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3.  The 1891-1920 birth cohort of Quebec chrysotile miners and millers: mortality 1976-88. 
British Journal of Industrial Medicine  1993;50(12):1073-1081.
A cohort of some 11,000 men born 1891-1920 and employed for at least one month in the chrysotile mines and mills of Quebec, was established in 1966 and has been followed ever since. Of the 5351 men surviving into 1976, only 16 could not be traced; 2508 were still alive in 1989, and 2827 had died; by the end of 1992 a further 698 were known to have died, giving an overall mortality of almost 80%. This paper presents the results of analysis of mortality for the period 1976 to 1988 inclusive, obtained by the subject-years method, with Quebec mortality for reference. In many respects the standardised mortality ratios (SMRs) 20 years or more after first employment were similar to those for the period 1951-75--namely, all causes 1.07 (1951-75, 1.09); heart disease 1.02 (1.04); cerebrovascular disease 1.06 (1.07); external causes 1.17 (1.17). The SMR for lung cancer, however, rose from 1.25 to 1.39 and deaths from mesothelioma increased from eight (10 before review) to 25; deaths from respiratory tuberculosis fell from 57 to five. Among men whose exposure by age 55 was at least 300 million particles per cubic foot x years (mpcf.y), the SMR (all causes) was elevated in the two main mining regions, Asbestos and Thetford Mines, and for the small factory in Asbestos; so were the SMRs for lung cancer, ischaemic heart disease, cerebrovascular disease, and respiratory disease other than pneumoconiosis. Except for lung cancer, however, there was little convincing evidence of gradients over four classes of exposure, divided at 30, 100, and 300 mpcf.y. Over seven narrower categories of exposure up to 300 mpcf.y the SMR for lung cancer fluctuated around 1.27 with no indication of trend, but increased steeply above that level. Mortality form pneumoconiosis was strongly related to exposure, and the trend for mesothelioma was not dissimilar. Mortality generally was related systematically to cigarette smoking habit, recorded in life from 99% of survivors into 1976; smokers of 20 or more cigarettes a day had the highest SMRs not only for lung cancer but also for all causes, cancer of the stomach, pancreas, and larynx, and ischaemic heart disease. For lung cancer SMRs increased fivefold with smoking, but the increase with dust exposure was comparatively slight for non-smokers, lower again for ex-smokers, and negligible for smokers of at least 20 cigarettes a day; thus the asbestos-smoking interaction was less than multiplicative. Of the 33 deaths from mesothelioma in the cohort to date, 28 were in miners and millers and five were in employees of a small asbestos products factory where commercial amphiboles had also been used. Preliminary analysis also suggest that the risk of mesothelioma was higher in the mines and mills at Thetford Mines than in those at Asbestos. More detailed studies of these differences and of exposure-response relations for lung cancer are under way.
PMCID: PMC1061330  PMID: 8280638
5.  Fathers' occupation and pregnancy outcome. 
Findings from a survey of 56,067 women in Montreal on maternal occupation and pregnancy outcome have been reported. Paternal occupation recorded in the same survey was analysed for spontaneous abortion in 24 occupational groups retaining the six main sectors of maternal occupation and allowing, by means of logistic regression, for seven potentially confounding variables. In only one of the 24 fathers' occupational groups was there a statistically significant excess of spontaneous abortions--mechanics, repairers, and certain assemblers (O/E = 1.10, 90% CI = 1.02-1.20); subdivision of this group suggested that this excess was mainly attributable to the large group of motor vehicle mechanics (O/E = 1.17). No significant excess of known chromosomally determined defects was found in any of the 24 occupational groups. An association of developmental defects was found with food and beverage processing (18 defects observed compared with 8.02 expected; p less than 0.05); however, there was no specificity in type of food, beverage, or congenital defect, and no obvious explanatory mechanism.
