Exposure of children to residential magnetic fields in Norway: Is proximity to power lines an adequate predictor of exposure?

The aim of this work was to study the exposure to magnetic fields of children living at different distances from a power line and to evaluate how well theoretical calculations compared with actual exposure. Personal exposure instruments were carried for 24 h by 65 schoolchildren living 28–325 m from a 300 kV transmission line; the current load was 200–700 A. About half of the children attended a school far from the power line, whereas the other half attended a school located about 25 m from the line. Exposure to magnetic fields was analyzed for three categories of location: at home, at school, and at all other places. Time spent in bed was analyzed separately. The results indicated that children who lived close to a power line had a higher magnetic field exposure than other children. The power line was the most important source of exposure when the magnetic field due to the line was greater than about 0.2 μT. Exposure at school influenced the 24 h time-weighted average results considerably in those cases where the distance between home and power line was very different from the distance between school and power line. The calculated magnetic field, based on line configuration, current load, and distance between home and power line, corresponded reasonably well with the measured field. However, the correlation depends on whether home only or 24 h exposure is used in the analysis and on which school the children attended. The calculated magnetic field seems to be a reasonably good predictor of actual exposure and could be used in epidemiological studies, at least in Norway, where the electrical system normally results in less ground current than in most other countries. Bioelectromagnetics 18:47–57, 1997. © 1997 Wiley-Liss, Inc.     

Residential exposure to magnetic fields generated by 110-400 kV power lines in Finland

In a specific case, the magnetic field generated in a building by a nearby power line is usually easy to calculate, although the accuracy of these calculations is sensitive to the quality of source information. To be able to study public health dimensions of magnetic field exposure (e.g., risk of cancer), it is necessary to evaluate the size and exposure of the population at risk. Relatively little quantitative information on public exposure to power-frequency magnetic fields of high-voltage power lines is available. This report describes residential exposure to magnetic fields from 110 kV, 220 kV, and 400 kV power lines in Finland at the national level, including 90% of the total line length in 1989. A geographical information system (GIS) was used to identify the buildings located near the power lines. After determining the distances between the lines and the buildings, historical data on load currents of these lines were used to calculate the magnetic fields. The residential magnetic field histories were then linked to the residents by means of a computerized central population register. The data obtained on personal exposure have also been utilized in a nationwide epidemiological study on magnetic field exposure of power lines and risk of cancer. The methods of exposure assessment and results of the number of buildings near 110 kV, 220 kV, and 400 kV power lines, their average annual magnetic fields, and personal exposure to magnetic fields from these lines are described. We found that 15,600 residents lived in an average residential magnetic field ≥0.1 μT caused by power lines in 1989. The number of these residents increased fivefold during 1970-1989. We estimated that 0.3% of the population was exposed in their residences to an annual average magnetic flux density from 110 kV, 220 kV, and 400 kV power lines higher than 0.1 μT, the level that the background magnetic flux density in general does not exceed in Finnish homes. Thus, the problem of magnetic field exposure generated by high-voltage lines concerns only a relatively small fraction of the total population in Finland. However, the size and exposure of the population at risk remain somewhat arbitrary in practical multisource situations, as the biological interaction mechanism, the concept of harmful dose, and, in particular, the significance of the duration of exposure are unknown. © 1995 Wiley-Liss, Inc.     

Health effects of static magnetic fields--a review of the epidemiological evidence

Potential health effects of static magnetic fields have received far less attention than, for example, power frequency or radiofrequency fields. Static fields are found in certain occupational settings, e.g. in the aluminium and chloralkali industries, in arc-welding processes, and certain railways systems. Magnetic resonance imaging (MRI) for medical diagnosis is another source. This paper summarizes the epidemiological evidence of static magnetic field exposure and long-term health effects. There are only a few epidemiological studies available, and the majority of these have focused on cancer risks. There are some reports on reproductive outcomes, and sporadic studies of other outcomes. Overall, few occupational studies have focused specifically on effects of static magnetic field exposure, and exposure assessment have consequently been poor or non-existent. Results from studies that have estimated static magnetic field exposure have not indicated any increased cancer risks, but they are generally based on small numbers of cases and crude exposure assessment. Control of confounding has been limited, and it is likely that the “healthy worker” effect have influenced the results. A few studies have reported results on reproductive outcomes among aluminium workers and MRI operators, but limitations in study designs prevent conclusions. A problem in epidemiological studies of static magnetic fields is that workers in exposed occupations are also exposed to a wide variety of other potentially harmful agents, including some known carcinogens. In conclusion, the available evidence from epidemiological studies is not sufficient to draw any conclusions about potential health effects of static magnetic field exposure.     

