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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.  Psychiatric disorders and occupational exposure to solvents. 
Three hundred and eighty one men admitted to hospital for the first time with any psychiatric diagnosis were individually matched for age and year to patients admitted to general hospitals. An occupational history was obtained from 90% of this study group by telephone interview or mail. Exposure to solvents was assessed by three methods, individual rating of each job recorded, application of an exposure matrix based on job title, and assessment of lifetime job histories of selected case-referent pairs. A sample of individual ratings used in the analysis was compared with ratings made by five experts. The panel values tended to be lower but all six sets of ratings correlated well. There was no increased risk of psychiatric illness among subjects exposed to moderate or greater solvent concentrations for at least 10 years (odds ratio (OR) 1.0, 90% confidence interval (90% CI) 0.7-1.4, individual rating; OR 1.1, 90% CI 0.6-2.0, job title matrix; OR 0.9, 90% CI 0.5-1.7, lifetime assessments). At higher exposures the risk was increased--although not to a statistically significant degree--especially for cases with non-psychotic diagnoses (ICD-9 codes 300-316). This negative result, by all three methods of assessment of exposure, contrasted with that from a parallel investigation of cases of organic psychoses and cerebral degeneration.
PMCID: PMC1061210  PMID: 1472438
6.  Organic brain damage and occupational solvent exposure. 
Three hundred and nine men with organic dementia, cerebral atrophy, or psycho-organic syndrome admitted for five nights or more to one of 18 Quebec hospitals were individually matched with patients admitted (1) with some other psychiatric diagnosis and (2) to a general hospital. Lifetime occupational histories were obtained by telephone. Occupational exposure to solvents was assessed blind to type of case by (1) individual ratings and (2) a job exposure matrix; men who worked in moderate or high solvent concentrations for at least 10 years were considered exposed. With the psychiatric referent series, an odds ratio of 1.4 (90% CI 1.0-2.0) was calculated by individual exposure ratings and 1.4 (90% CI 0.9-2.2) by job matrix. Increased risk was mainly in those with organic dementia or cerebral atrophy and an alcohol related diagnosis. The same pattern of risk was found against the general hospital referents. Adjustment for possible confounders did not alter the risk estimates appreciably. Also, lifetime job histories, compared in selected case-referent pairs, gave similar evidence of increased risk (odds ratio 2.3; 90% CI 1.0-5.5). It is concluded that the combined effect of occupational solvent exposure and alcohol intake is probably an important cause of organic brain damage.
PMCID: PMC1039325  PMID: 1463678
7.  Risk assessment using exposure intensity: an application to vermiculite mining. 
Estimation of exposure-response relations from epidemiological data is complicated by the fact that exposures usually vary in intensity over time. Cumulative exposure indices, which do not separate the effects of intensity and duration, are commonly used to circumvent this problem. In this paper the estimation of relative risk for specific ranges of exposure intensity from such data is considered using existing statistical methods for fitting multivariate relative risk models. This has the advantage that it does not assume that exposure intensity and duration have equivalent effects on risk. It also throws light on the possible existence of a threshold. The procedure was applied to data from a cohort of 406 vermiculite miners to examine the lung cancer risk associated with exposure to fibrous tremolite, which contaminated the vermiculite. The pattern of exposure-response differed substantially from that obtained using a cumulative exposure index to assess risk.
PMCID: PMC1035416  PMID: 1878311
8.  Occupational respiratory disease in the United Kingdom 1989: a report to the British Thoracic Society and the Society of Occupational Medicine by the SWORD project group. 
A voluntary scheme for the surveillance of work related and occupational respiratory disease (SWORD) was established in January 1989 with help from the British Thoracic Society and the Society of Occupational Medicine and support from the Health and Safety Executive. Three hundred and fifty four chest physicians representing 90% of the chest clinics in the United Kingdom and 361 occupational physicians submit reports regularly of newly diagnosed cases of work related respiratory illness with information on age, sex, residence, occupation, and suspected causal agent. In 1989 2101 cases were notified, of which frequent diagnoses were asthma (26%), mesothelioma (16%), pneumoconiosis (15%), benign pleural disease (11%), and allergic alveolitis (6%). Incidence rates calculated against denominators from the Labour Force Survey showed very large differences between occupational groups, especially for asthma and asbestos related diseases. Substantial regional variation in the incidence of asthma was not explained by the geographical distribution of high risk industries and was probably due to differing levels of ascertainment. The results imply that the true frequency of acute occupational respiratory disease in the United Kingdom may have been three times greater than that reported.
