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 Göteborg 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.

Cytoplasmic Ca2+ oscillations in human leukemia T-cells are reduced by 50 Hz magnetic fields.

The effect of 50 Hz magnetic fields on the cytosolic calcium oscillator in Jurkat E6.1 cells was investigated for field strengths within the range from 0 to 0.40 mT root mean square. The intracellular Ca2+ concentration data were collected for single Jurkat cells that exhibited a sustained spiking for at least 1 h while repeatedly exposing them to an alternating magnetic field in 10-min intervals interposed with nonexposure intervals of the same length. The obtained data were analysed by computing spectral densities of the Ca2+ oscillating patterns for each of these 10-min intervals. For every single-cell experiment the spectra of all exposure as well as nonexposure periods were then averaged separately. A comparison between the resulting averages showed that the total spectral power of the cytosolic Ca2+ oscillator was reduced by exposure of the cells to an alternating magnetic field and that the effect increased in an explicit dose-response manner. The same relationship was observed within the 0-10 mHz (10 x 10(-3) Hz) subinterval of the Ca2+ oscillation spectrum. For subintervals at higher frequencies, the change caused by the exposure to the magnetic field was not significant.

The influence of 50-Hz magnetic fields on cytoplasmic Ca2+ oscillations in human leukemia T-cells.

We have studied the effects of 50-Hz 100-microT rms magnetic fields on intracellular Ca2+ concentration in the Jurkat T lymphocyte variant E6.1 using fluorescent probes Indo-1 and Fura-2. We found, however, that the pattern of intracellular Ca2+ fluctuations also depended on the agent used for cell attachment, in our case the polypeptide poly-L-lysine. In order to isolate possible effects of magnetic field exposure from those of poly-L-lysine, the action of polypeptide on cytosolic Ca2+ was studied as well. It was found that a 10(-7)% concentration of polypeptide triggered prolonged Ca2+ spiking. Higher (10(-4)%) concentrations induced rapid increases in intracellular Ca2+ followed by high, unstable Ca2+ levels. The response of these cells to the monoclonal antibody anti-CD3 was also inhomogeneous, similar to one caused by poly-L-lysine. The effect of magnetic field exposure was studied on cells initially exhibiting (1) non-oscillating, low Ca2+ concentration and (2) prolonged Ca2+ concentration oscillations. In case (1) the result was negative. In case (2), statistically significant changes were found: the oscillation amplitude was reduced on average by 30%, and the frequency composition was shifted towards higher frequencies.

Ca2+ ion transport through patch-clamped cells exposed to magnetic fields.

The total current of Ca2+ ions through patch-clamped cell membranes was measured while exposing clonal insulin-producing beta-cells (RINm5F) to a combination of DC and AC magnetic fields at so-called cyclotron resonance conditions. Previous experimental evidence supports the theory that a resonant interaction between magnetic fields and organisms can exist. This experiment was designed to test one possible site of interaction: channels in the cell membrane. The transport of Ca2+ ions through the protein channels of the plasma membrane did not show any resonant behavior in the frequency range studied.

Effect of microwave radiation on permeability of liposomes. Evidence against non-thermal leakage.

The effect of 2.45 GHz microwave radiation on the permeability of unilamellar phosphatidylcholine liposomes has been studied. Leakage of 5(6)-carboxyfluorescein from the liposomes was measured using spectrofluorimetry after exposure to either microwaves or thermal heating for 5-20 min intervals. The exposure temperature, 37.6 +/- 0.5 degrees C, was well above the phase transition temperature of the lipid membrane. The microwave exposure did not result in any non-thermal increase in permeability above that produced by thermal heating. This study refutes the results reported by Saalman et al. [1] in which an increased liposome permeability due to microwave exposure was reported. The refined analysis in the present study shows that this increased liposome permeability was not a non-thermal microwave effect.

Theoretical study of the resonant behaviour of an ion confined to a potential well in a combination of AC and DC magnetic fields.

Numerical solutions are presented to the equation of motion for an ion confined to a region of space by a restoring force and subject to DC and AC magnetic fields. We have expanded on the theoretical work of Durney et al. [1988] by including a potential well as a confining factor. This additional term in the equation of motion, being nondissipative, could allow for the buildup of stored energy within the system to a level necessary for a macroscopic resonant phenomenon. Resonant behaviour has been studied, including calculation of the trajectory and energy (kinetic and potential) of a confined ion, with emphases on the appearance of both amplitude and frequency windows. The results are discussed in relation to ion transport through transmembrane channels exposed to magnetic fields. When realistic values of the frictional and restoring-force coefficients are considered, all predicted resonant behaviour disappears, except at very high field strengths.

Experimental search for combined AC and DC magnetic field effects on ion channels.

