報告書番号

V04017

タイトル（和文）

中間周波磁界の生物影響評価 --鶏胚による電磁界発生毒性研究の文献調査--

タイトル（英文）

Biological Effects of Intermediate Frequency Magnetic FieldsLiterature survey on developmental toxicity of electromagnetic fields in chick embryos

概要 （図表や脚注は「報告書全文」に掲載しております）

中間周波電磁界の安全性を確認する生物・健康影響評価研究が求められている。商用周波同様、外来の刺激に敏感な生物指標である発生・生殖研究が重要である。既開発の細胞用中間周波磁界曝露装置により、強い強度の曝露実験を動物レベルで実施可能な鶏胚について、既往の電磁界研究の文献を調査した。過去の研究では磁界影響について明確な結論が得られていない。主な原因は、高い自然発生異常率、標本数解析による必要十分な供試胚数が算出されていない、結果の再現性が確認されていない、曝露期間が初期胚のみで短すぎる、などであった。器官形成が未完了な極めて初期の胚については、統一された毒性評価基準がないことも、評価結果が不一致となった一因である。今後当所で行う鶏胚を用いた中間周波磁界の発生毒性評価研究では、本文献調査で抽出した問題点を解決した上で、研究を実施する。

概要 （英文）

We plan to conduct teratological and developmental toxicity studies of the intermediate frequency electromagnetic fields, because these fields are widely used but few toxicological studies have been carried out in that frequency. Prior to such studies, we performed literature survey on the studies with the chick embryos that evaluated electromagnetic field effects on the development. Aim of this survey is to delineate the outcomes of the developmental toxicity of electromagnetic field exposures using chick embryos and to discuss some difficulties associated with the chick embryo model and its application to the toxicity assessment. Chick embryos have been heavily studied for decades, and they are recognized as an excellent model for developmental biology. Because the chick embryo receives no biochemical influence from parental generation once it is laid, researchers can solely evaluate the direct effect of potential toxicants on the embryo development. Chick strains have not been rigorously established as an experimental model for toxicological evaluations. However, the chick embryos have been employed in nearly 30 electromagnetic field, developmental toxicity studies. Overall results were ambiguous, because over a half of research showed adverse effects and the rest of the research did not. This discrepancy is seemed to be due to the relatively small numbers of tested embryos in a study. In some of studies, the spontaneous abnormal rate in the embryos was not constantly low. Biological variety, particularly in the case of chick embryo, made investigators being difficult to lead a reliable answer from experiments with small number of embryos. Positive control group is seemed to be needed to verify whether the employed experimental protocol can actually detect developmental abnormalities with known teratogen treatment. Repeated experiments, at least three times, are also required to show the intra-laboratory reproducibility. Exposure term is another big issue. Chick embryo possesses high teratogenic sensitivity to exogenous stimuli during the earliest stage, i.e., 1 to 2 days, of embryogenesis. Naturally, about a half of all studies conducted a 2-days exposure. For this reason, the 2-day exposure experiment is of importance in regarding the comparativeness of our future studies. However, the second day of the embryogenesis is not even a half way of organogenesis for the chick embryo. This could argue that the developmental evaluations only at the second day are insufficient. Even if the investigators found abnormalities at the day-2, there is no way of verifying that the observed change is whether the death of embryos or the delay of the development, or the change is not fatal and development could continue till the hatch. This indicates definitive needs of a longer exposure experiments that at least cover a whole organogenesis of the first 5-days period.

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