Gilles Theriault

Mortality and cancer morbidity in a cohort of Canadian petroleum workers

Aims: To assess mortality and cancer morbidity in Canadian petroleum workers and explore exposure-response relations for specific petroleum agents. Methods: A total of 25 292 employees hired between 1964 and 1994 were linked to the Canadian tumour registry and national mortality database. Exposure-response trends were assessed for hydrocarbon solvents/fuels, hydrocarbon lubricants, petroleum coke/spent catalyst, and hydrogen sulphide (H2S). Results: External comparison analyses (mortality and incidence) showed deficits for all causes and all malignant neoplasms combined and were consistent with expectation for most malignant and non-malignant sites analysed. Gall bladder cancer mortality was increased among males based on four deaths, but cases had no common job assignments and the increase was focused in workers employed <10 years. Mesothelioma incidence was increased. Most exposure-specific analyses were compromised by small numbers. Statistically significant increases were observed for H2S exposure and a subgroup of accidental deaths as well as for petroleum coke/spent catalyst exposure and lung cancer. While both findings have a degree of biologic plausibility, the H2S association, which exhibited a clearer exposure-response pattern, could be subject to unmeasured confounders. Additionally, interpretation was complicated by the high correlation between hydrocarbon and H2S exposures. With regard to lung cancer, the analysis could not adequately control for smoking, was based on small numbers, and exhibited a tenuous exposure-response pattern. Conclusion: The findings for mesothelioma suggest the need for continued attention to asbestos in the petroleum industry. The relation between accidental deaths and H2S exposure deserves closer scrutiny in similarly exposed populations. Further analyses of lung cancer are underway and will be reported separately.

BLADDER CANCER IN THE ALUMINIUM INDUSTRY

The incidence of bladder cancer is unusually high in aluminium smelter workers. An epidemiological study showed that workers in Soderberg potrooms are at highest risk for bladder cancer, the adjusted overall relative risk being 2.39 (1.34-4.28). Exposure to polycyclic aromatic hydrocarbons, of which benz(a)pyrene (BaP) served as an indicator, seems to be the causative factor. The relative risk was evaluated at 12.38 for workers with 20 or more equivalent years of BaP exposure. Cigarette smoking contributed significantly to the appearance of bladder cancer in the population studied. There is a synergistic effect when cigarette smoking and BaP exposure are combined; the numbers in our population are too small to determine whether this interaction effect is multiplicative or additive. It is concluded that bladder cancer is associated with aluminium smelting (primarily with the Soderberg process).

Occupational rhinitis in workers investigated for occupational asthma

Background: The links between asthma and rhinitis are now referred to as united airways disease (UAD). Current evidence shows that the UAD model seems to be applicable to occupational rhinitis (OR) and occupational asthma (OA). A study was undertaken to objectively assess, in the context of specific inhalation challenge (SIC) testing, the concomitance of bronchial and nasal reaction in the investigation of OR and OA. Methods: 43 subjects with a history of work-related asthma symptoms underwent SIC for confirmation of OA and investigation of OR. Changes in bronchial calibre were measured by spirometry and nasal patency and airway inflammation were assessed by acoustic rhinometry and nasal lavage. Results: A positive nasal challenge was observed in 25 SIC tests and a positive bronchial challenge was observed in 17 SIC tests. A concomitant positive nasal and bronchial challenge was observed in 13 instances. This association was significant (risk ratio = 1.7; 95% CI 1.0 to 2.4; p = 0.04) and more frequent in subjects challenged with high molecular weight agents (n = 11/22) than with low molecular weight agents (n = 2/21). In subjects with a positive nasal challenge, nasal lavage showed a significant increase in eosinophils 30 min after exposure which correlated with changes in nasal patency. Conclusion: The results of this study provide objective evidence to support the concept of UAD using OR and OA as a model to demonstrate a significant concomitant physiological reaction of the nose and lungs after challenge. This study shows that OR can be assessed by objective means; it often coexists with OA but can be present without OA.

A mortality study of electrical utility workers in Québec.

