Study type: Medical/biological study (experimental study)

Two-year chronic bioassay study of rats exposed to a 1.6 GHz radiofrequency signal med./bio.

By: Anderson LE, Sheen DM, Wilson BW, Grumbein SL, Creim JA, Sasser LB
Published in: Radiat Res 2004; 162 (2): 201-210
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Aim of study (acc. to author)

To determine whether long-term exposure to a 1.6 GHz radiofrequency field would affect the incidence of cancer in rats. Whole-body far field exposures of pregnant rats were initiated at 19 days of gestation and continued for dams and pups after parturition until weaning (approximately 23 days old). The offspring of these dams were selected for near field treatment (divided in male and female groups). Near field exposures were initiated when the offspring were 36 +/- 1 days old and continued until the rats were 2 years old.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 1.62 GHz
Exposure duration: repeated daily exposure, 2 h/day, for about 27 days
Exposure 2: 1.62 GHz
Exposure duration: repeated daily exposure, 2 h/day, 5 days/week, from 35 days up to about 2 years of age

Exposure 1

Main characteristics
Frequency 1.62 GHz
Type
Charakteristic
Exposure duration repeated daily exposure, 2 h/day, for about 27 days
Modulation
Modulation type cf. additional info
Additional info

Iridium signal with differentially encoded quaternary phase shift keying (DEQPSK) and a frame length of 90 ms with 11 data slots per frame
Exposure setup
Exposure source
Distance between exposed object and exposure source 3 m
Chamber The exposure setup used a horizontal beam orientation in a flared plate design [Wilson et al., 2002]. The parallel-plate enclosure (2.48 m long) was lined with copper foil on top and bottom plates, and the sides were covered with pyramidal anechoic material. It was excited by a coaxial to waveguide adapter and provided for RF exposure (23 dB beam width) at the position of the animal cages in an area of 2.11 x 1.11 m at 3 to 3.5 m (approx. 12 λ) from the antenna, with a uniformity of better than 62.6 dB.
Setup Eighteen standard rat cages (45.7 x 24.1 x 20.3 cm) containing single rats with their offspring were located in a box (1.45 x 2.40 x 1.60 m) covered on five of the interior walls with pyramidal or grooved anechoic material. The cages were arranged in three rows of six cages with their front surfaces in the plane of the parallel plate aperture. The sham system was installed in an adjoining room.
Sham exposure A sham exposure was conducted.
Additional info Whole-body far-field exposures were initiated at 19 days of gestation and continued for dams and pups after parturition until weaning at about 23 days of age. The animal groups were not exposed in a blinded fashion.
Parameters
Measurand Value Type Method Mass Remarks
power density 0.33 mW/cm² mean measured - -
SAR 0.16 W/kg mean calculated brain 0.10-0.22 W/kg
SAR 0.06 W/kg mean calculated whole body 0.036-0.077 W/kg
Measurement and calculation details

SARs in the foetal brain were determined by a combination of computer modelling, calculations and direct measurement of field strength within empty animal cages positioned in the exposure system. Forward power and voltage standing wave ratio (VSWR) were monitored by a power meter and power sensor connected to a directional coupler. Power density at the cage position was derived from the power ratio received by a λ/2 dipole antenna and also measured directly with a calibrated analogue EM meter.

Exposure 2

Main characteristics
Frequency 1.62 GHz
Type
Charakteristic
Exposure duration repeated daily exposure, 2 h/day, 5 days/week, from 35 days up to about 2 years of age
Modulation
Modulation type cf. additional info
Additional info

Iridium signal with differentially encoded quaternary phase shift keying (DEQPSK) and a frame length of 90 ms with 11 data slots per frame
Exposure setup
Exposure source
Chamber The exposure facility contained nine partially shielded double units each housing two near-field exposure carousels that were similar to those described by Moros et al. [1998]. RF absorbing material was placed around each exposure unit.
Setup Ten animals per carousel were placed with their head first in cylindrical tubes arranged radially around a central antenna.
Sham exposure A sham exposure was conducted.
Additional info Six of the units were assigned to each of the three exposure conditions that were rotated every six weeks among the three zones. The animal groups were coded after far-field exposure so that near-field exposure and sham exposure were truly blind.
Parameters
Measurand Value Type Method Mass Remarks
SAR 0.16 W/kg mean calculated brain -
SAR 1.6 W/kg mean calculated brain -
Additional parameter details

Irradiated powers were adjusted to the increased size of the animals after 57 days when body mass continued to increase but brain mass had essentially attained adult size. Removed animals were replaced by a phantom rat (Nalgene bottle filled with saline solution) to maintain consistent dosimetry.

Measurement and calculation details

Forward and reflected powers were measured with a power meter before and every six weeks during the study. Antenna inputs were monitored with a crystal detector connected to a directional coupler. CW field levels with all 12 antennas active were measured at 10 cm from each antenna using a spectrum analyzer coupled with a λ/2 sleeved dipole. The dosimetric analysis was conducted using both detailed numerical (derived from MRI scans) and experimental rat phantoms for rats weighing 220-300 g [Schonborn et al., 2004]. SAR values measured in the rat brain were approximately 20-30% higher than the numerical calculations. SAR variations in the brain, due to animal size and slight movement of the head, were in the range of 115% to 230%. Exposure system and dosimetry were designed for head-only exposures, where the whole-body average SAR was between 12% and 15% of the brain average value, depending on the numerical rat model chosen.

Reference articles

  • Schönborn F et al. (2004): Dosimetric analysis of the carousel setup for the exposure of rats at 1.62 GHz
  • Wilson BW et al. (2002): Space efficient system for small animal, whole body microwave exposure at 1.6 GHz
  • Adey WR et al. (1999): Spontaneous and nitrosourea-induced primary tumors of the central nervous system in Fischer 344 rats chronically exposed to 836 MHz modulated microwaves
  • Moros EG et al. (1998): A compact shielded exposure system for the simultaneous long-term UHF irradiation of forty small mammals: I. Electromagnetic and environmental design

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

No statistically significant differences were revealed among treatment groups for number of live pups/litter, survival rate, and weaning weights, nor were there differences in clinical signs or neoplastic lesions. The percentages of rats surviving at the end of the near field irradiation were not different among the male groups. In the female groups a significant decrease in survival time was found for the cage control group.

Study character:

Study funded by

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