Mortality patterns by occupation in a cohort of electric utility workers.

BACKGROUND: Mortality patterns were examined in a United States cohort of 138,905 male electric utility workers from five companies to help interpret previous studies of health effects in this industry. METHODS: Using Poisson regression techniques, internal cohort analyses examined total mortality, cardiovascular disease, and cancer in relation to duration of employment in each of nineteen occupational categories which comprise utility operations. RESULTS: Relative to workers who were never involved in utility operations (e.g., administrative workers), mortality rate ratios among operations workers were higher for total mortality, cardiovascular disease, and total cancer. Lung cancer risk was consistently elevated, whereas increased mortality for other cancers was less consistent. CONCLUSIONS: The results of this study indicate excess risk of total mortality, cardiovascular disease, and some cancers among electric utility workers, which could be related to both occupational and non-occupational risk factors.

Case-cohort analysis of brain cancer and leukemia in electric utility workers using a refined magnetic field job-exposure matrix.

BACKGROUND: The potential association between occupational electric and magnetic field exposure and cancer is well documented in the literature, but there is uncertainty regarding a causal relation. METHODS: Using data from a completed cohort study, we sought to refine the job-exposure matrix in a case-cohort analysis by regrouping jobs into more homogeneous groups, but without making additional measurements. From the original cohort, we selected the 164 men who died of leukemia, 145 men who died of brain cancer, and a random subcohort of 800 men (0.6% of the cohort). Erroneous job assignments were corrected and job groups were subdivided based on differences in work environments or tasks performed. RESULTS: Magnetic field exposure remained unrelated to leukemia mortality and positively associated with brain cancer mortality based on both cumulative and average magnetic field indices. Although not monotonic across the middle intervals, increased risk of brain cancer was found in relation to career exposure, with risk ratios of 1.8 (95% CI = 0.7-4.7) and 2.5 (95% CI = 1.0-6.3) in the uppermost categories for cumulative and average exposure, stronger for exposure 2-10 years past. CONCLUSIONS: Improvements in exposure assignment based only on reassignment of job titles to occupational categories had little impact on the measured associations of magnetic fields with leukemia or brain cancer.

Exposure to electromagnetic fields and suicide among electric utility workers: a nested case-control study.

OBJECTIVE: To examine mortality from suicide in relation to estimated exposure to extremely low-frequency electromagnetic fields in a cohort of 138,905 male electric utility workers. METHODS: Case-control sampling, which included 536 deaths from suicide and 5, 348 eligible controls. Exposure was classified based on work in the most common jobs with increased exposure to magnetic fields and indices of cumulative exposure to magnetic fields based on a measurement survey. RESULTS: Suicide mortality was increased relative to work in exposed jobs and with indices of exposure to magnetic fields. Increased odds ratios (ORs) were found for years of employment as an electrician (OR, 2.18; 95% confidence interval [CI], 1.25-3.80) or line worker (OR, 1.59; 95% CI, 1.18-2.14), whereas a decreased OR was found for power plant operators (OR, 0.67; 95% CI, 0.33-1.40). A dose-response gradient with exposure to magnetic fields was found for exposure in the previous year, with a mortality OR of 1.70 (95% CI, 1.00-2.90) in the highest exposure category. Stronger associations, with ORs in the range of 2.12 to 3.62, were found for men younger than 50 years. CONCLUSIONS: These data provide evidence for an association between occupational electromagnetic fields and suicide that warrants further evaluation. A plausible mechanism related to melatonin and depression provides a direction for additional laboratory research and epidemiologic evaluation.

Exposure to electromagnetic fields and suicide among electric utility workers: a nested case-control study.

OBJECTIVES: This nested case-control study examines mortality from suicide in relation to estimated exposure to extremely low frequency electromagnetic fields (EMFs) in a cohort of 138,905 male electric utility workers. METHODS: Case-control sampling included 536 deaths from suicide and 5348 eligible controls. Exposure was classified based on work in the most common jobs with increased exposure to magnetic fields and indices of cumulative exposure to magnetic fields based on a measurement survey. RESULTS: Suicide mortality was increased relative to work in exposed jobs and with indices of exposure to magnetic fields. Increased odds ratios (ORs) were found for years of employment as an electrician (OR 2.18; 95% confidence interval (95% CI) 1.25 to 3.80) or lineman (OR 1.59; 95% CI 1.18 to 2.14), whereas a decreased OR was found for power plant operators (OR 0.67; 95% CI 0.33 to 1.40). A dose response gradient with exposure to magnetic fields was found for exposure in the previous year, with a mortality OR of 1.70 (95% CI 1.00 to 2.90) in the highest exposure category. Stronger associations, with ORs in the range of 2.12-3.62, were found for men <50 years of age. CONCLUSION: These data provide evidence for an association between occupational electromagnetic fields and suicide that warrants further evaluation. A plausible mechanism related to melatonin and depression provides a direction for additional laboratory research as well as epidemiological evaluation.

