Exposure to residential electric and magnetic fields and risk of childhood leukemia

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.

Development and evaluation of a location-specific wire code

The development of a wire code protocol based on a study of electrical installations in Melbourne, Australia, is described. Because of very significant differences between the Melbourne power distribution system and that used in Denver, Colorado, an approach different from that used by Wertheimer and Leeper was required. A combined practical and theoretical approach was used to determine a continuous exposure index, defined as a measure of the potential for exposure due to external electrical installations. The protocol was tested on a convenient sample of 41 homes in which the field was monitored over a 12 hour overnight period. A correlation of 0.85 (95% CI 0.74-0.92, P < .0001) was obtained between the measured time-weighted average and the wire coding exposure index. To assess the efficacy of the wiring configuration index, a computer simulation of a case-control study was then performed. It was concluded that, using the same basic reasoning of the Wertheimer and Leeper code, it is possible to develop a location-specific code that provides a good correlation with the residential time-weighted average and an acceptable degree of exposure misclassification.

Cyclic AMP response in cells exposed to electric fields of different frequencies and intensities

The action on intracellular cyclic AMP (cAMP) of therapeutically used 4000-Hz electric fields was investigated and compared with 50-Hz data. Cultured mouse fibroblasts were exposed for 5 minutes to 4000-Hz sine wave internal electric fields between 3 mV/m and 30 V/m applied within culture medium. A statistically significant decrease in cellular cAMP concentration relative to unexposed cells was observed for fields higher than 10 mV/m. The drop in cAMP was most pronounced at lower field strengths (71% of controls at 30 mV/m) and tended to disappear at higher field strengths. An increase of cAMP content was observed with 50-Hz electric fields, as was also the case when 4000-Hz fields were modulated with certain low frequencies.

Suggestion of concomitant changes of electric power consumption and childhood leukemia in Greece

Over a 14-year period (1976-89) 679 deaths from childhood leukemia were registered in Greece and the corresponding mortality over this period declined by almost 70%, with no evidence of differential reduction by gender or population type. For each of the nine geographical regions of the country, slopes of decreasing mortality from childhood leukemia over the study period were calculated and correlated with the corresponding slopes of increasing electric power consumption over the 16-year period 1970-85 (allowing for a postulated latency of about 5 years). A positive association was noted, which however was not statistically significant (p approximately 0.26). Studies of similar nature conducted in larger countries over more extended periods could contribute to the resolution of the controversy surrounding the role of electric power-generated extremely low frequency electric and magnetic fields in the etiology of childhood leukemia.

Risk of cancer in Finnish children living close to power lines

OBJECTIVE

To investigate the risk of cancer in children living close to overhead power lines with magnetic fields of > or = 0.01 microteslas (microT).

DESIGN

Cohort study.

SETTING

The whole of Finland.

SUBJECTS

68,300 boys and 66,500 girls aged 0-19 years living during 1970-89 within 500 m of overhead power lines of 110-400 kV in magnetic fields calculated to be > or = 0.01 microT. Subjects were identified by record linkages of nationwide registers.

MAIN OUTCOME MEASURES

Numbers of observed cases in follow up for cancer and standardised incidence ratios for all cancers and particularly for nervous system tumours, leukaemia, and lymphoma.

RESULTS

In the whole cohort 140 cases of cancer were observed (145 expected; standardised incidence ratio 0.97, 95% confidence interval 0.81 to 1.1). No statistically significant increases in all cancers and in leukaemia and lymphoma were found in children at any exposure level. A statistically significant excess of nervous system tumours was found in boys (but not in girls) who were exposed to magnetic fields of > or = 0.20 microT or cumulative exposure of > or = 0.40 microT years.

CONCLUSIONS

Residentia magnetic fields of transmission power lines do not constitute a major public health problem regarding childhood cancer. The small numbers do not allow further conclusions about the risk of cancer in stronger magnetic fields.