OBJECTIVES--The objective of this study was to investigate the mortality of electrical utility workers exposed to electric and magnetic fields. METHODS--A historical cohort mortality study was carried out on 21,744 workers who were employed in an electrical company in the province of Québec between 1970 and 1988. The last job held by each study subject was coded. A job exposure matrix (JEM) was used to estimate the exposure to 60 Hz electric and magnetic fields, and pulsed electromagnetic fields (as recorded by the PEMF (POSITRON) meter) in this job. Standardised mortality ratios (SMRs) were calculated relative to Québec men. Because the exposure was exclusively among blue collar workers, the remainder of the analyses by exposure were restricted to them. Rate ratios (RRs) in the exposed groups relative to the background groups were estimated with Poisson regression. There were 1582 deaths by the end of follow up. RESULTS--SMRs were almost all below one and never substantially increased, although there were a few increased rate ratios (RRs). There was a significant RR of 2.00 (95% confidence interval (95% CI) 1.37-2.93) for deaths caused by accidents and violence in workers exposed to magnetic fields, RR of 1.82 (95% CI 1.25-2.65) for electric fields, and RR of 1.62 (95% CI 1.13-2.32) for pulsed electromagnetic fields. Occupational accidents related to power lines explain some of the excess of deaths from accidents and violence. Some association was found between magnetic fields and leukaemia, brain cancer, and suicide, between electric fields and brain cancer and suicide, and between pulsed electromagnetic fields and lung cancer, but these were not significant. CONCLUSION--These results are broadly reassuring that major causes of death are not strongly associated with exposure to electric and magnetic fields, but small numbers and approximate exposure assessments preclude the denial of any risk, in particular if it were to affect a rare cause of death.

Comparative analyses of the studies of magnetic fields and cancer in electric utility workers: studies from France, Canada, and the United States.

OBJECTIVES: To summarise and to facilitate comparison of three major studies of electric utility workers that examined the relation between quantitative measurements of occupational exposure to magnetic fields and risk of brain cancer and leukaemia. These studies have been interpreted as providing conflicting evidence. METHODS: A common analytical approach was applied to data from the five cohorts included in the three studies based on original data from four of the cohorts, and published data from one additional cohort. A nested case-control design with conditional logistic regression was used to estimate the relative risk/10 microtesla-years (microT-years) for each of the contributing cohorts and for the combined data. The homogeneity of these estimates among the studies was also evaluated. RESULTS: Apparent inconsistencies in the findings of these studies can be explained by statistical variation. Overall, the studies suggest a small increase in risk of both brain cancer and leukaemia. Different methodological choices had little impact on the results. Based on a combined analysis of data from all five studies, the relative risk/10 microT-years was 1.12 (95% confidence interval (95% CI) 0.98 to 1.28) for brain cancer, and 1.09 (95% CI 0.98 to 1.21) for leukaemia. CONCLUSIONS: The combined estimates seem to provide the best summary measures of the data from all studies. However, fluctuations in risks among studies may reflect real differences, and the exposure measurements in different studies may not be entirely comparable.

Updated mortality among diverse operating segments of a petroleum company

OBJECTIVES To update mortality for 34 560 employees from diverse operating segments of a Canadian petroleum company; and to investigate potential relations with occupational factors. METHODS Employees from 1964–83 were linked to the Canadian mortality data base to provide 11 years additional follow up. There were 6760 deaths and 750 683 person-years of follow up compared with 3909 and 428 190, respectively, in the earlier study. Analyses used standardised mortality ratios (SMRs) to compare worker cause specific mortality with the Canadian general population. Duration of employment and latency analyses were performed for causes previously found to be increased in this and other petroleum cohorts, as well as any findings of interest. RESULTS For the period 1964–94, employees experienced significantly low overall mortality (SMR=0.86 men, SMR=0.80 women). Kidney cancer, which has been increased in some studies of petroleum workers, was not increased. Acute non-lymphocytic leukaemia in exposed operating segments was consistent with the expected or only slightly, non-significantly increased. The most notable finding was increased deaths from mesothelioma among refinery and petrochemical workers (SMR 8.68; 95% confidence interval (95% CI) 5.51 to 13.03), most of whom were long term employees in jobs with presumed exposure to asbestos (mechanical and pipefitters). Deaths from multiple myeloma among marketing and distribution workers, which were previously increased, remained increased (SMR 2.08; 95% CI 0.95 to 3.95) in the update period 1984–94; however, there was no clear pattern by duration of employment or latency. Aortic aneurysms, which also were previously significantly increased among marketing and distribution workers approached the expected in the update period (SMR 1.18; 95% CI 0.65–1.98). Analyses by duration of employment showed suggestive trends for aortic aneurysms, but earlier studies of this cohort have not found a relation between aortic aneurysms and exposure to hydrocarbons. CONCLUSION The additional 2851 deaths and 322 493 person-years of follow up strengthened the assessment of mortality patterns relative to occupational factors. With the exception of mesothelioma, no clear work related increases in disease were identified.