ELF magnetic fields in a city environment

Some epidemiological studies indicate an association between extremely low frequency electromagnetic field (ELF-EMF) exposure and cancer risks. These studies have mainly taken residential and occupational exposure into consideration. Outdoor environments are often considered as low level areas, but in this paper we show that this is not true in a city environment. We have mapped the ELF magnetic flux densities along certain stretches of sidewalk in central G?teborg City, Sweden. About 50% of the investigated street length shows flux densities of the same order of magnitude (0.2 microT and above) as those associated with increased risks of cancer in epidemiological studies. We conclude that the outdoor exposures in a city environment also should be considered in exposure assessments and risk evaluations. These elevated flux densities are probably due to stray currents. We also found strong magnetic flux densities (> 1.0 microT) close to ordinary distribution pillars, power substations, shoplifting alarms, and other electrical devices.     

An analysis of associations between social class and ambient magnetic fields in metropolitan Melbourne.

In the course of a study on residential magnetic-field exposure, some incidental data were obtained that bear on the issue of confounding of magnetic field exposure by social class. We have explored the possibility that the magnetic flux density of 50 Hz fields measured in Melbourne streets is correlated with a number of variables that index the socio-economic status of the neighborhood. We have examined also for a correlation between field-intensity levels and sums of some or all of the indicators, which were weighted to provide an overall score on socio-economic status. Although some of the indexes were weakly, but significantly, correlated with environmental levels of magnetic fields, the combined indices were not. These results indicate that socio-economic status is not likely to be a confounder in epidemiological studies of residential exposure to ELF magnetic fields in Melbourne.     

Long-term effects of 60-Hz electric vs. magnetic fields on IL-1 and IL-2 activity in sheep

This study was designed to assess the effect of exposure to long-term extremely low-frequency electric and magnetic fields (ELF-EMF) from a 500 kV transmission line on IL-1 and IL-2 activity in sheep. The primary hypothesis was that the reduction in IL-1 activity observed in our two previous short-term studies (10 months) was due to EMF exposure from this transmission line. To repeat and expand these studies and to characterize the components of EMF responsible for the previously observed reduction in IL-1 activity, the current experiment examined not only the effect of exposure to electric and magnetic fields, but also the magnetic field component alone. In the current study, IL-2 was examined to characterize the effects of EMF exposure on an indicator of T cell responses. 45 Suffolk ewe lambs were randomized into three groups of 15 animals each. One group of animals was placed in the EMF pen, located directly beneath the transmission line. A second group was placed in the shielded MF (magnetic field only) pen, also directly beneath the transmission line. The third group of animals was placed in the control pen located several hundred meters away from the transmission line. During the 27 month exposure period, blood samples were taken from all animals monthly. When the data were analyzed collectively over time, no significant differences between the groups were found for IL-1 or IL-2 activity. In previous studies ewe lambs of 8-10 weeks of age were used as the study animals and significant differences in IL-1 activity were observed after exposure of these animals to EMF at mean magnetic fields of 3.5-3.8 microT (35-38 mG) and mean electric fields of 5.2-5.8 kV/m. At the start of the current study EMF levels were reduced as compared to previous studies. One interpretation of the current data is that magnetic field strength and age of the animals may be important variables in determining whether EMF exposure will affect IL-1 activity.     

