We investigated the long-term effects of radiofrequency radiation (RFR) emitted from Wi-Fi systems on hearing. Sixteen Wistar albino rats were divided equally into two groups: sham control and exposure groups. The rats in the experimental group were exposed to 2.4 GHz RFR emitted from a Wi-Fi generator for 24 h/day for one year. The same procedure was applied to the rats in the sham group, except that the Wi-Fi generator was turned off. All groups were kept in Faraday cages during the 12 months to eliminate external electromagnetic fields. The distance between the Wi-Fi generator antenna and the exposure cages was 50 cm. Pre-exposure distortion product otoacoustic emissions (DPOAE) of all rats were measured at the beginning, 6th and 12th months of the study. The DPOAE values of the sham, baseline and exposure groups were compared statistically. For the 6000 Hz hearing frequency, the DPOAE values in the exposure group were lower than those in the sham group (p < 0.05). Similarly, the 6000 Hz hearing frequency values obtained at the end of the 12th month were also lower than the baseline and 6-month values in the exposure group (p < 0.05). In contrast, the DPOAE values at the 6th and 12th months of exposure for the 2000 Hz hearing frequency were higher than the baseline value (p < 0.05). These results indicated that 12 months of RFR (24 h/day) at 50 cm from a 2.4 GHz Wi-Fi source can affect hearing. However, further studies are necessary.
The biological effects of alternating electromagnetic fields (EMFs) have long been studied. In recent years, there has been an impressive growth in the number of processes and devices that use or emit radiofrequency (RF) and microwaves in developed countries. Such devices are being increasingly used in industry, engineering, telecommunications, medicine, education and home settings [1 Peyman A, Khalid M, Calderon C, et al. Assessment of exposure to electromagnetic fields from wireless computer networks (Wi-Fi) in schools: results of laboratory measurements. Health Phys. 2011;100(6):594–612.]. Thus, widespread use of devices generating EMFs has become a major public concern because of findings related to possible hazardous effects of this technology on human health. These technologies include wireless local area networks (WLANs) and Wi-Fi communication systems. Wi-Fi systems, which are used frequently indoors and outdoors, also emit radiofrequency radiation (RFR).
WLANs are networks that operate without physical wires connected to the terminal devices (‘clients’). Wi-Fi is the most common WLAN technology, in which devices and computers are connected to the local area network (LAN) wirelessly. The point of entry to the wired network is termed an ‘access point’ and is typically positioned in the vicinity, at a distance of a few tens of metres. Wi-Fi equipment transmits and receives radio waves to establish the wireless connection. This technology is popular among a wide range of users.
People using or in the proximity of Wi-Fi equipment are exposed to the radio signals emitted from it and will absorb some of the transmitted energy in their bodies. Thus, the recent increase in the popularity of Wi-Fi devices has become a cause of concern in view of the introduction of wireless computer systems in schools and the extent to which the pupils are exposed to radio waves emitted from such sources [1 Peyman A, Khalid M, Calderon C, et al. Assessment of exposure to electromagnetic fields from wireless computer networks (Wi-Fi) in schools: results of laboratory measurements. Health Phys. 2011;100(6):594–612.].
For the reasons mentioned above, one concern in public opinion is the biological effects of RFs emitted from Wi-Fi systems. Despite the intense public interest, usually focused on any relationship between RFR and cancer, there is not sufficient research on RF emitted from Wi-Fi systems. Another important point to be considered is whether RF emissions from Wi-Fi wireless communications affect hearing. The auditory system is the neural organ most frequently and directly exposed to RFs emitted from mobile phones and other similar equipment.
Otoacoustic emission (OAE) is low-level acoustic signals emitted by the cochlear outer hair cells (OHCs) either spontaneously or evoked by an auditory stimulus and recorded via the external acoustic meatus. OAE was originally described by Kemp [2 Kemp DT. Stimulated acoustic emissions from within the human auditory system. J Acoust Soc Am. 1978;64:1386–1391.]. OAE signals are evoked because of the motility of the cochlea’s sensory OHCs that make their way outward from the basilar membrane of the cochlea through the middle ear, vibrating the tympanic membrane and propagating into the external auditory canal [3 Kemp DT. Otoacoustic emissions, their origin in cochlear function, and use. Br Med Bull. 2002;63:223–241.]. OAE testing is commonly used as a method for evaluation of hearing problems. Distortion product otoacoustic emissions (DPOAEs) are evoked OAEs produced by the ear in response to two simultaneous pure tone stimuli. DPOAEs give information about the hearing and are frequently used in studies to investigate hearing problems [4 Probst R, Lonsbury-Martin BL, Martin GK. A review of otoacoustic emissions. J Acoust Soc Am. 1991;89(5):2027–2067.]. Generally, loss of OHCs or impairment of OHC function results in the attenuation of DPOAE amplitudes and sound/noise (S/N) ratios.
Whether RFR emitted from Wi-Fi systems affects hearing is a major concern in the general public. Thus, we investigated the long-term effects of 2.4 GHz RFR emitted from a Wi-Fi wireless system on hearing in rats using DPOAE. To our knowledge, no reported study has examined the long-term effects of Wi-Fi signals on the OHC function of the cochlea so far.