Occupational exposure to magnetic fields relative to mortality from brain tumours: updated and revised findings from a study of United Kingdom electricity generation and transmission workers, 1973-97

OBJECTIVE—To investigate whether risk of brain tumour is related to occupational exposure to magnetic fields.
METHODS—The mortality experienced by a cohort of 83 997 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-97. All workers were employed for at least 6 months with some employment in the period 1973-82. Computerised work histories were available for 79 972 study subjects for the period 1971-93. Detailed calculations had been performed by others to enable a novel assessment to be made of exposures to magnetic fields. Two analytical approaches were used, indirect standardisation (n=83 997) and Poisson regression (n=79 972).
RESULTS—Based on serial mortalities for England and Wales, deaths from brain cancer were close to expectation (observed 158, expected 146.4). No significant positive trends were shown for risks of brain tumours either with lifetime cumulative exposure to magnetic fields or with such exposures received in the most recent 5 years.
CONCLUSIONS—There are no discernible excess risks of brain tumours as a consequence of occupational exposure to magnetic fields in United Kingdom electricity generation and transmission workers.


Keywords: magnetic fields; brain tumours; electricity generation and transmission; cohort mortality study     

A method for assessing occupational exposure to power-frequency magnetic fields for electricity generation and transmission workers.

A new method for assessing both current and historical occupational exposures to magnetic fields has been developed and used in health studies involving a cohort of electricity generation and transmission workers in England and Wales. The exposure values are derived by calculation from engineering and operational data about the power stations rather than from measurements. They are provided for each of 11 job categories for each year of operation of each power station represented in the cohort. The engineering data are used to determine the average magnetic fields in specified areas of work within the power station and then applied to information about the time spent in these areas by each of the job categories. The operational data are used to adjust the exposures for each year according to the power station output for the year. Earlier methods used measurements or the advice of panels of experts to provide exposure scores for a number of job categories across all power stations and years. Such methods were not able to distinguish exposures from different power facilities or during the different years of their operation. Measurement surveys at 10 power stations of the magnetic fields in the work areas gave confidence that the calculations were realistic. Exposure measurements on 215 workers at three power stations were compared in job groups with the exposures predicted by the method. The Pearson correlation coefficient was 0.86 and the slope and intercept of the line of best fit were 0.87 and 0.07 microT respectively. The method gives a good prediction of measured exposure and is being used for studies of occupational exposure to magnetic fields and leukaemia, and of cardiovascular disease, and a reanalysis of brain cancer.     

Leukaemia mortality in relation to magnetic field exposure: findings from a study of United Kingdom electricity generation and transmission workers, 1973-97

OBJECTIVE—To investigate whether risks of leukaemia are related to occupational exposure to magnetic fields.
METHODS—The mortality experienced by a cohort of 83 997 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-97. All employees were employed for at least 6 months with some employment in the period 1973-82. Computerised work histories were available for 79 972 study subjects for the period 1971-93. Detailed calculations were performed by others to enable a novel assessment to be made of exposures to magnetic fields. Two analytical approaches were used, indirect standardisation (n=83 997) and Poisson regression (n=79 972).
RESULTS—Based on serial mortalities for England and Wales, the standardised mortality ratio of 84 for all leukaemias (observed 111, expected 132.3) was similar to that of 83 for all causes (observed 14 845, expected 17 918). No significant positive trends were found for the risks of various types of leukaemia (chronic lymphatic leukaemia, acute myeloid leukaemia, chronic myeloid leukaemia, all leukaemia) either with lifetime cumulative exposure to magnetic fields or with such exposures received in the most recent 5 years.
CONCLUSIONS—There are no discernible excess risks of leukaemia as a consequence of occupational exposure to magnetic fields in United Kingdom electricity generation and transmission workers.


