Static magnetic field measurements in residences in relation to resonance hypotheses of interactions between power-frequency magnetic fields and humans.

Bowman et al. used epidemiologic data to test a model in which subjects were classified as being "in-resonance" or "not-in-resonance" for 60-Hz magnetic-field exposures depending on single static magnetic-field measurements at the centers of their bedrooms. A second paper by Swanson concluded that a single static magnetic-field measurement is insufficient to meaningfully characterize a residential environment. The main objective of this study was to investigate exposure-related questions raised by these two papers in two U.S. data sets, one containing single spot measurements of static magnetic fields at two locations in homes located in eight states, and the other repeated spot measurements (seven times during the course of one year) of the static magnetic fields at the centers of bedrooms and family rooms and on the surfaces of beds in 51 single-family homes in two metropolitan areas. Using Bowman's criterion, bedrooms were first classified as being in-resonance or not-in-resonance based on the average of repeated measurements of the static magnetic field measured on the bed where the presumed important exposure actually occurred. Bedrooms were then classified a second time using single spot measurements taken at the centers of bedrooms, centers of family rooms, or on the surfaces of beds, as would be done in the typical epidemiologic study. The kappa statistics characterizing the degree of concordance between the first (on-bed averages) and second (spot measurements) methods of assessing resonance status were 0.44, 0.33, and 0.67, respectively. This level of misclassification could significantly affect the results of studies involving the determination of resonance status.     

Relative contribution of residential and occupational magnetic field exposure over twenty-four hours among people living close to and far from a power line

This study sought to estimate the relative contribution of exposure to 50 Hz magnetic fields experienced at home, at work/school, or elsewhere to the total exposure over 24 hr. Personal exposure meters were carried by 97 adults and children in the Stockholm area. About half of the subjects lived close (<50 m) to a transmission line and half far (>100 m) away. Spot measurements and calculations for the residential exposure were also made. For subjects living<50 m from the line, the exposure at home contributed about 80% of the total magnetic field exposure, measured in mT-hours. Adults living far away experienced only 38% of the total exposure at home, but children still received 55%. Subjects with low time-weighted average (TWA) exposure both at home and at work spent 84% of their time in fields <0.1 microT, and those with high TWA at both locations spent 69% of their time in fields > or = 0.2 microT. This contrast was diluted if only exposure at one location was considered. For spot measurements and calculations of the residential exposure, both sensitivity and specificity was good. However, the intermediate field exposure category (0.1-0.19 microT) showed poor correlation to the 24 hr personal measurements.     

Measuring temporal variability in residential magnetic field exposures

Considerable interest has developed during the past ten years regarding the hypothesis that living organisms may respond to temporal variability in ELF magnetic fields to which they are exposed. Consequently, methods to measure various aspects of temporal variability are of interest. In this paper, five measures of temporal variability were examined: Arithmetic means (D(mean)) and rms values (D(rms)) of the first differences (i.e., absolute value of the difference between consecutive measurements) of magnetic field recordings; "standardized" forms of D(rms), denoted RCMS, obtained by dividing D(rms) by the standard deviations of the magnetic field data; and mean (F(mean)) and rms (F(rms)) values of fractional first differences. Theoretical investigations showed that D(mean) and D(rms) are virtually unaffected by long-term systematic trends (changes) in exposure. These measures thus provide rather specific measures of short-term temporal variability. This was also true to a lesser extent for F(mean) and F(rms). In contrast, the RCMS metric was affected by both short-term and long-term exposure variabilities. The metrics were also investigated using a data set consisting of twice-repeated two-calendar-day recordings of bedroom magnetic fields and personal exposures of 203 women residing in the western portion of Washington State. The predominant source of short-term temporal variability in magnetic field exposures arose from the movement of subjects through spatially varying magnetic fields. Spearman correlations between TWA bedroom magnetic fields or TWA personal exposures and five measures of temporal variability were relatively low. Weak to moderate levels of correlation were observed between temporal variability measured during two different sessions separated in time by 3 or 6 months. We conclude that first difference and fractional difference metrics provide specific and fairly independent measures of short-term temporal variability. The RCMS metric does not provide an easily interpreted measure of short-term or long-term temporal variability. This last result raises uncertainties about the interpretation of published studies that use the RCMS metric.     

