報告書番号

V05010

タイトル（和文）

中間周波磁界の生物影響評価 --器官形成期鶏胚を用いた発生毒性評価--

タイトル（英文）

Developmental toxicity evaluation of intermediate frequency, magnetic field exposure in chick embryos- Effects of 7 days exposure to 20 kHz, sinusoidal field on the organogenesis-

概要 （図表や脚注は「報告書全文」に掲載しております）

中間周波磁界の生物影響研究が少ないため、発生毒性評価で重要な器官形成期にある鶏胚を用いて発生毒性を評価した。初めに、実験に使用する鶏胚の自然発生異常率が低く、既知の催奇形性物質（レチノイン酸）に対する反応が良好で、確実に奇形を検出可能であることを確認した。次に無曝露実験を行い、曝露設備が影響評価実験に適していることを確認した。その上で盲検法を用い、1群60個の有精卵に、20 kHz、1.1 mTrms（ICNIRP公衆ガイドラインの176倍）の垂直磁界をふ卵開始から7日間曝露する実験、および、RAを事前投与した陽性対照群（40～60％の異常を誘発）に同じ磁界を曝露する実験を、各3回繰り返して実施した。胚の発生段階、翼長、脚長、実体顕微鏡下で観察した総異常（死亡と形態異常）の出現率に関し、全ての繰り返し実験で対照群と曝露群間に統計学的な有意差は認められず、器官形成期での磁界影響は無かった。

概要 （英文）

Biological studies to evaluate the effects of the intermediate frequency (IF) electromagnetic field exposure are needed because of the lack of such studies for the assessment on potential health risks. This study aims to determine whether or not a 20 kHz, magnetic field (MF) exposure has effects on the chick embryo organogenesis. A magnetically permeable incubator was placed in the middle of a pair of Helmholtz-type coils. The generated sinusoidal, 20 kHz MF contained very few harmonics, and the field inside the incubator varied less than 3 % of its average intensity. The incubator was made of polyvinylchloride. It had a water-jacketed structure to maintain the temperature at 38 +/- 0.4 oC. Relative humidity ranged from 60 to 80 %. When the exposure coils emitted the maximum intensity of 1.1 mTrms MF at 20 kHz, background plus stray fields at 20 kHz and 50 Hz in the control incubator were less than 0.001 and 0.03 microTrms, respectively. White Leghorn, fertile eggs were purchased from an experimental animal breeder. Sham-sham experiment was conducted to validate our two identical exposure facilities. Two facilities gave no statistic difference in the development of chick embryo when no current was loaded in the exposure coil. A group of 60 eggs was exposed to sinusoidal 20 kHz, vertical MF for 7 days. The employed MF intensity of 1.1 mTrms was 176 times higher than the International Commission on Non-Ionizing Radiation Protection exposure limit for general public, 6.25 microT. The same number of intact eggs was served as negative-control. Experiments were conducted in a blind fashion. After MF exposure, embryos were fixed in 10 % neutral buffered formalin, and they were examined under stereoscopic microscope for abnormalities, such as exencephaly, anophthalmia, thoracoceloschisis, delayed development or death. Developmental stage under H&H definition, wing and leg length were recorded. Statistical evaluation revealed that there have been no adverse effects of the MF exposure on all endpoints measured or observed when the MF exposed group was compared to the negative-control. Additionally, 120 eggs given 0.1 mg of all-trans retinoic acid (RA), a known teratogen, were divided into two groups, one was exposed and the other was not, i.e., positive control, to investigate any modifications in teratogenicity by the MF exposure. RA injection produced teratogenic responses in 40 to 60% of embryos. However the MF exposure did not change the proportion of abnormal embryo significantly in comparison with that of the positive-control group. Three times repeated experiments on both intact and RA-treated groups gave the same results. Under the present experimental conditions tested, a 20 kHz sinusoidal, 1.1 mTrms MF exposure for the first 7 days of embryogenesis did not produce any significant adverse effects on the chick embryo development. Lack of progressive effects by the field on the teratogenicity with a known teratogen pretreatment was also demonstrated.

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