Residence near high voltage facilities and risk of cancer in children

OBJECTIVE

To investigate whether residence before and after birth near 50 Hz high voltage installations increases a child's risk of cancer and whether risk correlates with the strength of the magnetic field.

DESIGN

A population based case-control study.

SETTING

Denmark.

SUBJECTS

1707 children under the age of 15 with leukaemia, tumour of the central nervous system, or malignant lymphoma diagnosed in 1968-86 and 4788 children taken from the central population register.

MAIN OUTCOME MEASURES

Proximity before and after birth to existing or former 50-400 kV electrical transmission connections and substations and associated historical electromagnetic fields calculated on the basis of current load on line, phase ordering of line, and distance from the dwelling.

RESULTS

A significant association was seen between all major types of childhood cancer combined and exposure to magnetic fields from high voltage installations of > or = 0.4 microT (odds ratio 5.6). At > or = 0.25 microT no significant association was seen (odds ratio 1.5). A possible association was also seen with cases of Hodgkin's disease separately at > or = 0.1 microT.

CONCLUSIONS

On the basis these results and additional descriptive data on electricity consumption and incidence of childhood cancer in Denmark since the 1940s it was concluded that the proportion of childhood cancer possibly caused by 50 Hz electromagnetic fields must be small.

Intracellular calcium oscillations induced in a T-cell line by a weak 50 Hz magnetic field

Applied weak magnetic fields have been shown to affect cellular activity on several levels, but the mechanisms involved remain elusive. We have decided to study an early signal transduction event in the human T cell line Jurkat; oscillations of free [Ca2+]i, of the type seen by crosslinking the CD3 complex. Cells were exposed to a 50 Hz, 0.1 mT, sinusoidal magnetic field while intracellular free calcium was measured in individual cells, using fura-2 as a probe. An acute response was observed with oscillatory increases in [Ca2+]i, which subsided when the field was turned off. The effect of the magnetic field on [Ca2+]i was comparable to that achieved by an anti-CD3 monoclonal antibody.

Incidence of cancer in persons with occupational exposure to electromagnetic fields in Denmark

Several studies suggest that work in electrical occupations is associated with an increased risk of cancer, mainly leukaemia and brain tumours. These studies may, however, not be representative if there is a publication bias where mainly positive results are reported. To study an unselected population the incidence of cancer was followed up over a 17 year period (1970-87) in a cohort of 2.8 million Danes aged 20-64 years in 1970. Each person was classified by his or her industry and occupation in 1970. Before tabulation of the data on incidence of cancer, each industry-occupation group was coded for potential exposure to magnetic fields above the threshold 0.3 microT. Some 154,000 men were considered intermittently exposed and 18,000 continuously exposed. The numbers for women were 79,000 and 4000 respectively. Intermittent exposure was not associated with an increased risk of leukaemia, brain tumours, or melanoma. Men with continuous exposure, however, had an excess risk of leukaemia (observed (obs) 39, expected (exp) 23.80, obs/exp 1.64, 95% CI 1.20-2.24) with equal contributions from acute and other leukaemias. These men had no excess risk of brain tumours or melanoma. A risk for breast cancer was suggested in exposed men but not in women. The risk for leukaemia in continuously exposed men was mainly in electricians in installation works and iron foundry workers. Besides electromagnetic fields other exposures should be considered as possible aetiological agents.

Electromagnetic fields: a cancer promoter?

This paper discusses some of the current questions observed in updated research analyzing the association of electromagnetic fields (EMF) exposure and cancer. It reveals the predominant efforts toward obtaining more accurate levels of EMF exposure as a crucial key to gain knowledge about that association. A general picture of a molecular biological model of cancer is presented, showing that EMF presents certain compatible characteristics of a cancer promoter. Further, we raise the hypothesis that EMF action is probably linked with other unknown initiator agents, rather than acting alone as presently assumed in epidemiologic studies. Finally this paper reinforces the importance of strong descriptive analysis of potential factors acting together on EMF and cancer association.