Study of high- and low-current-configuration homes from the 1988 Denver Childhood Cancer Study

An epidemiological study conducted by Savitz et al. reported that residential wire codes were more strongly associated with childhood cancer than were measured magnetic fields, a peculiar result because wire codes were originally developed to be a surrogate for residential magnetic fields. The primary purpose of the study reported here, known as the Back to Denver (BTD) study, was to obtain data to help in the interpretation of the original results of Savitz et al. The BTD study included 81 homes that had been occupied by case and control subjects of Savitz et al., stratified by wire code as follows: 18 high current configuration (HCC) case homes; 20 HCC control homes; 20 low current configuration (LCC) case homes; and 23 LCC control homes. Analysis of new data acquired in these homes led to the following previously unpublished conclusions. The home-averaged (i.e., mean of fields measured in subjects' bedrooms, family/living rooms, and rooms where meals normally eaten) spot 60 Hz, 180 Hz, and harmonic (i.e., 60-420 Hz) magnetic fields were associated with wire codes. The 180 Hz and harmonic components, but not the 60 Hz component, were associated with case/control status. Measured static magnetic fields were only weakly correlated (rapproximately 0.2) between rooms in homes. The BTD data provide little support for, but are too sparse to definitively test, the 1995 resonance hypothesis proposed by Bowman et al. Case and control homes had similar concentrations of copper in their tap water. Copper concentration was not associated with wire codes nor with the level of electric current carried by a home's water pipe. These results of the BTD study suggest that future case/control studies investigating power frequency magnetic fields might wish to include measurements of 180 Hz or harmonic magnetic fields in order to examine their associations (if any) with disease status.     

Comparison of residential power-frequency magnetic fields away from appliances in different countries

The purpose of this paper is to review measurements of residential power-frequency magnetic fields made in different countries and to determine whether average magnetic fields away from appliances are higher in some countries than in others. The paper includes 27 studies reporting measurements of residential magnetic fields in samples of homes: 14 from North America, 5 from the United Kingdom, and 8 from other European countries. Various factors that might make the results from individual studies unrepresentative of average fields in the relevant country are identified and discussed. Because distributions of magnetic fields generally are approximately log-normal, they are summarised by their geometric means. The best estimate of the geometric means of long-term average background fields in the United States is 60-70 nT and in the United Kingdom approximately 36-39 nT. In other countries, there are insufficient studies to draw firm conclusions on average fields. Measurements of personal exposure are higher than measurements of background fields, perhaps because they include exposures from appliances and other sources in the home. The ratio of personal exposure to background field seems, on average, to be approximately 1.4.     

Magnetic field exposure assessment for adult residents of Maine who live near and far away from overhead transmission lines.

Sixty-Hz magnetic field exposures were measured for 45 adult residents of Maine. Thirty of the subjects resided near rights-of-way (ROWs) with either 345- and 115-kV transmission lines, or ROWs with only 115-kV transmission lines; fifteen resided far from any transmission lines. Personal exposure data for a single 24-hour period was acquired with the EMDEX. The EMDEX's event-marker button was used to partition exposures into Home and Away components. Also, three area measurements were taken for each subject during the personal exposure measurement period: 1) 24-hr fixed-site bedroom measurement with a second EMDEX; 2) Spot measurements in at least three rooms of every residence; and 3) Spot measurements outside each residence. Residence near transmission lines highly loaded during the measurement period was associated with increased Home and Total exposure relative to a far-away population. Average exposure level while away from home was uniform (at about 2 mG) throughout the study population. On a quantitative level, Home exposure was correlated equivalently with Spot-In (r = .70) and the 24-hr fixed site measurement (r = .68). Correlations of area measurements with Total exposure were weaker because of the dilution effect of Away exposure (r = .64 for Spot-In; r = .61 for 24-h Bedroom). Away and Home exposures were not correlated (r = .14), which reinforced our confidence that the participants used the EMDEX correctly. The data suggest the need for caution before inferences are drawn about total personal exposure from area measurements. The study demonstrates the feasibility of obtaining valid measures of magnetic-field exposure with the personal exposure monitors that have been developed.     