ELF-magnetic flux densities measured in a city environment in summer and winter

Epidemiological studies have indicated a connection between extremely low frequency magnetic flux densities above 0.4 microT (time weighted average) and childhood leukemia risks. This conclusion is based mainly on indoor exposure measurements. We therefore regarded it important to map outdoor magnetic flux densities in public areas in Trondheim, Norway. Because of seasonal power consumption variations, the fields were measured during both summer and winter. Magnetic flux density was mapped 1.0 m above the ground along 17 km of pavements in downtown Trondheim. The spectrum was measured at some spots and the magnetic flux density emanated mainly from the power frequency of 50 Hz. In summer less than 4% of the streets showed values exceeding 0.4 microT, increasing to 29% and 34% on cold and on snowy winter days, respectively. The average levels were 0.13 microT (summer), 0.85 microT (winter, cold), and 0.90 microT (winter, snow), with the highest recorded value of 37 microT. High spot measurements were usually encountered above underground transformer substations. In winter electric heating of pavements also gave rise to relatively high flux densities. There was no indication that the ICNIRP basic restriction was exceeded. It would be of interest to map the flux density situation in other cities and towns with a cold climate.     

Evaluating alternative exposure indices in epidemiologic studies on extremely low-frequency magnetic fields

Choosing the right exposure index for epidemiological studies on 50–60 Hz magnetic fields is difficult due to the lack of knowledge about critical exposure parameters for the biological effects of magnetic fields. This paper uses data from a previously published epidemiological investigation on early pregnancy loss (EPL) to study the methods of evaluating the exposure-response relationship of 50 Hz magnetic fields. Two approaches were used. The first approach was to apply generalized additive modeling to suggest the functional form of the relationship between EPL and magnetic field strength. The second approach evaluated the goodness of fit of the EPL data with eight alternative exposure indices: the 24 h average of magnetic field strength, three indices measuring the proportion of time above specified thresholds, and four indices measuring the proportion of time within specified intensity windows. Because the original exposure data included only spot measurements, estimates for the selected exposure indices were calculated indirectly from the spot measurements using empirical nonlinear equations derived from 24 h recordings in 60 residences. The results did not support intensity windows, and a threshold-type dependence on field strength appeared to be more plausible than a linear relationship. In addition, the study produced data suggesting that spot measurements may be used as surrogates for other exposure indices besides the time average field strength. No final conclusions should be drawn from this study alone, but we hope that this exercise stimulates evaluation of alternative exposure indices in other planned and ongoing epidemiological studies. © 1996 Wiley-Liss, Inc.     

Exposure classification of MRI workers in epidemiological studies

We estimate that there are about 100,000 workers from different disciplines, such as radiographers, nurses, anesthetists, technicians, engineers, etc., who can be exposed to substantial electromagnetic fields (compared to normal background levels) around magnetic resonance imaging (MRI) scanners. There is a need for well‐designed epidemiological studies of MRI workers but since the exposure from MRI equipment is a very complex mixture of static magnetic fields, switched gradient magnetic fields, and radiofrequency electromagnetic fields (RF EMF), it is necessary to discuss how to assess the exposure in epidemiological studies. As an alternative to the use of job title as a proxy of exposure, we propose an exposure categorization for the different professions working with MRI equipment. Specifically, we propose defining exposure in three categories, depending on whether people are exposed to only the static field, to the static plus switched gradient fields or to the static plus switched gradient plus RF fields, as a basis for exposure assessment in epidemiological studies. Bioelectromagnetics 34:81–84, 2013. © 2012 Wiley Periodicals, Inc.     

Exposure assessment of ELF magnetic fields in urban environments in Extremadura (Spain)

We present the results of a study of the extremely low frequency (ELF) magnetic fields in urban environments of the Extremadura region (Spain). The study included a spectral analysis, an analysis of the temporal variation, and spot measurements in the streets of four cities. The spectral analysis showed that the main source of magnetic field exposure was that corresponding to the principal power frequency (50 Hz) and its third harmonic. The magnetic flux density measured at one point over 24 h presented rapid fluctuations in short time periods. Smoothing the time series eliminated these fluctuations, showing a temporal evolution associated with the differing levels of power consumption over the course of the day. The values of the spot measurements taken in the streets were all below the ICNIRP reference level, although 30% surpassed 0.2 microT, the value that some epidemiological studies take as the threshold above which there exist risks of effects that could be harmful to health. The values found for the magnetic flux density in these urban settings were generally greater than values reported in the literature for residential areas, and similar to, although in some cases less than those in workplace environments.     