A critical review of the genotoxic potential of electric and magnetic fields

55 published articles were identified which reported results of tests of ELF (extremely low frequency) or static electric or magnetic fields for genotoxic effects. The biological assays used spanned a wide range, including microbial systems, plants, Drosophila, mammalian and human cells in vitro and in vivo. Experimental results were grouped into four exposure categories: ELF Electric; ELF Magnetic; Static Electric; and Static Magnetic. The internal electric fields present in media (for in vitro experiments) and in the torso and extremities (for in vivo experiments) were estimated, providing an index of comparison. All experiments were critically analyzed with respect to basic data quality criteria. Experiments within each exposure category were then compared to determine if results reinforced or contradicted one another. The preponderance of evidence suggests that neither ELF nor static electric or magnetic fields have a clearly demonstrated potential to cause genotoxic effects. However, there may be genotoxic activity from exposure under conditions where phenomena auxiliary to an electric field, such as spark discharges, electrical shocks, or corona can occur. In addition, two unconfirmed reports suggest the genotoxic potential of certain chemical mutagens or ionizing radiation may be affected by co-exposure to electric or magnetic fields. Certain exposure categories are not represented or are under-represented by tests in some genotoxicity test systems that are usually included in minimal test batteries as specified by EPA for chemicals. It is suggested that consideration be given to whether additional genotoxicity testing is warranted to fill these gaps.

A system for the exposure of small laboratory animals to a 25-mT 60-Hz alternating or traveling magnetic field

This paper describes a versatile exposure system which can be used to investigate the effects of a 60-Hz alternating magnetic field or traveling magnetic field on small laboratory animals. The system was designed and built as part of an extensive experimental effort to find out what effects, if any, these fields would have on the various biological systems of animals. Special attention was given to the design of the electric circuit to simplify the supply requirements and to keep the overall current to a minimum. Magnetic field having a flux density up to 30 mT (300 G) can be generated, and a traveling magnetic field is obtained by reconnecting the coils to a three-phase supply. The total magnetic field due to the currents in the three coils used in the exposure system is analyzed by considering the x, y, and z components of the flux density due to each coil, and then using the method of superposition to obtain the flux density B at any point in the region of the three coils. A computer program was written to evaluate the magnetic field in the region where the animals are located. The computed values are also compared with those obtained from actual measurements. The difference between the measured and the computed values of the flux density is attributed to the idealized representation of the multiturn, multilayer coils by equivalent single-turn coils.

Selection bias from differential residential mobility as an explanation for associations of wire codes with childhood cancer

Several studies of childhood cancer, especially leukemia, in residential areas have reported an association with wire configuration codes. These codes were suggested to be surrogates of electromagnetic field exposure. However, the selection criteria used in several of the studies caused the case and control populations to be non-comparable, especially with respect to residential mobility. Specifically, controls were required to be residentially stable but cases were not. Thus, an artificial association between residential mobility and cancer was created by the subject selection procedure. The present study of 5721 residences in Columbus, Ohio was conducted to learn if bias due to differences in residential mobility, rather than electromagnetic fields, could explain the reported association between wire configuration codes and childhood cancer. It was found that the proportion of homes classified as "high" wire code in the non-stable population was 31% greater than the corresponding proportion in the stable population. This finding shows that high wire codes are associated with homes in which the residents are mobile and low wire codes are associated with homes occupied by stable residents. Thus, as a consequence of this association between residential mobility and high wire codes, studies that created an artificial association between residential mobility and childhood cancer will also produce a false association between high wire codes and cancer.

International Commission for Protection Against Environmental Mutagens and Carcinogens. Power frequency electric and magnetic fields: a review of genetic toxicology

Epidemiologic studies have reported a modestly increased risk of childhood leukemia associated with certain electric power wire configurations. Since cancer likely involves DNA damage, this review discusses the evidence of direct and indirect genetic toxicity effects for both electric and magnetic fields at 50- and 60-Hz and miscellaneous pulsed exposures. Exposure conditions vary greatly among different end points measured, making comparisons and conclusions among experiments difficult. Although most of the available evidence does not suggest that electric and/or magnetic fields cause DNA damage, the existence of some positive findings and limitations in the set of studies carried out suggest a need for additional work.

