Investigation of a spontaneous abortion cluster: Lessons learned

An investigation of a reported spontaneous abortion excess in an office environment was undertaken employing a multidisciplinary approach, including (1) an epidemiologic/ validation step; (2) an industrial hygiene survey, including electromagnetic field measurements and indoor air quality determinations; and (3) a risk perception/risk communication component. This approach was needed because there are numerous chemical and physical agents and psychosocial stressors that may potentially impact the reproductive status of female office workers. Although video display terminals (VDTs) are typically the focus of spontaneous abortion (SAB) investigations, one cannot ignore other stressors in the environment. Magnetic field exposures within a payroll area were determined using a hand-held survey meter and data logging dosimeter. On average, the full shift time-weighted average exposures of workers to extremely low frequency (ELF) magnetic fields in the payroll office area ranged from 1.0 to 5.6 mG. Influencing the investigation's protocol design were the Centers for Disease Control's (CDC's) recent Guidelines for Investigating Clusters of Health Events. Although these guidelines grew primarily out of cancer cluster investigations, we applied them in this instance and found them to be generalizable to reproductive hazards investigations. A spontaneous abortion excess was validated over a 2-year period among 26 women with 32 reproductive events, with rates 1.5–2.5 times the expected, depending on comparison figures used. Lessons learned in the investigation, including the applicability of the CDC's Cluster Investigation Protocol and the enormous importance of risk perception and risk communication, are described. © 1994 Wiley-Liss, Inc.     

Comparison of extremely low frequency (ELF) magnetic field personal exposure monitors

The MultiWave System III (MW III), a recently developed personal monitor for extremely low frequency (ELF) magnetic fields, was compared with the standard EMDEX Lite (Electric and Magnetic Field Digital Exposure System), the type of monitor widely used in epidemiology and other exposure assessments. The MW III captures three-axis magnetic field waveforms for the calculation of many exposure metrics, while the EMDEX monitors measure only the root-mean-squared (RMS) vector magnitude (or resultant). Thirty-eight partial period personal samples were monitored in six different job classifications. The sampling time for each personal sample ranged from 90 to 133 min, with a mean sample time of 110 min. The EMDEX Lite and MW III were evaluated by comparing the maximum and partial period time-weighted average (TWA) of the ELF magnitude. TWA exposures measured for the 38 partial period samples by the EMDEX Lite ranged from 1.2 to 65.3 mG, with a mean of 18.1 mG, while corresponding values for the MW III ranged from 1.1 to 65.8 mG, with a mean of 17.7 mG. The maximum magnetic field exposures measured for the 38 partial period personal samples by the EMDEX Lite ranged from 27.0 to 420.2 mG, with a mean of 216.3 mG, while corresponding values for the MW III ranged from 40.2 to 1311.8 mG, with a mean of 368.4 mG. The maximum and TWA ELF magnetic field exposures measured by the EMDEX Lite and MW III were compared using a two-tailed, paired t-test. Analyses indicate that there was no significant difference in the TWA magnetic field magnitude measured by the EMDEX Lite and MW III. On the other hand, the EMDEX Lite reported significantly lower (P=0.002) maximum magnetic field measurements compared to the MW III. From a detailed analysis of the time traces, the EMDEX Lite appears to measure the ELF magnitude inaccurately when the field changes rapidly over a 4-s sampling interval. The results of this comparison suggest that the standard EMDEX Lite and MW III provide similar measure of the TWA magnetic field in a variety of occupational settings and ELF magnetic field magnitudes. However, the EMDEX Lite underestimates maximum exposures when compared to the MW III.     

