中間周波磁界の生物影響評価 －発生段階の進んだ鶏胚による20 kHzまたは60 kHz磁界の発生毒性評価－
Biological effects of intermediate frequency magnetic field exposure - Chick embryotoxicity by exposure to 20 kHz or 60 kHz magnetic field for 19 days during embryogenesis -
中間周波磁界の生物研究が少ないため、動物個体レベルで強い磁界を曝露できる鶏胚を用いて発生毒性を評価した。1群60個の有精卵に20 kHz、1.1 mT（ICNIRP公衆ガイドラインの40.7倍）、または60 kHz、0.11 mTの正弦波、垂直磁界を曝露した。胚発生への最終的な影響を明らかにするには、げっ歯類での研究と同様に発生が十分進んだ胚を用いて評価すべき、という指摘があるため、ふ卵開始からふ化2日前の19日目まで磁界を連続曝露した。曝露終了後に胚の生死、発生段階、嘴長、脚指長と形態学的な異常（外表異常と骨格異常）の出現率を評価した。発生毒性の評価は、結果の信頼性を確保するため盲検法下で行った。実験は結果の再現性を確認するため、周波数ごとに3回繰り返した。その結果、いずれの繰り返し実験においても全ての評価項目に関し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。
Evaluation of potential health risks of the intermediate frequency (IF) electromagnetic field exposure is still inconclusive. Because some chick embryo studies have suggested that IF magnetic field (MF) exposure could be embryotoxic, this needs to be confirmed and substantiated. We have demonstrated that exposure to 20 or 60 kHz MFs for up to 11 days was not teratogenic to chick embryogenesis. The present study extended the findings in prolonged MF exposure because of a criticism that teratological evaluations should be performed after chick embryos were fully developed. A group of 60 White Leghorn, fertile eggs was exposed to either 20 kHz or 60 kHz MF for 19 days from the first day of embryogenesis. The same number of eggs was served as sham-exposed (control). At the facility maximum intensity of 1.1 mT(rms) MF at 20 kHz or 0.11 mT(rms) at 60 kHz, background plus stray field in the sham-exposed incubator was less than 0.001 micro-T(rms). The employed intensity of 1.1 mT is 40.7 times higher than the exposure limit guideline value for the general public, that is 27 micro-T(rms), set by the International Commission on Non-Ionizing Radiation Protection. Experiments were triplicated and teratological evaluations were conducted in a blind fashion. After MF exposure, live embryos were fixed and examined for morphological abnormalities such as mandibular edema and kinky tail. Results showed comparable incidence of abnormalities between paired MF-exposed and sham-exposed groups. Developmental stages of embryos were recorded, and length from nostril to tip of upper bill and length of third toe were measured. These numerical endpoints in MF-exposed group did not statistically differ from these in concurrent sham-exposed group. Embryos were thereafter stained and examined skeletal abnormalities such as wavy rib and tailbone defect. Incidence of such abnormalities was low across experiments and no significant group differences were manifest. Obtained results indicated no MF exposure related changes in any of the endpoints; and this finding was consistent across triplicated experiments at either 20 kHz or 60 kHz MF exposure. Under these experimental conditions, a 20 kHz, 1.1 mT(rms) or a 60 kHz 0.11 mT(rms) MF exposure up to 19 days of chick embryogenesis did not produce any significant teratogenic effects.
|中間周波磁界||Intermediate frequency magnetic field|