Design and fabrication of well confined uniform magnetic field exposure systems

Exposure systems that provide good magnetic field uniformity, minimum stray fields, and minimal heating, vibration, and hum, as well as capability for true sham exposure in which current flows in the coils, are needed to determine rigorously the biological effects of weak magnetic fields. Designs based on acrylic polymer coil support structures and twisted pair bifilary coil windings were employed to fabricate several different systems for the exposure of laboratory animals and cell cultures to magnetic fields. These systems exhibit excellent performance characteristics in terms of exposure field uniformity, stray field containment, and exposure field cancellation in the sham exposure mode. A custom-written computer program was used to determine the best arrangement for coils with regard to field uniformity in the exposure volume and stray field containment. For in vivo exposures, modules were made up of four Merritt four-coil sets, built into a single structure and positioned to form an octapole with fields directed in the horizontal plane. For in vitro applications, two different coil configurations were selected to produce the vertical fields required. A quadrupole system, comprising modules consisting of two Merritt four-coil sets arranged side by side to limit stray fields, was built as a prototype. In the second configuration, one Merritt four-coil set was positioned inside the other to form a concentric coil set. In both in vitro systems, exposure chambers were connected to remote commercial incubators in order to reduce ambient magnetic fields in the exposure volume. An active field cancellation circuit was developed for reducing ambient AC magnetic fields in the in vitro sham exposure chamber, when necessary. These design and fabrication approaches provide systems that offer uniform field exposures and excellent stray field containment when needed and are portable, washable, and relatively inexpensive. © 1994 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Alternative magnetic field exposure metrics: relationship to TWA, appliance use, and demographic characteristics of children in a leukemia survival study.

The ongoing Childhood Leukemia Survival Study is examining the possible association between magnetic field exposure and survival of children with newly diagnosed acute lymphocytic leukemia (ALL). We report the results of the first year 24 h personal magnetic field monitoring for 356 US and Canadian children by time weighted average TWA and alternative exposure metrics. The mean TWA of 0.12 microT was similar to earlier personal exposure studies involving children. A high correlation was found between 24 h TWA and alternative metrics: 12 h day TWA, 12 night TWA, geometric mean, 95th percentile value, percentage time over 0.2 and 0.3 microT, and an estimate of field stability (Constant Field Metric). Two measures of field intermittency, rate of change metric (RCM) and standardized rate of change metric (RCMS), were not highly correlated with TWA. The strongest predictor of TWA was location of residence, with highest TWAs associated with urban areas. Residence in an apartment, lower paternal educational level, and residential mobility were also associated with higher TWAs. There were no significant differences in the appliance use patterns of children with higher TWA values. Children with the highest field intermittency (high RCM) were more likely to sit within 3 feet of a video game attached to the TV. Our results suggest that 24 h TWA is a representative metric for certain patterns of exposure, but is not highly correlated with two metrics that estimate field intermittency.     

Extremely low-frequency magnetic fields of transformers and possible biological and health effects

Physiological processes in organisms can be influenced by extremely low-frequency (ELF) electromagnetic energy. Biological effect studies have great importance; as well as measurement studies since they provide information on the real exposure situations. In this study, the leakage magnetic fields around a transformer were measured in an apartment building in Küçükçekmece, Istanbul, and the measurement results were evaluated with respect to the international exposure standards. The transformer station was on the bottom floor of a three-floor building. It was found that people living and working in the building were exposed to ELF magnetic fields higher than the threshold magnetic field value of the International Agency for Research on Cancer (IARC). Many people living in this building reported health complaints such as immunological problems of their children. There were child-workers working in the textile factories located in the building. Safe distances or areas for these people should be recommended. Protective measures could be implemented to minimize these exposures. Further residential exposure studies are needed to demonstrate the exposure levels of ELF magnetic fields. Precautions should, therefore, be taken either to reduce leakage or minimize the exposed fields. Shielding techniques should be used to minimize the leakage magnetic fields in such cases.     

