中間周波磁界の生物影響評価 －60 kHz磁界のラット胚・胎児の発生に関する生殖発生毒性評価－
Reproductive and developmental toxicity of intermediate frequency magnetic field exposure - Effects of 60 kHz, 0.10 mT, sinusoidal magnetic field exposure on the rat organogenesis -
生殖発生過程で重要な器官形成期にあるラットを用いて、最近利用が広がっている60 kHzの中間周波磁界の生殖発生毒性を評価した。1群25匹の妊娠Crl:CD(SD)ラットに、60 kHz、0.10 mT(rms) （ICNIRP公衆ガイドラインの16倍）の一様な正弦波、垂直磁界を1日22時間、妊娠7～17日目に曝露した。妊娠20日目に雌親を解剖して胎児を摘出し、生殖発生への影響を検査した。曝露実験は盲検法にて実施し、2回繰り返して再現性を確認した。対照群と曝露群間で、雌親の妊娠中の体重増加、血液学的検査、血液生化学的検査、および、着床後の胚や胎児死亡率、生存胎児数や胎児体重、胎児の性比、雌親あたりの胎児外表異常、内臓異常、骨格異常出現率のいずれにおいても、再現性のある統計学的な有意差はなかった。本実験条件下では、中間周波磁界はラットの胚と胎児の発生過程に影響を与えないことが明らかとなった。
Biological studies to evaluate the effects of exposure to intermediate frequency electromagnetic field are needed because of the potential health risks. This study aimed to determine whether a 60 kHz magnetic field (MF) exposure had embryotoxic, fetotoxic and/or teratogenic potential. Two identical animal exposure facilities were constructed and a Merritt-type exposure coil was set in the center of each animal room. Animal cages were made of polycarbonate to avoid currents induced by MF exposure. The vertical sinusoidal MF generated inside the coils varied less than 2%. At the maximum MF intensity of 0.10 mT(rms) at 60 kHz, background plus stray MFs in the sham-exposed facility were less than 0.001 microT(rms) at 60 kHz and 0.03 microT(rms) at 50 Hz. Fifty pregnant Crl:CD(SD) rats were assigned randomly to sham-exposed or MF-exposed groups: 25 in each, with experiments conducted in a blind fashion. The rats were sham-exposed or exposed to the MF for 22 h/d from gestational days 7 to 17, dams were euthanized at gestational day 20 and their fetuses were examined. Experiments were repeated twice to confirm the reproducibility of outcomes. No reproducible changes related to MF exposure were found in terms of body weight gain, clinical signs, hematology, blood biochemistry or gross pathology in the dams. Numbers of implants, number of postimplantation fetuses, numbers and body weights of live fetuses and the incidence of low body weight fetuses also did not differ significantly between the sham- and MF-exposed groups. The fetal sex ratio was changed in the second experiment; however, the change arose from a decreased male-to-female ratio in the control group rather than a change in the MF-exposed group. No significant changes caused by MF exposure were found in the incidence of external, skeletal and visceral malformations or in skeletal variations. One type of fetal ossification showed a change between groups in the first experiment suggesting possible developmental retardation in MF-exposed fetuses. However, the similar mean fetal body weight between groups and the fewer low body weight fetuses in the MF-exposed group did not support this possibility. In addition, this change in ossification was not seen in the second experiment. Under these experimental conditions, a 60 kHz sinusoidal, 0.10 mT(rms) MF exposure during organogenesis was neither embryo/fetotoxic nor teratogenic and did not interfere with fetal development in this rat model.
|生殖発生毒性||REPRODUCTIVE AND DEVELOPMENTAL TOXICITY|
|中間周波磁界||INTERMEDIATE FREQUENCY MAGNETIC FIELD|
|60 kHz||60 kHz|