Exposures of children in Canada to 60-Hz magnetic and electric fields.

OBJECTIVES: This study sought to characterize personal exposures of Canadian children to 60-Hz magnetic and electric fields and explain the variability. METHODS: Altogether 382 Canadian children up to 15 years of age wore meters recording 60-Hz electric and magnetic fields over 2 days. Meter location was noted. Thereafter, meters measured fields in the center of the children's bedrooms for 24 hours. Personal exposures were calculated for home, school or day care, outside the home, bedroom at night, and all categories combined (total). RESULTS: The arithmetic mean (AM) was 0.121 microT [geometric mean (GM): 0.085 microT), range 0.01-0.8 microT] for total magnetic fields. Fifteen percent of the total exposures exceeded 0.2 microT. The AM of the total electric fields was 14.4 (GM 12.3, range 0.82-64.7) V/m. By location category, the highest and lowest magnetic fields occurred at home during the day (0.142 microT) and during the night (0.112 microT), respectively. Measurements during sleep provided the highest correlation with total magnetic field exposure. Province of measurement explained 14.7% of the variation in the logarithms of total magnetic fields, and season accounted for an additional 1.5%. CONCLUSIONS: This study has identified differences in children's magnetic field exposures between provinces. Measurements at night provided the best surrogate for predicting total magnetic field exposure, followed by at-home exposure and 24-hour bedroom measurements. Electrical heating and air conditioning, wiring type, and type of housing appear to be promising indicators of magnetic field levels.     

Household appliance use and residential exposure to 60-hz magnetic fields

We characterized the distribution of exposure to magnetic fields (MFs) during daily activities and during household appliance use, and estimated the relative contribution of various activities and appliances to total daily exposure. One hundred sixty-two subjects provided information on their patterns of appliance use and wore personal monitors for 24 h to collect MF exposure data. Of total exposure, 27% accumulated while subjects were in bed; 41% while at home but not in bed; 9% at work; and 24% elsewhere. Less than 2% of the total MF exposure accumulated during the use of each of the eight individual appliances considered, except computers, during the use of which 9% of the total exposure accumulated. Of the time subjects spent at exposure levels higher than 2 microT, 8% accumulated while they were using microwave ovens, and 4% and 3% while using computers and electric stoves, respectively. Mean MF measurements tended to be lowest when subjects were in bed and highest at work and during the use of microwave ovens, coffee grinders, hair dryers, and electric shavers. Results from questionnaires on household appliance use in the past year were not useful in predicting the total mean exposure level and over-threshold exposures measured by 24-h personal monitors. Significant MF exposure accumulates at home, at work, and elsewhere; therefore, accurate exposure assessment needs to consider residential, occupational, and other sources together. Questionnaire-based information on appliance use has limited value in the assessment of average and over-threshold exposure to MFs.     

Residential and occupational exposures to 50-Hz magnetic fields and breast cancer in women: a population-based study

A case-control study was conducted to investigate whether residential and occupational exposures to magnetic fields increased the risk for breast cancer among women. Cases of breast cancer diagnosed during 1980-1996 were identified in a cohort of women living near a high-voltage power line in Norway in 1980 or between 1986 and 1996. Each case was matched by year of birth, municipality, and first year of entry into the cohort with two randomly selected controls without cancer. Residential exposure to magnetic fields was calculated as that generated by the lines before diagnosis, and occupational exposure was based on exposure matrix data. Women with residential exposure had an odds ratio of 1.58 (95% confidence interval (CI): 1.30, 1.92) when compared with unexposed women. The odds ratios for exposed women versus unexposed women with estrogen receptor (ER)-positive and ER-negative breast cancer were 1.33 (95% CI: 0.93, 1.90) and 1.40 (95% CI: 0.78, 2.50), respectively (ER status was available for 44% of the cases). Women with the highest occupational exposure had an odds ratio of 1.13 (95% CI: 0.91, 1.40) when compared with those unexposed at work. The findings suggest an association between exposure to magnetic fields and breast cancer in women.     