Keywords: magnetic fields; leukaemia; electricity generation and transmission; cohort mortality study     

Occupational exposure to extremely low frequency magnetic fields and mortality from cardiovascular disease

The authors evaluated the relation between occupational exposure to extremely low frequency (ELF) magnetic fields and mortality from cardiovascular diseases. The study was based on 27,790 subjects from the Swedish Twin Registry. Exposure to ELF magnetic fields was assessed by linking occupation reported in 1967 or 1973 to a job exposure matrix. Four levels of exposure were related to cause-specific mortality through 1996, and primary and contributing causes of death were considered. The authors estimated relative risks by Cox regression, with adjustment for several cardiovascular disease risk indicators. The authors calculated the synergy index to evaluate potential interaction between exposure to ELF magnetic fields (>0.2 microT) and genetic susceptibility to acute myocardial infarction (AMI). Arrhythmia-related death, ischemic heart disease other than AMI, and atherosclerosis showed no association with ELF magnetic fields. The authors found a low-level increase in AMI risk in the highest exposure group (relative risk=1.3, 95% confidence interval: 0.9, 1.9) and suggestions of an exposure-response relation (p=0.02). A synergy index of 2.7 (95% confidence interval: 1.1, 6.6) in monozygotic twins indicated that the risk of AMI was strengthened among ELF magnetic field-exposed subjects with genetic susceptibility to the disease. The results for AMI corroborate previous findings from the United States. The unusual opportunity to include genetic susceptibility in the present analyses showed that evaluations of effect modification in vulnerable subjects are warranted in ELF magnetic field research.     

Mortality from cardiovascular disease in relation to magnetic field exposure: findings from a study of UK electricity generation and transmission workers, 1973-1997

BACKGROUND: Experimental and epidemiological studies have indicated that magnetic field exposure might influence heart rate variability and consequent risks of arrhythmia related deaths. METHODS: The mortality experience of a cohort of 83,997 employees of the former Central Electricity Generating Board (CEGB) of England and Wales was investigated for the period 1973-1997. Cohort members were employed for at least 6 months from 1973 to 1982. Computerized work histories were available for 79,972 study subjects for the period 1971-1993. Detailed calculations had been performed by others to enable a novel assessment to be made of exposures to magnetic fields. Two analytical approaches were used, indirect standardization (n = 83,997) and Poisson regression (n = 79,972). RESULTS: Based on serial mortality rates for England and Wales, deaths from four categories of cardiovascular disease were below expectation: arrhythmia-related disease (ICD-9 426-7), observed (obs) 32, expected (exp) 43.5, standardized mortality ratio (SMR) 74; acute myocardial infarction (ICD-9 410), obs 3,320, exp 3878.3, SMR 86; atherosclerosis (ICD-9 440), obs 25, exp 39.2, SMR 64; chronic/sub-acute coronary disease (ICD-9 411-414), obs 1,552, exp 2021.7, SMR 77). No statistically significant trends were shown for risks of any of these four disease groupings to increase either with lifetime cumulative exposure to magnetic fields or with such exposures received in the most recent 5 years. CONCLUSIONS: There are no discernible excess risks of mortality from cardiovascular diseases as a consequence of occupational exposure to magnetic fields in UK electricity generation and transmission workers.     

Occupational sunlight exposure and mortality from non-Hodgkin lymphoma among electric utility workers.

This case-control study examined occupational sunlight exposure and death from non-Hodgkin lymphoma (NHL) and NHL subtypes among 188 cases and 1880 controls selected from a cohort of 138,905 male electric utility workers. Exposure was classified according to work history linked to indices of cumulative sunlight exposure. Odds ratios and 95% confidence intervals were derived from conditional logistic regression models and were conditioned on the matching factors birth year and ethnicity. Mortality from NHL and intermediate/high-grade lymphomas was not related to cumulative sunlight exposure, with odds ratios around the null. For low-grade lymphomas, a dose-response gradient was observed for exposure in the past 12 to 21 years, but this result seemed to be sensitive to cut points for categorization of cumulative exposure. These data do not provide evidence for an association between occupational sunlight exposure and mortality from NHL or NHL subtypes.     

Lymphoma and multiple myeloma mortality in relation to magnetic field exposure among electric utility workers

Associations between occupational magnetic field exposure and non-Hodgkin's lymphoma (NHL), Hodgkin's disease, and multiple myeloma mortality were evaluated in 138,905 electrical utility workers. A job-exposure matrix based on measured magnetic fields was used to derive individual exposure estimates. There was a small positive association between all NHL and low-grade NHL and duration of employment in any magnetic field-exposed job, but only up to 20 years. Cumulative magnetic field exposure was associated with a rising, then falling, risk of NHL. Rate ratios for intermediate/high-grade lymphoma were increased for the highest levels of lifetime cumulative exposure (RR = 3.7 and RR = 2.3), and were most pronounced for those exposures occurring 10–20 years previously. Hodgkin's disease and multiple myeloma mortality did not appear to be associated with exposure. Associations were stronger for NHL subgroups, suggesting that further analysis by subgroup may be warranted, but the absence of dose-response gradients diminishes the likelihood that associations represent causal relationships. Am. J. Ind. Med. 32:392–402, 1997. © 1997 Wiley-Liss, Inc.     

