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The authors carried out two in vivo and one in vitro experiment to test the effect of microwaves on the ears of guinea pigs. In the first experiment, 3 groups of 8 animals had their left ear exposed for 1 hour/day, 5 days/week, for 2 months to GSM radiation (900 MHz, GSM modulated) at SARs of 1, 2, and 4 W/kg. A fourth group was sham-exposed. Distortion-product otoacoustic emissions (DPOAEs) were measured for each ear before exposure, at the end of the 2-months' exposure, and 2 months later. In the second experiment the same protocol was applied to 8 sham-exposed and 16 exposed guinea pigs at 4 W/kg, but the auditory brain-stem response (ABR) thresholds were monitored. There were no differences in DPOAE amplitudes or in ABR thresholds between the exposed and non-exposed ears and between sham-exposed and exposed animals. ABR thresholds were also assessed before and just after a 1-hour exposure during the second experiment. No difference was observed, indicating a lack of an acute effect. The in vitro experiment consisted of isolating the two organs of Corti (OC) from each of 15 newborn rats and placing them in culture. One OC was exposed for 24-48 hours to 1 W/kg microwaves and the other was sham-exposed. After 2-3 days each OC was examined by light microscopy. They all appeared normal. The results provided no evidence that microwave radiation, at the levels produced by mobile phones, caused damage to the inner ear or the auditory pathways of the guinea pigs.
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