No influence of short-term exposure to 50-Hz magnetic fields on cognitive performance function in human

Objectives To examine whether 50-Hz magnetic fields acutely influence cognitive performance function in humans.Methods The exposure experiment was conducted in a wooden room with three-axis coils. Twenty young subjects were exposed to circularly polarized 50-Hz/20-T magnetic fields for 55 min, during which they were requested to perform four cognitive performance tests for evaluation of simple reaction time, time and accuracy of choice reaction, time perception, and figure perception.Results No subject detected the existence of the field. Statistical analysis revealed no significant influence of the exposure on the results of the tests.Conclusions The results indicate that extremely low-frequency electromagnetic fields in the occupational environment are unlikely to interfere with human brain function so much as to lower working efficiency or accuracy.     

Case-control study of bladder cancer and exposure to arsenic in Argentina

Studies have found increased bladder cancer risks associated with high levels of arsenic in drinking water, but little information exists about risks at lower concentrations. Ecologic studies in Argentina have found increased bladder cancer mortality in Córdoba Province, where some wells are contaminated with moderate arsenic concentrations. This population-based bladder cancer case-control study in two Córdoba counties recruited 114 case-control pairs, matched on age, sex, and county, during 1996-2000. Water samples, particularly from wells, were obtained from subjects' current residences and residences in the last 40 years. Statistical analyses showed no evidence of associations with exposure estimates based on arsenic concentrations in drinking water. However, when well-water consumption per se was used as the exposure measure, time-window analyses suggested that use of well water more than 50 years before interview was associated with increased bladder cancer risk. This association was limited to ever smokers (odds ratio = 2.5, 95% confidence interval: 1.1, 5.5 for 51-70 years before interview), and the possibility that this association is due to chance cannot be excluded. This study suggests lower bladder cancer risks for arsenic than predicted from other studies but adds to evidence that the latency for arsenic-induced bladder cancers may be longer than previously thought.     

Implantable cardioverter defibrillator and 50-Hz electric and magnetic fields exposure in the workplace

Purpose  

The operation of implantable cardioverter defibrillators (ICD) can be disrupted by exposure to electromagnetic fields (EMF). In the workplace, some workers can be exposed to EMF higher than in daily life. We present an approach aimed at assessing fitness for work in this type of situation, based on in situ case studies in the absence of clinical and in vivo studies.     

Rodent cell transformation and immediate early gene expression following 60-Hz magnetic field exposure.

Some epidemiological studies suggest that exposure to power frequency magnetic fields (MFs) may be associated with an elevated risk of human cancer, but the experimental database remains limited and controversial. We investigated the hypothesis that 60-Hz MF action at the cellular level produces changes in gene expression that can result in neoplastic transformation. Twenty-four hour 200 microT continuous MF exposure produced negative results in two standard transformation systems (Syrian hamster embryo cells and C3H/10T1/2 murine fibroblasts) with or without postexposure to a chemical promoter. This prompted a reexamination of previously reported MF-induced changes in gene expression in human HL60 cells. Extensive testing using both coded and uncoded analyses was negative for an MF effect. Using the same exposure conditions as in the transformation studies, no MF-induced changes in ornithine decarboxylase expression were observed in C3H/10T1/2 cells, casting doubt on a promotional role of MF for the tested cells and experimental conditions.     

Maternal occupational exposure to extremely low frequency magnetic fields during pregnancy and childhood leukemia

