General properties of the interaction between animals and ELF electric fields

Progress in the Knowledge, Application and Influence of Extremely Low Frequency Signals

This paper describes the characteristics of contributions made by researchers worldwide in the field of ELF (extremely low frequency) waves from 1957 to 2019. The data were collected through the Scopus database and processed with analytical and bibliometric techniques. The selection of the keywords is an essential step, because ELF has a very different meaning in some areas of medicine, where it is associated with a gene. A total of 12,436 documents were worked on in 12 thematic communities according to their collaborative relationships between authors and documents. Studies included authors publishing in the different thematic areas and the country where the USA stands first with more researchers in this theme than China and Japan. Documents were analyzed from the temporal perspective, their overall contribution, means of publication, and the language of the publication. Research requires extra effort and multidisciplinary collaboration to improve the knowledge, the application, and influence of these fields.

Plasma concentrations of thyroxine in dairy cows exposed to 60 Hz electric and magnetic fields

Two experiments were carried out to assess the effects of electric and magnetic fields (EMF) on blood thyroxine (T4) in dairy cattle. In experiment 1, 16 lactating pregnant Holstein cows were exposed to 10 kV/m, 30 microTesla (microT) EMF. The animals were divided into two groups of eight animals each. Each group was exposed to EMF according to one of two treatment sequences of three periods of 28 days each. Sequence 1 was EMF OFF-ON-OFF and sequence 2 was EMF ON-OFF-ON. During the last day of each treatment period, blood samples were collected every 4 h for 24 h to estimate T4 plasma concentrations. In experiment 2, 16 nonlactating, nonpregnant, multiparous Holsteins were exposed to 10 kV/m, 30 microT EMF. The animals were divided into two groups of eight animals each. Each group was exposed to EMF according to one of the two treatment sequences described above, except that each period amounted to the number of days corresponding to one estrous cycle. During treatment, blood samples were collected every other day for T4 analysis. In both experiments, the light cycle emulated a short photoperiod (8 h light/16 h dark). During the ON periods, the animals were exposed to EMF for 16 h, 8 h of the light period plus the first 8 h of during the dark period. In experiment 1, exposed animals did not have any change in T4 plasma concentrations due to treatment (P = .0968), but, the time of sample collection revealed a significant difference (P = .0012). In experiment 2, the effect of period (P = .0009) and the treatment by days interaction (P = .0003) were statistically significant. We conclude that a worst case scenario exposure of dairy cattle to 10 kV/m, 30 microT EMF influences, in a moderate fashion, the blood levels of thyroxine.

Lack of effect of 10 kV/m 60 Hz electric field exposure on pregnant dairy heifer hormones

Sixteen pregnant Holstein heifers weighing 521 +/- 46 kg, at 3.3 +/- 0.7 months of gestation and 2.2 +/- 2.0 months of age were confined to wooden metabolism cages and were exposed to a vertical electric field (EF) of 10.0 +/- 0.4 kV/m and an artificial light cycle of 12 h light-12 h dark. The heifers were divided into two replicates of eight each. Each replicate was divided into two groups of four animals each, one group becoming the non-exposed and the second, the EF exposed group. The exposed group were housed in metabolism cages in an area where EF were generated, and the non-exposed group, in metabolism cages located in the adjacent area where the EF was less than 2% of that present in the exposed area. The test animals were subject to the different treatments for 4 weeks continuously. After 4 weeks, the animals switched treatment, the exposed group becoming the non-exposed group and vice-versa. Then the treatment continued for 4 more weeks. Catheters were inserted into the jugular vein of the animals, and blood samples were collected on twice a week to estimate the serum concentration of progesterone (P4), melatonin (MLT), prolactin (PRL), and insulin-like growth factor-1 (IGF-1). Feed consumption was measured daily and feed samples were collected twice a week. The results indicated that exposure of dairy cattle to EF similar to those encountered directly underneath a 735 kV high tension electrical power line carrying a maximum load of current, cannot be associated with any variation in the experimental variables mentioned above. An exception to this, is the variation in MLT, which was associated with the EF exposure. Due to the inconsistency of the MLT response in the different replicates, caution should be exercised in the interpretation of this phenomenon.