Plasmid DNA and low-frequency electromagnetic fields

Physico-chemical and biological properties were studied in recombinant plasmids exposed to electric and magnetic fields (EMFs). The absence of slow-migrating DNA species and failure to identify induced DNA conformers, suggests that EMFs do not have any obvious genotoxic effect in any of the experimentally tested conditions.

Psychological studies in nonionizing electromagnetic energy research

Research on nonionizing electromagnetic (NIEM) energy has focused on potential hazards, and to a lesser degree beneficial applications, of radiofrequency (RF) fields and extremely low frequency (ELF) fields. The history of research on the potential biological effects of NIEM contains many psychological investigations. These psychological investigations were conducted primarily in the discipline of biopsychology and included interdisciplinary cooperation with engineering, physical sciences, and other disciplines not routinely associated with psychology. The current recommended exposure level for RF is based on behavioral observations of laboratory animals. Psychology has been and continues to be in the midst of controversy regarding the ability of low-frequency, low-level electromagnetic energy or electric and magnetic fields to affect living organisms.

Rat liver foci study on coexposure with 50 Hz magnetic fields and known carcinogens

A study was performed to investigate possible interactions by magnetic fields (MF) with the processes of initiation and promotion of chemically induced preneoplastic lesions in rat liver. Male Sprague-Dawley rats were subjected to a 70% partial hepatectomy followed after 24 h by i.p. injection of diethylnitrosamine (DENA) as a tumour initiator. Starting one week after the DENA-treatment phenobarbital (PB) was given to promote growth of enzymatically altered foci of liver cells. MF was applied immediately after the partial hepatectomy and continued until sacrifice after 12 weeks of PB exposure. Homogenous horizontal AC magnetic fields with a frequency of 50 Hz and flux densities of 0.5 mu T or 0.5 mT were used. The rats coexposed with MF and DENA plus PB did not gain weight as much as the rats exposed to the chemical agents only. The MF-exposure also resulted in a slight reduction in size and numbers of the focal lesions. The results suggest an interaction of MF with the processes of chemical carcinogenesis either as a result of stress or depending on effects on the proliferation of preneoplastic cells.

Biologic effects of prolonged exposure to ELF electromagnetic fields in rats. I. 50 Hz electric fields

A three-year investigation was conducted on the biological effects of high-intensity electric field exposures of rats for up to 18% of their life span. Two hundred and forty adult male rats, divided into groups of 20 animals each, were exposed at ground potential for 8 h/day at 25-kV/m and 100-kV/m 50-Hz electric fields or were sham exposed for 280, 440, and 1240 h. The corresponding ages at sacrifice were 140, 164, and 315 days. An additional group of 40 rats was investigated under similar experimental conditions after 440 h of exposure at floating potential. Independent of exposure duration, mode of grounding, and field strength, no statistical differences in body weight, morphology, and histology of the liver, heart, mesenteric lymph nodes, and blood variables (hematology and serum chemistry) were found in comparison with sham-exposed animals. Plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone (TS) at sacrifice varied widely among experimental animals in the same group but did not differ in exposed compared with sham-exposed rats. A nonsignificant tendency toward a decrease in the testes/body weight ratio was found after 1240 h of exposure. Microscopic examination of a large number of specimens showed no quantitative or qualitative statistical differences in testes alterations either among exposed animals or between exposed and their corresponding sham-exposed groups. We conclude that 50-Hz electric field exposure, even of long duration at very high field strengths, does not induce harmful effects on tissues with high cellular turnover rates and does not impair the reproductive function of rats. Moreover, after exposure, all variables investigated were well within the normal physiological range.

