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

[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] med./bio.

Spontaneous and nitrosourea-induced primary tumors of the central nervous system in Fischer 344 rats chronically exposed to 836 MHz modulated microwaves

著者: Adey WR, Byus CV, Cain CD, Higgins RJ, Jones RA, Kean CJ, Kuster N, MacMurray A, Stagg RB, Zimmerman G, Phillips JL, Haggren W
掲載誌: Radiat Res 1999; 152 (3): 293-302
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この研究は、致死ばく露を含む、2年間のバイオアッセイで、北米デジタルセルラー（NADC）の変調の836.55MHz電磁界（TDMA）の影響を調べた。妊娠フィッシャー344ラットからの出生仔を用いて、断続的なTDMAばく露を24ヶ月間行った後の、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回投与による誘発性を調べた。遠方界ばく露を妊娠19日目から21日齢での離乳時まで、それに引き続近傍界ばく露を35日齢から22ヶ月間継続した。ばく露は1日2時間、週4日連続で行い、SARレベルは、携帯電話ユーザ頭部での局所ピーク値をシミュレーションした。実験開始時の236匹のラットのうち、実験終了時に生存していた182匹（77％）は709-712日齢で屠殺し、分析した。また、実験途中で死亡した54匹（23％）も参考のため別途分析した。その結果、TDMA、ばく露によるCNSでの腫瘍発生的影響の証拠はなかった；一方、ばく露によるいくらかの腫瘍抑制効果が見られた；全般的に言えば、TDMA電磁界にばく露したラットでは、CNS腫瘍の自然発生率およびENU誘発性腫瘍発生率が減少する傾向にあった；実験中に死亡したラットの内、原発性神経腫瘍が死因と判定されたもので調べると、電磁界はENU誘発腫瘍発生を減少させた，と報告している。

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研究目的（著者による）

To evaluate whether the TDMA (Time Division Multiple Access) cellular phone met some of the defining criteria of known neurocarcinogenic agents (in this case ENU (ethylnitrosourea, a carcinogen)) in an animal model which include 1) a consistent capability to increase tumor incidence, 2) a reduction in latent period, 3) establishment of a direct dose-effect relationship, 4) a shift toward more anaplastic tumor types, and 5) an increased susceptibility of fetal tissues to neurocarcinogens compared with adult tissues.

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: pulsed
ばく露時間: continuous for about 25 days, see add. information
-
ばく露2: 836.55 MHz
Modulation type: pulsed
ばく露時間: repeated daily intermittent exposure, 7.5 min on/off, 2h/day, 4 days/week for up to 680 days, see add. information
  • 電力: 2.5 W (± 0.1 W)
  • SAR: 1.4 W/kg average over mass (brain) (male 250 g at 30 cm)
  • SAR: 1.2 W/kg average over mass (brain) (male 450 g at 45 cm)
  • SAR: 1.1 W/kg average over mass (brain) (female 150 g at 30 cm)
  • SAR: 1 W/kg average over mass (brain) (female 250 g at 45 cm)

General information

Rats were assigned to four experimental groups: Sham/Sham, Sham/Field, ENU/Sham and ENU/Field. A single dose of ENU was applied on gestation day 18 via the tail vein. Buffer alone was applied to the sham-injected groups.

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 pulsed
Duty cycle 33.33 %
Repetition frequency 50 Hz
Additional information

NADC with π/4 DQPSK
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 of square aperture (2 x 2 m²) and 4.2 m length (about 12 wavelengths). Circular polarization was achieved using crossed dipole antennae placed in front of a ground plane at the apex of the horn and phase-shifted antenna feeds.
ばく露装置の詳細 Rat cages were positioned (not randomized daily) in a vertically oriented 3 x 3 matrix at the aperture of the horn in a "target chamber" that was 2.5 m square and 1.5 m deep, and lined with RF-absorbing foam. Sham exposures were performed in a square chamber of identical dimensions and materials, but the tapered section was truncated to 58 cm.
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

No parameters are specified for this exposure.

測定および計算の詳細

Plane wave equivalent power densities were measured using an electric field probe and meter unit. 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
偏波
  • unspecified
ばく露時間 repeated daily intermittent exposure, 7.5 min on/off, 2h/day, 4 days/week for up to 680 days, see add. information
Modulation
Modulation type pulsed
Duty cycle 33.33 %
Repetition frequency 50 Hz
Additional information

NADC with π/4 DQPSK
ばく露装置
ばく露の発生源／構造
  • plastic-encapsulated half-wave sleeved dipole
チャンバの詳細 Twelve carousel exposure platforms were used each with 10 rats confined in PVC tubular restraints of different sizes and oriented radially around a central antenna. The antennas of adjacent carousels were spaced 1.7 m apart. Sham exposure was performed in identical carousels located in a different room.
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.
Additional information Near field exposure began at age 33 days and was performed on 4 consecutive days weekly until termination of the experiment at 709-712 days of age (376 exposures in total).
パラメータ
測定量 値 種別 Method Mass 備考
電力 2.5 W - - - ± 0.1 W
SAR 1.4 W/kg average over mass 計算値 brain male 250 g at 30 cm
SAR 1.2 W/kg average over mass 計算値 brain male 450 g at 45 cm
SAR 1.1 W/kg average over mass 計算値 brain female 150 g at 30 cm
SAR 1 W/kg average over mass 計算値 brain female 250 g at 45 cm
Additional parameter details

SARs indicated are "slot" average values, time averaged values are one third of these. Ambient ELF magnetic fields measured with a gaussmeter above each antenna ranged from <0.01 to 0.04 µT rms. Ambient static magnetic fields were between 31 and 39 µT.

測定および計算の詳細

An RF power meter and RF sensor were coupled directly to the feedline of the antenna connector. Antennas were tested for impedance matching (VSWR) and feedpoint impedances. Field patterns have been modelled in detail in the reference article. Dosimetric assessments were made by three different techniques: numerical modelling (FDTD and FIT) based on MRI data sets of a rat cadaver (verified by electric probe measurements in the brain), thermometric probes and thermography. The uncertainty of the numerical dosimetry was estimated to be less than ± 1.5 dB. 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:
  • ばく露中
  • ばく露後

研究の主なアウトカム（著者による）

The study shows no increased tumorigenesis in the mammalian CNS from exposure to TDMA signals. Overall, the TDMA field-exposed animals exhibited trends toward a reduced incidence of spontaneous CNS tumors and ENU (ethylnitrosourea)-induced CNS tumors.

研究の種別:

研究助成

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