PMCID: PMC1009776  PMID: 2751931
6.  Work in pregnancy and birth weight for gestational age. 
In a recent report on prematurity and work in pregnancy based on the Montreal survey noteworthy increases in both preterm births (less than 37 weeks) and infants of low birth weight (less than or equal to 2500 g) were found in women in certain specific occupations or whose work entailed heavy lifting, shift work, long hours, or great fatigue. Because of the large overlap between preterm births and low birth weight, the latter was further analysed with allowance for gestational age in order better to separate factors retarding fetal growth from those shortening gestation. The association of low birth weight with specific occupations, long working hours, and fatigue largely disappeared, suggesting that the effect of these factors was to shorten gestation. By contrast, the association with lifting heavy weights and with shift work persisted, suggesting that these factors retarded fetal growth as well as increasing the risk of preterm birth.
PMCID: PMC1009753  PMID: 2930730
7.  Respiratory cancer in chrysotile textile and mining industries: exposure inferences from lung analysis. 
In an attempt to explain the much greater risk of respiratory cancer at the same cumulative exposure in asbestos textile workers in Charleston, South Carolina, than in Quebec miners and millers, both exposed to chrysotile from the same source, 161 lung tissue samples taken at necropsy from dead cohort members were analysed by transmission electron microscopy. Altogether 1828 chrysotile and 3270 tremolite fibres were identified; in both cohorts tremolite predominated and fibre dimensions were closely similar. Lung fibre concentrations were analysed statistically (a) in 32 paired subjects matched for duration of employment and time from last employment to death and (b) in 136 subjects stratified by the same time variables. Both analyses indicated that the Quebec/Charleston ratios for chrysotile fibre concentration in lung tissue were even higher than the corresponding ratios of estimated exposure intensity (mpcf). After allowance for the fact that regression analyses suggested that the proportion of tremolite in dust was probably 2.5 times higher in Thetford Mines, Quebec, than in Charleston, the results from both matched pair and stratification analyses of tremolite fibre concentrations in lung were almost the same as for chrysotile. It is concluded that neither fibre dimensional differences nor errors in estimation of exposure can explain the higher risks of lung cancer observed in asbestos textile workers. The possible co-carcinogenic role of mineral oil used in the past in asbestos textile plants to control dust provides an alternative hypothesis deserving consideration.
PMCID: PMC1009750  PMID: 2539184
8.  Health of vermiculite miners exposed to trace amounts of fibrous tremolite. 
A small cohort of 194 men with low exposure to fibrous tremolite (mean 0.75 f/ml y) in the mining and milling of vermiculite in South Carolina experienced 51 deaths 15 years or more from first employment. The SMR (all causes) was 1.17 reflecting excess deaths from circulatory disease. There were four deaths from lung cancer and 3.31 expected (SMR 1.21, 95% CI 0.33-3.09). Three of the four deaths were in the lowest exposure category (less than 1 f/ml y); no death was attributed to mesothelioma or pneumoconiosis. These findings contrast with those in Montana where the vermiculite ore was heavily contaminated with fibrous tremolite. A radiographic survey of 86 current and recent South Carolina employees found four with small parenchymal opacities (greater than or equal to 1/0) and seven with pleural thickening. These proportions were not higher than in a non-exposed group and much lower than had been observed in Montana. Examination of sputum from 76 current employees showed that only two specimens contained typical ferruginous bodies, confirming low cumulative fibre exposure. Any possible adverse effects of work with vermiculite, minimally contaminated with fibrous or non-fibrous tremolite, were thus beyond the limits of detection in this workforce.