60 hertz magnetic field exposure assessment for an investigation of leukemia in telephone lineworkers

The purpose of this paper is to present the assessment of magnetic field exposure conducted as a part of a nested case-control investigation of leukemia mortality in telephone lineworkers. For the purposes of exposure classification, telephone company jobs were initially divided into two classes: those with potential for working in an electric environment, referred to as linework jobs, and those not working in an electric environment, referred to as nonlinework jobs. Linework jobs were further divided into the following four categories: outside plant technicians (OPT), installation/maintenance/repair (IMR) technicians, central office technicians (COT), and cable splicing technicians (CST). These job groupings were based on similarity of work tasks and exposure environments. Emdex data-logging dosimeters were used to measure personal exposures to ELF magnetic fields for 204 telephone company workers. Three general classes of exposure indices were calculated for each exposure record: measures of central tendency, measures of peak or maximum exposure, and measures of exposure variability. CSTs had the highest full-shift mean and median exposure, 4.3 and 3.2 mG, respectively. CSTs also ranked the highest, with average peak, average 95th percentile, and average time above background equal to 99.2 mG, 11.1 mG, and 156 min, respectively. In addition, the results suggest the OPT and IMR technicians have exposures similar to nonlineworkers. Exposure classifications, therefore, which misclassify all lineworkers into one “telephone lineworker” job grouping are not appropriate and future studies should concentrate on cable splicing technicians.     

Individual estimation of exposures to extremely low frequency magnetic fields in jobs commonly held by women

Exposures to extremely low frequency (ELF) magnetic fields have not been documented extensively in occupations besides the work environments of electric or telephone utilities. A 1980-1993 study of childhood acute lymphoblastic leukemia (ALL) in Québec, Canada, gathered detailed information about the occupations of 491 mothers of ALL cases and mothers of a similar number of healthy controls. This information was combined with published data on the intensities of ELF magnetic fields associated with sources or work environments to estimate ELF magnetic field exposures for a wide range of jobs commonly held by women. Estimated exposures for 61 job categories ranged from 0.03 to 0.68 microT; the 25th, 50th, and 75th percentiles were 0.135, 0.17, and 0.23 microT, respectively. By job category, the most highly exposed jobs (>0.23 microT) included bakery worker, cashier, cook and kitchen worker, electronics worker, residential and industrial sewing machine operator, and textile machine operator. By work environment, the most highly exposed job categories were electronics worker in an assembly plant (0.70 microT) and sewing machine operators in a textile factory (0.68 microT) and shoe factory (0.66 microT). These results provide new information on expected levels of exposure in a wide range of jobs commonly held by women.     

Assessment of magnetic field exposures for a mortality study at a uranium enrichment plant

A survey of workplace exposures to 60-Hz magnetic fields was carried out at a large uranium enrichment facility to assign exposures for an updated mortality study. Stratified random selection was used to choose workers for measurement in all jobs and areas, to determine whether consistent distinctions could be made between job groups based on average magnetic field exposures. A total of 252 workdays was measured with a personal monitor, and individual average magnetic field exposures ranged from 0.20 to 82.6 mG. A priori job groups showed significant differences between geometric mean exposures, which ranged from 0.80 to 3.51 mG. Most of these groups showed widely ranging exposures, so they were subdivided based on location and job title to improve the precision of the exposure assignments for the mortality study. These final assignments were made up of 26 groups having arithmetic means ranging from 0.43 to 24.9 mG, with most groups defined by location in addition to job title. In general, electrical maintenance workers did not have elevated magnetic field exposures (> 3 mG), but the exposures of the electricians in switchyard (substation) jobs were elevated. Available employment records did not allow most electricians to be distinguished based on location, so they were assigned exposures based on their plantwide average (above 7 mG). An estimated 9% of the work time of this cohort was spent at daily average exposures above 3 mG, despite the very large electric power consumption at this plant.     

Flight deck magnetic fields in commercial aircraft

BACKGROUND: Airline pilots are exposed to magnetic fields generated by the aircraft's electrical system. The objectives of this study were (1) to directly measure flight deck magnetic fields in terms of personal exposure to the pilots when flying on different aircraft types over a 75-hour flight-duty month, and (2) to compare magnetic field exposures across flight deck types and job titles. METHODS: Measurements were taken using personal dosimeters carried by either the Captain or the First Officer on Boeing 737/200, Boeing 747/400, Boeing 767/300ER, and Airbus 320 aircraft. RESULTS: Approximately 1,008 block hours were recorded at a sampling frequency of 3 seconds. Total block time exposure to the pilots ranged from a harmonic geometric mean of 6.7 milliGauss (mG) for the Boeing 767/300ER to 12.7 mG for the Boeing 737/200. CONCLUSIONS: Measured flight deck magnetic field levels were substantially above the 0.8-1 mG level typically found in the home or office and suggest the need for further study to evaluate potential health effects of long-term exposure.     