Effect of 10 kV, 30 ?T, 60 Hz electric and magnetic fields on milk production and feed intake in nonpregnant dairy cattle

Milk production is the main agricultural income in the province of Québec, and the electrical distribution network traverses the rural dairy production region. This study evaluates the hypothesis that electric and magnetic fields may affect dairy production. Sixteen multiparous nonpregnant lactating Holstein cows (weighing 662 +/- 65 kg and with 150.4 +/- 40 days of lactation) were confined to wooden metabolic crates during the experiment with a 12:12 h light:dark cycle. The cows were divided into two replicates of eight cows each and exposed to a vertical EF of 10 kV/m and an uniform horizontal MF of 30 microT at 60 Hz. Replicate one was exposed for three periods. Each period was represented by an estrous cycle ranging from 24 to 27 days. During the first period, the electric and magnetic fields (E&MF) were off; during the second period they were on; and during the final period, they were off. The second replicate was exposed for three periods also, but the exposure protocol was reversed (first period, on; second period, off; last period, on). Exposure to E&MF (on) resulted in an average decrease of 4.97, 13.78, and 16.39% in milk yield, fat corrected milk yield, and milk fat, respectively; and an increase of 4.75% in dry matter intake.

Magnetic fields produced by hand held hair dryers, stereo headsets, home sewing machines, and electric clocks

A recent epidemiologic study reported associations between leukemia risk in children and their personal use of television (TV) sets, hair dryers, and stereo headsets, and the prenatal use by their mothers of sewing machines. To provide exposure data to aid in the interpretation of these findings, extremely and very low frequency (ELF and VLF) magnetic fields produced by a sample of each type of appliance were characterized in a field study of volunteers conducted in Washington DC and its Maryland suburbs. Questionnaire data regarding children's or mothers' patterns of usage of each type of appliance were also collected. ELF magnetic fields measured 10 cm from the nozzles of hair dryers were elevated over the ambient by a mean factor of 17 when these devices were in use. Fields near headsets being used to listen to music were not distinguishable from ambient levels except at frequencies below and well above 60 Hz and, even then, field levels were < 0.01 microT. Home sewing machines produced ELF magnetic fields that were elevated by a factor of 2.8 over ambient levels at the front surfaces of the lower abdomens of mothers. Estimated mean daily times of usage of hair dryers, stereo headsets, and sewing machines were 2.6, 19, and 17 minutes, respectively. These data and previously published data on TV sets, do not provide a consistent picture of increased (or decreased) leukemia risk in relation to increasing peak or time weighted average (TWA) ELF magnetic field exposure. The data could, however, conceivably be compatible with some more complex biophysical model with unknown properties. Overall, the results of this study provide little evidence supporting the hypothesis that peak or TWA ELF magnetic fields produced by appliances are causally related to the risk of childhood leukemia in children.

Extremely low-frequency magnetic fields and childhood acute lymphoblastic leukemia: an exploratory analysis of alternative exposure metrics

Data collected by the National Cancer Institute-Children's Cancer Group were utilized to explore various metrics of magnetic field levels and risk of acute lymphoblastic leukemia (ALL) in children. Cases were aged 0-14 years, were diagnosed with ALL during 1989-1993, were registered with the Children's Cancer Group, and resided in one home for at least 70 percent of the 5 years immediately prior to diagnosis. Controls were identified by using random digit dialing and met the same residential requirements. With 30-second ("spot") measurements and components of the 24-hour measurement obtained in the subject's bedroom, metrics evaluated included measures of central tendency, peak exposures, threshold values, and measures of short-term temporal variability. Measures of central tendency and the threshold measures showed good-to-high correlation, but these metrics correlated less well with the others. Small increases in risk (ranging from 1.02 to 1.69 for subjects in the highest exposure category) were associated with some measures of central tendency, but peak exposures, threshold values, measures of short-term variability, and spot measurements demonstrated little association with risk of childhood ALL. In general, risk estimates were slightly higher for the nighttime (10 p.m.-6 a.m.) interval than for the corresponding 24-hour period.

