Chick embryos were either continuously or repeatedly exposed to extremely low frequency or radiofrequency electromagnetic fields to assay for HSP70 induction or survival following hypoxia/re-oxygenation insult.
It was hypothesized that de-protection against hypoxia should occur following long-term, continuous, or daily, repeated exposures to electromagnetic fields.
Experiments are based on a study in which long-term (4 days), continuous exposure to extremely low frequency electromagnetic fields decreased protection against ultraviolet radiation.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
60 Hz
Exposure duration:
continuous for 30 min or 4 days, or repeated daily exposure for 20, 30 or 60 min, once or twice daily, for 4 days
|
|
|
Exposure 2:
915 MHz
Exposure duration:
continuous for 30 min, or repeated daily exposure, 30 or 60 min/day, for 4 days
|
Positive control embryos were heated by placing eggs into plastic bags and submerging them in a 43°C water bath for 60 min. Other samples were heated at 39 or 41°C for 30 min to mimic the heating which might occur during an RF-EMF exposure.
| Frequency | 60 Hz |
|---|---|
| Type | |
| Waveform |
|
| Exposure duration | continuous for 30 min or 4 days, or repeated daily exposure for 20, 30 or 60 min, once or twice daily, for 4 days |
| Exposure source |
|
|---|---|
| Chamber | Fields were produced by paired Helmholtz coils, wound and connected as described previously with slight modification [Berman et al., 1990]. A coil diameter of 15 inches provided a region of nearly uniform magnetic field (±5%). Six paired Helmholtz coils were housed in water-jacketed incubators maintained at 37.8°C. Up to 24 embryos (in shells) could be exposed at a time. |
| Setup | Helmholtz coils were wired such that one coil could produce a cancelled field while the other coil produced a 60 Hz field. Thus, control (sham-exposed) embryos received no field exposure, but did experience all other environmental conditions (e.g., generation of heat or vibration) that might be produced by an activated coil. |
| Additional info | In some experiments, random ELF-EMF noise (band width 30-90 Hz, 8 µT) produced by a random noise generator, incorporated into an audio amplifier, was superimposed using the Helmholtz coils as described above. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 8 µT | - | measured | - | - |
| Frequency | 915 MHz |
|---|---|
| Type | |
| Charakteristic |
|
| Exposure duration | continuous for 30 min, or repeated daily exposure, 30 or 60 min/day, for 4 days |
| Modulation type | unspecified |
|---|
| Exposure source | |
|---|---|
| Chamber | The Crawford cell having two sample chambers located on either side of the center conductor, and a double stub tuner was mounted vertically on a rotary table installed inside an incubator chamber maintained at 37.5°C. |
| Setup | Up to eight embryos (in shells) could be exposed simultaneously. Control embryos were placed outside the Crawford cell. |
| Additional info | Thermocouple readings indicated that the temperature increase of the embryo was less than 0.6 or 1.2°C during the 30 or 60 min exposures, respectively (to below 39.0°C final temperature). In some experiments, random ELF-EMF noise (band width 30-90 Hz, 8 µT) produced by a random noise generator, incorporated into an audio amplifier, was superimposed using the Helmholtz coils as described above. |
Several of the exposure protocols yielded embryos that had statistically significant decreases in protection against hypoxic stress (continuous exposure and 30 or 60 min extremely low frequency (twice daily); or 30 or 60 min once daily radiofrequency). This is consistent with the result that following 4 days of extremely low frequency electromagnetic field exposure, HSP70 levels declined by 27% as compared to controls. In addition, the superposition of extremely low frequency electromagnetic field noise inhibited hypoxia de-protection caused by long-term, continuous extremely low frequency or daily, repeated radiofrequency exposures.
This electromagnetic field-induced decrease in HSP70 levels and resulting decline in cytoprotection suggests a mechanism by which daily exposure (such as might be experienced by mobile phone users) could enhance the probability of cancer and other diseases.
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