Comparison of personal exposure meter placement for the determination of office worker ELF magnetic field exposures.

This article compares extremely low frequency (ELF) magnetic field exposures measured by placing EMDEX Lite personal exposure meters (PEMs) at the head, chest, and waist level for a group of office workers. Twenty-three volunteers were solicited to wear three PEMs simultaneously; one was attached to a baseball cap worn on the head, one was attached to a band and worn around the neck (positioned on the chest), and one was worn in a belted pouch around the waist (positioned on the right side of the hip). The effect of PEM placement was evaluated by comparing full-shift average exposures and daily maximum or peak exposure. The results of this investigation indicate that time-weighted average magnetic field exposures determined at the hip provide the highest mean exposure estimates. Averages of the full-shift mean magnetic field measurements taken at hip and head levels were statistically greater than measurements taken at the chest level by 33 and 22%, respectively. Comparisons of the maximum or peak magnetic field exposures by body position indicate that the hip position produced an average exposure estimate that was 136% greater than the average head-level measurement. Results suggest that for office workers PEM meter placement on the body does not produce large differences in full-shift average ELF magnetic flux density exposures. However, the hip position produced the largest daily maximum or peak exposures. It is recommended that PEMs be placed on the hip for exposure assessments in office environments, because this placement is the most commonly used, the most convenient, and resulted in the highest magnetic field exposures.     

Risks of leukaemia among residents close to high voltage transmission electric lines.

OBJECTIVES: To reassess the risk of leukaemia associated with residential exposure near high voltage transmission electric lines of 49 kV and above in view of the recent publications. METHODS: Through a review of papers considering the risk of leukaemia among people living near high voltage transmission lines, the combined risks of leukaemia were calculated for distances < or = 50 m and < or = 25 m and for exposures at 2 mG, 3 mG, 4 mG, and 10 mG. RESULTS: The combined analysis of the contributive studies indicated an estimate of risk (odds ratio (OR)) for exposure > or = 2 mG of 1.3, 95% confidence interval (95%CI) 1.0 to 1.7. The ORs increased with exposures at 3 mG, 4 mG, and 10 mG. The risks were also increased for distances of 50 and 25 m from the lines. CONCLUSIONS: This meta-analysis tends to confirm the presence of an association between exposure to magnetic fields and leukaemia among people who reside in the vicinity of high voltage transmission electric lines of > or = 49 kV. There is consistency across studies. Measures of exposure used in the studies were either distance from the lines or calculated fields estimated from pertinent line features. The results apply to adults as well as to children.     

Parental occupational exposures to electromagnetic fields and radiation and the incidence of neuroblastoma in offspring

We examined parental occupational exposures to electromagnetic fields and radiation and the incidence of neuroblastoma in offspring. Cases were 538 children diagnosed with neuroblastoma between 1992 and 1994 in the United States or Canada. Age-matched controls were selected by random-digit dialing. Occupational exposures to electrical equipment and radiation sources were classified by an industrial hygienist, and average exposures to extremely low frequency magnetic fields were estimated using a job exposure matrix. Maternal exposure to a broad grouping of sources that produce radiofrequency radiation was associated with an increased incidence of neuroblastoma (odds ratio = 2.8; 95% confidence interval = 0.9-8.7). Paternal exposure to battery-powered forklifts was positively associated with neuroblastoma (odds ratio = 1.6; 95% confidence interval = 0.8-3.2), as were some types of equipment that emit radiofrequency radiation (odds ratios congruent with 2.0); however, the broad groupings of sources that produce ELF fields, radiofrequency radiation, or ionizing radiation were not associated with neuroblastoma. Paternal average extremely low frequency magnetic field exposure >0.4 microTesla was weakly associated with neuroblastoma (odds ratio = 1.6; 95% confidence interval = 0.9-2.8), whereas maternal exposure was not. Overall, there was scant supportive evidence of strong associations between parental exposures in electromagnetic spectrum and neuroblastoma in offspring.     