The relationship between residential magnetic fields and contact voltage: a pooled analysis

It has been suggested that residential exposure to contact currents may be more directly associated with the potential for an increased risk of leukemia in childhood than magnetic fields. Contact current exposure occurs when a child contacts a bathtub's water fixtures, which are usually contiguous with a residence's electrical ground, and when the drainpipe is conductive. The Northern California Childhood Leukemia Study (NCCLS) is the only epidemiological study known to address whether contact current may confound the reported association between residential magnetic fields and childhood leukemia. The study contributed contact voltage and magnetic-field data for over 500 residences of leukemia cases and control children. We combined these data with the results of previous measurement studies of contact voltage in other communities to conduct an analysis of the relationship of magnetic fields with contact voltage for a total sample of 702 residences. The Spearman correlation of magnetic field with contact voltage was 0.29 (Spearman, P < 0.0001). Magnetic-field and contact voltage data were both divided into tertiles, with an upper magnetic-field cutpoint of 0.3 μT suggested by values used in epidemiological results and an upper contact voltage cutpoint of 60 mV based on dosimetric considerations. Expressed as an exposure odds ratios (EOR), we report an association of contact voltage with magnetic fields of 15.1 (95% CI 3.6-61) as well as a statistically significant positive trend across magnetic-field strata (EOR of 4.2 per stratum with 95% CI 2.4-7.4). The associations appear to be large enough to support the possibility that contact current could be responsible for the association of childhood leukemia with magnetic fields.     

Electromagnetic fields and epidemiology: An overview inspired by the fourth course at the International School of Bioelectromagnetics

The fourth course at the International School of Bioelectromagnetics addressed various aspects of the epidemiology of exposure to electromagnetic fields (EMF). In this overview, inspired by the lectures and the discussions among participants, we summarize current knowledge on exposure to EMF and disease risk, with emphasis on studies of use of mobile phones and brain tumours and exposure to power lines and childhood leukaemia. Sources of bias and error hamper straightforward conclusions in some areas and, in order to move forward, improvements in study design and exposure assessment are necessary. The scientific evidence available to date on possible long‐term effects from exposure to ELF and RF fields is not strong enough to revise current protection limits based on the known acute effects of such exposures. Precautionary measures may be considered to reduce ELF exposure of children or exposure to RF during mobile phone use, keeping in mind that it is unclear whether they involve any preventive benefit. Possible health effects from mobile phone use in adults and in children should be investigated further by prospective epidemiological studies with improved exposure assessment and brain tumour incidence rates should be monitored. Further studies on the relation between childhood leukaemia and ELF magnetic fields would be worthwhile if they focus on heavily exposed groups and attempt to minimize possible selection bias. In conclusion, epidemiological studies conducted with appropriate diligence can play a key role in finding the answers. Bioelectromagnetics 30:511–524, 2009. © 2009 Wiley‐Liss, Inc.     

Power frequency magnetic fields and risk of childhood leukaemia: Misclassification of exposure from the use of the ‘distance from power line’ exposure surrogate

A recent study examining the relationship between distance to nearby power lines and childhood cancer risk re‐opened the debate about which exposure metrics are appropriate for power frequency magnetic field investigations. Using data from two large population‐based UK and German studies we demonstrate that distance to power lines is a comparatively poor predictor of measured residential magnetic fields. Even at proximities of 50 m or less, the positive predictive value of having a household measurement over 0.2 µT was only 19.4%. Clearly using distance from power lines, without taking account of other variables such as load, results in a poor proxy of residential magnetic field exposure. We conclude that such high levels of exposure misclassification render the findings from studies that rely on distance alone uninterpretable. Bioelectromagnetics 30:183–188, 2009. © 2008 Wiley‐Liss, Inc.     