Ambient 60-Hz magnetic flux density in an urban neighborhood

A residential neighborhood in Buffalo, NY, was surveyed with a magnetic field meter to evaluate whether or not spot measurements are reliable predictors of the 60-Hz fields at street corners and residences. The results of repeated measurements over 7 days at 33 street corners in this neighborhood indicate that day-to-day variation in power line magnetic fields is negligible (intraclass correlation coefficient = 0.94). Multivariate linear regression analysis of the data indicates that transmission lines and thick, three-phase primary wires near the field measurement site are strong predictors and account for the majority of the ambient magnetic field variance between locations (multiple correlation coefficient squared = 0.60; F ratio = 22.2, P less than .001). Magnetic fields measured at the front sidewalk were highly correlated with fields at the front doorsteps of 45 homes in this neighborhood (gamma = 0.81). These results suggest that ambient power line magnetic field levels at urban residences can be reliably characterized on a one-time site inspection using a hand-held magnetic field meter and a simple wiring classification system.     

Exposure of welders and other metal workers to ELF magnetic fields

This study assessed exposure to extremely low frequency (ELF) magnetic fields of welders and other metal workers and compared exposure from different welding processes. Exposure to ELF magnetic fields was measured for 50 workers selected from a nationwide cohort of metal workers and 15 nonrandomly selected full-time welders in a shipyard. The measurements were carried out with personal exposure meters during 3 days of work for the metal workers and 1 day of work for the shipyard welders. To record a large dynamic range of ELF magnetic field values, the measurements were carried out with “high/low” pairs of personal exposure meters. Additional measurements of static magnetic fields at fixed positions close to welding installations were done with a Hall-effect fluxmeter. The total time of measurement was 1273 hours. The metal workers reported welding activity for 5.8% of the time, and the median of the work-period mean exposure to ELF magnetic fields was 0.18 μT. DC metal inert or active gas welding (MIG/MAG) was used 80% of the time for welding, and AC manual metal arc welding (MMA) was used 10% of the time. The shipyard welders reported welding activity for 56% of the time, and the median and maximum of the workday mean exposure to ELF magnetic fields was 4.70 and 27.5 μT, respectively. For full-shift welders the average workday mean was 21.2 μT for MMA welders and 2.3 μT for MIG/MAG welders. The average exposure during the effective time of welding was estimated to be 65 μT for the MMA welding process and 7 μT for the MIG/MAG welding process. The time of exposure above 1 μT was found to be a useful measure of the effective time of welding. Large differences in exposure to ELF magnetic fields were found between different groups of welders, depending on the welding process and effective time of welding. MMA (AC) welding caused roughly 10 times higher exposure to ELF magnetic fields compared with MIG/MAG (DC) welding. The measurements of static fields suggest that the combined exposure to static and ELF fields of MIG/MAG (DC) welders and the exposure to ELF fields of MMA (AC) welders are roughly of the same level. Bioelectromagnetics 18:470–477, 1997. © 1997 Wiley-Liss, Inc.     

Magnetic-field flux density and spectral characteristics of motor-driven personal appliances

Flux density and spectral measurements were carried out on magnetic fields generated by several types of motor-driven personal appliances used near the body. Among the units tested were several for which the average flux densities, as determined at the surfaces of the appliance, exceeded 0.4 mT. Time-rates-of-change (dB/dt) for several units exceeded 1000 T/s, and several units exhibited high-frequency components in the low-MHz range. Use of such appliances, although normally of short duration, can represent exposure to magnetic fields of relatively high flux density, which may also have high-frequency components. Compared to other household and commercial sources of magnetic fields, those generated by certain motor-driven personal appliances may represent a significant contribution to time-weighted average exposure and may represent an important source of local induced currents in the body. Furthermore, high-frequency transients that represent only a minor contribution to time-weighted average exposure may generate significant instantaneous induced currents. © 1994 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Hypothesis: The risk of childhood leukemia is related to combinations of power-frequency and static magnetic fields

