%. This trend is also likely to have exaggerated the difference in lung cancer rales in relation to exposure, but by how much it is imix)$siblc to say. Taking all these considerations into ac count we are inclined to conclude that the true difference between itiosc"maximally and ly dust-related and partly time-related. We propose in future nnnlvsps "'tuny a |npgr period of observation will ftnvp yielded data, to use an exposure index based on tltp"*" 1 concept of amount of dust inhaled and time that it remains jn the, lung. OJr" findings so far appear compatible with sucEfS! a model. - In the Canadian survey mentioned ean% Her,10 primary malignant mesothelial tumorg^) were rarely associated with chrysotile asbesC,- - tos production in Quebec and the present*^.. survey bears this out. Three deaths fronCZ this cause were found among" nearly 2.f>0f) deaths Iroin all causes in the cohort. This ia -- probably more than would be expected in a* comparable numoer of deaths in the general population, but, quite out nl line with tha * findings oi ' t-'elikoll' <'t al"' in insulation^.* workers and those of Nowhouspli |'f in a Lon<TM% don asbestos lactory. The magnitude of thefy dillcrcncc can beInferred from the figures in Table 8. Though these figures arc not entire ly comparable, because of age, methods of ascertainment, or other factors, they suggest that the results of Newhouses-,T are similar to those of Sclikoff ot al10 for mesothelial tumors and, perhaps, lung cancer. It is clear that the Quebec chrysotile workers have had nolKin_g__lik_e__1_1_11:_1 _P_A_p_t_'l_iPIHir'tfful the Amcruaan insulation workers or the London factory workers with respecF'fo malignant, maeothe- lioma.'and it seems unlikely that they arc compatible with respect to lung cancer. Those findings strongly .suggest either that chrysotile is less likely to cause malignant disease of the lung and pleura than other forms of asbestos, such as crocidolite, or that workers engaged in insulation and process ing are exposed to additional factors which explain the difference. This work was undertaken with the assifdnnco nf n grant from the Institute of Occupational and Environmental Health of the Quelsjc AsIjcsIos Min- inn Association Paul M. Cartier, MD, medical director of the 'i 'll Arch Environ Health--Vol 22, June 1071 cc \m ,~B 00 05370 i ( G8G MOltTALlTY AND CHItYSOTILE MINES--McDONALU KT AL 'lltcthird I n<lusl tinI Clinir, nnd T. Roper Grainpcr, MI), medienl director of I ho Canadian Johns-Mnnville Company assisted nnd cooperated in this study. Memlicrs of unions nnd management personnel of the Quolicc AslicsUis Mining Industry gave their supi>orL The Department of Demography, Quebec, and other departments of vital statistics helped us obtain death corlilienlea. The Department of Na tional Health and Welfnrc, Ottawa, and the Canadi an Unemployment Insuranre Commission assisted in the follow-up. Julienne Roy, Fernando rroulx, and Joseph-AJlicrt Carrier, and others traced ex-em ployees, nnd Gernldine Jacobs and Jean Peabody helped with the data processing. References 1. Aslieslos: A review of the Canadian industry. Mining in Canada, Ort 1907, pp 17-38. 2. Wright GW: Asbestos and health in 19G9. Amur lift! Heap Dm 100:407-479, 19(59. 3. Merewethcr KRA: Asbeslosis and carcinoma of the lung, in Annual Report of the Chief Inspector of Factories for the Year 19-17. l-ondon, Her Majesty's Stationery Office, 1949, pp 79-87. 4. Wagner Sleggs CA, Mnrchand I': Diffuse pleural mesothelioma nnd asbestos exposure in the North Western Cape Province- Brit J Industr Med 17:200-271, 1900. r>. Doll It: Mortality from lung cancer in asbestos workers, llrit J Industr Med 12:R1-8G, 1955. 0. Knox ,JK, Holmes S, Doll R, et al: Mortality from lung cancer and other causes among workers in an aslieslos textile fnelory. llrit J Industr Med 25:293-303, 1908. 7. Knterline PK. Kendiick MA: Asliestos-dust exposures at various levels and mortality. Arch Environ Health 15:181-180, 1907. 8. Newhou.se MI,: A study of the mortality of workers in an asbestos factory. Brit J Industr Med 26:29-1-301, 1909. 9. SelikotT J-l, Hammond KC, Churg J: Aslieslos exposure, smoking and neoplasia. JAMA 204:106- 112, 1908. 10. McDonald AD, Harper A, HI Altar OA, et nl: Kpidcmiology of primary malignant mosothclia! tu mors in CanHdn. Cancer 26:914-919,1970. 11. Drnun DC, Truan TD: An epidemiological study of lung enneer in aslieslos miners. Arch Industr Health 17:034-653, 1958. 12. Kogan PM, Troitsky SY, Gulevsknya Mil: On the carcinogenic elfeet of aslieslos dust Gig Tr Fraf Zahnl 8:28-33, 1900. 13. Hill AH: Principles of Medical Statistics, cd 8. I-ondon, Lnncet Ltd, 19C0, p 209. 14. Derry G: Parametric analysis of disease inci dences in multiway tables. Biometrics 26:572-579, 1970. 15. Yates F: The use of transformations and maximum likelihood in the analyses of ipiiinlal experiments involving two treatments, Biomctriha 42:382-403, 1955. 16. SelikolT IJ, Hammond KC, Oiurg J: Mortali ty experiences of aslieslos insuluLion workers, in Proceedings of the International Conference on Pneumoconiosis Johannesburg, 1969, to be pub lished. 17. Ncwhousc MR Wagner JC: Validation ot death ecrlilieales in aslieslos workers, llrit J Industr Med 2G:302-307, 1909. ' 1 1 ' ') ' ' wt Papetv Acadsr Medic Thi Theodc One upon v nre bap may be ance at succcssf icant tt demons ostablio creat st justificr a dctci would 1 zero lev probnbl trial sit: itiR prii the utn industri efTort, tl others c: ress of i to dome of such constant society health r they nut problem.' corrective curs. There complish Arch Environ llcullh--Vol 22, Julie VJ71 rn U'j Submit (< Mmvh J). Hr. Unit School of Mild ( vironmeiifp i \crsjtv of i svnijjosiutti /Minn ftdvL Henri be I Amcrimn i 1 i MjKilmnnl ! i Nil n:t.M7 I --t.jO . \ BB 000^^22-1