Lack of alterations on meiotic chromosomes and morphological characteristics of male germ cells in mice exposed to a 60 Hz and 2.0 mT magnetic field

The effect of in vivo exposure of mice to a 60 Hz sinusoidal magnetic field (MF) at 2.0 mT on male germ cells was studied. The cytological endpoints measured included meiotic chromosome aberrations in spermatocytes and sperm morphology. Three independent experiments were carried out: (a) animals exposed for 72 h, (b) 10 days/8 h daily, and (c) 72 h exposure to MF plus 5 mg/kg of Mitomycin-C. No statistically significant differences indicative of MF effects were observed between MF exposed and control animals. In addition, an opposite effect between MF exposure and Mitomycin-C treatment in terms of chromosomal aberrations and sperm morphology was observed.     

Amplification of evoked potentials recorded from mouse hippocampal slices by very low repetition rate pulsed magnetic fields

The influence of low repetition rate pulsed magnetic fields (LRMF) on the evoked potential (population spike) recorded from mouse hippocampal slices was investigated. LRMF were applied according to two protocols. In protocol A, LRMF applied with a constant strength (15 mT) and frequency ranging from 0.03 to 0.5 Hz resulted in an amplification of the potential. Although the frequency of 0.16 Hz was the most effective, enhancing the population spike by over 280%, it also caused an increase in spontaneous activity, seizures, and cessation of neuronal activity in 50% of the slices. In protocol B, LRMF were applied with a variable intensity (9-15 mT) and in cycles of different duration ranging from 5 to 20 min. While an increase in the amplitude of the population spike was observed in all slices exposed to LRMF applied according to protocol B, the longest exposure was the most effective. Neither seizures nor an increase in the spontaneous activity were observed in this group of the slices. These results support and extend our previous data and characterize further the relation between the pattern of applied magnetic fields and their influence on the nervous system.     

Hypersensitivity symptoms associated with exposure to cellular telephones: no causal link

The hypothesis that there exist hypersensitive persons who perceive subjective symptoms from radiofrequency (RF) fields emitted by hand held mobile phones (cellular phones) was tested using double blind provocation experiments. We also tested whether sensitive subjects are able to determine whether the phone is on or off by sensing RF fields. The study group consisted of 20 volunteers (13 women and 7 men) who reported themselves as being sensitive to cellular phones. The RF exposure sources were one analogue NMT phone (900 MHz) and two digital GSM phones (900 and 1800 MHz). The duration of a test session was 30 min, and three or four sessions were performed in random order for each subject during 1 day. The subjects were asked to report symptoms or sensations as soon as they perceived any abnormal feelings. In addition, the subjects' blood pressure, heart rate, and breathing frequency were monitored every 5 min. The results of the study indicated that various symptoms were reported, and most of them appeared in the head region. However, the number of reported symptoms was higher during sham exposure than during real exposure conditions. In addition, none of the test persons could distinguish real RF exposure from sham exposure. Hence, we conclude that adverse subjective symptoms or sensations, though unquestionably perceived by the test subjects, were not produced by cellular phones.     

Relative contribution of residential and occupational magnetic field exposure over twenty-four hours among people living close to and far from a power line

This study sought to estimate the relative contribution of exposure to 50 Hz magnetic fields experienced at home, at work/school, or elsewhere to the total exposure over 24 hr. Personal exposure meters were carried by 97 adults and children in the Stockholm area. About half of the subjects lived close (<50 m) to a transmission line and half far (>100 m) away. Spot measurements and calculations for the residential exposure were also made. For subjects living<50 m from the line, the exposure at home contributed about 80% of the total magnetic field exposure, measured in mT-hours. Adults living far away experienced only 38% of the total exposure at home, but children still received 55%. Subjects with low time-weighted average (TWA) exposure both at home and at work spent 84% of their time in fields <0.1 microT, and those with high TWA at both locations spent 69% of their time in fields > or = 0.2 microT. This contrast was diluted if only exposure at one location was considered. For spot measurements and calculations of the residential exposure, both sensitivity and specificity was good. However, the intermediate field exposure category (0.1-0.19 microT) showed poor correlation to the 24 hr personal measurements.     

Potential motion related bias in the worn dosimeter measurements of two childhood leukemia studies

Time averaged field measurements produced by a Positron dosimeter worn by study subjects was the primary method of exposure evaluation in two Canadian studies of childhood leukemia and AC magnetic field exposure. Statistically significant but mutually contradictory results obtained in the two studies, done in different locales but under similar study conditions, have not been explained. This report examines operational features of the Positron meter, including an unanticipated sensitivity to wearer motion. If the convalescent cases studied were less active than their healthy controls, as one might expect, then the meter's characteristic responses to motion, particularly as they would affect case-control distributions above and below the different referent group cutpoints used in the two studies, could help to explain both the unexpected inverse risks reported in the larger study and the unusually high risks reported in the smaller study.     