The hypothesis that specific combinations of DC and low frequency AC magnetic fields at so-called cyclotron-resonance conditions could affect the transport of ions through ion channels, or alter the kinetics of ion channels (opening and closing rates), has been tested. As a model system, the ion channels formed by gramicidin A incorporated in lipid bilayer membranes were studied. No significant changes in channel conductance, average lifetime, or formation rate as a function of applied fields could be detected over a wide range of frequencies and field strengths. Experiments were carried out to measure the time-resolved single-channel events and the average conductances of many-channel events in the presence of K+ and H+ ions. The channel blocking effect of Ca++ was also studied.

Effect of 2.45 GHz microwave radiation on permeability of unilamellar liposomes to 5(6)-carboxyfluorescein. Evidence of non-thermal leakage.

The influence of 2.45 GHz microwave radiation on the membrane permeability of unilamellar liposomes was studied using the marker 5(6)-carboxyfluorescein trapped in phosphatidylcholine liposomes. The release of the fluorescent marker was followed by spectrofluorimetry after an exposure of 10 minutes to either microwave radiation or to heat alone of the liposome solutions. A significant increase of the permeability of carboxyfluorescein through the membrane was observed for the microwave-exposed samples compared to those exposed to normal heating only. Exposure to 2.45 GHz microwave radiation of liposomes has been previously found to produce increased membrane permeability as compared with heating. However, in contrast to previous studies, the observations reported here were made above the phase transition temperature of the lipid membrane. The experimental setup included monitoring of the temperature during microwave exposure simultaneously at several points in the solution volume using a fiberoptic thermometer. Possible mechanisms to explain the observations are discussed.

Microwave effects on the central nervous system--a study of radar mechanics.

Seventeen radar mechanics and engineers and 12 unexposed referents were examined, using extensive neurological, psychometric and neuropsychiatric techniques to determine whether there were any indications of central nervous system effects of microwave exposure. Pathological neurological findings were not more common in the exposed group than among the referents. In addition, the psychometric tests and the psychiatric rating scales did not reveal any statistically significant adverse effects of microwave exposure. The frequency of the occurrence of an increased protein band with an isoelectric point of 4.5 in the cerebrospinal fluid was higher among the men exposed to microwaves than among the referents. The nature and clinical significance of this or these proteins are still unclear. The time derivative of the magnetic flux density close to some of the transmitter units was surprisingly high (up to 350 T s-1).

Biological effects of high-frequency electromagnetic fields on Salmonella typhimurium and Drosophila melanogaster.

Salmonella typhimurium and Drosophila melanogaster were exposed to continuous wave (CW) 2.45-GHz electromagnetic radiation, pulsed 3.10-GHz electromagnetic radiation, CW 27.12-MHz magnetic fields, or CW 27.12-MHz electric fields (only Drosophila). The temperatures of the treated sample and the nonexposed control sample were kept constant. The temperature difference between exposed and control samples was less than +/- 0.3 degrees C. Ames' assays were made on bacteria that had been exposed to microwaves (SAR 60-130 W/kg) or RF fields (SAR up to 20 W/kg) when growing exponentially in nutrient broth. Survival and number of induced revertants to histidine prototrophy were determined by common plating techniques on rich and minimal agar plates. The Drosophila test consisted of a sensitive somatic system where the mutagenicity was measured by means of mutations in a gene-controlling eye pigmentation. In none of these test systems did microwave or radiofrequency fields induce an elevated mutation frequency. However, a significantly higher concentration of cells was found in the bacterial cultures exposed to the 27-MHz magnetic field or 2.45-GHz CW and 3.10-GHz pulsed microwave radiation.

A negative test for mutagenic action of microwave radiation in Drosophila melanogaster.

Microwave radiation (2450 MHz CW) was tested for mutagenicity in Drosophila melanogaster. Embryos in water were exposed to the electromagnetic field with a mean specific absorption rate of 100 W/kg. A sensitive somatic test system was used, in which mutagenicity was measured as the frequency of somatic mutations for eye pigmentation. With the test system used, microwaves did not show any mutagenic activity.

Retinal damage experimentally induced by microwave radiation at 55 mW/cm2.

The action of 550 W/m2 (mean) 3100 MHz pulsed radiation on the rabbit retina in vivo was investigated by fundus photography, blood-retinal barrier tracers, light and electron microscopy, either after a single 1--1.5 h exposure or after a series of repeated 1 h exposures for up to 53 h during about 100 days. The electron microscopic investigation of the repeatedly exposed retinas revealed degenerative changes in the retinal neurons. The neurons appeared depleted of their cytoplasmic constituents and often contained phago-lysosomal structures with myelin bodies. There were many degenerating synaptic boutons. The glial cells displayed reactive changes. These ultrastructural changes could not be demonstrated by the other methods used. A single microwave exposure, followed by an induced 70--100% blood-pressure increase, did not enhance blood-retina barrier permeability to tracers. There was no evidence of blood brain barrier leakage. These studies show that the rabbit eye can be affected by microwave radiation at intensities lower than previously reported.