Melatonin and magnetic fields

There is public health concern raised by epidemiological studies indicating that extremely low frequency electric and magnetic fields generated by electric power distribution systems in the environment may be hazardous. Possible carcinogenic effects of magnetic field in combination with suggested oncostatic action of melatonin lead to the hypothesis that the primary effects of electric and magnetic fields exposure is a reduction of melatonin synthesis which, in turn, may promote cancer growth. In this review the data on the influence of magnetic fields on melatonin synthesis, both in the animals and humans, are briefly presented and discussed.     

Numerical computation of distortions in magnetic fields and induced currents in physiological solutions produced by microscope objectives

Identifying distortions produced by commonly employed microscope objectives and their components in uniform DC and 60 Hz AC magnetic fields is important in imaging studies involving exposure of cells to spatially uniform or nonuniform magnetic fields. In this study, DC and 60 Hz AC magnetic flux densities were numerically computed in the presence of finite element models of various components of commonly utilized microscope objectives, as well as a model of a complete objective. Also computed were the distortions in the current density induced by an applied time-varying magnetic field in a physiological buffer contained within a Petri dish. We show that the magnetic flux density could be increased up to 65% in the presence of the nickel-chrome plating of an objective housing and that the presence of ferromagnetic components like a screw or spring could produce peaks that are 7% higher than the undistorted value of magnetic flux density. In addition, a slight tilt of 1% in the objective with respect to the magnetic field could cause a 93% deviation in magnetic flux density from the unperturbed value. These results correlate well with previously published experimental measurements that showed the presence of significant and sometimes asymmetric distortions in both DC and 60 Hz magnetic fields. Moreover, this study further reports that induced current density changed up to 37% compared to values in the absence of the objective. The existence of distortions in applied magnetic fields and induced currents could affect the interpretation of results of cell function studies if it is assumed that the cells are exposed to uniform magnetic flux densities in the presence of a microscope objective. Such assumptions of uniform magnetic flux density could also account for the lack of reproducibility in several studies that examined changes in intracellular calcium by imaging techniques.     

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.     

Comparison of indices of ambient exposure to 60-hertz electric and magnetic fields

Occupational, environmental, or domestic exposure of human beings to extremely low-frequency (50- or 60-Hz) electric and magnetic fields varies continuously over time. In epidemiological studies of possible health effects, exposures over long durations must be aggregated in terms of simple summary indices. However, there are many different, biologically plausible, ways of aggregating the data. While awake, each of 20 electric utility personnel and 16 office workers had provided minute-by-minute measures of incident electric (V/m) and magnetic (muT) fields over a 7-day period via personal dosimeters. Once the measures were aggregated as means, medians, peaks, and other indices, intercorrelations between all index pairs were calculated; correlation matrices are presented for the utility and office workers both by group and when pooled. Product-moment coefficients (r) greater that .80 were found between the time-weighted arithmetic mean (TWA) and indices that explicitly emphasize short but highly intense exposures, such as peak values and time above thresholds. Medians and geometric means were less highly correlated with the TWA. Use of only a few indices, perhaps the TWA alone, may sacrifice but little statistical power in most epidemiological studies of utility workers exposed to ELF fields. However, correlations between electric-field strength and magnetic-field density were generally quite weak, as were correlations of either with high-frequency transients; these findings underscore the need to measure each of these variables in epidemiological studies. Indices of exposure incurred outside the workplace were less strongly correlated, which may indicate the need to use several indices in general-population studies.     