PMCID: PMC1012037  PMID: 2039741
9.  Occupational health at the London School of Hygiene & Tropical Medicine. 
The London School of Hygiene and Tropical Medicine, founded in 1929 to study all aspects of public health, set up an occupational health unit in 1956 funded by the Rockefeller Foundation. With financial aid from the Trades Union Congress it expanded into an institute with an information and advisory service. Employers and trade unions sought advice on health problems which led to research projects and enriched teaching. Postgraduate courses in occupational medicine and hygiene attracted many students from all over the world. If the threat to close the institute takes place it will deprive the western world of a major centre for teaching and research in occupational health.
PMCID: PMC1035116  PMID: 2178674
10.  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
11.  Silica, silicosis, and lung cancer. 
PMCID: PMC1009770  PMID: 2546576
12.  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
13.  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
14.  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
15.  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
17.  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
18.  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
19.  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
20.  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
21.  Radiological survey of past and present vermiculite miners exposed to tremolite. 
Chest radiographs taken by a standard technique were obtained from 173 current employees (164 men, 9 women) of a vermiculite mine in Montana, from 80 of 110 past employees resident within 200 miles, and from 47 men from the same area without known exposure to dust. In 43 of the 80 and 24 of the 47 an earlier chest x ray film was retrieved from the hospital archives. All 367 films were assessed blind and independently by three experienced readers using the ILO 1980 classification. Median radiographic assessment scores were analysed in relation to estimated cumulative exposure to the amphibole fibres that contaminate the vermiculite. Logistic regression analyses showed independent effects of age, smoking, and exposure on the prevalence of small opacities and of age and probably of exposure on pleural thickening. Overall, the data suggest that by retirement age the increase in prevalence of small opacities (greater than or equal to 1/0) lies between 5% and 10% per 100 f/ml years. This gradient may be somewhat steeper than for chrysotile miners and millers, but not much so.
PMCID: PMC1007683  PMID: 3013279
22.  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.
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PMCID: PMC1007682  PMID: 3013278
23.  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
24.  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
25.  Radiological findings as predictors of mortality in Quebec asbestos workers. 
Two cohorts of chrysotile miners and millers in Quebec were selected to study the extent to which chest radiographs taken while still employed predict mortality. The paper presents mainly findings in much the larger cohort, which consisted of 4559 men (two-thirds past workers) whose latest radiograph had been assessed by one of six experienced readers into what became the UICC/Cincinnati (U/C) classification; by the end of 1975 there had been 1543 deaths in this cohort. The findings were generally confirmed in the other cohort, comprising 988 current male workers, who had been examined in 1967-8 by questionnaires on respiratory symptoms and smoking and by lung function tests, and for whom all six readers had assessed their 1966 radiographs into the U/C classification; 130 men had died by the end of 1975. Men with any radiographic abnormality, heavy dust exposure, or a history of cigarette smoking had relative risks (RRs) of total mortality greater than unity. Death from pneumoconiosis was associated with small parenchymal opacities, usually irregular, of profusion l/l or more, and with heavy dust exposure but not with smoking. Most who died from lung cancer had smoked cigarettes, or had been heavily exposed to dust, or both. Small parenchymal opacities were present in most but not all the excess deaths due to lung cancer. Deaths from other malignant diseases showed no consistent dust or x-ray patterns. RRs of deaths from most other causes were raised for certain radiographic features. Failures in forecasting mortality were primarily due to deaths in which asbestos-related disease was not the primary cause but may have been a contributing factor. The main findings validated the U/C classification convincingly, particulary as the films had been taken as routine and were of modest quality. Despite objective rules for the reading and the fact that all six readers were contributing to the development of the classification, there was inevitably some observer variation. The importance of radiographic technique and the need for careful control of the reading is evident. Our results provide support for the use of the chest radiograph for surveillance of asbestos workers, and for environmental monitoring. Its protective value for individual workers, however, is limited to the extent that radiological progression continues after withdrawal from exposure, and by the carcinogenic risk associated with dust already retained.
PMCID: PMC1008705  PMID: 7426477

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