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1. Introduction
With the widespread use of mobile phones in modern life, adolescents are exposed to radiofrequency (RF) fields from mobile phones and base stations much more frequently than ever. According to one report, 90% of adolescents have a mobile phone and about 40% of them are considered as heavy mobile phone users [1]. Therefore, this has raised public concerns about the potential health hazard of RF fields on adolescents.
RF field is a kind of electromagnetic radiation with frequencies ranging from 100 kHz to 300 GHz, which is used extensively in wireless communications, such as mobile phones, radios and televisions. The RF field produced by mobile phones and base stations is mainly at the frequencies of 800-2000 MHz [2]. It was reported that the average field density of the mobile phone antenna nearby was about 200 μW/cm2-300 μW/cm2 [3], exceeding the limit stipulated by the national standard in China (40 μW/cm2) [4].
The head receives much more RF energy than any other part of body because the mobile phone is usually held at the ear during communication. Whether RF exposure results in brain dysfunction, has become a major topic of investigation [5]. Based on the evidence from epidemiological and laboratory studies, RF fields in the 30 kHz-300 GHz frequency range were classified as a possible human carcinogen (Group 2B) by the International Agency for Research on Cancer (IARC) in 2011 [6]. In addition, it was reported that exposure to RF fields could cause insomnia, headache, tinnitus, fatigue, cognitive disturbances, dysesthesias (abnormal sensation), dizziness, and depression [7,8,9].
In terms of the effects of RF field on brain function, Wang found that although single exposure to 1800 MHz RF field for 30 min with specific absorption rates (SARs) in brain at 2.42, 2.86 and 3.3 W/kg did not affect spontaneous locomotor activity, it increased recognition memory in mice [10]. In addition, Bouji reported that after exposing the heads of the animals to 900 MHz RF field for 1 month (SAR 6 W/kg, 45 min/day), the spatial memory, emotional memory and locomotor activity did not change, but the anxiety-related behavior decreased in male senescent rats [11]. Arendash reported that exposure to 918 MHz RF field (SAR: 0.25 W/kg, 1 h/day for 4-7...