Synchronization of pacemaker cell firing by weak ELF fields: simulation by a circuit model

Entrainment of output action potentials from repetitively firing pacemaker cells, brought about by regularly spaced excitatory or inhibitory postsynaptic inputs, is a well-known phenomenon. Synchronization of neural firing patterns by extremely low frequency (ELF) external electric fields has also been observed. Whereas current densities of approximately 10 A-m(-2) are required for direct excitation of otherwise quiescent neural tissue, much lower peak current densities (approximately 10[-2] A-m2) have been reported to entrain spontaneously firing molluscan pacemaker cells. We have developed a neural spike generator circuit model that simulates repetitive spike generation by a space clamped patch (area approximately 10[-7] m2) of excitable membrane subjected to depolarizing current. Picoampere (pA) range variation of DC depolarizing current causes a corresponding smooth variation of neural spike frequency, producing a physiologically realistic stimulus-response (S-R) characteristic. When lower pA range 60 Hz AC current is superposed upon the DC depolarizing current, smooth variation of the S-R characteristic is distorted by subharmonic locking of the spike generator at 30, 20, 15, 12, 10 Hz, and higher order subharmonic frequencies. Although the additional superposition of a physiologically realistic level of "white" current noise, covering the bandwidth 4-200 Hz, suffices to obscure higher order subharmonic locking, locking at 30, 20, and 15 Hz is still clearly evident in the presence of noise. Subharmonic locking is observed at an root mean square AC simulated tissue current density of approximately 10(-5) A-m(-2).

Children's exposure to magnetic fields produced by U.S. television sets used for viewing programs and playing video games

Two epidemiologic studies have reported increased risk of childhood leukemia associated with the length of time children watched television (TV) programs or played video games connected to TV sets. To evaluate magnetic field exposures resulting from these activities, the static, ELF, and VLF magnetic fields produced by 72 TV sets used by children to watch TV programs and 34 TV sets used to play video games were characterized in a field study conducted in Washington DC and its Maryland suburbs. The resulting TV-specific magnetic field data were combined with information collected through questionnaires to estimate the magnetic field exposure levels associated with TV watching and video game playing. The geometric means of the ELF and VLF exposure levels so calculated were 0.0091 and 0.0016 microT, respectively, for children watching TV programs and 0.023 and 0.0038 microT, respectively, for children playing video games. Geometric means of ambient ELF and VLF levels with TV sets turned off were 0.10 and 0.0027 microT, respectively. Summed over the ELF frequency range (6-3066 Hz), the exposure levels were small compared to ambient levels. However, in restricted ELF frequency ranges (120 Hz and 606-3066 Hz) and in the VLF band, TV exposure levels were comparable to or larger than normal ambient levels. Even so, the strengths of the 120 Hz or 606-3066 Hz components of TV fields were small relative to the overall ambient levels. Consequently, our results provide little support for a linkage between childhood leukemia and exposure to the ELF magnetic fields produced by TV sets. Our results do suggest that any future research on possible health effects of magnetic fields from television sets might focus on the VLF electric and magnetic fields produced by TV sets because of their enhanced ability relative to ELF fields to induce electric currents.

Effects of electric and magnetic fields on nocturnal melatonin concentrations in dairy cows

Sixteen multiparous, pregnant, lactating Holstein cows (weighing 600 +/- 50 kg, at 184.8 +/- 52 d of lactation, and at 101.9 +/- 43 d of gestation) were confined to wooden metabolism cages and exposed to a vertical electric field of 10 kV/m and a uniform horizontal magnetic field of 30 microT. The trial was conducted using a switchback statistical design. Cows were divided into two sequence groups of 8 cows each. One sequence group was exposed for three periods of 28 d each. The electric and magnetic fields were off during the first period, on during the second period, and off during the final period. The second sequence group was exposed for three periods also, but the activity of the fields was reversed (on during the first period, off during the second period, and on during the third period). On d 25 of each exposure period, blood samples were obtained every 0.5 h for 14 h starting at 1700 h to determine melatonin concentration. Nocturnal melatonin concentrations did not show any variation that could be attributed to exposure to electric and magnetic fields.

Biological effects of electric and magnetic fields on productivity of dairy cows

Sixteen multiparous Holstein cows (weighing 600 +/- 50 kg, in 184.8 +/- 52 d of lactation, and at 101.9 +/- 43 d of gestation) were confined to wooden metabolic cages and exposed to a vertical electric field of 10 kV/ m and to a uniform horizontal magnetic field of 30 microT (microtesla). The trial was conducted as a switch-back statistical design. Cows were divided into two replicates of 8 cows each. One replicate was exposed for three periods of 28 d each. During the first period, the electric and magnetic fields were off; during the second period, they were on; and, during the final period, they were off. The second replicate was exposed for three periods also, but the activity of the fields was reversed (first period, on; second period, off; and third period, on). Blood samples were obtained twice weekly for the determination of cortisol and progesterone and once weekly for the determination of pH and blood gases. Milk samples were collected once weekly to determine milk components (fat, protein, SNF, and SCC). Milk yield and feed consumption were measured daily. Most of the variables studied (bicarbonate, pH, O2 and CO2 partial pressures, cortisol concentration in blood, uncorrected milk yield, and milk components other than milk fat) showed no variation that could be attributed to exposure to electric and magnetic fields. Associations were found between the electric and magnetic fields and increased DMI, 4% FCM yield, milk fat content, and plasma progesterone.

