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

[周波数変調マイクロ波に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] med./bio.

Spontaneous and nitrosourea-induced primary tumors of the central nervous system in Fischer 344 rats exposed to frequency-modulated microwave fields

著者: Adey WR, Byus CV, Cain CD, Higgins RJ, Jones RA, Kean CJ, Kuster N, MacMurray A, Stagg RB, Zimmerman G
掲載誌: Cancer Res 2000; 60 (7): 1857-1863
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この研究は、携帯電話ユーザの頭部ばく露を模擬した836.55 MHz周波数変調（FM）信号シグナルにばく露したフィッシャー344ラットによる2年間のバイオアッセイである。妊娠フィッシャー344ラットからの出生仔を用いて、中枢神経系（CNS）腫瘍の自然発生および発がん物質エチルニトロソ尿素（ENU）の子宮内１回投与（この投与量で、26ヶ月の平均寿命における脳腫瘍発生率10-15％が期待される）による誘発性腫瘍発生率への影響を調べた。妊娠したラット（ｎ＝102）を無作為に6群に分け、それぞれの出生仔による6群で実験した（各群n＝90、合計ｎ＝540）；FM／ENUが擬似／擬似；擬似／真；真／擬似；真／真の4群の他、ENU投与のケージ対照、ENU擬似投与のケージ対照である。断続的なFMばく露を妊娠19日目に開始し、21日齢まで継続し、その後再開して、31日齢から731-734日齢まで継続した。ラット脳の比吸収率（SAR）は携帯電話ユーザ頭部の局所ピーク値と同レベルとした（雄1.2W/kg、雌1.0W/kg）。実験開始時の540匹のうち、実験終了前に168匹が死亡した。分析の結果、ENUは有意に生存期間を短縮した（ENUなしの3群平均708日、ENU処置の3群平均645日）；ENU処置の有無に関わらず、生存率に対するFMばく露の影響は見られなかった；対照群のCNS腫瘍の自然発生率1.1-4.4％に比べ、ENU処置群では有意に高くなった（14.4-22.2％、P<0.0001）；自然発生およびENU誘発のどちらにおいても、数、発生率、組織学的タイプに対するFMばく露影響は見られず、発生数における性差への影響もなかった、と報告している。これらの結果が、同著者のTDMAでの結果（Adey WR: Radiat. Res. 152 pp.293-302:1999）と相反する点についても議論している。

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研究目的（著者による）

The study was designed as a 2-year bioassay to test the hypothesis that frequency modulated field exposure might alter either survival or CNS primary tumor incidence.

詳細情報

A life-long exposure was simulated, beginning with exposures of fetal and preweanling rats. A low dose of ENU (ethylnitrosourea, a carcinogen) was selected to give maximum sensitivity for detection of a modification of tumor incidence.

影響評価項目

ばく露

ばく露 パラメータ
ばく露1: 836.55 MHz
Modulation type: FM
ばく露時間: continuous for about 25 days, see add. information
ばく露2: 836.55 MHz
Modulation type: FM
ばく露時間: repeated daily exposure, 2h/day, 4 days/week, for up to 700 days, see add. information
  • 電力: 2.5 W mean (± 0.1 W)
  • SAR: 1.2 W/kg average over mass (brain) (male 450 g)
  • SAR: 0.27 W/kg average over mass (whole body) (male 450 g)
  • SAR: 1 W/kg average over mass (brain) (female 236 g)
  • SAR: 0.42 W/kg average over mass (whole body) (female 236 g)

General information

Rats were assigned to six groups: sham ENU + sham field, sham ENU + field, ENU + sham field, ENU + field, ENU + cage control, sham ENU + cage control. A single dose of ENU was applied on gestation day 18 via the lateral tail vein. Buffer alone was applied to the sham-injected groups. Exposure systems have been described in [Lai et al., 1996].

ばく露1

主たる特性
周波数 836.55 MHz
タイプ
  • electromagnetic field
特性
  • far field
偏波
  • circular
ばく露時間 continuous for about 25 days, see add. information
Modulation
Modulation type FM
Modulation frequency 12.5 kHz
Additional information

modulation by a recorded 2-min pattern of "balanced speech"
ばく露装置
ばく露の発生源／構造
チャンバの詳細 Far field conditions were simulated with an approx. plane wave in a large tapered horn radiator.
ばく露装置の詳細 Rat cages were positioned in a vertically oriented 3 x 3 matrix at the square aperture (2 x 2 m²) of the horn. Sham exposures were performed in a square chamber of identical dimensions and materials.
Sham exposure A sham exposure was conducted.
Additional information Far field exposure of rats in their home cages began on gestation day 19 and continued until the pups were aged 21 days (about 25 days in total).
パラメータ
測定量 値 種別 Method Mass 備考
電力密度 2.6 mW/cm² mean - - ± 0.5 mW/cm²
測定および計算の詳細

Wavefront circularity (axial ratio) was within 2.3 dB, and power density was within 1.6 dB across the cage exposure area.

ばく露2

主たる特性
周波数 836.55 MHz
タイプ
  • electromagnetic field
特性
  • near field
ばく露時間 repeated daily exposure, 2h/day, 4 days/week, for up to 700 days, see add. information
Modulation
Modulation type FM
Modulation frequency 12.5 kHz
Additional information

modulation by a recorded 2-min pattern of "balanced speech"
ばく露装置
ばく露の発生源／構造
  • half-wave sleeved dipole
Distance between exposed object and exposure source 45 mm
チャンバの詳細 Twelve carousel exposure platforms were used each with 10 rats confined in plastic tubular restraints and oriented radially around a central antenna.
ばく露装置の詳細 The distance to the antenna from the tip of the nose was 30 mm from weaning to 120 days, and 45 mm thereafter.
Sham exposure A sham exposure was conducted.
Additional information Near field exposure began at age 31 days and was performed on 4 consecutive days weekly until termination of the experiment at 731-734 days of age (384 exposures in total).
パラメータ
測定量 値 種別 Method Mass 備考
電力 2.5 W mean - - ± 0.1 W
SAR 1.2 W/kg average over mass 計算値 brain male 450 g
SAR 0.27 W/kg average over mass 計算値 whole body male 450 g
SAR 1 W/kg average over mass 計算値 brain female 236 g
SAR 0.42 W/kg average over mass 計算値 whole body female 236 g
測定および計算の詳細

Dosimetric assessments were made by two different techniques, each of which was verified by an independent method: numerical modelling [Burkhardt et al., 1997] verified by electric probe measurement, and thermography verified by thermometric probes. The uncertainty of the numerical dosimetry was estimated to be less than ± 1.5 dB for the brain average and less than ± 1 dB for the whole body average. Uncertainty in thermography is less than ± 3 dB.

Reference articles

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:
調査の時期:
  • ばく露後

研究の主なアウトカム（著者による）

There were no effects on incidence of either spontaneous or ENU-induced primary tumors of the CNS associated with lifetime exposure of rats to frequency modulated microwave fields simulating electrical characteristics of hand-held mobile telephone transmissions at the head of the user.

研究の種別:

研究助成

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