Refinements in magnetic field exposure assignment for a case-cohort study of electrical utility workers.

This study examined the effect of refinements in exposure assignment on annual and career exposure to 60 Hz magnetic fields, using all deaths from brain cancer (145) and leukemia (164) and a random sample of 800 workers from a cohort of 138,905 men. Reassessment of 1060 job titles in the measurement database generated 20 subcategories in addition to 28 occupational categories used in the original cohort mortality study. Furthermore, previously misclassified jobs were corrected. The complete work history of each sub-cohort member was re-examined. Original and refined average annual exposures were 0.086 and 0.088 microT, respectively. The average career cumulative exposures were 1.40 and 1.44 microT-years, respectively. Spearman correlation coefficients between the original and refined methods across the companies were 0.81 for annual exposure and 0.93 for career cumulative exposure. 23% of the workers were assigned to another exposure ranking after refinement, but 85% of these moved to an adjacent group, suggesting that the differences in exposure ranking are small. The results of this study indicate that refinements have modest influence on the average annual and career exposures. However, the refinements may only change a very rough exposure assessment into one that is slightly less crude. The proportion of workers assigned to another exposure ranking indicated that nondifferential exposure misclassification in the original cohort mortality study may have occurred. Implications of these changes for the risk estimates of brain cancer and leukemia cases will to be examined.

Fatal occupational injuries among electric power company workers.

Surveillance data suggest high rates of electrocutions and fatal falls among workers in electric utility companies, who may be exposed to electric current, heights, flammable agents, and frequent motor vehicle travel. To characterize the occurrence of fatal injuries among electric utility workers, we studied workers in five electric power companies in the United States. A cohort of 127,129 men hired between 1950 and 1986 was followed through 1988. Injuries at work were identified through manual review of death certificates. The occurrence of occupational injuries was analyzed with directly adjusted rates and Poisson regression. The overall rate of fatal occupational injuries was 13.20 per 100,000 person-years (n = 192), with 76% due to electric current, homicide, and falls from heights. Deaths were concentrated in a few groups with elevated injury rates, notably linemen (rate ratio (RR) 3.33), electricians (RR 2.79), and painters (RR 3.27). Occupations requiring daily work on elevations or frequent, direct contact with energized electrical equipment experienced markedly higher rates of fatal injury from falls and electrocutions with rate ratios of 21.8 (95% confidence interval (CI) 11.4-41.5) and 16.7 (95% CI 6.6-42.6), respectively, independent of worker age and seniority. Although fatal injury rates in this industry have declined in recent decades, significant numbers of deaths still occur. Based on the premise that all injuries are preventable, a need for continued vigilance and efforts at prevention is indicated.

Magnetic field exposure and cardiovascular disease mortality among electric utility workers.

Laboratory studies suggest that electric and magnetic field exposure may affect heart rate and heart rate variability. Epidemiologic evidence indicates that depressed heart rate variability is associated with reduced survival from coronary heart disease as well as increased risk of developing coronary heart disease. The authors examined mortality from cardiovascular disease in relation to occupational magnetic field exposure among a cohort of 138,903 male electric utility workers from five US companies over the period 1950-1988. Cardiovascular disease deaths were categorized as arrhythmia related (n = 212), acute myocardial infarction (n = 4,238), atherosclerosis (n = 142), or chronic coronary heart disease (n = 2,210). Exposure was classified by duration of work in jobs with elevated magnetic field exposure and indices of cumulative magnetic field exposure. Adjusting for age, year, race, social class, and active work status, longer duration in jobs with elevated magnetic field exposure was associated with increased risk of death from arrhythmia-related conditions and acute myocardial infarction. Indices of magnetic field exposure were consistently related to mortality from arrhythmia and acute myocardial infarction, with mortality rate ratios of 1.5-3.3 in the uppermost categories. No gradients in risk were found for atherosclerosis or for chronic coronary heart disease. These data suggest a possible association between occupational magnetic fields and arrhythmia-related heart disease.

Uncertainty in the relation between exposure to magnetic fields and brain cancer due to assessment and assignment of exposure and analytical methods in dose-response modeling.