A scheme for incorporating DC magnetic fields into epidemiological studies of EMF exposure

Experimental data on calcium-ion release in chicken brain tissue suggest that biological effects of electric and magnetic fields (EMFs) are concentrated near certain "active combinations" of DC magnetic field strength and "effective" AC magnetic field frequencies. We hypothesize that active AC/DC combinations may exist and suggest that epidemiologic data, coupled with DC magnetic field measurement, may be used to identify critical exposure conditions. An empirical model is used to calculate these multiple active combinations at any given DC magnetic field strength and to define a rating system that incorporates the proximity of AC magnetic field frequencies generated by electric power lines to the new, computed effective frequencies. Such an exposure score may be useful in investigating correlations of EMF exposure with disease incidence. For 60 Hz and 50 Hz, the highest EMF exposure scores occurred at DC field strengths of 506 mG and 422 mG, respectively. The exposure score contains a factor which may be adjusted to reflect the importance of harmonics of the AC magnetic field as well as of the fundamental frequency. Using this factor, we consider two important special cases consistent with chick brain data: 1) we consider active pairs associated with all detectable harmonics (up to 660 Hz) without regard to relative intensity of the harmonics, and 2) we use the relative intensities of the AC field frequencies to adjust their contribution to the exposure score.

Effects of magnetic fields on mammary tumor development induced by 7,12-dimethylbenz(a)anthracene in rats

A series of epidemiological studies have indicated associations between exposure to magnetic fields (MFs) and a variety of cancers, including breast cancer. In order to test the possibility that MF acts as a cancer promoter or copromoter, four separate experiments have been conducted in rats in which the effects of chronic exposure to MFs on the development of mammary tumors induced by 7,12-dimethylbenz(a)anthracene (DMBA) were determined. Female rats were exposed in magnetic coils for 91 days (24 h/day) to either alternating current (AC; 50 Hz)-MF or direct current (DC)-MF. Magnetic flux density of the DC-MF was 15 mT. Two AC-MF exposures used a homogeneous field with a flux density of 30 mT (rms); one used a gradient field with flux density ranging from 0.3-1 microT. DMBA (5 mg) was administered orally at the onset of MF exposure and was repeated thrice at intervals of 1 week. In each experiment, 18-36 animals were exposed in 6 magnetic coils. The same number of rats were used as sham-exposed control. These control animals were treated with DMBA and were placed in dummy coils in the same room as the MF-exposed rats. Furthermore, groups of age-matched rats (reference controls) were treated with DMBA but housed in another room to exclude any MF exposure due to the magnetic stray field from the MF produced by coils. At the end of the exposure or sham-exposure period, tumor number and weight or size of tumors were determined at necropsy. Results were as follows: In sham-exposed animals or reference controls, the tumor incidence varied between 50 and 78% in the 4 experiments. The average number of mammary tumors per tumor-bearing animal varied between 1.6 and 2.9. In none of the experiments did MFs significantly alter tumor incidence, but in one of the experiments with AC-MF exposure at 30 mT, the number of tumors per tumor-bearing animal was significantly increased. Furthermore, exposure to a DC-MF at 15 mT significantly enhanced the tumor weight. Exposure to a gradient AC-MF at 0.3-1 microT exerted no significant effects. These experiments seem to indicate that MFs at high flux densities may act as a promoter or copromoter of breast cancer. However, this interpretation must be considered only a tentative conclusion because of the limitations of this study, particularly the small sample size used for MF exposure and the lack of repetition of data.

Mechanisms of electromagnetic interaction with cellular systems

The question of how electromagnetic fields--static or low to high frequency--interact with biological systems is of great interest. The current discussion among biologists, chemists, and physicists emphasizes aspects of experimental verification and of defining microscopic and macroscopic mechanisms. Both aspects are reviewed here. We emphasize that in certain situations nonthermal interactions of electromagnetic fields occur with cellular systems.