We present a hypothesis that the risk of childhood leukemia is related to exposure to specific combinations of static and extremely-low-frequency (ELF) magnetic fields. Laboratory data from calcium efflux and diatom mobility experiments were used with the gyromagnetic equation to predict combinations of 60 Hz and static magnetic fields hypothesized to enhance leukemia risk. The laboratory data predicted 19 bands of the static field magnitude with a bandwidth of 9.1 μT that, together with 60 Hz magnetic fields, are expected to have biological activity. We then assessed the association between this exposure metric and childhood leukemia using data from a case-control study in Los Angeles County. ELF and static magnetic fields were measured in the bedrooms of 124 cases determined from a tumor registry and 99 controls drawn from friends and random digit dialing. Among these subjects, 26 cases and 20 controls were exposed to static magnetic fields lying in the predicted bands of biological activity centered at 38.0 μT and 50.6 μT. Although no association was found for childhood leukemia in relation to measured ELF or static magnetic fields alone, an increasing trend of leukemia risk with measured ELF fields was found for subjects within these static field bands (P for trend = 0.041). The odds ratio (OR) was 3.3 [95% confidence interval (CI) = 0.4–30.5] for subjects exposed to static fields within the derived bands and to ELF magnetic field above 0.30 μT (compared to subjects exposed to static fields outside the bands and ELF magnetic fields below 0.07 μT). When the 60 Hz magnetic fields were assessed according to the Wertheimer-Leeper code for wiring configurations, leukemia risks were again greater with the hypothesized exposure conditions (OR = 9.2 for very high current configurations within the static field bands: 95% CI = 1.3–64.6). Although the risk estimates are based on limited magnetic field measurements for a small number of subjects, these findings suggest that the risk of childhood leukemia may be related to the combined effects of the static and ELF magnetic fields. Further tests of the hypothesis are proposed. © 1995 Wiley-Liss, Inc.     

Magnetic field exposure assessment: a comparison of various methods

The accurate and valid measurement of personal exposure to magnetic fields poses a major challenge for epidemiologic studies. When considering the various methods to assess exposure, it is unclear which measures are most relevant for studies of human disease, if any. Given these uncertainties, the Electromagnetic Fields and Breast Cancer on Long Island Study (EBCLIS) undertook a pilot study to develop the data collection protocol for a case-control study of breast cancer and magnetic fields. The pilot study used and compared various methods to assess residential exposures to magnetic fields, and related these measures to personal exposures. It included 31 women without breast cancer (mean age, 63+/-7 yr) who lived in their present homes for at least 15 yr. The pilot study consisted of an in-home interview, spot and 24-h magnetic field waveforms and broadband recordings, ground currents, wire coding, and personal 24-h broadband measurements. From the regression analyses, the model that best predicted personal magnetic field exposures included 24-h measurements in the bedroom and in the most lived-in room; as well as ground current test loads taken at the center of this most lived in room (r(2)=86%). The addition of other variables in this regression model yielded only small and nonsignificant increases in r(2). As a direct result of this pilot, EBCLIS will include ground current measurements in its protocol, which have not previously been collected as part of an epidemiologic study. Ground currents may be important because they may be richer in 180 Hz components than are the other currents in a power system. EBCLIS will have the opportunity to examine the ground-current hypothesis in the context of female breast cancer.     

ELF magnetic fields in electric and gasoline‐powered vehicles

We conducted a pilot study to assess magnetic field levels in electric compared to gasoline‐powered vehicles, and established a methodology that would provide valid data for further assessments. The sample consisted of 14 vehicles, all manufactured between January 2000 and April 2009; 6 were gasoline‐powered vehicles and 8 were electric vehicles of various types. Of the eight models available, three were represented by a gasoline‐powered vehicle and at least one electric vehicle, enabling intra‐model comparisons. Vehicles were driven over a 16.3 km test route. Each vehicle was equipped with six EMDEX Lite broadband meters with a 40–1,000 Hz bandwidth programmed to sample every 4 s. Standard statistical testing was based on the fact that the autocorrelation statistic damped quickly with time. For seven electric cars, the geometric mean (GM) of all measurements (N = 18,318) was 0.095 µT with a geometric standard deviation (GSD) of 2.66, compared to 0.051 µT (N = 9,301; GSD = 2.11) for four gasoline‐powered cars (P < 0.0001). Using the data from a previous exposure assessment of residential exposure in eight geographic regions in the United States as a basis for comparison (N = 218), the broadband magnetic fields in electric vehicles covered the same range as personal exposure levels recorded in that study. All fields measured in all vehicles were much less than the exposure limits published by the International Commission on Non‐Ionizing Radiation Protection (ICNIRP) and the Institute of Electrical and Electronics Engineers (IEEE). Future studies should include larger sample sizes representative of a greater cross‐section of electric‐type vehicles. Bioelectromagnetics 34:156–161, 2013. © 2012 Wiley Periodicals, Inc.     