PMCID: PMC1009667  PMID: 2846033
9.  Congenital defects and work in pregnancy. 
The risk of congenital defect was examined in 47,913 pregnancies of women employed for 15 hours a week or more at time of conception. The rate of defects of all types per 1000 births in this series was 25.0; 1.8 from defects classified as chromosomal (group A), 10.8 as developmental (group B), and 12.5 as musculoskeletal (group C). Some evidence of an excess in the risk ratio (p less than 0.05) was found in the services sector and in four occupations--agriculture and horticulture (2.61), telephone and postal clerks (1.74), a miscellaneous group of service jobs (1.68), and receptionists and information clerks (1.47); excesses of lower statistical significance (p less than 0.1) were found in those engaged in plastics and rubber manufacture (2.02) and in child minders (1.84). There were two cases of tracheo-oesophageal fistula--a rare defect--among eight defects (1.32 expected) in agriculture and horticulture. Overall, the distribution of risk ratios in the 60 occupations examined was not significantly heterogeneous. Analysis of chemical exposure profiles for each occupational group showed no evidence of any increased risk, perhaps due to lack of sensitivity and discrimination in this method of exposure estimation. In 152 pregnancies of doctors and nurses who had administered antineoplastic drugs in the first month eight defects, miscellaneous in type, were observed compared with 4.05 expected (p = 0.05). Special study of musculoskeletal defects and work demands showed some evidence of an association with a long working week (greater than or equal to 46 hours) but no other ergonomic factor. With these few exceptions the survey failed to identify appreciable risk of congenital defect related to occupation.
PMCID: PMC1009659  PMID: 3179232
10.  Work and pregnancy. 
PMCID: PMC1009658  PMID: 3052569
11.  Work with visual display units in pregnancy. 
Data from the Montreal survey on occupational factors in pregnancy were used to test the hypothesis that visual display units (VDUs) constitute a hazard to reproduction. Use of a VDU was recorded in 4712 current and 2164 previous pregnancies of women in full time employment at time of conception. After allowance for seven confounding variables, the risk of spontaneous abortion in current pregnancies relative to all working women was 1.19 (90% CI 1.09-1.30) and in previous pregnancies, 0.97. In an analysis by occupational title, in which 60 occupational groups were aggregated into eight categories according to use of VDUs, the relative risk for spontaneous abortion was 1.06 (90% CI 0.8-1.4) in current pregnancies and 1.01 (90% CI 0.7-1.3) in previous pregnancies. This suggests that the small excess of spontaneous abortions among individual women reporting the use of VDUs in current pregnancies may have been due to recall bias. Relative risks for stillbirth, preterm birth, and low birth weight all had 90% confidence limits which included unity. In an analysis of congenital defects the number of pregnancies was increased to include women who worked 15 or more hours a week. In all but one of nine groups of congenital defect examined confidence limits for the relative risk included unity in both current and previous pregnancies. The relative risks for the renal urinary group of defects were raised in both current (1.84, 90% CI 1.07-3.15) and previous pregnancies (1.66, 90% CI 0.82-3.25). There being no prior reason to suspect a causal link with this type of defect, interpretation remains open to question.
PMCID: PMC1009643  PMID: 3415916
12.  Fetal death and work in pregnancy. 
The relation between spontaneous abortion (n = 5010), stillbirth without congenital defect (n = 210), and working conditions was analysed in 22,613 previous pregnancies of 56,067 women interviewed, 1982-4, immediately after termination of their most recent (current) pregnancy. The 22,613 previous pregnancies were those in which at time of conception the women were employed 30 or more hours a week. Ratios of observed (O) to expected (E) fetal deaths after allowance by logistic regression for seven non-occupational confounding variables were calculated at four stages of pregnancy in 60 occupational groups and six main sectors for women whose work entailed various physical demands, environmental conditions, and exposure to chemicals. The O/E ratios for abortion were raised in the sales sector (1.13, p less than 0.05) and services sector (1.11, p less than 0.01) and for stillbirth in the sales sector (1.50, p less than 0.1). Substantially increased O/E ratios for late but not early abortion were found in operating room nurses (2.92, p less than 0.05), radiology technicians (3.82, p less than 0.01), and employees in agriculture and horticulture (2.40, p less than 0.05); in all categories the O/E ratio for stillbirth were also raised but only significantly (5.55, p less than 0.01) in the latter group. The O/E ratio for stillbirth was also raised in leather manufacture (3.09, p less than 0.01). In both individual and grouped analysis (the latter undertaken to minimise the possible effect of recall bias) significantly increased O/E ratios for abortion were found in women exposed to various high levels of physical stress, particularly weight lifting, other physical effort, and standing (p less than 0.01). Increased ratios for stillbirth at this level of significance (p less than 0.01) were found for other physical effort and vibration. Noteworthy chemical exposure was identified only in the health, services, and manufacturing sectors; the O/E ratio for stillbirth approached two in women exposed to solvents, almost all in manufacturing (p less than 0.01). In the latter sector exposed to solvents was also associated with an approximately 20% increase in abortion ratio at similar probability level.