BACKGROUND: Pregnancy is a target period for events that could induce childhood leukemia. There has been little attention to possible effects of maternal occupational exposure to extremely low frequency magnetic fields (ELF-MF) during pregnancy. METHODS: We conducted a population-based, case-control study of 491 incident cases of acute lymphoblastic leukemia in children 0-9 years of age, matched on age and sex to 491 healthy controls. Cases were diagnosed in the Province of Québec between 1980 and 1993. Mothers were interviewed to obtain detailed prenatal occupational history; individual exposure to ELF-MF was estimated based on a method we recently developed. We used 3 metrics for analyzing exposure: cumulative, average and maximum levels. Analyses were carried out among all study women and among working women only. RESULTS: Comparing the highest 10% of exposed mothers to the others, the risk of leukemia among offspring was moderately increased by using any metric, in all women and among working women only. The highest odds ratio of 2.5 (95% confidence interval = 1.2-5.0) was found for maximum exposure attained in an occupation (>/=0.4 microtesla). CONCLUSIONS: Our results are compatible with an increased risk of childhood leukemia among children whose mothers were exposed to the highest occupational levels of ELF-MF during pregnancy.     

Occupational and residential 60-Hz electromagnetic fields and high-frequency electric transients: exposure assessment using a new dosimeter

One problem that has limited past epidemiologic studies of cancer and exposure to extremely low-frequency (0-100 Hz) electric and magnetic fields has been the lack of adequate methods for assessing personal exposure to these fields. A new 60-Hz electromagnetic field dosimeter was tested to assess occupational and residential exposures of a group of electrical utility workers and a comparison background group over a 7-day period. Comparing work periods only, utility workers' exposures were significantly higher than background levels by a factor of about 10 for electric (E) and magnetic (B) fields and by a factor of 171 for high-frequency transient electric (HFTE) fields. When overall weekly time-weighted averages combining work and nonwork exposures were compared, ratios of the exposed to background groups were lower. B and HFTE exposure ratios remained statistically significant, with values of 3.5 and 58, respectively, whereas the electric field exposure ratio was no longer significant, with a value of 1.7. E-field exposures of the background group were the highest during the nonwork period, probably reflecting the use of electrical appliances at home. Residential E- and B-field exposures were in the same range as published results from other surveys, whereas occupational E-field exposures tended to be lower than exposures reported in other studies. The high variability associated with occupational exposures probably accounts for the latter discrepancy. Worker acceptance of wearing the dosimeter was good: 95% of participants found it to be of little or no inconvenience while at work. At home, 37% found the device to be inconvenient in its present form but would not object to wearing a slightly smaller and lighter dosimeter.     

Melatonin metabolite levels in workers exposed to 60-Hz magnetic fields: work in substations and with 3-phase conductors

Melatonin suppression by 50/60-Hz magnetic fields represents a plausible biological mechanism for explaining increased health risks in workers. Personal exposure to magnetic fields and ambient light, and excretion of the melatonin metabolite 6-hydroxymelatonin sulfate (6-OHMS), were measured over 3 consecutive workdays in electric utility workers. There was a magnetic field-dependent reduction in adjusted mean nocturnal and post-work 6-OHMS levels among men working more than 2 hours per day in substation and 3-phase environments and no effect among those working 2 hours or less. No changes were observed among men working in 1-phase environments. The results suggest that circular or elliptical magnetic field polarization, or another factor linked to substations and 3-phase electricity, is associated with magnetic field induced melatonin suppression in humans.     

Case-control study on occupational exposure to diesel exhaust and lung cancer risk.

The association between lung cancer and occupations with probable exposure to diesel exhaust (DE) was studied among 2,584 cases and 5,099 hospital controls. The crude odds ratio (OR) for probable exposure was 1.31 (95% confidence interval [CI] 1.09-1.57), but adjustment for smoking and other confounders reduced the estimate to 0.95 (95% CI = 0.78-1.16). Similar results were observed for truck drivers, the only occupational category large enough for separate analysis. Data on self-reported exposure for 477 cases and 946 controls revealed a crude OR of 1.45 (95% CI = 0.93-2.27), which was reduced to 1.21 (95% CI = 0.78-2.02) after controlling for smoking and other confounders. The present results and a review of the literature do not definitively support an etiologic association between DE exposure and elevated lung cancer risk.     

