Exposure assessment for mobile phone use and radiofrequency electromagnetic fields and the application in a Swiss cohort study

Background
Mobile phones and other wireless communication devices emitting radiofrequency electromagnetic fields (RF-EMF) are nowadays omnipresent and adolescents are among the heaviest users. This results in ubiquitous RF-EMF exposure, though little is known about the levels of this exposure, especially in adolescents.
Exposure to RF-EMF can be divided into two parts, the exposure from the use of wireless communication devices (near-field) and the exposure from environmental sources (far-field). In previous studies, the near-field exposure was quantified using the amount of device use only. The RF-EMF exposure resulting from the device use, however, is not only dependent on the duration of use, but additionally for instance on the mode of use and the network used for mobile phone calls. The far-field exposure from fixed site transmitters such as broadcast transmitters for radio and television (TV) and mobile phone base stations was modelled using geospatial propagation models or measured using portable RF-EMF measurement devices. But this part of the exposure also depends on the duration a person is exposed to modelled or measured exposure levels. Therefore a dosimetric approach is needed that allows taking into account these additional aspects of exposure and to combine the near-field and the far-field exposure to one exposure surrogate.
Since the mobile phone use increased in the last decade, there is concern that this use may have a negative impact on adolescents. To date, epidemiological studies in adolescents are scarce. In addition, the ones existing used self-reported device use that is known to be inaccurate and the amount of device use was used as proxy for the RF-EMF exposure not taking into account other RF-EMF sources. Furthermore, most of these studies were of cross-sectional design not allowing to draw conclusions about causal relationships between mobile phone use and health, behaviour and cognitive function of adolescents. To overcome these limitations, the HERMES (Health Effects Related to Mobile phonE use in adolescentS) study was conducted.
Objectives
The objective of the HERMES study was to prospectively investigate whether mobile phone use and the use of other wireless communication devices or RF-EMF exposure have an impact on the health and the behaviour of adolescents and if cognitive function of adolescents is affected by these exposures.
The objectives of this thesis were to improve the exposure assessment for mobile phone use and RF-EMF exposure and to investigate its relations to behavioural problems and concentration capacity of adolescents.
Methods
The HERMES study was a prospective cohort study with a one year follow-up period. It was conducted in Central Switzerland in adolescents attending the 7th school grade. The investigation took place in the schools during school time and consisted of filling in a paper and pencil questionnaire and performing computerized cognitive tests. In addition, a questionnaire for the parents was distributed that was directly sent back to the study managers.
Additionally to the amount of mobile phone and other device use, problematic aspects of mobile phone use such as loss of control, withdrawal, negative life consequences and craving were asked in the questionnaire.
In a subgroup of the study participants, personal RF-EMF measurements were conducted. The participating adolescents carried a portable measurement device for three consecutive days and filled in a time-activity diary to record their locations during the measurement period.
The questionnaire data and the personal RF-EMF measurements together with geospatial propagation modelling for the exposure originating from fixed site transmitters at home and in the schools as well as operator-recorded mobile phone use data for a subgroup of the study participants were used to develop an RF-EMF exposure surrogate combining the exposure from the use of wireless communication devices and environmental sources. This exposure surrogate was then used to conduct cross-sectional and longitudinal analyses of RF-EMF exposure and behaviour and concentration capacity of adolescents.
Results
439 adolescents participated in the HERMES study (participation rate of 36.8%) with a follow-up rate of 96.8%. Operator records were available for 234 adolescents and personal RF-EMF measurements were available for a subgroup of 90 adolescents.
We found that problematic mobile phone use in adolescents was related to behavioural problems such as hyperactivity, conduct problems, emotional symptoms and antisocial behaviour and impaired health related quality of life (HRQOL) facets such as home life and school environment.
The main contributor to the measured personal RF-EMF exposure was the mobile internet use on the mobile phone. For the adolescents not using mobile internet, mobile phone base stations contributed most to their exposure. Having wireless internet (WLAN) at home and attending a school with WLAN had very little impact on the average measured WLAN exposure.
According to the developed RF-EMF exposure surrogate combining near-field and far-field exposure, the exposure from environmental sources such as fixed site transmitters, cordless phone and WLAN base stations and mobile phones in the surroundings plays a minor role compared to the exposure from the use of wireless communication devices (mobile phones, cordless phones, computers, laptops and tablets connected to WLAN). The near-field dose accounted for 98.4% of the brain dose and 94.0% of the whole body dose.
In applying the developed RF-EMF dose surrogate in combination with use measures derived from self-reported device use and operator-recorded mobile phone use, the relations to behavioural problems and the concentration capacity of adolescents were investigated. No systematic pattern in relation to RF-EMF exposure was observed indicating no causal relationship between RF-EMF exposure and behavioural problems and concentration capacity of adolescents.
Conclusions
Environmental sources play a minor role for the RF-EMF exposure of adolescents compared to the use of wireless devices. Having WLAN at home and attending a school with WLAN have very little impact on the average measured WLAN exposure. The use of mobile internet results in higher measured exposure from mobile phones. Therefore, precautionary measures to reduce the exposure to RF-EMF should focus on the use of wireless devices.
The behaviour and the concentration capacity of adolescents were not affected by RF-EMF exposure. In contrary, behavioural problems and impaired HRQOL were associated with problematic aspects of mobile phone use. Therefore, problematic mobile phone use should be considered if dealing with adolescents showing behavioural problems or impaired mental health.
The HERMES study was the first study applying a comprehensive exposure assessment including operator-recorded mobile phone use and cumulative RF-EMF dose calculations. The study provided new insights into the mobile phone use of Swiss adolescents and its impact on health, behaviour and cognitive function using a longitudinal approach allowing to draw conclusions about causal relationships. The applied methods can be used in future epidemiological studies on RF-EMF exposure and its influence on humans.