Magnetic field exposure of commercial airline pilots

PURPOSE: Airline pilots are exposed to magnetic fields generated by the aircraft's electrical and electronic systems. The purpose of this study was to directly measure the flight deck magnetic fields to which commercial airline pilots are exposed when flying on different aircraft types over a 75-hour flight-duty month.METHODS: Magentic field measurements were taken using personal dosimeters capable of measuring magnetic fields in the 40-800 Hz frequency range. Dosimeters were carried by either the Captain or the First Officer on Boeing 737/200, Boeing 747/400, Boeing 767/300ER, and Airbus 320 aircraft. The data were analyzed by aircraft type, with statistics based on block hours. Block hours begin when the aircraft departs the gate prior to take off and end when the aircraft returns to the gate after landing.RESULTS: Approximately 1008 block hours were recorded at a sampling rate of 3 seconds. Total block time exposure to the pilots ranged from a harmonic geometric mean of 6.7 milliGauss (mG) for the Boeing 767/300ER to 12.7 mG for the Boeing 737/200.CONCLUSIONS: Measured flight deck magnetic field levels were substantially above the 0.8 to 1 mG level typically found in the home or office and suggest the need for further study to evaluate potential health effects of long-term exposure.     

Exposure to extremely low frequency magnetic fields among working women and homemakers.

Given concerns with potential health effects of exposure to magnetic fields, the goal of this study was to examine the magnitude and sources of occupational and residential exposure to extremely low frequency (primarily 60 Hz) magnetic fields among women. Exposure to 60 Hz magnetic fields was surveyed among cases and controls recruited for a study of breast cancer in 25 counties in North Carolina. The 273 women who participated wore an integrating personal magnetic-field exposure meter (AMEX 3-D) that measured their time-weighted average (TWA) exposure. A questionnaire was administered to determine the duration and frequency of electric appliance and machinery use. The geometric mean (GM) of the TWA exposure for employed women was 0.138 microT (range 0.022-3.636 microT) and for homemakers 0.113 microT (range 0.022-0.403 microT). Women working in manufacturing and industrial facilities had the highest exposure (GM 0.265 microT, range 0.054-3.436 microT), while nurses and health technicians (GM 0.134 microT, range 0.032-0.285 microT) and teachers and school administrators (GM 0.099 microT, range 0.035-0.673 microT) had the lowest exposures. Job titles, unless very limited in scope and/or environment, self-reported information about equipment use, potential exposure sources, time, and distance were not good predictors of magnetic-field exposure. Furthermore, the results show that occupations previously observed to have increased risk of breast cancer, such as teachers, nurses, administrative support, and housewives, did not have elevated average magnetic field exposures. Therefore, it is questionable whether exposure to power frequency magnetic fields is the cause of the increased breast cancer risk seen in these occupations.     

Occupational exposures of pharmacists and pharmaceutical assistants to 60 Hz magnetic fields

We carried out the study to assess, using field surveys and personal dosimetry, the potential exposure of pharmacists and pharmaceutical assistants to 60 Hz magnetic fields in a medical center of Taiwan. Field surveys were conducted twice in the pharmacy where two workers were randomly selected and solicited to wear personal dosimetry instruments for a full-shift assessment of personal exposure. We used an EMDEX II for on site measurements and did not consider any specific instrument or equipment for health care services as potential sources of magnetic field. The results showed that the average magnetic flux densities for the selected areas were between 0.63 mill-Gauss (mG) and 2.23 mG, while the full-shift time-weighted-average exposure for the two selected workers was 4.98 mG and 6.54 mG, respectively. Both inadequate consideration for the field survey of the temporal variability in magnetic flux densities over the workday and that the monitored workers spent almost half of the full-shift working in places outside of the study areas may have contributed to such discrepancy in results between field survey and personal dosimetry. This study suggests that the potential for elevated exposure to 60 Hz magnetic fields in health care settings does exist, and that using job title as a surrogate for magnetic fields exposure classification might entail certain degrees of misclassification. Although limited in its scope and sample size, the study presented here seems to demonstrate the inadequacy of using stationary workplace measurements for the assessment of personal occupational exposure to 60 Hz magnetic fields.     