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.

Experimental macroscopic dosimetry for extremely-low-frequency electric and magnetic fields

Environmental and laboratory exposure to electric and magnetic fields (EMF) in the extremely-low-frequency range (ELF) produces electrical quantities that interact directly with the exposed biological system on a scale small compared to the size of the human body but large with respect to cellular dimensions. The purpose of this paper is to describe these macroscopic electrical quantities and their characterization through measurements on living systems and experimental models. Electric field exposure results in a total induced current, surface electric fields, internal electric fields, and internal currents. Magnetic field exposure results in internal magnetic field, internal electric fields, and internal currents. Basic properties of fields and matter determine the methods by which these quantities can be measured. Quantification or dosimetry for these parameters on a macroscopic basis can be directed to the whole body, a cross section across the body, a local surface area, or a local volume. Models of varying degrees of sophistication have been used to establish spatial distributions of external fields and internal fields and currents.

Numerical and analytical methods to determine the current density distributions produced in human and rat models by electric and magnetic fields

Some numerical and analytical methods used to estimate the internal electric fields and current densities produced within human and animal models by low-frequency electric and magnetic fields are surveyed. A major goal of such modeling is the design of laboratory experiments on cellular systems or animal models to produce a dosage comparable to that experienced by humans in a particular situation. Specific comparisons are made between the results of ellipsoidal approximations and finite-difference methods applied to irregularly-shaped, homogeneous, human and rat models for applied 60 Hz electric (10 kV/m) and magnetic (10(-4) T) fields. For scaling purposes, the induced current densities in various parts of the body are compared for rat and human models for both types of field. In addition, the current density distribution induced in rectangular culture dishes by applied magnetic fields is also described. The extension of these methods to inhomogeneous models and localized sources may not be simple.

Numerical dosimetry at power-line frequencies using anatomically based models

We have used the finite-difference time-domain (FDTD) method to calculate induced current densities in a 1.31-cm (nominal 1/2 in) resolution anatomically based model of the human body for exposure to purely electric, purely magnetic, and combined electric and magnetic fields at 60 Hz. This model based on anatomic sectional diagrams consists of 45,024 cubic cells of dimension 1.31 cm for which the volume-averaged tissue properties are prescribed. It is recognized that the conductivities of several tissues (skeletal muscle, bone, etc.) are highly anisotropic for power-line frequencies. This has, however, been neglected in the first instance and will be included in future calculations. Because of the quasi-static nature of coupling at the power-line frequencies, a higher quasi-static frequency f' may be used for irradiation of the model, and the internal fields E' thus calculated can be scaled back to the frequency of interest, e.g., 60 Hz. Since in the FDTD method one needs to calculate in the time domain until convergence is obtained (typically 3-4 time periods), this frequency scaling to 5-10 MHz for f' reduces the needed number of iterations by over 5 orders of magnitude. The data calculated for the induced current and its variation as a function of height are in excellent agreement with the data published in the literature. The average current densities calculated for the various sections of the body for the magnetic field component (H) are considerably smaller (by a factor of 20-50) than those due to the vertically polarized electric field component when the ratio E/H is 377 ohms. We have also used the previously described impedance method to calculate the induced current densities for the anatomically based model of the human body for the various orientations of the time-varying magnetic fields, namely from side to side, front to back, or from top to bottom of the model, respectively.

Dosimetry of extremely-low-frequency magnetic fields

Extrapolation of quantitative measurements across biological systems requires knowledge of field-organism interaction mechanisms. In the absence of such knowledge, one can only indicate which parameters would be important under some plausible assumptions that still lack experimental proof. In the first part of the paper it is assumed that biological effects of low intensity, extremely low frequency magnetic fields are caused by the electric fields which they induce. It is shown that detailed knowledge of electrical properties on a microscale is important to predict effects that may be due to local current density, electric field strength, surface charge distribution, and mechanical forces. In the second part of the paper, it is shown that all proposed mechanisms for direct interaction between alternating magnetic fields and cells involve also the magnitude and direction of a simultaneously present static magnetic field. Reviewed are "cyclotron resonance," quantum mechanical effects on ions weakly bound to proteins, nuclear magnetic resonance, and recent progress in magneto chemistry dealing with effects of magnetic fields of a few hundred microtesla on chemical reactions that involve free radicals.