Mechanism of action of moderate-intensity static magnetic fields on biological systems

There is substantial evidence indicating that moderate-intensity static magnetic fields (SMF) are capable of influencing a number of biological systems, particularly those whose function is closely linked to the properties of membrane channels. Most of the reported moderate SMF effects may be explained on the basis of alterations in membrane calcium ion flux. The mechanism suggested to explain these effects is based on the diamagnetic anisitropic properties of membrane phospholipids. It is proposed that reorientation of these molecules during moderate SMF exposure will result in the deformation of imbedded ion channels, thereby altering their activation kinetics. Channel inactivation would not be expected to be influenced by these fields because this mechanism is not located within the intramembraneous portion of the channel. Patch-clamp studies of calcium channels have provided support for this hypothesis, as well as demonstrating a temperature dependency that is understandable on the basis of the membrane thermotropic phase transition. Additional studies have demonstrated that sodium channels are similarly affected by SMFs, although to a lesser degree. These findings support the view that moderate SMF effects on biological membranes represent a general phenomenon, with some channels being more susceptible than others to membrane deformation.     

Occupational magnetic field exposures of garment workers: results of personal and survey measurements

To explore the feasibility of performing an epidemiologic study of female breast cancer and magnetic field (MF) exposures, we chose to study garment workers, who reportedly have some of the highest MF exposures. We collected personal exposure (PE, n = 48) and survey measurements (n = 77) near commercial sewing machines at three garment facilities and conducted a pilot interview among 25 garment workers asking about exposure duration, activities, and machine characteristics. MF levels were higher for older machines with alternating current (AC) than newer machines with direct current (DC) motors. MF levels were comparable for both idling and sewing activities. Most interviewed workers could describe duration of exposure and machine type (automatic/manual), but not other machine characteristics. Measurements were lower than previously reported for garment workers but were higher than exposures to most women. A historical exposure assessment can be conducted by linking duration of exposure with reconstructed exposure measurements but may be limited by the accuracy of work history data.     

Effect of a 125 mT static magnetic field on the kinetics of voltage activated Na+ channels in GH3 cells

Voltage activated Na(+) channels were examined in GH3 cells, using the whole cell patch clamp method. Channel currents were recorded before, during, and after a 150 s exposure to a 125 mT static magnetic field. There was a slight shift in the current-voltage relationship and a less than 5% reduction in peak current during magnetic field exposure. More pronounced, however, was an increase in the activation time constant, tau(m), during and for at least 100 s following exposure to the field. This change in tau(m) was seen primarily at lower activation voltages. No change was noted in the inactivation time constant, tau(h). Changes were clearly temperature dependent, being evident only at and above 35 degrees C. These findings are consistent with the hypothesis that reorientation of diamagnetic anisotropic molecules in the cell membrane are capable of distorting imbedded ion channels sufficiently to alter their function. The temperature dependence of this phenomenon is probably due to the greater ease with which a liquid crystal membrane can be deformed.     

The effect of exposure to high flux density static and pulsed magnetic fields on lymphocyte function

We investigated whether a combination of static electromagnetic field (EMF) at a flux density of 4.75 T together with pulsed EMF at a flux density of 0.7 mT generated by an NMR apparatus (NMRF), could promote movements of Ca(2+), cell proliferation, and the eventual production of proinflammatory cytokines in human lymphocytes as well as in Jurkat cells, after exposure to the field for 1 h. The same study was also performed after activation of cells with 5 micro g/ml phytohaemagglutinin (PHA) immediately before the exposure period. Our results clearly demonstrate that NMRF exposure increases the [Ca(2+)](i), without any proliferative, or activating, or proinflammatory effect on both normal and PHA stimulated lymphocytes. Accordingly, the levels of interferon gamma, tumor necrosis factor alpha, interleukin-1beta, interleukin-2, and interleukin-6 remained unvaried after exposure. Exposure of Jurkat cells statistically decreased the [Ca(2+)](i) and the proliferation. This is consistent with the low levels of IL-2 measured in supernatants of these cells after exposure. On the whole our data suggest that static and pulsed NMRF exposure contribute synergistically in the increase of the [Ca(2+)](i) without any activating or proinflammatory effect either in normal or in PHA challenged lymphocytes. In Jurkat cells, by changing the properties of cell membranes, NMRF exposure can influence Ca(2+) transport processes and hence Ca(2+) homeostasis, causing a marked decrease of proliferation.