Power lines and the geomagnetic field

The metric of prime interest in power line epidemiological studies has been AC magnetic intensity. To consider also possible geomagnetic involvement, the orientation of a long straight power line is examined relative to a uniform geomagnetic field (GMF) with dip angle α. An expression is derived for the component of the total GMF that is parallel, at an elevation β, to the circuital magnetic field that surrounds the line. This component is a function of the angles α and β, the total geomagnetic intensity B_T, and the angle θ between the axis of the power line and magnetic north. Plotting these geomagnetic parameters for known leukemia residences allows one to test for possible ion cyclotron resonance or other GMF interactions. This approach, in principle, is an easy addition to existing or planned studies, because residential access is not required to obtain local values for α, β, θ, and B_T. We recommend including these parameters in the design of epidemiological studies examining power line fields and childhood leukemia. © 1995 Wiley-Liss, Inc.     

Cancer promotion in a mouse-skin model by a 60-Hz magnetic field: I. Experimental design and exposure system.

The rationale for selection of an animal model, the experimental design, and the design and evaluation of an exposure system used in studies of 60-Hz magnetic fields are described. The studies were conceived to assay development of cancer and immune responsiveness in mice exposed to magnetic fields. The exposure system utilized a quadrupole-coil configuration to minimize stray magnetic fields. Four square-wound coil provided a uniform field within a volume occupied by 16 animal cages. The magnetic field had a mean flux density of 2 mT that varied less than +/- 10% within the volume occupied by animals' cages. The flux density decreased to less than 0.1 microT at a distance of 2 m from the coils. In each exposure system 32 animals could be housed in plastic cages.     

Pilot study of extremely low frequency magnetic fields emitted by transformers in dwellings. Social aspects

A large number of epidemiologic studies examining the potential effect of residential exposure to extremely-low frequency (ELF) magnetic fields and childhood leukemia have been published. Two pooled analyses [Ahlbom A, Day N, Feychting M, Roman E, Skinner J, Dockerty J, Linet M, et al. (2000). A pooled analysis of magnetic fields and childhood leukaemia. Br J Cancer. 83(5):692–698; Greenland S, Sheppard AR, Kaune WT, Poole C, Kelsh AM (2000). A pooled analysis of magnetic fields, wire codes, and childhood leukemia. Epidemiology. 11(6):624–634], which included the major epidemiologic studies on ELF magnetic fields and childhood leukemia showed twofold increase in childhood leukemia risk in association with residential ELF exposure above 0.3–0.4 μT. Based on “limited” epidemiologic evidence linking ELF exposure to childhood leukemia and “inadequate evidence” for carcinogenicity of ELF in rodent bioassays, the International Agency for Research on Cancer (IARC) classified ELF magnetic fields as a possible human carcinogen (2B classification) [International Agency for Research on Cancer (IARC) (2002). Non-ionizing radiation, Part 1: Static and extremely low-frequency (ELF) electric and magnetic fields. IARC monographs on the evaluation of carcinogenic risks to humans. Vol. 80. IARC Press: Lyon], confirmed by WHO on the basis of studies published after 2000 [World Health Organization. Extremely low frequency fields. In: 238 Environmental health criteria, Geneva: WHO; 2007]. The analysis of more recent studies of ELF magnetic fields and childhood leukemia had small findings and propose methodological improvements concerning the uncertainties in epidemiological approaches and exposure assessment, bias in selection of controls [Kheifets L, Oksuzyan S (2008). Exposure assessment and other challenges in non-ionizing radiation studies of childhood leukaemia. Radiat Prot Dosimetry. 132(2):139–147]. By the end of 2010, 37 countries had been identified for possible participation in the International study TRANSEXPO. The pilot work has been completed in five countries (Finland, Hungary, Israel, Switzerland and Bulgaria). In 2008, Bulgaria through the National Centre of Public Health Protection joined with pilot study in TRANSEXPO Project. At this first stage of the project our investigation was directed to performing measurements in dwellings with built-in transformer stations, collecting data of population and cancer registry and choosing the epidemiology design feasible for continuing the project. Taking into account the available sources of information in Bulgaria (different registers of the population) needed for epidemiological approach, it was found that the most appropriate epidemiology design would be the nested case-control study. Control group could be collected in accordance with the international requirements for such epidemiological studies. This approach could be modified in the course of the further study in order to ensure achievement of the purposes of the main international requirements of the study.