Occupational exposure to magnetic fields and brain tumours in Central Sweden

Occupations with exposure to magnetic fields were studied in a population-based case-control study of male glioma and meningioma in Central Sweden. The study included 84 cases of glioma, 20 cases of meningioma and 155 controls. Information about job titles was obtained by means of a questionnaire. Three different methods were used to classify exposure 1) 'electrical occupations', 2) assessment of magnetic fields by an electrical engineer, 3) job values based on magnetic field measurements at work sites for occupational groups. When analyses were based on 'electrical occupations' a relative risk (RR) of 1.0 (95% CI: 0.4–2.4) was seen for glioma and 1.8 (95% CI: 0.3–3.6) for meningioma. When analyses were based on measurements a relative risk of 1.9 (95% CI: 0.8–5.0) was seen for glioma and 1.6 (95% CI: 0.3–10.2) for those ever in an exposed job of an average mean value of > 0.4T. A larger number of individuals was classified as exposed, when exposure was based on measurements. Information was available regarding several potential confounders, but none of them seemed to be of any importance. Our conclusion is that the results based on magnetic field measurements give some support to the hypothesis that magnetic fields exposure may play a role in the development of brain tumours.     

Occupational sunlight exposure in relation to suicide among electric utility workers

BACKGROUND: Occupational sunlight exposure was examined in relation to death from suicide in a United States cohort of 138,905 male electric utility workers. METHODS: Case-control sampling included 536 deaths from suicide and 5,348 eligible controls randomly selected from the cohort. Exposure was classified based on work history linked to indices of cumulative sunlight exposure. RESULTS: Mortality from suicide was not associated with estimates of recent and career occupational sunlight exposure, with adjusted odds ratios around unity. Occupational sunlight exposure was positively associated with nonviolent suicides, but no dose-response gradient was observed and risk estimates were notably imprecise. CONCLUSIONS: These data provide evidence against an association between occupational sunlight exposure and mortality from suicide.     

Occupational exposure to 50 Hz magnetic fields in workers employed in various jobs

BACKGROUND: Information on occupational exposure to ELF magnetic fields (MF) in workers is largely insufficient, and is mostly based on results obtained in Scandinavian countries and North America. Accordingly, the collection of further data is needed, especially in workers exposed in other countries, including in Italy. METHODS: One hundred and fifty workers (84 males and 66 females) employed in 28 different jobs in the Emilia-Romagna Region of Italy were examined. Individual exposure was measured using personal monitors worn on the hip in a belted pouch during three whole work-shifts (8 hours each) of a normal working week. A sampling interval of 10 seconds was adopted, resulting in the collection of more than 8600 measurements for each worker. The individual Time-Weighted Average (TWA) occupational exposure of workers was calculated as the arithmetic mean of all measurements during each work-shift. Environmental non-occupational exposure was also measured. RESULTS: The 50 degrees percentile of individual TWA in the whole group was 0.15 microT, and the 5 degrees - 95 degrees percentile was respectively 0.02-1.45 microT. Job-related exposure (expressed as the mean of the TWA measured in all workers engaged in that job) was highest in substation electric power plant workers (1.12 microT) and in sewing machine workers (0.84 microT), but was lower than 0.2 microT in more than the 70% of the examined jobs. Considering the geometric mean of individual TWA are 27 out of 28 the jobs inducing an exposure lower than 0.2 microT. The lowest exposure was observed in infant school teachers. A high variability was observed among different workers engaged in the same occupation, mainly in substation electric power plant workers, machine testers and grinders in the engineering industry and in sewing machine workers and quality control in garment production. A marked variability of the pattern of exposure during the work-shift was also observed The overall environmental (non-occupational) exposure was 0.044 microT, and individual exposure was lower than 0.2 microT in about 97% of the examined subjects. Occupational exposure was usually higher and was not correlated with environmental exposure. CONCLUSIONS: The results show that the occupational component of overall exposure must be considered in studies on the biological effects of ELF-MF in populations. The high variability observed among workers engaged in the same occupation and the variability of the pattern of exposure certainly constitute major problems and could be a cause of the scarce coherence of the results of epidemiological studies on biological effects of ELF-MF to date. An improvement in protocols for the evaluation of exposure in workers, including the use of personal monitoring, is certainly needed.     