Occupational magnetic field exposures of garment workers: results of personal and survey measurements

To explore the feasibility of performing an epidemiologic study of female breast cancer and magnetic field (MF) exposures, we chose to study garment workers, who reportedly have some of the highest MF exposures. We collected personal exposure (PE, n = 48) and survey measurements (n = 77) near commercial sewing machines at three garment facilities and conducted a pilot interview among 25 garment workers asking about exposure duration, activities, and machine characteristics. MF levels were higher for older machines with alternating current (AC) than newer machines with direct current (DC) motors. MF levels were comparable for both idling and sewing activities. Most interviewed workers could describe duration of exposure and machine type (automatic/manual), but not other machine characteristics. Measurements were lower than previously reported for garment workers but were higher than exposures to most women. A historical exposure assessment can be conducted by linking duration of exposure with reconstructed exposure measurements but may be limited by the accuracy of work history data.     

Power-frequency magnetic fields at 50 Hz do not affect fertility and development in rats and mice

In the present study, the effects of power-frequency magnetic fields (PF-MF) on fertility and development were investigated in rats and mice. Adult Sprague-Dawley rats and C57BL/6J mice were divided into four groups: a sham exposure group and 30-µT, 100-µT and 500-µT PF-MF exposure groups. The rats were exposed for 24 weeks, and the exposure time for mice ranged from 18 d to 12 weeks, dependent on the different investigated end points. The rats and mice were exposed for 20 h/d. Plasma hormone levels in rats and mice were analyzed. Furthermore, pregnancy rates and implanted embryos were recorded in pregnant mice. Finally, the neonatal growth of mice was evaluated. The results showed that none of the three intensities affected the body weight and paired ovary weight in female rats. Meanwhile, none of the three intensities affected the body weight, weights of paired testes, weights of paired epididymis and sperm count in male rats. Similarly, no significant differences were found in plasma sex hormone levels between the different PF-MF exposure groups and the sham exposure group. In addition, the pregnancy rates and implanted embryos were not significantly different between the four groups. Moreover, PF-MF exposures had no effects on either the number of fetuses in pregnant mice or the growth and development of neonatal mice.     

Estimation of 50-Hz Electrically Vs. Magnetically Generated Body Currents in Sleeping Subjects

The exposure from low-frequency electric and magnetic fields to sleeping subjects was analyzed at 343 sites. To establish the exposure due to electric fields, a new method was used to measure the current density on the body surface of the test subjects lying in their beds. The exposure due to magnetic fields was determined by short-term measurements of the magnetic flux density using induction coils. The exposures from the electric and magnetic fields were compared. The result was that, in general, the electric fields contribute much more to the total exposure than the magnetic fields.     

Magnetic field characteristics of electric bed-heating devices

Measurements of the flux density and spectra of magnetic fields (MFs) generated by several types of electric bed heaters (EBH) were made in order to characterize the MFs to which the fetus may be exposed in utero from the mother's use of these devices. Data on MFs were gathered from more than 1,300 in-home and laboratory spot measurements. In-home measurements taken at seven different positions 10 cm from the EBHs determined that the mean flux density at the estimated position of the fetus relative to the device was 0.45 μT (4.5 mG) for electric blankets and 0.20 μT (2.0 mG) for electrically heated water beds. A rate-of-change (RC) metric applied to the nighttime segment of 24 h EMDEX-C personal-dosimeter measurements, which were taken next to the bed of volunteers, yielded an approximate fourfold to sixfold higher value for electric blanket users compared to water-bed heater users. These same data records yielded an approximate twofold difference for the same measurements when evaluated by the time-weighted-average (TWA) MF exposure metric. Performance of exposure meters was checked against standard fields generated in the laboratory, and studies of sources of variance in the in-home measurement protocols were carried out. Spectral measurements showed that the EBH's measured produced no appreciable high-frequency MFs. Data gathered during this work will be used in interpreting results from a component of the California Pregnancy Outcome Study, which evaluates the use of EBHs as a possible risk factor in miscarriage. © 1996 Wiley-Liss, Inc.