Prediction of magnetically induced electric fields in biological tissue

There are many potential medical applications in which it is desirable to noninvasively induce electric fields. One such application that serves as the backdrop of this work is that of stimulating neurons in the brain. The magnetic fields necessary must be quite high in magnitude, and fluctuate rapidly in time to induce the internal electric fields necessary for stimulation. Attention is focused on the calculation of the induced electric fields commensurate with rapidly changing magnetic fields in biological tissue. The problem is not a true eddy current problem in that the magnetic fields induced do not influence the source fields. Two techniques are introduced for numerically predicting the fields, each employing a different gauge for the potentials used to represent the electric field. The first method employs a current vector potential (analogous to A in classical magnetic field theory where DEL x A = B) and is best suited to two-dimensional (2-D) models. The second represents the electric field as the sum of a vector plus the gradient of a scalar field; because the vector can be determined quickly using Biot Savart (which for circular coils degenerates to an efficient evaluation employing elliptic integrals), the numerical model is a scalar problem even in the most complicated three dimensional geometry. These two models are solved for the case of a circular current carrying coil near a conducting body with sharp corners.

Use of a spread sheet to calculate the current-density distribution produced in human and rat models by low-frequency electric fields

The current-density distribution produced inside irregularly shaped, homogeneous human and rat models by low-frequency electric fields is obtained by a two-stage finite-difference procedure. In the first stage the model is assumed to be equipotential. Laplace's equation is solved by iteration in the external region to obtain the capacitive-current densities at the model's surface elements. These values then provide the boundary conditions for the second-stage relaxation solution, which yields the internal current-density distribution. Calculations were performed with the Excel spread-sheet program on a Macintosh-II microcomputer. A spread sheet is a two-dimensional array of cells. Each cell of the sheet can represent a square element of space. Equations relating the values of the cells can represent the relationships between the potentials in the corresponding spatial elements. Extension to three dimensions is readily made. Good agreement was obtained with current densities measured on human models with both, one, or no legs grounded and on rat models in four different grounding configurations. The results also compared well with predictions of more sophisticated numerical analyses. Spread sheets can provide an inexpensive and relatively simple means to perform good, approximate dosimetric calculations on irregularly shaped objects.

Dominant lethal studies in male mice after exposure to a 50-Hz electric field

Male C3H/He mice were sham-exposed or exposed continuously for 2 weeks to a vertical, 50-Hz, electric field at 20 kV/m rms. Densities of currents induced in the testes are estimated to be near 100 microA/m2. After the exposure, each male was mated with two different female mice each week during a period of 8 weeks. By this schedule, female mice were impregnated with sperm that had been exposed to the electric field at different stages of the spermatogenic cycle. No significant differences as a function of exposure condition were observed in pregnancy rates or in survival of embryos before or after implantation. The absence of effects was not due to insensitivity of assays; other mice that were exposed to X-rays (dose to testes = 1.5 Gy) presented reliable evidence of mutagenesis.

A numerical method for the computation of induced currents inside 3-D heterogeneous biological bodies by ELF--LF electric fields

A numerical technique, based on the combination of surface-charge integral equations (SCIE) and an impedance network method, has been developed to compute internal electric fields and currents inside 3-D heterogeneous biological bodies with arbitrary grounding impedances induced by ELF-LF electric fields. The method has been applied to a biological concentric-sphere and the numerical results agree well with an existing analytical solution. Numerical results of the induced current inside a simplified heterogeneous model of the human head computed by this method are also presented.

Current densities induced in swine and rat models by power-frequency electric fields

Measurements have been made of vector current densities induced by vertical, uniform, 60-Hz electric fields in the torsos of homogeneous models of swine and rats. The observed data were a strong function of the five grounding configurations invested: all four feet grounded, only front feet grounded, only rear feet grounded, left front and right rear feet grounded, and right front and left rear feet grounded. In the first configuration and with an exposure field strength of 10 kV/m, average total current densities induced in the torsos of pigs and rats were 34 nA/cm2 and 20 nA/cm2, respectively. The corresponding value for human exposure is about 250 nA/cm2, 7.3 and 12.5 times larger than for swine and rats, respectively. Current densities measured at 60 Hz can be linearly extrapolated to frequencies in a range extending from at least 1 Hz to 1 MHz. Human and animal current-density data can provide an improved rationale for extrapolating biological data across species. In addition, these data can be used to validate the predictions of numerical models.

