Study type: Medical/biological study (experimental study)

Bioeffects induced by exposure to microwaves are mitigated by superposition of ELF noise. med./bio.

Published in: Bioelectromagnetics 1997; 18 (6): 422-430

Aim of study (acc. to author)

The authors speculated that the superimposition of electromagnetic noise fields, which have been shown to inhibit biological responses due to extremely low frequency exposure (see publication 344 and publication 2809), may also inhibit the effects of modulated microwaves.
The aim of the study was to investigate this possibility by conducting experiments in which biological samples were exposed concurrently to amplitude modulation and extremely low frequency noise fields.

Background/further details

L929 cells were exposed to 60 Hz amplitude modulated microwave fields or a 50 Hz burst-modulated DAMPS (Digital Advanced Mobile Phone System) digital cellular phone field at levels known to produce ornithine decarboxylase enhancement, together with band-limited 30-100 Hz extremely low frequency noise with root mean square amplitude of up to 10 µT.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 835 MHz
Modulation type: AM
Exposure duration: continuous for 8 h
Exposure 2: 840 MHz
Modulation type: pulsed
Exposure duration: continuous for 8 h
Exposure 3: 30–100 Hz
Exposure duration: continuous for 8 h

General information

The ELF/MW exposure system was designed for concurrent exposure to ELF and MW fields. Controls were performed concurrently inside a separate incubator at 37°C. The four flasks were stacked one on top of another and covered with a 12.7 cm x 7.6 cm x 8.9 cm mil-annealed mu-metal enclosure which was, however, not fully sealed against its base.

Exposure 1

Main characteristics
Frequency 835 MHz
Type
Charakteristic
  • guided field
Exposure duration continuous for 8 h
Modulation
Modulation type AM
Modulation frequency 60 Hz
Modulation depth 23 %
Additional info

sinusoidal

Exposure setup
Exposure source
Chamber The Crawford cell having two chambers and a double stub tuner was mounted vertically on a rotary table positioned within a pair of Helmholtz coils installed inside a water-jacketed incubator maintained at 37°C. The detailed arrangement of this exposure system has been described in the reference article.
Setup Four 25 cm² tissue culture flasks, each containing 5 ml of culture medium, were placed as pairs, end to end, on either side of the center conductor, flat on non-conducting shelves located at approx. 7 cm from the junction between the center rectangular section and the lower tapered end. The MW EF was perpendicular to the direction of propagation which was parallel to the long axis of the exposure chamber.
Additional info There was no measurable temperature increase in the samples over the exposure period.
Parameters
Measurand Value Type Method Mass Remarks
power 1 W mean measured - -
electric field strength 1 V/cm mean calculated - -
SAR 2.5 W/kg mean measured - -

Exposure 2

Main characteristics
Frequency 840 MHz
Type
Charakteristic
  • guided field
Exposure duration continuous for 8 h
Modulation
Modulation type pulsed
Pulse width 7 ms
Duty cycle 33 %
Repetition frequency 50 Hz
Additional info

D-AMPS, pseudo-random test sequence in TDMA mode

Exposure setup
Parameters
Measurand Value Type Method Mass Remarks
power 1 W mean measured - peak power of 3.8 W
electric field strength 1 V/cm mean calculated - -
SAR 2.5 W/kg mean measured - -

Exposure 3

Main characteristics
Frequency 30–100 Hz
Type
Exposure duration continuous for 8 h
Additional info ELF noise MF superimposed on E1 and E2
Modulation
Modulation type cf. additional info
Additional info

AC field with random amplitude variations in time

Exposure setup
Exposure source
Chamber In order to ensure a uniform MF, the coils were positioned so that the sample flasks placed in the Crawford cell were contained within a 12.7-cm cylinder with its axis parallel to the axis of the coils. The calculated attenuation of the ELF MF due to eddy currents was 0.08 dB which means that the Crawford cell should be nearly transparent to the ELF MF.
Setup The coils consisting of 10 turns of 26-gauge magnet wire wound on a support ring made of hard plastic tubing had a diameter of 46 cm and a separation of 23 cm and were assembled on a Plexiglas frame positioned around the Crawford cell. The ELF MF was parallel to the base of the flasks so that the ELF EF induced in the cells was parallel to the MW EF. The ELF noise MF was generated using a custom made band limited noise generator connected to the coils via an audio amplifier.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 4 µT effective value measured - 0.25, 0.5, 1, 2 and 4 µT concurrent with E1
magnetic flux density 10 µT effective value measured - 1, 2, 5 and 10 µT concurrent with E2

Reference articles

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

In both cases, the ornithine decarboxylase activity enhancement was found to decrease exponentially as a function of the noise root mean square amplitude: With 60 Hz amplitude modulated microwaves, complete inhibition (of ornithine decarboxylase enhancement effect) was obtained with noise levels at or above 2 µT. With the DAMPS digital cellular phone signal, complete inhibition occurred with noise levels at or above 5 µT.
These findings suggest a possible practical means to inhibit biological effects from exposure to both extremely low frequency and microwave fields.

Study character:

Study funded by

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