報告書番号

V04018

タイトル（和文）

中間周波磁界の生物影響評価 --初期鶏胚を用いた発生毒性評価--

タイトル（英文）

Biological Effects of Intermediate Frequency Magnetic FieldsDevelopmental toxicity evaluation in chick early embryogenesis

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、外来の刺激に対して高感受性である発生初期段階の鶏胚を用いて発生毒性を評価した。初めに毒性評価に必要な背景データとして、当所の実験系は自然発生の異常出現率が低く、既知の催奇形性物質（RA）投与より明確に奇形が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48時間曝露する実験、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。胚の体節数、体長、発生段階、実体顕微鏡下で観察した総異常（死亡と形態異常）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 (IF) electromagnetic field exposure are needed because of the lack of such studies for the assessment on potential health risks. This study aims at determining whether or not a 20 kHz, magnetic field (MF) exposure has effects on the chick embryo development, particularly at the most sensitive stage of the first 48 hours of embryogenesis. A magnetically permeable incubator was placed in the middle of a pair of Helmholtz-type coils. The produced sinusoidal, 20 kHz MF contained very few harmonics, and the field inside the incubator, 20 x 20 x 20 cm, varied less than 3 % to its average intensity. The incubator made of polyvinylchloride had water-jacketed structure to maintain the temperature at 38 +/- 0.4 C. Relative humidity ranged from 60 to 80 %. When the exposure coils emitted the facility maximum intensity of 1.1 mTrms MF at 20 kHz, background plus stray fields in 20 kHz and 50 Hz in the control incubator were less than 0.001 and 0.03 micro-Trms, respectively. White Leghorn, fertile eggs were used. Sham-sham experiment was first 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 48 hours. The employed MF intensity of 1.1 mTrms was 176 times greater than the ICNIRP exposure limit for general public, 6.25 micro-T. The same number of intact eggs was served as negative-control. Additionally, 120 eggs given 1 micro-g of all-trans retinoic acid (RA), a known teratogen, were divided into two groups, one exposed and the other not exposed, i.e., positive control, to investigate if any modifications occur in teratogenicity by the MF exposure. Exposure condition was blinded to experimental personnel. After the exposure, embryos were fixed, and they were examined under stereoscopic microscope for abnormalities such as opened neural tube, delayed development or death. Number of somites, developmental stage under H&H definition, and body length were recorded. Statistical evaluation revealed that there has been no adverse effect of the MF exposure in every endpoint measured or observed when the non-treated, MF exposed group was compared to the negative-control. RA injection produced a medium degree (40 to 60 %) of teratogenic responses, however the field 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 all gave the same results. Under the experimental conditions tested, a 20 kHz sinusoidal, 1.1 mTrms MF exposure for the first 48 hours of embryogenesis did not produce any significant adverse effect 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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