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.     

Mortality from Alzheimer's, motor neuron and Parkinson's disease in relation to magnetic field exposure: findings from the study of UK electricity generation and transmission workers, 1973-2004

Background

There are a number of reports linking magnetic field exposure to increased risks of Alzheimer''s disease and motor neuron disease.

Methods

The mortality experienced by a cohort of 83 997 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973–2004. All employees were employed for at least six months with some employment in the period 1973–82. Computerised work histories were available for 79 972 study subjects for the period 1971–93. Information on job and facility (location) were used to estimate exposures to magnetic fields. Two analytical approaches were used to evaluate risks, indirect standardisation (n = 83 997) and Poisson regression (n = 79 972).

Results

Based on serial mortality rates for England and Wales, deaths from Alzheimer''s disease and motor neuron disease were unexceptional. There was an excess of deaths from Parkinson''s disease of borderline significance. No statistically significant trends were shown for risks of any of these diseases to increase with lifetime cumulative exposure to magnetic fields (RR per 10 μT-y: Alzheimer''s disease 1.10 (95% CI 0.90 to 1.33); motor neuron disease 1.06 (95% CI 0.86 to 1.32); Parkinson''s disease 0.88 (95% CI 0.74 to 1.05))

Conclusions

There is no convincing evidence that UK electricity generation and transmission workers have suffered increased risks from neurodegenerative diseases as a consequence of exposure to magnetic fields.A large number of studies have investigated risks of cancer and other diseases in “electrical and electronic” workers. In addition, large-scale cohort mortality studies of electric utility workers that incorporate magnetic field exposure assessments are also available.^1,2,3,4,5 The question has also been raised as to whether employment in “electrical” occupations or exposure to magnetic fields might have an effect on risks of neurodegenerative disease. The literature relating to Alzheimer''s disease and magnetic fields is difficult to assess. It was suggested that increased risks could be substantial.⁶ Although this initial report was based on the combined results of three sub-studies, it should be regarded only as hypothesis forming, as the findings were much influenced by the reclassification of exposure groups. The Alzheimer''s/magnetic fields hypothesis was supported by the findings of another case-control study⁷ and was weakly supported by a proportional mortality ratio analysis of causes of death as recorded on US death certificates.⁸ The hypothesis was not supported, however, by the three studies that were able to provide quantified estimates of individual exposures.^9,10,11 One case-control study⁹ did not show risk to be associated with the individual''s primary occupation, but did show a substantial and statistically significant risk with the last recorded occupation, which would have been the association recorded in the death certificate study.⁸ Neither of the cohort studies,^10,11 however, provided evidence of a risk with increasing exposure, nor, in the one study that provided such information, was there any excess mortality in power plant workers. However, these studies relied on mortality records that are known to under-report Alzheimer''s disease and the distinction between Alzheimer''s disease and dementia is not always clearly made on death certificates. Three more recent studies also provided mixed findings: one providing weak evidence of a risk for males in the highest exposure group,¹² another (overlapping) study focusing on resistance welders showed a positive effect,¹³ and a third study showed an effect in males, but not in females.¹⁴ While initial, hypothesis-generating studies indicated a potential threefold risk, most of the subsequent research has found risks at or below unity, with only a few elevated risks of around 2.0 in selected subgroups. Thus the hypothesis that 50–60 Hz electromagnetic fields (EMFs) increase the risk of Alzheimer''s disease is neither proven nor excluded.More consistent evidence is available for motor neuron disease (some studies are concerned with its principal subtype amyotrophic lateral sclerosis (ALS)).^{8,10,11,12,13,15,16,17,18,19,20,21,22} A number of reports investigating the relation between electrical work or the experience of electrical shocks have been published since the original suggestion was made that electric shocks might increase the risk of the disease.²⁰ Two early studies from Japan (reported in a single paper), where the prevalence both of electrical work (as recorded in medical histories) and electrical shock was low, failed to provide any support for the hypothesis.²¹ However, an increased risk of ALS from electric shocks has been reported in several later studies.^16,22 The US study also found an increased risk associated with the employment in electrical occupations¹⁶ and this was supported by other studies from Sweden¹⁸ and the USA.⁸ Later studies focused on magnetic field exposure^10,11,15 and found twofold risks to be associated with exposure, albeit these excess risks were not always statistically significant. Recent and overlapping studies from Sweden focusing on magnetic field exposure and electric shock are inconsistent, with one showing no effect and the other indicting a twofold risk in the two highest exposure categories.^12,13 The epidemiological evidence suggests that employment in electrical occupations may increase the risk of ALS. However, separating any increased risk as a result of receiving an electric shock from any increased exposure to magnetic fields is important, albeit difficult.A number of epidemiological studies have been carried out on environmental associations with Parkinson''s disease.^{8,10,11,12,13,19,23} No study has provided clear evidence of an association with above average exposures to extremely low frequency EMFs (most risks close to unity) and, in the absence of laboratory evidence to the contrary, it seems unlikely that such exposures are involved in the disease process. Nevertheless, Parkinson''s disease was included as a health outcome of interest in this study for the sake of completeness.This paper seeks to obtain important new information on the topic of occupational magnetic field exposure and risks of mortality from neurodegenerative diseases by examining data from the ongoing epidemiological study of UK electric utility workers; this topic has been identified as a priority in recent reviews.^23,25     