PMCID: PMC1007961  PMID: 3348991
13.  Prematurity and work in pregnancy. 
The frequency of low birth weight (less than or equal to 2500 g) and of preterm birth (less than 37 weeks) was studied in 22,761 single live births in relation to maternal employment, taking account of 11 nonoccupational confounding factors. There was some increase of low statistical significance in both types of prematurity in service and manufacturing sectors of industry. A substantial excess of preterm births was seen in women employed in food and beverage service (O/E = 1.29, p = 0.03) and psychiatric nursing (O/E = 2.47, p less than 0.01) and of low birth weight in food and beverage service (O/E = 1.30, p = 0.02), in chambermaids and cleaners (O/E = 1.42, p = 0.03), and in those employed in the manufacture of metal and electrical and certain other goods (O/E = 1.57, p less than 0.01). Heavy lifting and long hours of work were consistently related to both outcomes, changing shift work less consistently. Noise was associated with low birth weight in the health and manufacturing sectors. The findings of this study are unlikely to have resulted from subject or observer bias but the role of unidentified factors related to selection for work are difficult to assess.
PMCID: PMC1007945  PMID: 3342188
14.  Chemical exposures at work in early pregnancy and congenital defect: a case-referent study. 
Three hundred and one women who in their most recent pregnancy had given birth to an infant with an important congenital defect were individually matched with 301 women whose children were normal. Both cases and referents were drawn from a comprehensive survey of pregnancies in Montreal, 1982-4, and limited to women employed 30 or more hours a week until at least the 13th week of gestation. Occupational exposure to chemicals was investigated and the results classified without knowledge of case-referent status. In matched pair analysis the overall frequency of chemical exposure was higher in cases than referents (63:47), due to excesses in the cardiac and miscellaneous defect groups (ratios of 10:5 and 15:7 respectively). In analyses by nine chemical categories only exposure to aromatic solvents showed a clear excess (18:8; p approximately equal to 0.04), most evident in the urinary tract group (9:0). A comparison of cases and referents exposed to aromatic solvents showed that most of the excess was associated with toluene; the defects were varied but predominantly renal-urinary or gastrointestinal.
PMCID: PMC1007871  PMID: 3651351
15.  Occupation and pregnancy outcome. 
Over a two year period, 1982-4, 56067 women, delivered or treated for a spontaneous abortion in 11 Montreal hospitals covering 90% of such admissions, were interviewed in detail regarding their occupational, social, and personal characteristics in their most recent and past pregnancies--104,649 in all. These data were analysed in relation to four main adverse outcomes--spontaneous abortion, stillbirth (without defect), congenital defect, and low birth weight (less than or equal to 2500 g). For comparison with observed numbers, expected figures were calculated by logistic regression using up to eight potentially confounding variables. Sixty occupational groups in six main industrial sectors were examined in current and previous pregnancies, with tests for heterogeneity between these two estimates of risk. Women in managerial, health, and clerical sectors had little evidence of excess of any of the four outcomes, by contrast with those in sales, service, and manufacturing sectors. Substantial and statistically significant excesses of spontaneous abortion were observed in nursing aides, women in sales occupations and food and beverage service; of stillbirth in agriculture and horticulture, leatherwork, and certain sales occupations; of congenital defects in women in child care, certain service occupations, and the manufacture of metal and electrical goods; and of low birth weight in chambermaids, cleaners, and janitors, and in women employed in the manufacture of food and drink, metal and electrical goods, and clothing.