Human exposure to static and time-varying magnetic fields

In recent years there has been an increased interest in biological effects of magnetic fields. Both, beneficial applications and potential hazards due to exposure to static and time-varying magnetic fields have been considered. In this context it is important to know levels of human exposure to these fields in occupational and everyday situations. In this paper human exposures to magnetic fields in various areas of human activity are reviewed: high-energy technologies, induction heating, medical imaging, electricity distribution and others. Fields of frequencies from zero to a few hundred kilohertz are included.     

Restricting exposure to pulsed and broadband magnetic fields

A general procedure is described for application of the new ICNIRP exposure guidelines to pulsed and broadband magnetic fields below 100 kHz. The procedure involves weighting of the spectral components with a function that takes into account the basic restrictions and reference levels. A simple first-order RC response or its piecewise linear equivalent is proposed for the weighting function. The weighting can be performed either on the Fourier transformed sample of the measured signal or in real time by processing the signal with an analog or digital filter circuit. The cut-off frequency of the filter is 820 Hz. The occupational exposure criteria are exceeded when the weighted peak magnetic flux density exceeds 43 microT or equivalently the weighted peak dB/dt exceeds 0.22 T s(-1). The maximal peak exposures allowed by the proposed approach are compared with the stimulation thresholds computed with a stimulation model. The results strongly suggest that the safety margin to the stimulation is greater for non-sinusoidal than for sinusoidal waveforms, and at low frequencies it is higher than at high frequencies. The increase of the low-frequency safety margin is desirable to avoid magnetophosphenes and possible CNS effects that may occur below the level predicted by the classical nerve models. Measurement techniques and examples of measured magnetic fields are presented. Particularly high exposures were measured inside MRI equipment and anti-theft gates.     

No association of 6-sulfatoxymelatonin with in-bed 60-Hz magnetic field exposure or illumination level among older adults

We examined the association of 6-sulfatoxymelatonin (aMT6s) excretion with in-bed 60-Hz magnetic field (MF) exposure and other potential regulators. Adults aged 50-81 years (n=242 years, mean 67.6+/-5.7 years) were monitored for 1 week in their home environments. Mean and maximum MF exposure were assessed with EMDEX Lite instruments. Illumination mesor, amplitude, and acrophase (peak time) were determined from 24-h Actillume wrist monitors. Other regulators of aMT6s assessed were age, usage of melatonin-altering medications, and day length. During two 24-h intervals, all urine voidings were collected. The mesor, amplitude, and acrophase of aMT6s excretion were determined. Multiple regression analyses revealed no association between MF and aMT6s. Medication usage was associated with significantly lower aMT6s mesor and amplitude. Illumination acrophase and amplitude were significantly associated with aMT6s acrophase. These data suggest no influence of nocturnal environmental MF exposure on aMT6s excretion in older adults.     

Brain cancer and occupational exposure to magnetic fields among men: results from a Canadian population-based case-control study

BACKGROUND: The relationship between occupational exposure to magnetic fields and brain cancer in men was investigated using population-based case-control data collected in eight Canadian provinces. Emphasis was placed on examining the variations in risk across different histological types. METHODS: A list of occupations was compiled for 543 cases and 543 controls that were individually matched by age. Occupations were categorized according to their average magnetic field exposure through blinded expert review (<0.3, 0.3-<0.6, and > or = 0.6 microT). In total, 133 cases (14%) and 123 controls (12%) were estimated to have at least one occupation whereby magnetic field exposures exceeded 0.3 microT. Odds ratios (OR) were generated using conditional logistic regression, and were adjusted for suspected occupational risk factors for brain cancer. RESULTS: A non-significantly increased risk of brain cancer was observed among men who had ever held a job with an average magnetic field exposure >0.6 microT relative to those with exposures <0.3 microT (OR = 1.33, 95% CI : 0.75-2.36). A more pronounced risk was observed among men diagnosed with glioblastoma multiforme (OR = 5.36, 95% CI : 1.16-24.78). Moreover, a cumulative time weighted index score of magnetic field exposure was significantly related to glioblastoma multiforme (P = 0.02). In contrast, magnetic field exposures were not associated with astrocytoma or other brain cancers. CONCLUSIONS: Our findings support the hypothesis that occupational magnetic field exposure increases the risk of glioblastoma multiforme.     