Finite difference calculations of current densities in a homogeneous model of a man exposed to extremely low frequency electric fields

This paper presents three-dimensional finite difference calculations of induced current densities in a grounded, homogeneous, realistically human-shaped phantom. Comparison is made with published experimental values of current density at 60 Hz, measured in conducting saline manikins with their arms down by the side. The congruence between calculation and experiment gives confidence in the applicability of the numerical method and phantom shape to other configurations. The effect of raising both arms above the head is to reduce the current densities in the head and neck by approximately 50% and to increase those from the thorax downwards by 20-30%. A sensitivity analysis was performed on the shape and dimensions of the phantom, from a 45-kg, 1.5-m-tall person to a 140-kg, 1.9-m-tall person. When the phantom is grounded through both feet the current densities range from 50 to 90 microAm-2 in the head (all values for a 60-Hz, 1-kVm-1, vertical applied field), 70 to 140 microAm-2 in the thorax, 150 to 440 microAm-2 at the crotch, and 500 to 2,230 microAm-2 in the ankle. When grounded through only one foot the current densities at the crotch range from 400 to 1,000 microAm-2 and from 1,000 to 4,400 microAm-2 in the ankle of the grounded leg. Scale transformations of the short-circuit current with phantom height, weight, and surface area are confirmed.

The effect of low-level 60-Hz electromagnetic fields on human lymphoid cells. II. Sister-chromatid exchanges in peripheral lymphocytes and lymphoblastoid cell lines

Dividing human peripheral lymphocytes from 10 normal adults (5 males and 5 females) as well as lymphoid cell lines from patients with the chromosomal instability syndromes were exposed to low-level 60-Hz sinusoidal electromagnetic fields (EMF). The current density of the electrical field was 30 microA/cm2 while the strength of the magnetic field was either 1 or 2 gauss. The cytological endpoints measured included the frequency of sister-chromatid exchanges per chromosome; the distribution of first-, second-, and third-division cells and chromosome breakage (lymphoblastoid cells only). No statistically significant differences, indicative of EMF effects were observed between the treated and control cells regarding SCE frequency, cell cycle progression or chromosome breakage.

Effect of low-level, 60-Hz electromagnetic fields on human lymphoid cells: I. Mitotic rate and chromosome breakage in human peripheral lymphocytes

Dividing human peripheral lymphocytes from 10 normal adults (5 males and 5 females) were exposed in vitro to low level 60-Hz electromagnetic fields for 69 hours. The current density of the electrical field was 30 microA/cm2, while the magnetic field was either 1 or 2 gauss. The cytological endpoints measured were mitotic rate and chromosome breakage. No statistically significant differences, indicative of a field effect, were observed between treated and control cells whether exposed to an electric field, a magnetic field, or to various combinations of the two.

Low-voltage ELF electric field measurements in ionic media

Low-voltage electric fields were measured in conductive tissue culture media using three techniques: voltage slope, current density-conductivity, and dipole methods. All three methods tested yielded comparable results. However, all three techniques have associated errors. These errors fall into three major categories: those associated with the measurement equipment, those associated with electrodes, and errors in cross-sectional area measurements. Each source of error is discussed so that all can be taken into account during construction and/or testing of exposure equipment.

Current densities measured in human models exposed to 60-Hz electric fields

This paper gives current densities measured in homogeneous grounded human models exposed to vertical, 60-Hz electric fields. The methods used for these measurements were validated by measuring the current densities induced in a grounded hemisphere and in a grounded prolate hemispheroid; agreement between measurement and theory was good. For an unperturbed field strength of 10 kV/m, current densities measured in the human chest were in the range 125-300 nA/cm2. A strong horizontal current-density enhancement was observed in the axillae, with peak values of about 400 nA/cm2. The vertical current density in the arms, when held downward, was in the opposite direction to that in the chest. Current densities in the abdomen, pelvis, and legs were a strong function of whether the body was grounded through one or both feet. With one foot grounded, the horizontal current density in the lower pelvic region, just above the crotch, was 770 nA/cm2. This value was the largest of those measured in the head, arms, or torso of the human model. Scaling factors derived from these data and similar data for animals will provide a quantitative basis for comparing animal and human exposure to 60-Hz electric fields. In addition, current-density data given in this paper can be directly extrapolated to higher frequencies, at least to 1 MHz. These extrapolated data may be useful to individuals and groups involved in the determination of safety standards for the lower radiofrequency region.