Occupational exposure and cancer incidence among workers from an aluminum smelter in western Norway.

OBJECTIVES: This study investigated the associations between specific cancers and occupational exposure to polycyclic aromatic hydrocarbons (PAH), asbestos, electromagnetic fields, and heat in a cohort of workers from a Norwegian aluminum smelter. METHODS: Cancer incidence between 1953 and 1993 was observed for 2647 male short-term workers and 2 cohorts of men with at least 4 years' employment (2888 production workers and 373 maintenance workers). Standardized incidence ratios (SIR) were calculated from the national male cancer incidence, and associations with cumulative exposure were investigated by stratified analysis. Cumulative exposure in 15-year time windows was used as an alternative dose indicator. RESULTS: Investigation of the a priori hypotheses in the production cohort revealed a positive association between bladder cancer and PAH exposure 30 years or more before observation. The results also suggested an association between PAH and pancreatic cancer, although not statistically significant. No association was seen between exposure to PAH and cancers of the lungs or between magnetic field exposure and lymphatic and hematopoietic cancer. In the maintenance cohort there was a positive association between employment as an electrician and lymphatic and hematopoietic cancer and a statistically nonsignificant association between PAH and lung cancer. The short-term workers showed a statistically significant excess of lung cancer. CONCLUSIONS: The results support previous findings of an association between exposure to PAH and bladder cancer.     

Lymphohaematopoeitic cancer mortality among workers with benzene exposure

Lymphohaematopoeitic cancer mortality was examined among 4417 workers at a chemical plant by cumulative and peak benzene exposure. There was little evidence of increasing risk with increasing cumulative exposure for all leukaemias or acute non-lymphocytic leukaemias (ANL), or the other lymphohaematopoeitic cancers with the exception of multiple myeloma. For multiple myeloma, the SMRs were 1.1 (95% CI 0.3 to 2.5) in the non-exposed group, 1.4 (95% CI 0.2 to 5.1) in the <1 ppm-years, 1.5 (95% CI 0.2 to 5.4) in the 1–6 ppm-years, and 2.6 (95% CI 0.7 to 6.7) in the >6 ppm-years group. We found no trends by peak exposures for any of the cancers. However, when peak exposures over 100 ppm for 40 or more days were considered, the observed number of all leukaemias (SMR = 2.7, 95% CI 0.8 to 6.4), ANL (SMR = 4.1, 95% CI 0.5 to 14.9), and multiple myeloma (SMR = 4.0, 95% CI 0.8 to 11.7) were greater than expected. While the observed number of deaths is small in this study, the number of peak exposures greater than 100 ppm to benzene is a better predictor of risk than cumulative exposure. The dose rate of benzene and a threshold for exposure response may be important factors for evaluating lymphohaematopoietic risk.     