Progress in the treatment of childhood leukaemias

The Nordic Society for Pediatric Hematology and Oncology (NOPHO) has run a population-based registry on all cases of acute leukaemias in the Nordic countries since 1981. Data on close to 2000 children with these diagnoses are presented and used as a background for a general discussion of progress in the therapy of these challenging conditions. Our material is unique in that it is population based. The results obtained are comparable to those obtained by all other major cooperative groups. Since January 1992, the treatment protocols for all types of acute leukaemias in childhood have been harmonized in the Nordic countries.

Magnetite biomineralization in the human brain

Although the mineral magnetite (Fe3O4) is precipitated biochemically by bacteria, protists, and a variety of animals, it has not been documented previously in human tissue. Using an ultrasensitive superconducting magnetometer in a clean-lab environment, we have detected the presence of ferromagnetic material in a variety of tissues from the human brain. Magnetic particle extracts from solubilized brain tissues examined with high-resolution transmission electron microscopy, electron diffraction, and elemental analyses identify minerals in the magnetite-maghemite family, with many of the crystal morphologies and structures resembling strongly those precipitated by magnetotactic bacteria and fish. These magnetic and high-resolution transmission electron microscopy measurements imply the presence of a minimum of 5 million single-domain crystals per gram for most tissues in the brain and greater than 100 million crystals per gram for pia and dura. Magnetic property data indicate the crystals are in clumps of between 50 and 100 particles. Biogenic magnetite in the human brain may account for high-field saturation effects observed in the T1 and T2 values of magnetic resonance imaging and, perhaps, for a variety of biological effects of low-frequency magnetic fields.

Small integrating meter for assessing long-term exposure to magnetic fields

A small, lightweight meter has been developed for magnetic-field measurements, particularly those needed for exposure-assessment purposes. This meter, known as the AMEX-3D, continuously measures all three axes of magnetic-flux density and electronically combines the data into a single estimate of cumulative exposure to the root-mean-square (rms) resultant flux density. The AMEX-3D weighs about 120 g, measures 2.7 cm x 5.1 cm x 10.2 cm, and is battery powered. Two panel-mounted jacks are provided for measuring battery voltage and for reading cumulative exposure data from the unit. The instrument has, within 3 dB, a flat response to magnetic flux densities at all frequencies in its 30-1,000 Hz bandwidth. A detailed analysis of error sources in the AMEX-3D leads to an estimate of +/- 20% as the accuracy of the instrument over its dynamic range, which extends from 0.02 to 15 microT. The AMEX-3D was tested in the field by asking electric-utility distribution linemen to wear AMEX-3D and EMDEX meters simultaneously while working. Agreement between the two measures of exposure was excellent.

Magnetite in human tissues: a mechanism for the biological effects of weak ELF magnetic fields

Due to the apparent lack of a biophysical mechanism, the question of whether weak, low-frequency magnetic fields are able to influence living organisms has long been one of the most controversial subjects in any field of science. However, two developments during the past decade have changed this perception dramatically, the first being the discovery that many organisms, including humans, biochemically precipitate the ferrimagnetic mineral magnetite (Fe3O4). In the magnetotactic bacteria, the geomagnetic response is based on either biogenic magnetite or greigite (Fe3S4), and reasonably good evidence exists that this is also the case in higher animals such as the honey bee. Second, the development of simple behavioral conditioning experiments for training honey bees to discriminate magnetic fields demonstrates conclusively that at least one terrestrial animal is capable of detecting earth-strength magnetic fields through a sensory process. In turn, the existence of this ability implies the presence of specialized receptors which interact at the cellular level with weak magnetic fields in a fashion exceeding thermal noise. A simple calculation shows that magnetosomes moving in response to earth-strength ELF fields are capable of opening trans-membrane ion channels, in a fashion similar to those predicted by ionic resonance models. Hence, the presence of trace levels of biogenic magnetite in virtually all human tissues examined suggests that similar biophysical processes may explain a variety of weak field ELF bioeffects.