Interaction of extremely low frequency electric and magnetic fields with humans

The dosimetry and physical interaction mechanisms of electromagnetic fields with frequencies in the extremely low frequency (ELF) range (below 300 Hz) are described. The mechanisms through which ELF electric and magnetic fields induce electric currents in living organisms are summarized, with particular emphasis on humans. Topics that are discussed include: (1) sources and measurements of ELF electric and magnetic fields; (2) direct and indirect coupling of these fields to humans; (3) transient discharges and contact currents, and the thresholds for human response to these phenomena; (4) protective measures for the mitigation of potential ELF field effects on humans; and (5) mechanisms of interaction of ELF fields with cellular and tissue systems, with emphasis on field transduction mechanisms involving the cell membrane.     

Electric and magnetic field exposures for people living near a 735-kilovolt power line.

The purpose of this study was to assess the effect of a 735-kV transmission line on the electric and magnetic field exposures of people living at the edge of the line's right of way. Exposure of 18 adults, mostly white-collar workers, living in different bungalows located 190-240 feet from the line (exposed subjects) was compared to that of 17 adults living in similar residences far away from any transmission line. Each subject carried a Positron meter for 24 hr during 1 workday, which measured 60-Hz electric and magnetic fields every minute. All measurements were carried out in parallel for exposed and unexposed subjects during the same weeks between September and December. During measurements the average loading on the line varied between 600 and 1100 A. The average magnetic field intensity while at home was 4.4 times higher among exposed subjects than unexposed (7.1 versus 1.6 mG, p = 0.0001) and 6.2 times higher when considering only the sleeping period (6.8 versus 1.1 mG, p = 0.0001). Based on the 24-hr measurement, average magnetic field exposure was three times higher among the exposed. Electric field intensity was also higher among the exposed while at home (26.3 versus 14.0 V/m, p = 0.03). Magnetic field intensity among the exposed was positively correlated with the loading on the line (r = 0.8, p = 0.001). Percentage of time above a magnetic field threshold (2 mG or 7.8 mG) was a good indicator to distinguish the two types of exposure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exposure to extremely-low-frequency electromagnetic fields and radiofrequency radiation: cardiovascular effects in humans

Cardiovascular changes in humans exposed to nonionizing radiation [including extremely-low-frequency electromagnetic fields (ELF EMFs) and radiofrequency radiation (RFR)] are reviewed. Both acute and long-term effects have been investigated. In general, if heating does not occur during exposure, current flow appears to be necessary for major cardiovascular effects to ensue, such as those due to electric shock. Whereas most studies have revealed no acute effect of static or time-varying ELF EMFs on the blood pressure, heart rate, or electrocardiogram waveform, others have reported subtle effects on the heart rate. The possible health consequences of these results are unknown. Regarding long-term effects of ELF EMFs, reports from the former Soviet Union in the early 1960s indicated arrhythmias and tachycardia in high-voltage-switchyard workers. Subsequent studies in Western countries, however, did not confirm these findings. These studies are limited by uncertainties regarding exposure durations and appropriate control groups. Investigations of acute cardiovascular changes in humans purposely exposed to RFR have been limited to studies of magnetic resonance imaging (which, in addition to RFR, involves static and time-varying magnetic fields). It has been concluded that such exposures, as presently performed, are not likely to cause adverse cardiovascular effects. Reports of hypertension in workers potentially exposed to high levels of RFR during accidents are considered to be incidental (due to anxiety and posttraumatic stress). Soviet investigators have also indicated that long-term RFR exposure may result in hypotension and bradycardia or tachycardia. Other researchers, however, have been incapable of replicating these results, and some scientists have attributed the effects to chance variations and mishandling of data. In summary, studies have not yielded any obvious cardiovascular-related hazards of acute or long-term exposures to ELF EMFs or RFR at levels below current exposure standards. Received: 18 July 1996 / Accepted: 29 November 1996     

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.     

