報告書番号

V06006

タイトル（和文）

中間周波磁界の生物影響評価 －器官成長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 20 kHz, sinusoidal field exposure on the early 11 days of embryonic development -

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研究が少ないため、発生毒性で重要な器官成長期にある鶏胚を用いて磁界の発生毒性を評価した。まず、実験用鶏胚の自然発生異常率が低く、既知の催奇形性物質に対する反応が良好で、発生異常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。磁界曝露実験は、1群60個の有精卵に20 kHz、1.1 mT(rms)（ICNIRP公衆ガイドラインの176倍）の垂直磁界をふ卵開始から11日間曝露する実験と、催奇形性物質を事前投与した有精卵（40～60％の異常を誘発）に同じ磁界を曝露する実験を、盲検法により各3回繰り返して実施した。胚の発生段階、嘴長、翼指長、脚指長および実体顕微鏡下で観察した総異常（骨格異常を含む形態異常と死亡）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、磁界影響は無かった。

概要 （英文）

Biological studies to evaluate the effects of the intermediate frequency 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 embryonic development. A magnetically permeable incubator was placed in the middle of a pair of Helmholtz-type coils. The generated sinusoidal, vertical MF inside the incubator varied less than +/- 3 %. The incubator had a water-jacketed structure to maintain the temperature at 38 +/- 0.4 C. Relative humidity was controlled at 70 +/- 10 %. At the maximum intensity of 1.1 mT(rms) MF at 20 kHz, background plus stray fields in the control incubator were less than 0.001 micro-T(rms) at 20 kHz and 0.03 micro-T(rms) at 50 Hz. 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 11 days. The employed intensity of 1.1 mT is 176 times higher than the International Commission on Non-Ionizing Radiation Protection exposure limit for general public, 6.25 micro-T. The same number of intact eggs was served as sham-exposed. Experiments were conducted in a blind fashion. After MF exposure, live embryos were fixed in 10 % neutral buffered formalin, and they were examined under stereoscopic microscope for skeletal abnormalities such as crossbite and tailbone defect, morphological abnormalities such as exencephaly and anophthalmia, delayed development. Developmental stages under H&H definition, wing finger and leg finger lengths 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 sham-exposed group. Additional 120 eggs given 0.01 micro-g of all-trans retinoic acid (RA), a known teratogen, were divided into two groups, one for exposed and another for sham-exposed, to investigate any modifications in teratogenicity by the MF exposure. RA injection produced teratogenic responses in 40 to 60 % of embryos in the sham-exposed group. However the proportion of abnormal embryos in the exposed group did not significantly differ from that in the sham-exposed group. The same results were obtained consistently in the 3 times repeated experiments in both intact and RA-treated experiments. Under the present experimental conditions, a 20 kHz sinusoidal, 1.1 mT(rms) MF exposure for 11 days from the first day of embryogenesis did not produce any significant adverse effects on the chick embryo development. Lack of progressive effects by the field on the teratogenicity induced by a known teratogen was also demonstrated.

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