研究のタイプ: 医学／生物学の研究 (experimental study)

[1.6 GHz無線周波信号にばく露されたラットの2年間の慢性バイオアッセイ研究] med./bio.

Two-year chronic bioassay study of rats exposed to a 1.6 GHz radiofrequency signal

著者: Anderson LE, Sheen DM, Wilson BW, Grumbein SL, Creim JA, Sasser LB
掲載誌: Radiat Res 2004; 162 (2): 201-210
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この研究は、Fischer344ラットの発がん率に対する1.6GHz無線周波（RF）への長期ばく露の影響を調べた。妊娠時期を調整した妊娠ラットへの遠方界ばく露実験（母ラットへのばく露レベルは、胎仔脳の平均SARで0.16W/kgとなるように設定し、妊娠19日目から、1日2時間、週7日で、出生仔の離乳（～23日齢）まで継続）と、胎児期から離乳期までばく露した仔ラットへの近傍界ばく露実験（1日2時間、週5日で36±1日齢から2歳まで継続）を行った。母ラットへの遠方界ばく露実験は、妊娠雌ラットのばく露群72匹（36匹1群として2群で実験）、擬似ばく露群36匹。ケージコントロール群42匹とした。仔ラットへの近傍界ばく露実験は、雌雄各90匹1群としてばく露群2群（2レベル：脳内SARで1.6、0.16 W/kg）、擬似ばく露群1群、および雌雄各80匹のケージコントロール群とした（仔ラット実験は合計700匹）。その結果、遠方界ばく露群では、生存出生数／腹、生存指数、離乳時体重、臨床症状、腫瘍病変に有意差はなかった；近傍界ばく露仔ラッが実験終了まで生存した割合は、雄では差がなかったが、雌ではケージ対照群で生存時間の減少が見られた、と報告している。

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研究目的（著者による）

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.

影響評価項目

ばく露

ばく露 パラメータ
ばく露1: 1.62 GHz
ばく露時間: repeated daily exposure, 2 h/day, for about 27 days
  • 電力密度: 0.33 mW/cm² mean
  • SAR: 0.16 W/kg mean (brain) (0.10-0.22 W/kg)
  • SAR: 0.06 W/kg mean (whole body) (0.036-0.077 W/kg)
ばく露2: 1.62 GHz
ばく露時間: repeated daily exposure, 2 h/day, 5 days/week, from 35 days up to about 2 years of age
  • SAR: 0.16 W/kg mean (brain)
  • SAR: 1.6 W/kg mean (brain)

ばく露1

主たる特性
周波数 1.62 GHz
タイプ
  • electromagnetic field
特性
  • far field
ばく露時間 repeated daily exposure, 2 h/day, for about 27 days
Modulation
Modulation type cf. additional information
Additional information

Iridium signal with differentially encoded quaternary phase shift keying (DEQPSK) and a frame length of 90 ms with 11 data slots per frame
ばく露装置
ばく露の発生源／構造
  • 導波管
  • flared parallel-plate exposure system
Distance between exposed object and exposure source 3 m
チャンバの詳細 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.
ばく露装置の詳細 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 information 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.
パラメータ
測定量 値 種別 Method Mass 備考
電力密度 0.33 mW/cm² mean 測定値 - -
SAR 0.16 W/kg mean 計算値 brain 0.10-0.22 W/kg
SAR 0.06 W/kg mean 計算値 whole body 0.036-0.077 W/kg
測定および計算の詳細

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.

ばく露2

主たる特性
周波数 1.62 GHz
タイプ
  • electromagnetic field
特性
  • near field
ばく露時間 repeated daily exposure, 2 h/day, 5 days/week, from 35 days up to about 2 years of age
Modulation
Modulation type cf. additional information
Additional information

Iridium signal with differentially encoded quaternary phase shift keying (DEQPSK) and a frame length of 90 ms with 11 data slots per frame
ばく露装置
ばく露の発生源／構造
チャンバの詳細 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.
ばく露装置の詳細 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 information 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.
パラメータ
測定量 値 種別 Method Mass 備考
SAR 0.16 W/kg mean 計算値 brain -
SAR 1.6 W/kg mean 計算値 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.

測定および計算の詳細

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): [1.62 GHzでのラットばく露用のカルーソル使用のドジメトリー]
  • Wilson BW et al. (2002): [1.6 GHzのマイクロ波照射用小動物、全身ばく露用の効率的なシステム]
  • Adey WR et al. (1999): [835 MHz変調マイクロ波に長期ばく露されたフィッシャー344ラットにおける自然発生およびニトロソ尿素誘発の中枢神経系原発腫瘍]
  • Moros EG et al. (1998): [小動物の長期間のUHF照射用のコンパクトなばく露装置：1電磁および環境面を考慮した設計]

ばく露を受けた生物:

方法 影響評価項目／測定パラメータ／方法

研究対象とした生物試料:
研究対象とした臓器系:
  • 脳／腫瘍
  • lung, spleen, mammary gland, thyroid, testis, skin, eye, blood, nose
調査の時期:
  • ばく露中
  • ばく露後

研究の主なアウトカム（著者による）

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.

研究の種別:

研究助成

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