Numerical calculation and measurement of 60-Hz current densities induced in an upright grounded cylinder

Power-frequency electric fields are strongly perturbed in the vicinity of human beings and experimental animals. As a consequence, the extrapolation of biological data from laboratory animals to human-exposure situations cannot use the unperturbed exposure field strength as a common exposure parameter. Rather, comparisons between species must be based on the actual electric fields at the outer surfaces of and inside the bodies of the subjects. Experimental data have been published on surface and internal fields for a few exposure situations, but it is not feasible to characterize experimentally more than a small fraction of the diverse types of exposures which occur in the laboratory and in the field. A predictive numerical model is needed, one whose predictions have been verified in situations where experimental data are available, and one whose results can be used with confidence in new exposure situations. This paper describes a numerical technique which can be used to develop such a model, and it carries out this development for a test case, that of a homogeneous right-circular cylinder resting upright on-end on a ground plane and exposed to a vertical, uniform, 60-Hz electric field. The accuracy of the model is tested by comparing short-circuit currents and induced current densities predicted by it to measured values: Agreement is good.

Short-circuit currents, surface electric fields, and axial current densities for guinea pigs exposed to ELF electric fields

Short-circuit currents, surface electric fields, and axial current densities were measured in electrically grounded guinea pigs exposed to a uniform, vertical, ELF electric field. These data are 70-110% of corresponding values obtained in grounded rats exposed to the same electric field.

System for the exposure of cell suspensions to power-frequency electric fields

A system is described that uses an oscillating magnetic field to produce power-frequency electric fields with strengths in excess of those produced in an animal or human standing under a high-voltage electric-power transmission line. In contrast to other types of exposure systems capable of generating fields of this size, no electrodes are placed in the conducting growth media: the possibility of electrode contamination of the exposed suspension is thereby eliminated. Electric fields in the range 0.02-3.5 V/m can be produced in a cell culture with total harmonic distortions less than 1.5%. The magnetic field used to produce electric fields for exposure is largely confined within a closed ferromagnetic circuit, and experimental and control cells are exposed to leakage magnetic flux densities less than 5 microT . The temperatures of the experimental and control cell suspensions are held fixed within +/- 0.1 degrees C by a water bath. Special chambers were developed to hold cell cultures during exposure and sham exposure. Chinese hamster ovary (CHO) cells incubated in these chambers grew for at least 48 h and had population doubling times of 16-17 h, approximately the same as for CHO cells grown under standard cell-culture conditions.

Theoretical and experimental determination of SAR patterns for spherical tissue models in a rectangular resonant cavity

Specific absorption rates (SARs) were determined theoretically and experimentally for several spherical models of tissue exposed to electrical fields of TE101 mode in a rectangular cavity of 57.3 MHz resonant frequency. The approximate theoretical SAR can be calculated according to the Mie theory by superposition of four plane waves representing the fields excited in the cavity. The theoretical and thermographically determined SAR patterns in spheres with radii of 5, 7.5, and 10 cm and with conductivities of 0.1, 1, and 10 S/m were compared. For a sphere with radius less than 7.5 cm and conductivity less than 1 S/m, the SAR was quite uniform. When conductivity was increased to 10 S/m, the SAR patterns showed higher absorption in the periphery of the largest sphere (10-cm radius). These characteristics are important in evaluating the scaling technique of exposing a model of a human to very-high-frequency fields to obtain power absorption data in humans exposed to high-frequency or very-low-frequency fields.

Determination of electric current distributions in animals and humans exposed to a uniform 60-Hz high-intensity electric field