Exposure assessment for electric and magnetic fields.

Exposure assessment for extremely low frequency (ELF) electric and magnetic fields (EMF) is discussed. It is suggested that such assessments can be designed by attempting to mimic the receptor's experience of interest. Present efforts are, however, hampered by the lack of clearly defined human health effects, or even important interaction mechanisms, which might be used to define the appropriate exposure measure, the experience of interest. The state of the art of ELF EMF exposure assessment is described, including the use of surrogates, models, and available instrumentation. Data indicate that magnetic field levels in the home are of the order of 0.1 microT and that nonoccupational total exposures may best be predicted by levels in the bedroom. Occupational exposures may be orders of magnitude higher where high currents are present.     

The cardiovascular response to an acute 1800-μT, 60-Hz magnetic field exposure in humans

Purpose  

Previously published literature has suggested an effect of extremely low-frequency (ELF) magnetic fields (MF) on human heart rate (HR) and heart rate variability (HRV). The combined response of the microcirculation and macrocirculation to ELF MF exposure has not previously been studied in humans. This study investigated the effects of 1-h exposure to an 1800-μT, 60-Hz MF on human microcirculation (represented in this study as skin blood perfusion), HR, low-frequency HRV, and high-frequency HRV.     

Epidemiological studies of work with video display terminals and adverse pregnancy outcomes (1984–1992)

Many epidemiological studies have investigated the claim that work with video display terminals (VDT) is a risk factor during pregnancy. Results have been inconsistent, although in the majority of cases the hypothesis was not supported. Exposure assessment has been very poor and the statistical power of the studies generally low. Overall, the studies indicate that VDT operators are not at greater risk than the general population, because very low frequency (VLF) magnetic fields do not appear to be a risk factor and extremely low frequency (ELF) magnetic field exposure is not significantly greater than that experienced in other occupational and residential environments. However, since some studies lend support to the hypothesis that ELF magnetic fields may be a risk factor for pregnancy outcome, studies of subjects exposed to higher than average ELF fields are justified.     

Hazard surveillance for industrial magnetic fields: II. Field characteristics from waveform measurements

Magnetic field characteristics have been surveyed systematically in six factories with the Multiwave(R) II waveform capture instrument. These six facilities manufactured plastics, pharmaceuticals, cement, liquid air products, aluminum parts, and aluminum-framed filters. The study goals were to survey the physical characteristics of magnetic fields that may be related to biological effects under various interaction mechanisms and to relate those characteristics to the field's sources. From 59 waveform measurements at worker locations near sources, we calculated the extremely low frequency (ELF) and static field magnitudes, their frequency characteristics, and spatial characteristics of the 60Hz component. The RMS vector magnitude of the ELF magnetic field (the usual exposure metric in most studies) had medians ranging from 0.53 to 12.83 microT in the six factories. The static magnetic field magnitudes had medians of 24.2-46.2 microT, which is well below the geomagnetic reference field of 55.0 microT because of shielding from steel structures. The maximum static field was 128.6 microT near a DC motor. The frequency spectra of the most common fields is dominated by 60Hz, and has a median total harmonic distortion equal to 14.8%. The most common higher frequencies are the third, fifth, and second harmonics of 60Hz. However, magnetic fields in these workplaces had many other 60Hz harmonics and non-harmonic frequencies due particularly to electric motors and computer monitors. The 60Hz component magnetic fields have elliptical polarization with median axial ratio of 25.4%. The average proportion of the 60Hz component parallel to the static field vector was 51.5+/-3.0%, which indicates a significant trend towards perpendicular orientation between these two field components. In this survey of only six factories, the Multiwave(R) II measurements documented a wide diversity of complex magnetic field characteristics and non-sinusoidal waveforms. Although these characteristics are important to the various mechanisms postulated to explain biological effects, they are overlooked by the popular exposure assessment methods which only measure the ELF magnitude. Therefore, spot measurements with the Multiwave(R) II or similar waveform capture instruments are necessary for a complete magnetic field exposure assessment.