Occupational exposure to low frequency magnetic fields and dementia: a case-control study

Background

Several studies point to a potential aetiological relevance to dementia of exposure to low‐frequency magnetic fields, but the evidence is inconclusive.

Objective

To further examine the relationship between low frequency magnetic fields and dementia.

Methods

From 23 general practices, 195 patients with dementia were recruited. Of these, 108 had possible Alzheimer''s disease, 59 had possible vascular dementia and 28 had secondary or unclassified dementia. A total of 229 controls were recruited: 122 population controls and 107 ambulatory patients free from dementia. Data were gathered in a structured personal interview; in cases, the interview was administered to the next of kin. Exposure to low‐frequency electromagnetic fields was assessed by expert rating. To identify occupations suspected to be associated with dementia, major occupations were a priori formed. Odds ratios were calculated using logistic regression, to control for age, region, sex, dementia in parents and smoking.

Results

Exposure to magnetic fields was not significantly associated with dementia; restriction of the analysis to cases with possible Alzheimer''s disease or possible vascular dementia did not lead to statistically significant results. We found an increased risk of dementia in blue‐collar occupations (electrical and electronics workers, metal workers, construction workers, food and beverage processors and labourers).

Conclusions

Our study does not support a strong association between occupational exposure to low‐frequency magnetic fields and dementia. Further studies should consider the relationship between blue‐collar work and the late development of dementia.Alzheimer''s dementia and vascular dementia are the two major forms of dementia in elderly people. Some recent epidemiological studies have analysed the role of low‐frequency magnetic fields in the aetiology of dementia. On the basis of mortality studies, the evidence is equivocal: several,^1,2,3,4 but not all,^5,6 death certificate‐based studies—partly showing considerable overlap in the study populations—find a significant association between exposure to magnetic fields and dementia.Most case–control studies show an association between occupational exposure to magnetic fields and dementia,^7,8,9,10 two case–control studies do not confirm the relationship between exposure to magnetic fields and dementia¹¹ or cognitive impairment.¹² Recently, a prospective cohort study conducted in the Kungsholmen district of Stockholm¹³ found a relationship between exposure to electromagnetic fields in the lifetime principal job and Alzheimer''s disease in men, but not in women.As a pathophysiological explanation of the potential association between exposure to magnetic fields and Alzheimer''s disease, Sobel and Davanipour¹⁴ hypothesise the following mechanism: initiated by increased intracellular calcium ion levels in some cell systems, soluble amyloid β production might increase (eg, in skin cells). Apolipoproteins E and J might bind to the soluble amyloid β in blood and might therefore assist in its crossing the blood–brain barrier. A cascade of further events might lead to the formation of insoluble neurotoxic β‐pleated sheets of amyloid fibril, senile plaques and eventually Alzheimer''s disease.¹⁴ Analysing blood and urine samples of male electric utility workers, Noonan et al¹⁵ found a weak relationship between mean exposure to magnetic fields and the concentration of soluble amyloid β in the blood, which was not statistically significant. Therefore, the pathophysiological pathway by which dementia might be linked with exposure to magnetic fields still remains unclear.The aim of this case–control study is to further examine the relationship between electromagnetic fields assessed by expert rating and dementia. Furthermore, the present study intends to identify occupations suspected to be associated with the risk for lymphoma.     

工频磁场抑制细胞缝隙连接通讯功能的剂量-效应研究

目的 研究５０Ｈｚ磁场对细胞缝隙连接通讯（ＧＪＩＣ）功能抑制作用的剂量－效应关系及其有关机理。方法 利用微注射法将荧光染料引入单个中国仓鼠肺来源成纤维（ＣＨＬ）细胞内,以５分钟后的荧光偶合细胞数作为ＧＪＩＣ功能的指标。