この研究は、オオミジンコ（Daphnia magna Straus）に超低周波および低周波の交番磁界（AMF）ばく露を7日間与え、その影響を調べた。ミジンコの生態は、発達と成熟の期間（第1期）と子孫が放出された期間（第2期）に分けられるため、第１期と第2期の実験条件の組み合わせを次の4通りとした。1）対照-対照、2）対照-ばく露、3）ばく露-対照、4）ばく露-ばく露。急性ばく露実験では、磁界ばく露は7日間続き、さまざまな周波数（17 Hz、50 Hz、500 Hz、5 kHz、50 kHz、200 kHz）が用いられた。さらに、500 Hzで慢性ばく露実験（21日間）も実施した。その結果、AMFは生存と性的成熟に達するまでの時間を短縮する可能性があることが示された；500 HzのAMFは、生存と成熟に最も顕著な悪影響を及ぼした；50 HzのAMFは、成熟を加速した；500 Hzでの慢性実験では、磁界の影響下で成熟した親世代から生まれた子孫において、生きた子孫の割合が増加したが、体サイズは減少した；子孫を放出する前のミジンコに対する500 Hz AMFの作用は、生殖期における新生個体の数の増加をもたらす、と報告している。
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To reveal which alternating magnetic field frequency falls in the field of efficiency upon survival and development for Daphnia magna, to determine if the magnet-biological effect depends on the stage of ontogenesis and to reveal if the exposure causes long-term effects.
Four different experimental variants were studied: 1) control-control, 2) control-exposure, 3) exposure-control and 4) exposure-exposure. The first part indicates the conditions under which Daphnia developed and matured, and the second part indicates under which conditions progeny was released. In the acute experiment, the magnetic field exposure lasted seven days and different frequencies (17 Hz, 50 Hz, 500 Hz, 5 kHz, 50 kHz, 200 kHz) were tested. Additionally, the frequency of 500 Hz was used for a chronic experiment (21 days).
| 周波数 | 500 Hz |
|---|---|
| タイプ |
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| 波形 |
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| ばく露時間 | continuous for 21 days |
| Additional information | chronic exposure |
| ばく露の発生源／構造 |
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|---|
| 測定量 | 値 | 種別 | Method | Mass | 備考 |
|---|---|---|---|---|---|
| 磁束密度 | 150 µT | - | - | - | - |
Acute experiment: The alternating magnetic field with a frequency of 50 Hz had a weak stimulating effect upon maturation and survival of Daphnia magna. This could be due to the fact that the animals have lived for generations under laboratory conditions where they were exposed to 50 Hz fields and may have adapted to these conditions (preliminary assumption).
In all other trials, the effect was negative. The most negative effects upon survival and maturation were observed in D. magna exposed to alternating magnetic fields with the frequency of 17 Hz and 500 Hz.
Chronic experiment: Exposure to a frequency of 500 Hz during the juvenile stage of ontogenesis caused a malfunction in the reproduction program. This was manifested by an increase in the share of nonviable progeny and smaller body sizes of newborns from the first litters of parental daphnia exposed during the juvenile stage. Moreover, exposure to 500 Hz in a further reproductive period during the juvenile stage resulted in an increased number of newborns. The body sizes of newborns decreased, while the share of nonviable juvenils increased. The field thus had a long-term effect.
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