PMCID: PMC1007870  PMID: 3651350
16.  Cohort study of mortality of vermiculite miners exposed to tremolite. 
A cohort of 406 men employed before 1963 for at least one year in a vermiculite mine in Montana was followed up until July 1983. The vermiculite ore as fed to the mill contained 4-6% of amphibole fibre in the tremolite series. Vital status was established in all but one of the 406 and death certificates were obtained and coded for 163 of the 165 men who died. Compared with white men in the United States, the cohort experienced excess mortality from all causes (SMR 1.17), respiratory cancer (SMR 2.45), non-malignant respiratory disease (SMR 2.55), and accidents (SMR 2.14). Four deaths were from malignant mesothelioma (proportional mortality 2.4%). Compared with Montana death rates, the SMR for respiratory cancer was somewhat higher (3.03). Man-year analyses of respiratory cancer and estimated cumulative exposure gave a relation that did not depart significantly from linearity. The results of this and case-referent analyses indicate an increased risk of mortality from respiratory cancer in this cohort of about 1% for each fibre year of exposure. In relation to estimated exposure the mortality experienced by the cohort from both lung cancer and mesothelial tumours was higher than in chrysotile mining.
PMCID: PMC1007682  PMID: 3013278
17.  Dust exposure and mortality in an American chrysotile asbestos friction products plant. 
Cohort studies in three American asbestos factories were undertaken to investigate the effect of fibre type and manufacturing process on lung cancer, mesothelioma, and asbestosis. Reports have been published on a chrysotile textile plant in South Carolina and a mainly textile plant in Pennsylvania, which also used amphiboles. In the third plant in Connecticut friction products and packings were made from chrysotile only. In a cohort of 3641 men employed for one month or more, 1938-58, 3513 (96.5%) were traced, 1267 (36%) had died, and death certificates were obtained for 1228 (96.9%). Individual exposures were estimated (in mcpf . years) from impinger measurements. Life table analyses using Connecticut mortality rates gave an SMR for all causes of 108.5 (USA 107.9). The SMR (all causes) for men who had worked for less than a year was 129.9 and for those who had worked for a year or more, 101.2. The equivalent SMRs for respiratory cancer were 167.4 and 136.7 respectively. Excluding men who had worked for less than a year, there was possible evidence of some increase in risk of lung cancer with increasing exposure, supported also by a "log-rank" (case-control) analysis, of the same order as that observed in chrysotile mining and milling. These findings may be compared with chrysotile textile manufacture where the risk of lung cancer was some 50-fold greater. It is suggested that the differences in risk are perhaps related to the higher proportion of submicroscopic fibres in textile manufacture that may result from the traumatic carding , spinning, and weaving processes. No case of mesothelioma was found, consistent with a much lower risk of this tumour with chrysotile than with amphiboles. Twelve deaths (nine in men with very short and low asbestos exposure) were given ICD code 523 (pneumoconiosis); all but two were ascribed to anthracosilicosis or silicosis and none to asbestosis.
PMCID: PMC1009276  PMID: 6326794
18.  Dust exposure and mortality in an American factory using chrysotile, amosite, and crocidolite in mainly textile manufacture. 
This report describes the second in a series of three parallel cohort studies of asbestos factories in South Carolina, Pennsylvania, and Connecticut to assess the effects of mineral fibre type and industrial process on mortality from malignant mesothelioma, respiratory cancer, and asbestosis. In the present plant (in Pennsylvania) mainly chrysotile, with some amosite and a small amount of crocidolite, were used primarily in textile manufacture. Of a cohort of 4137 men comprising all those employed 1938-59 for at least a month, 97% were traced. By the end of 1974, 1400 (35%) had died, 74 from asbestosis and 70 from lung cancer. Mesothelioma was mentioned on the certificate in 14 deaths mostly coded to other causes. All these deaths occurred after 1959, and there were indications that additional cases of mesothelioma may have gone unrecognised, especially before that date. The exposure for each man was estimated in terms of duration and dust concentration in millions of dust particles per cubic foot (mpcf) from available measurements. Analyses were made both by life table and case referent methods. The standardised mortality ratio for respiratory cancer for the whole cohort was 105.0, but the risk rose linearly from 66.9 for men with less than 10 mpcf.y to 416.1 for those with 80 mpcf.y or more. Lines fitted to relative risks derived from SMRs in this and the textile plant studied in South Carolina were almost identical in slope. This was confirmed by case referent analysis. These findings support the conclusion from the South Carolina study that the risk of lung cancer in textile processing is very much greater than in chrysotile production and probably than in the friction products industry. The much greater risk of mesothelioma from exposure to processes in which even quite small quantities of amphiboles were used was also confirmed.
