Principal Research Results

Evaluation of Biological Effects of Intermediate Frequency Magnetic Field− Reproductive and Developmental Toxicity in Rats and Genotoxicity
in Mammalian Cell Line−
Background
Biological studies to evaluate the effects of the intermediate frequency magnetic field exposures are needed because of lackof such studies for the assessment on potential health risks. Our previous studies revealed that intermediate frequency magnetic field
exposure did not affect the chick embryogenesis and micronucleus formation in mammalian cells.

Objectives
This study aims to determine whether or not a 20 kHz, magnetic field exposure has embryotoxic, fetotoxic and/or teratogenic potential. Another aim is to determine chromosomal aberration or point mutation ＊ 1 potentials of 2 kHz, 20 kHz or 60 kHz
magnetic fields by mouse lymphoma assay.

Principal Results
1. Embryotoxic, fetotoxic and/or teratogenic effects in rats
A 20 kHz, 0.2 mT (rms) sinusoidal magnetic field (32-fold greater than ICNIRP guidelines ＊ 2 for the general public) was
either exposed or sham-exposed to a group of 25 pregnant Crl:CD (SD) rats from gestation day 7 to day 17 for 22hr/d. Experiments
were conducted in a blind fashion. Identical experiments were repeated twice to confirm the reproducibility of outcome. No reproducible changes related to magnetic field exposure were found in the body weight gain, clinical signs, hematology, blood biochemistry
and gross pathology of dams. Number of implants, number of postimplantation loss, number and body weight of live fetuses, sex ratio
and incidence of low body weight fetuses also did not significantly differ between sham-exposed (control) and magnetic field exposedgroups. No significant changes were found in the incidence of external, skeletal and visceral malformations in the exposed fetuses.
Under the present experimental conditions, a 20 kHz sinusoidal, 0.2 mT (rms) magnetic field exposure during organogenesis
was neither embryo/fetotoxic nor teratogenic and did not interfere with the fetal development in the rat.
2. Evaluation of genotoxic effects by mouse lymphoma assay
A mouse lymphoma cell line, L5178Y tk+/- -3.7.2c, was chosen to estimate the effects of the magnetic field exposure ondirect genotoxixity and DNA damage repair caused by methylmethane sulfonate (MMS). The cells were exposed to magnetic fields of
0.91mTrms (146 times greater than ICNIRP guideline ＊ 2) at 2kHz, 1.1mTrms (176 times) at 20kHz and 0.11mTrms (18 times) at
60kHz, for 24h at 37℃ in 5% carbon dioxide. In statistical analysis, neither significant nor reproducible difference was found between
the mutation frequencies for all magnetic field exposure conditions (Table 2). To examine the effects on DNA damage, the cells wereexposed to each magnetic field with MMS which potentiates mutation. In statistical analysis, neither significant nor reproducible
difference was found between the mutation frequencies for all magnetic field exposure conditions (Table 2).
These results indicated that the intermediate frequency magnetic fields used in this study did not induce point mutation andchromosomal aberration, and did not affect DNA damaged by MMS or DNA damage repair system in mammalian cells.

Future Developments
Magnetic field will be exposed from premating to preimplantation period to examine the toxicity in reproduction and malefertility in the rats. Estimation of the effect of the intermediate frequency magnetic fields by transformation tests, chromosomal aberration test of global gene expression tests will be performed.
Main Researcher: Izumi Nishimura, Ph. D., and Satoshi Nakasono, Ph.D.,
Senior Research Scientist, EMF Environment Sector, Environmental Science Research Laboratory
Reference
I. Nishimura, et.al., 2008, “Reproductive and developmental toxicity of intermediate frequency magnetic field exposure, - Effects of20 kHz, 0.2 mT, sinusoidal magnetic field exposure on the rat organogenesis”, CRIEPI Report V07003 (in Japanese)
S. Nakasono, et.al., 2008, “Evaluation of genotoxicity of intermediate frequency magnetic fields by mouse lymphoma assay”, CRIEPI
Report V07005 (in Japanese)＊1：A type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA.
＊2：Magnetic field exposure limits for the public (6.25μT, from 0.8 to 150 kHz) were set by The International Commission on Non-ionizing
Radiation Protection (ICNIRP). The value includes 50 times reduction factor based on nerve stimulation phenomena.

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2. Environment

Preimplantation

Fertilization
Ovary

Corpus Luteum

GD 7

GD 17

Organogenesis

GD 20

Prenatal Period

Parturition

GD 0

Implantation

Fertilization

MatingGametogenesis

Magnetic Field Exposure

Fertilized ovum

Ovum
Ovulation

Implantation

EmbryoFetus

Fig.1 Time Course of Fetal Development in the Rat

2
Table 1 Effects of 20 kHz, 0.20 mT(rms) Magnetic Field Exposure during Rat Organogenesis

Experiment 1Control25368
14.7±1.2 a)
7／25
2.3±4.0 a)
1／25
0／25
1／25
0／25

Endpoint
Number (no.) of examined dams: ED
Total no. of examined fetuses
No. of fetuses per dam
No. of dams with dead embryos and fetuses／ED% of dead embryos and fetuses per dam
No. of dams with low body weight fetuses b)／ED
No. of dams with externally malformed fetuses／ED
No. of dams with viscerally malformed fetuses／ED
No. of dams with skeletally malformed fetuses／ED

Exposed25349
14.0±1.68 ／25
2.8±4.5
1 ／25
2 ／25
4 ／25
1 ／25

Experiment 2Control
25349
14.0±1.5
9 ／25
2.7±3.9
1 ／25
1 ／25
3 ／25
0 ／25

Exposed25345
13.8±1.87／25
1.9±3.1
0／250／25
1／250／25a) mean ±SD; b) no more than 2.5 g
No reproductive and developmental endpoints showed statistically significant changes due to 20 kHz magnetic field
exposures

Table 2 Effect of 2 kHz, 20 kHz or 60 kHz Magnetic Field on Genotoxicity in Mouse Lymphoma Assay

Mutagen-+Endpoints(Mutation Frequency)
Number of Tests
Point Mutation
Chromosomal Aberration0
Total Mutation d)
Point Mutation
Chromosomal Aberration0
Total Mutation d)a)

Sham6 times b)
01(↑)
2(↓↓)
0Exposure Conditions
2kHz, 0.91mT20kHz, 1.1mT5 times
5 timesc)
1(↑)
0000000000060kHz, 0.11mT
5 times001(↓)
000a) Non-energized exposure condition to confirm the equivalence between control and exposure systems.
b) Six flasks were used for each test (three for control and another three for exposure).
c) The number shows a number of significant changes. The arrow shows a direction of the change.
d) Sum of point mutation and chromosomal aberration
These results indicated that the intermediate frequency magnetic fields used in this study did not induce point mutationand chromosomal aberration, and did not affect DNA damaged by MMS or DNA damage repair system in mammaliancells.

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