The thermographic method for determining specific absorption rate (SAR) in animals and models of tissues or bodies exposed to electromagnetic fields was applied to the problem of quantifying the current distribution in homogeneous bodies of arbitrary shape exposed to 60-Hz electric fields. The 60-Hz field exposures were simulated by exposing scale models of high electrical conductivity to 57.3-MHz VHF fields of high strength in a large 3.66 X 3.66 X 2.44-m TE101 mode resonant cavity. After exposure periods of 2-30 s, the models were quickly disassembled so that the temperature distribution (maximum value up to 7 degrees C) along internal cross-sectional planes of the model could be recorded thermographically. The SAR, W', calculated from the temperature changes at any point in the scale model was used to determine the SAR, W, for a full-scale model exposed to a 60-Hz electric field of the same strength by the relation W = (60/f')2 . (sigma'/sigma) . W' where f' is the model exposure frequency, sigma' is the conductivity of the scale model at the VHF exposure frequency, and sigma is the conductivity of the full-scale subject at 60 Hz. The SAR was used to calculate either the electric field strength or the current density for the full-scale subject. The models were used to simulate the exposure of the full-scale subject located either in free space or in contact with a conducting ground plane. Measurements made on a number of spheroidal models with axial ratios from 1 to 10 and conductivity from 1 to 10 s/m agreed well with theoretical predictions. Maximum current densities of 200nA/cm2 predicted in the ankles of man models and 50 nA/cm2 predicted in the legs of pig models exposed to 60-Hz fields at 1kV/m agreed well with independent measurements on full-scale models.

Chronic exposure to a 60-Hz electric field: effects on neuromuscular function in the rat

Neuromuscular function in adult male rats was studied following 30 days of exposure to a 60-Hz electric field at 100 kV/m (unperturbed field strength). Isometric force transducers were attached to the tendons of the plantaris (predominantly fast twitch), and soleus (predominantly slow twitch) muscles in the urethan-anesthetized rat. Square-wave stimuli were delivered to the distal stump of the transected sciatic nerve. Several measurements were used to characterized neuromuscular function, including twitch characteristics, chronaxie, tetanic and posttetanic potentiation, and fatigue and recovery. The results from three independent series of experiments are reported. Only recovery from fatigue in slow-twitch muscles was consistently and significantly affected (enhanced) by electric-field exposure. This effect does not appear to be mediated by field-induced changes in either neuromuscular transmission, or in the contractile mechanism itself. It is suggested that the effect may be mediated secondary to an effect on mechanisms regulating muscle blood flow or metabolism.

Effects of intermittent 60-Hz high voltage electric fields on metabolism, activity, and temperature in mice

Transient effects of 100-kV/m extremely low frequency electric fields were studied in the white footed deermouse, Peromyscus leucopus. Gross motor activity, carbon dioxide production, oxygen consumption, and core body temperature were monitored before, during, and after intermittent field exposures (four hour-long exposures, at one-hour intervals). Thirty-four mice were exposed in cages with plastic floors floating above ground potential, and 21 mice were exposed in cages with grounded metal floor plates. The first field exposure produced an immediate, transient increase of activity and gas measures during the inactive phase of the circadian cycle. All measures returned to baseline levels before the second exposure and were not significantly changed throughout the remainder of the exposures. The rapid habituation of field-induced arousal suggests that significant metabolic changes will not be measured in experiments in which the interval between exposure and measurement is greater than two hours.

Endocrinological effects of strong 60-Hz electric fields on rats

Adult male rats were exposed or sham-exposed to 60-Hz electric fields without spark discharges, ozone, or significant levels of other secondary variables. No effects were observed on body weights or plasma hormone levels after 30 days of exposure at an effective field strength of 68 kV/m. After 120 days of exposure (effective field strength = 64 kV/m, effects were inconsistent, with significant reductions in body weight and plasma levels of follicle-stimulating hormone and corticosterone occurring in one replicate experiment but not in the other. Plasma testosterone levels were significantly reduced after 120 days of exposure in one experiment, with a similar but not statistically significant reduction in a replicate experiment. Weanling rats, exposed or sham-exposed in electric fields with an effective field strength of 80 kV/m from 20 to 56 days of age, exhibited identical or closely similar growth trends in body and organ weights. Hormone levels in exposed and sham-exposed groups were also similar. However, there was an apparent phase shift between the two groups in the cyclic variations of concentrations of hormones at different stages of development, particularly with respect to follicle-stimulating hormone and corticosterone. We concluded that 60-Hz electric fields may bring about subtle changes in the endocrine system of rats, and that these changes may be related to alterations in episodic rhythms.

Power-frequency electric fields averaged over the body surfaces of grounded humans and animals

Calculated electric-field strengths averaged over the body surfaces of grounded humans, swine, rats, horses, and cattle exposed to vertical, uniform, power-frequency electric fields are presented. To produce the same average fields over the body surfaces of grounded animals, as that experienced by a grounded man exposed to an unperturbed vertical field of 10 kV/m, the following unperturbed fields are required; swine, 19 kV/m; rat, 37 kV/m; horse, 18 kV/m; cow, 18 kV/m.