Incomplete scientific knowledge ensures that, in every study, uncertainty will enter the processes of exposure estimation and exposure-response modeling. In the light of the heated debate about the health effects of magnetic fields resulting from power production and usage, we undertook a sensitivity analysis to evaluate uncertainty related to key decisions in a previous study of brain cancer and occupational exposure to magnetic fields. The findings appeared to be relatively insensitive to most variations in the methods of exposure assessment, exposure assignment, and data analysis. The results can be visualized by defining bands of uncertainty about a best-bet estimate of the association based on our original study. These bands of methodological uncertainties were similar in magnitude to the conventional 95% confidence interval, but they provide a measure of the potential range of systematic bias in the results, rather than reflecting statistical variability alone. The methodology employed here can be applied to other studies, and other researchers are encouraged to conduct sensitivity analysis in order to estimate methodological uncertainty as an alternative to statistical confidence intervals.

Effects of the analytical treatment of exposure data on associations of cancer and occupational magnetic field exposure.

Epidemiological studies of cancer among workers exposed to magnetic fields have yielded inconsistent results. This variability may be partly explained by differences in study methods. To assess sensitivity to such methods, data from a previous study of brain cancer and leukemia among electric power company workers were reanalyzed using alternative models, which incorporated uncertainty about the intensity of historical exposures, alternative cut points for categorizing the exposure variable for analysis, and a range of lags for describing cancer latency. Mortality rate ratios for leukemia ranged from 0.8-1.5. For brain cancer, increasing cumulative magnetic field exposure was associated with increasing mortality in virtually all models, with rate ratios between 1.3-3.4 for the most exposed workers. These rate ratios are consistent with previous analyses suggesting a 1.5-3.0-fold increase in the risk of brain cancer but no association with leukemia, and confirm that the previous results are not dependent on arbitrary decisions in applying the exposure data.

Sensitivity of the relation between cumulative magnetic field exposure and brain cancer mortality to choice of monitoring data grouping scheme.

We examined the effectiveness of alternative grouping strategies with respect to cumulative exposure to magnetic fields and brain cancer mortality among electric utility workers. We applied a statistically optimal job-exposure matrix to calculate cumulative exposure over full work histories. We studied the sensitivity of the exposure-disease relation by assigning an array of different quantitative exposure estimates based on six schemes for grouping exposure measurements. The quantitative relation between cumulative magnetic field exposure and brain cancer mortality appeared to be sensitive to the choice of grouping scheme, with the optimized grouping scheme indicating stronger relations than standard schemes.

Assessment and grouping of occupational magnetic field exposure in five electric utility companies.

OBJECTIVES: Occupational exposure to 60-Hz magnetic fields was surveyed among randomly selected workers in five electric power companies. METHODS: The study facilitated the examination of exposure variability and provided the base for a job-exposure matrix linking health outcomes and occupational magnetic field exposures. RESULTS: Average exposures ranged from 0.11 to 1.50 microT. The differences among the five companies were small, the more urban companies showing somewhat higher averages. The day-to-day component of variance exceeded the within- and between-group components of variance. The final job-exposure matrix consisted of five groups with average exposure levels of 0.12, 0.21, 0.39, 0.62, and 1.27 microT. Given the variance in exposure, even this optimal grouping considerably overlapped. CONCLUSIONS: The job-exposure matrix used in this study efficiently incorporated the differences in exposure within occupational categories between companies and provided an objective and statistically based method for estimating cumulative magnetic field exposure.

Maternal employment and reproductive risk factors.

Studies of reproductive hazards in the workplace must address potential biases related to selection for employment. The National Natality Survey, a probability sample of live births to married women in 1980, was used to examine the relation between female employment during pregnancy and factors that might affect reproductive outcome by analyzing the 5,927 women with complete occupational data. Demographic and behavioral attributes as well as reproductive history were compared for the 3,712 women employed and the 2,215 women not employed during pregnancy. Employed mothers were of more optimal reproductive age, were more highly educated, had higher incomes, began prenatal care earlier, had greater weight gain during pregnancy, and were slightly less likely to be heavy smokers. Employed women had markedly fewer previous births and less favorable reproductive histories (more stillbirths, miscarriages, and induced abortions) than unemployed women, controlling for gravidity. Full- and part-time workers were similar with regard to demographic and behavioral characteristics, but part-time workers had higher parity. Differences were noted by employment sector: professional women had especially favorable demographic and behavioral traits, and women employed as operatives and service workers were less advantaged. These results indicate that substantial differences in pregnancy-related risk factors exist in relation to employment, with working women generally having more favorable demographic and behavioral characteristics and less favorable reproductive histories. This pattern could produce selection bias in studies of work and reproductive health, and it encourages the restriction of comparison groups to other employed women, with a need to consider heterogeneity among working women as well.

Magnetic field exposure from electric appliances and childhood cancer.