PMCID: PMC1009208  PMID: 6313033
19.  Dust exposure and mortality in an American chrysotile textile plant. 
Three parallel cohort studies of asbestos factory workers were undertaken to investigate the effects of mineral fibre type and industrial process on malignant mesothelioma, respiratory cancer, and asbestosis. This report describes the mortality of a cohort of 2543 men, defined as all those employed for at least a month from 1938 to 1958 in a textile plant in South Carolina in which chrysotile was the only type of asbestos used. Of these, 863 men (34%) had died before 31 December 1977, one from malignant mesothelioma. Twenty one deaths were ascribed to asbestosis and 66 to cancer of the lung. Compared with the number expected from South Carolina, there was an excess of 30 deaths from respiratory cancer (ICD 160-164) in men 20 or more years after first employment (SMR 199.5). In men employed five years or more, no SMRs for this category rose above 300. Individual exposures were estimated (in mpcf X years) from recorded environmental measurements. Life table analyses and "log-rank" (case-control) analyses both showed a steep linear exposure-response that was some 50-fold greater at similar accumulated dust exposures than in Canadian chrysotile mining and milling. These findings agree closely with those from another study in this plant and confirm that mesothelioma is rarely associated with chrysotile exposure. Cigarette smoking habits did not greatly differ between the textile workers and the Canadian miners and millers. The far greater risk of lung cancer in the textile industry, if not attributable to other identified cocarcinogens, may be related to major differences in the size distribution of fibres in the submicroscopic range which are not detected by the usual fibre or particle counting procedures.
PMCID: PMC1009207  PMID: 6313032
20.  Dust exposure and mortality in chrysotile mining, 1910-75. 
We report a further follow-up of a birth cohort of 11 379 workers exposed to chrysotile. The cohort consisted of 10 939 men and 440 women, born 1891-1920, who had worked for at least a month in the mines and mills of Asbestos and Thetford Mines in Quebec. For all subjects, length of service and estimates of accumulated dust exposure were obtained, with a smoking history for the vast majority. Three methods of analysis, two based on the "man-years" methods, the other a "case-and-multiple-controls" approach, gave results consistent with one another and with previous analyses. By the end of 1975, 4463 men and 84 women had died. Among men, the overall excess mortality, 1926-75 was 2% at Asbestos and 10% at Thetford Mines, much the dustier region. The women, mostly employed at Asbestos, had a standardised mortality ratio (SMR) all causes, 1936-75) of 0.90. Analysis of deaths 20 years or more after first employment showed that in men with short service (less than five years) there was no discernible correlation with dust exposure. Among men employed at least 20 years, there were clear excesses in those exposed to the heaviest dust concentrations. Reanalysis in terms of exposure to age 45 showed definite and consistent trends for SMRs for total mortality, for lung cancer, and for pneumoconiosis to be higher the heavier the exposure. The response to increasing dose was effectively linear for lung cancer and for pneumoconiosis. Lung cancer deaths occurred in non-smokers, and showed a greater increase of incidence with increasing exposure than did lung cancer in smokers, but there was insufficient evidence to distinguish between multiplicative and additive risk models. There were no excess deaths from laryngeal cancer, but a clear association with smoking. Ten men and one woman died from pleural mesothelioma. If the only subjects studied had been the 1904 men with at least 20 years' employment in the lower dust concentrations, averaging 6.6 million particles per cubic foot (or about 20 fibres/cc), excess mortality would not have been considered statistically significant, except for pneumoconiosis. The inability of such a large epidemiological survey to detect increased risk at what, today, are considered unacceptable dust concentrations, and the consequent importance of exposure-response models are therefore emphasised.
PMCID: PMC1008640  PMID: 7370189

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