Risk of bladder cancer in foundry workers: a meta-analysis

To clarify the inconsistent reports of bladder cancer risk in foundry workers, a meta-analytic review of epidemiological studies was undertaken. Summary risk estimates (SRE) were calculated from 40 systematically extracted results. Weakly increased risks were observed overall, with an SRE of 1.11. Twenty three selected study results with better exposure information yielded an SRE of 1.16. This weak increase in risk is consistent with estimates obtained from dose-response trends of PAH exposures in aluminium smelter workers. Summary estimates did not vary substantially with exposure quality, study design, control for smoking, or when limiting the meta-analysis to large study results. Exposure-response findings showed significantly increased risks of about 1.6 to 1.7 after 20 or more years of employment, but this was based on few studies. Occupation specific SREs showed a 40–50% increased risk among moulders, casters, and unskilled foundry labourers. There was limited evidence that bladder cancer risk correlated with lung cancer risk, which is a more established risk among foundry workers. The small increased risk observed is prone to bias and confounding. Further studies of dose-response trends would greatly aid in determining whether this observed association is causal.

A case cohort study of suicide in relation to exposure to electric and magnetic fields among electrical utility workers

OBJECTIVES--This case cohort study examines whether there is an association between exposure to electric and magnetic fields and suicide in a population of 21,744 male electrical utility workers from the Canadian Province of Québec. METHODS--49 deaths from suicide were identified between 1970 and 1988 and a subcohort was selected comprising a 1% random sample from this cohort as a basis for risk estimation. Cumulative and current exposures to electric fields, magnetic fields, and pulsed electromagnetic fields (as recorded by the POSITRON meter) were estimated for the subcohort and cases through a job exposure matrix. Two versions of each of these six indices were calculated, one based on the arithmetic mean (AM), and one on the geometric mean (GM) of field strengths. RESULTS--For cumulative exposure, rate ratios (RR) for all three fields showed mostly small non-significant increases in the medium and high exposure groups. The most increased risk was found in the medium exposure group for the GM of the electric field (RR = 2.76, 95% CI 1.15-6.62). The results did not differ after adjustment for socioeconomic state, alcohol use, marital state, and mental disorders. There was a little evidence for an association of risk with exposure immediately before the suicide. CONCLUSION--Some evidence for an association between suicide and cumulative exposure to the GM of the electric fields was found. This specific index was not initially identified as the most relevant index, but rather emerged afterwards as showing the most positive association with suicide among the 10 indices studied. Thus the evidence from this study for a causal association between exposure to electric fields and suicide is weak. Small sample size (deaths from suicide) and inability to control for all potential confounding factors were the main limitations of this study.

LUNG CANCER MORTALITY AND SILICOSIS IN QUEBEC, 1938-85

Men who had received compensation for silicosis in Québec between 1938 and 1985 were studied up to the end of 1986 to estimate risk of lung cancer mortality. Particular attention was paid to selection biases inherent in the study of such workers. Age-specific and calendar-year-specific mortality rates of Québec men from 1931 to 1985 were used for comparison. Risk of death from lung cancer in men who had received compensation for silicosis was more than 3 times higher than expected; silicosis may be a strong risk factor for lung cancer mortality.

Lung cancer in relation to employment in the electrical utility industry and exposure to magnetic fields.

OBJECTIVES: A recent study found that lung cancer may be associated with exposures encountered in the electrical utility industry. To further evaluate this possibility, data were collected and analysed from five large electrical utility companies in the United States. METHODS: A cohort of 138905 male workers employed between 1950 and 1986 was followed up for mortality to the end of 1988, with 20733 deaths identified of which 1692 were due to lung cancer. Mortality from lung cancer was examined in relation to the duration of employment in specific jobs thought to have high exposure to 60 Hz magnetic fields and to an index of cumulative exposure to magnetic fields based on personal measurements. Exposure to pulsed electromagnetic fields (PEMFs) as estimated from another study was also considered. Poisson regression generated rate ratios for categories of exposure based on comparisons within the cohort adjusted for age, calendar year, race, socioeconomic status, work status, and estimated exposure to asbestos. RESULTS: Mortality rose modestly with duration of work as an electrician or power plant operator reaching rate ratios of 1.4 with > or = 20 years in those jobs but not with duration of work as a lineman or a combination of jobs thought to have high exposures to 60 Hz magnetic fields or PEMFs. Cumulative indices of exposure to 60 Hz magnetic fields and PEMFs were both associated with rate ratios of 1.2-1.3 in the highest intervals. CONCLUSIONS: These data suggest that lung cancer is not strongly associated with duration of employment in specific jobs associated with high potential exposure to 60 Hz magnetic fields or to PEMFs. Small associations of lung cancer with indices of both 60 Hz magnetic fields and PEMFs leave open the possibility that larger associations have been diluted through exposure misclassification. Refined exposure assessment, especially to PEMFs, would be required to evaluate that possibility.