Medical/biological study (experimental study)

Effects of 2.45-GHz electromagnetic fields with a wide range of SARs on micronucleus formation in CHO-K1 cells med./bio.

By: Koyama S, Isozumi Y, Suzuki Y, Taki M, Miyakoshi J

Published in: ScientificWorldJournal 2004; 4: 29-40

Aim of study (acc. to author)

This study was conducted to investigate the effects of 2.45 GHz electromagnetic fields with a wide range of specific absorption rates on micronucleus formation in a cell line.

Endpoint

genotoxicity/mutation: micronuclei formation

Exposure

- 2.45 GHz
- microwaves

Exposure	Parameters
Exposure 1: 2.45 GHz Modulation type: CW Exposure duration: continuous for 2 h	SAR: 5 W/kg mean SAR: 10 W/kg mean SAR: 20 W/kg mean SAR: 50 W/kg mean SAR: 100 W/kg mean SAR: 200 W/kg mean

Exposure 1

Main characteristics

Frequency	2.45 GHz
Type	electromagnetic field
Waveform	sinusoidal
Charakteristic	guided field
Exposure duration	continuous for 2 h

Modulation

Modulation type	CW

Exposure setup

Exposure source	waveguide 110 x 55 x 310 mm (W x H x L), TE₁₀ mode
Chamber	Two rectangular waveguide applicators were placed in an incubator at 37°C with 95% air and 5% CO₂. One end of the waveguide was terminated with a short-circuiting plate to generate standing waves.
Setup	Cells in culture medium were exposed in a culture dish that was placed on two slits bored into the wider wall of the waveguide. The two slits were pinch shaped which enhanced the coupling of the EMF to increase the effective exposure area. The culture dish was rectangular in shape and divided into four compartments. The thickness of the medium was chosen based on numerical analysis to be 8 mm, which corresponded to half a wavelength in the medium, in order to maximise the SAR at the bottom of the well where the cells were present.
Sham exposure	A sham exposure was conducted.
Additional info	For sham exposure, the cells were incubated in a conventional incubator. Heat treatment was performed at temperatures of 38, 39, 40, 41, and 42°C. The cells were also treated with bleomycin alone (positive control) or combined with RF exposure or heat.

Parameters

Measurand	Value	Type	Method	Mass	Remarks
SAR	5 W/kg	mean	-	-	-
SAR	10 W/kg	mean	-	-	-
SAR	20 W/kg	mean	-	-	-
SAR	50 W/kg	mean	-	-	-
SAR	100 W/kg	mean	-	-	-
SAR	200 W/kg	mean	-	-	-

Additional parameter details

It is not clear from the article, where the indicated average SARs were determined. The maximum SAR appeared at the bottom in the middle of the second compartment from the termination of the waveguide where the coupling with the field was strongest. The maximum SAR values in the adjacent compartments were 80 and 85% of this. The minimum SAR in the fourth compartment from the termination was 1%.

Measurement and calculation details

Power sensors monitored the incident and reflected powers, and the signal generator precisely controlled the incident power. The SAR distribution in the exposure apparatus was calculated using the FDTD method and was measured using a DASY3 system with a thermistor probe. The results of both methods showed good agreement. The temperature of the culture medium was measured during exposure using a fluoroptic temperature probe. It increased from an initial value of 37 °C after about 2000 s to a stable level approximately proportional to the SAR value as shown in a figure. A numerical calculation showed that the temperature distribution was not homogeneous.

Exposed system:

intact cell/cell culture
CHO-K1 (Chinese hamster ovary K1) cells

Methods Endpoint/measurement parameters/methodology

genotoxicity/mutation: micronuclei formation (cells containing at least one micronucleus (MN) were counted as having MN formation, a total of 1000 binucleated cells each were evaluated: propidium iodid staining, fluorescence microscopy)

Main outcome of study (acc. to author)

There was no statistically significant effect on micronuleus formation in cells exposed to high frequency electromagnetic fields at specific absorption rates from 5 to 50 W/kg. However, statistically significant increase in micronucleus formation was found in cells exposed to specific absorption rates of 100 and 200 W/kg.
There was no apparent effect of co-exposure (high frequency electromagnetic field exposure plus bleomycin treatment).
The heat treatment revealed micronucleus frequency increase in a temperature-dependent manner. Additionally, the increase in specific absorption rate caused a rise in temperature. Therefore, the observed increases in micronucleus formation were attributed to the temperature rise caused by the high frequency electromagneitc fields.

Study character:

medical/biological study
experimental study
full/main study
double blind study

Study funded by

Committee to Promote Research on the Possible Biological Effects of Electromagnetic Fields, Japan

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