報告書番号

V04008

タイトル（和文）

中間周波磁界の生物影響評価 -－細胞用中間周波磁界曝露装置の開発と微生物を用いた変異原性評価－-

タイトル（英文）

Biological Effects of Intermediate Frequency (IF) Magnetic Fields -Evaluation of mutagenisity of IF magnetic fields by bacterial mutation assay-

概要 （図表や脚注は「報告書全文」に掲載しております）

近年、中間周波数帯の電磁界の利用が増加しているが、その生物影響については、ほとんど研究されていない。本研究では、中間周波磁界の生物影響に関する科学的知見を得るために、細胞試験用の中間周波磁界曝露装置を開発し、微生物復帰変異試験により磁界の変異原性について検討した。その結果、2kHzで910μT（国際ガイドラインの146倍）、20kHzで1.1mT（176倍）、60Hzでは110μT（18倍）の磁界を発生できるヘルムホルツ型の中間周波磁界曝露装置を開発できた。この装置を用い、様々な点突然変異を検出できる合計６種類の試験菌株に対し、2kHz、20kHzおよび60Hzの磁界を、最高磁束密度で、それぞれ48時間曝露した。その結果、いずれの菌株でも再現性のある有意な復帰変異コロニー数の増加は見られなかったことから、本研究で検討した高いレベルの中間周波磁界に、変異原性がないことが明らかとなった。

概要 （英文）

In contrast of extremely low frequency and radio frequency electromagnetic fields (EMF), the biological effect of the intermediate frequency (IF; 300Hz to 10MHz) EMF has not been studied very well. In this research, to provide toxicological information of the IF fields, we have investigated the mutagenic potential of the IF magnetic field (MF) by using bacterial mutation test. Firstly, we constructed a Helmholtz type exposure system for the in vitro research, which can generate a vertical and sinusoidal MF in the frequency range from 2 to 60 kHz. The maximum field strength depends on the MF frequency, and 910μTrms (146 times greater than the strength of ICNIRP guideline), 1.1mTrms (176 times) and 110μTrms (18 times) of MF was generated at 2 kHz, 20 kHz and 60 kHz, respectively. This system can provide a large uniform MF environment (20cm-cube, field variation below 5%), for the microbial mutation testing. Incubator with water jacket was located in the center of the system, and the incubation temperature was controlled at 37～0.2℃. Secondly, four strains of Salmonella typhimurium (TA98, TA100, TA1535, TA1537) and two strains of Escherichia coli (WP2 uvrA, WP2 uvrA/pKM101) were chosen to cover a wide point mutation spectrum, including AT base substitution, GC base substitution, suppressor mutation, and frame shift. Twelve plates randomly divided into two groups; six plates were placed at the center of the MF exposure system while the other six were placed in a control incubator. Revertant colonies were scored after 48 hr of incubation at 37℃. Each experiment was repeated at least four times. Student’s t-test was used for the statistical analysis of the results. In all test set, all of the test strain were resposive against corresponding positive controls, such as 2-(2-Furyl)-3-(5-nitro-2-furyl) acrylamide, Sodium azide (DNA reactive reagents), 2-amino anthracene (frameshift), 9-amino acridine and Benzo[a]pyrene (DNA reactive promutagen which activated metabolically by rat S9mix). Mutagenicity tests of four MF exposure conditions, such as 910μT at 2kHz, 270μT or 1mT at 20kHz and 110μT at 60Hz, were carried out. The ratio of the colony number between exposed and unexposed control groups were mostly in the range of 0.7 to 1.4. Most of large difference of the ratio was found in low colony number strains. In statistically analysis, neither significant nor reproducible difference was found between exposed and unexposed control groups in all exposure condition with six tester strains. The shape and size of revertant colony were almost same between the exposed and the unexposed control groups. These results indicate that the strong IF MF exposure could not affect the mutation frequency in each strain.

報告者

キーワード