Occupational sunlight exposure and cancer incidence among Swedish construction workers

We studied sunlight exposure from outdoor work in relation to cancer, using data from 323,860 men participating in an occupational health service program of the Swedish construction industry. An experienced industrial hygienist assessed the exposure for 200 job tasks. We estimated relative risks (RRs) adjusted for age, smoking, and magnetic field exposure. There was an increased RR in the high-exposure group for myeloid leukemia [RR = 2.0, 95% confidence interval (95% CI) = 1.1-3.6] and lymphocytic leukemia (RR = 1.7, 95% CI = 0.9-3.2). For non-Hodgkin's lymphoma there was a 30% increase in risk in the high-exposure group (95% CI = 0.9-1.9). There was no increased risk of malignant melanoma, except for tumors of the head, face, and neck in the high-exposure group (RR = 2.0, 95% CI = 0.8-5.2), and we also found an increased risk for malignant melanoma of the eye in this group (RR = 3.4, 95% CI = 1.1-10.5). Outdoor workers had no increased risk of nonmelanoma skin cancer. Nevertheless, the RR for lip cancer (squamous cell carcinoma) among the high-exposure group was estimated at 1.8 (95% CI = 0.8-3.7). Among other sites, an increased risk of stomach cancer was suggested in this group (RR = 1.4, 95% CI = 1.0-1.9). The results for lymphoma, leukemia, and possibly also for stomach cancer might reflect a suppression of the immune system from ultraviolet light in outdoor workers.     

Occupational exposure to ionising radiation and mortality among workers of the former Spanish Nuclear Energy Board.

OBJECTIVES: Firstly, to ascertain whether mortality among workers of the former Spanish Nuclear Energy Board (Junta de Energía Nuclear-JEN) was higher than that for the Spanish population overall; and secondly, if this were so, to ascertain whether this difference was associated with exposure to ionising radiation. METHODS: A retrospective follow up of a cohort of 5657 workers was carried out for the period 1954-92. Cohort mortality was compared with that for the Spanish population overall, with standardised mortality ratios (SMRs) adjusted for sex, age, and calendar period. Also, Poisson models were used to analyse mortality from lung cancer in the cohort by level of exposure to ionising radiation. RESULTS: Workers' median and mean cumulative exposures were 4.04 and 11.42 mSv, respectively. Mean annual exposure was 1.33 mSv. Excess mortality due to bone tumours was found for the cohort as a whole (six deaths observed; SMR 2.95; 95% confidence interval (95% CI) 1.08 to 6.43). Among miners, excess mortality was found for non-malignant respiratory diseases (SMR 2.94; 95% CI 2.27 to 3.75), and for lung cancer bordering on statistical significance (SMR 1.50; 95% CI 0.96 to 2.23; P = 0.055). Relative risks of dying of lung cancer from ionising radiation in the dose quartiles 2, 3, and 4 versus the lowest dose quartile, were 1.00, 1.64, and 0.94, respectively. CONCLUSIONS: Excess mortality from lung cancer was found among JEN miners. Nevertheless, no clear relation was found between mortality from lung cancer and level of exposure to ionising radiation in the JEN cohort. Continued follow up of the cohort is required to confirm excess mortality from bone tumours.     

Occupational magnetic field exposure and cardiovascular mortality in a cohort of electric utility workers

In electric utility workers, occupational exposure to magnetic fields has previously been associated with mortality from acute myocardial infarction (AMI) and arrhythmia but not from chronic coronary heart disease (CCHD) or atherosclerosis. To investigate these health endpoints further, the authors examined mortality from AMI (n = 407) and CCHD (n = 369) in a cohort of 35,391 male workers at the Southern California Edison Company between 1960 and 1992. Exposure was estimated according to duration of employment in occupations associated with high levels of magnetic field exposure and was calculated as cumulative exposure to magnetic fields expressed in micro-Tesla-years. Adjustment was made for age, calendar time, socioeconomic status, race, and worker status (active or inactive). The authors found that men working longer in high-exposure occupations or working as electricians, linemen, or power plant operators had no increased risk of dying from either AMI or CCHD compared with men who never worked in high-exposure occupations. For cumulative exposure, no association was observed with mortality from AMI (rate ratio per 1 micro T-year = 1.01, 95% confidence interval: 0.99, 1.02) or CCHD (rate ratio per 1 micro T-year = 1.00, 95% confidence interval: 0.99, 1.02). These results, indicating no exposure-related risk increase for AMI mortality, do not confirm previous results.