The effect on childhood cancer of prolonged exposure to 60-H magnetic fields from electric appliances was examined using interview data from a recently completed case-control study. Exposures of children aged 0-14 years whose incident cancers were diagnosed between 1976 and 1983 and who resided in the Denver, Colorado, Standard Metropolitan Statistical Area were compared with those of controls selected by random digit dialing, matched on age, sex, and telephone exchange area. Parents of 252 cases and 222 controls were interviewed at home about the use of electric appliances by the mother during pregnancy (prenatal exposure) and by the child (postnatal exposure). After adjustment for income, prenatal electric blanket exposure was associated with a small increase in the incidence of childhood cancers (odds ratio (OR) = 1.3, 95% confidence interval (CI) 0.7-2.2) that was more pronounced for leukemia (OR = 1.7, 95% CI 0.8-3.6) and brain cancer (OR = 2.5, 95% CI 1.1-5.5). Postnatal exposure to electric blankets was also weakly associated with childhood cancer (OR = 1.5, 95% CI 0.6-3.4), with a larger but imprecise association with acute lymphocytic leukemia (OR = 1.9, 95% CI 0.6-6.5). Water beds and bedside electric clocks were unrelated to childhood cancer incidence. Results are limited by nonresponse and imprecision resulting from the rarity of appliance use, especially for subgroups of cases. Nonetheless, electric blankets, one of the principal sources of prolonged magnetic field exposure, were weakly associated with childhood cancer and warrant a more thorough evaluation.

Self-reported exposure to pesticides and radiation related to pregnancy outcome--results from National Natality and Fetal Mortality Surveys.

Although fetal development is known to be sensitive to environmental agents, relatively little epidemiologic research has addressed this concern. Effects on pregnancy outcome of self-reported parental exposure to pesticides and to radiation were examined using data from the National Natality and Fetal Mortality Surveys, large national probability samples of live births and stillbirths occurring in 1980. In case-control analyses, maternal exposure to pesticides at home or work was associated with increased risk of stillbirth (odds ratios (ORs) = 1.5-1.6). Paternal pesticide exposure was associated with stillbirth (ORs = 1.2-1.4) and delivery of small-for-gestational-age infants (ORs = 1.4-2.0). A small increased risk of stillbirth (OR = 1.3) was found in relation to either parent's reported exposure to radiation. In spite of limitations in the quality of exposure data and the possibility of biased recall related to pregnancy outcome, associations of reported pesticide exposure to either parent with risk of stillbirth and small-for-gestational-age infants warrant further evaluation.

Effect of parents' occupational exposures on risk of stillbirth, preterm delivery, and small-for-gestational-age infants.

Epidemiologic research on the effects of parental occupational exposures on fetal development has been limited. The National Natality and Fetal Mortality surveys obtained applicable data on probability samples of live births and fetal deaths which occurred in the US in 1980 among married women. Analyses were conducted for case groups of stillbirths (2,096 mothers, 3,170 fathers), preterm deliveries (less than 37 weeks completed gestation) (363 mothers, 552 fathers), and small-for-gestational-age infants (218 mothers, 371 fathers) compared with controls. Occupational exposures were defined by industry of employment and by imputed exposures based on a job-exposure linkage system. For stillbirth, maternal work in the rubber, plastics, and synthetics industry (odds ratio (OR) = 1.8, 95% confidence interval (Cl) 0.8-4.0) and lead exposure (OR = 1.6, 95% Cl 0.8-3.1), and paternal employment in the textile industry (OR = 1.9, 95% Cl 1.2-2.9), had the largest odds ratios. Preterm birth was most strongly associated with maternal lead exposure (OR = 2.3, 95% Cl 0.7-7.0), corroborating previous findings. Twofold increased risk of preterm delivery was found with paternal employment in the glass, clay, and stone; textile; and mining industries. Paternal exposures to x-rays and polyvinyl alcohol were associated with 1.5-fold increase in risk. The occupation of the mother was not associated with delivery of a small-for-gestational-age infant, in contrast to paternal employment in the art (OR = 2.6, 95% Cl 1.2-5.6) and textile industries (OR = 2.5, 95% Cl 1.3-4.7). Several toxic agents were associated with risk elevation of 1.3 or greater for fathers, most notably benzene (OR = 1.5, 95% Cl 1.1-2.3). In spite of limitations in the exposure data, the size of the exposed populations, and possible confounding, the results in this study encourage further evaluation of the effects of maternal exposure to lead and possibly solvents, as well as paternal exposure in the textile industry and to x-rays and benzene.

Swim bladder volume maintenance related to initial oceanic migratory depth in silver-phase Anguilla rostrata.

Gas deposition rates in the swim bladders of postmetamorphic (silver) Anguilla rostrata eels are about five times greater than those of premetamorphic (yellow) individuals. This extends the maximum depth at which silver eels can maintain swim bladder volume and prepares them for their spawning migration to the Sargasso Sea.