In vivo genotoxicity of high-intensity intermediate frequency magnetic fields in somatic cells and germ cells

Abstract

Intermediate frequency magnetic fields (IF-MFs) at ~85 kHz are one of the components of wireless power transfer (WPT) systems. However, the available data needed for the assessment of the safety of organisms from IF-MF exposure are scarce. Thus, there is an imminent need to accumulate evidence-based assessment data. In particular, if humans are exposed to IF-MF due to an accident or trouble, they are at increased risk of being exposed to high-intensity IF-MF within a short period. The already existing exposure system was improved to a system that could intermittently expose animals at 3 s intervals. This system allows the exposure of a mouse to high-intensity IF-MF (frequency: 82.3 kHz; induced electric field: 87 V/m, which was 3.8 times the basic restriction level for occupational exposure in the ICNIRP guideline), while regulating the heat generated by the coil. In vivo genotoxicity after IF-MF exposure was assessed using micronucleus (MN) test, Pig-a assay, and gpt assay. The results of MN test and Pig-a assay in hematopoietic cells revealed that neither the reticulocytes nor the mature erythrocytes exhibited significant increases in the IF-MF-exposed group compared with that in the sham-exposed group. In germ cells, MN test and gpt assay outcomes showed that IF-MF exposure did not cause any genetic or chromosomal abnormality. Based on these data, there was no genotoxic effect of our set IF-MF exposure on somatic and germ cells. These findings can contribute to the widespread use of WPT systems as effective data of IF-MF safety assessment.

Keywords: genotoxicity; germ cell; intermediate frequency magnetic field (IF-MF); rodent; somatic cell; wireless power transfer system (WPT).

Fig. 1

Overview of the IF-MF exposure system (A), capacitor (B), and solenoid coil with the mouse-specific holder (C).

Fig. 2

Duration of IF-MF exposure and sampling points. In the MN test, the blood samples were extracted from mice before the exposure (pre) and at days 0, 2, 6, 10 and 14 after 1 day and 10 days of exposure. In the Pig-a assay, the blood was extracted before (pre) and at days 2, 7 and 14 after the exposure. The testis in the MN test and the liver, bone marrow, spleen and testis in the gpt assay were extracted from mice at day 7 after the last day of the 10-day exposure period.

Fig. 3

Classification and identification of germ cells composed of micronuclei (or not). These images show germ cells in the testis. A typical MN-contained spermatid is indicated by a dotted circle, a typical spermatid is indicated by a filled arrow and a typical spermatocyte is indicated by a filled triangle, as shown in the image on the left. A typical MN test outcome suggested that the samples contained the following cells: spermatocytes indicated by a dotted circle, spermatogonia indicated by an arrow filled with dots, and a typical sperm indicated by a triangle filled with dots, as shown in the image on the right.

Fig. 4

MN mutation frequency in germ cells. (A) denotes mixed germ cells (spermatids, spermatocytes and spermatogonia), and (B) denotes only spermatids. Following the Kruskal–Wallis tests, the significant levels were analyzed using the post-hoc Dunn’s test (^* denotes P < 0.05 and ^** denotes P < 0.01).