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Health effects of TETRA
Investigation of the effects of the TETRA radio signal on cognitive functions of volunteers
Duration: 01. October 2009 - 30. September 2013
Project Management: Charité - Universitätsmedizin Berlin
- IMST GmbH Kamp Lintfort
- Seibersdorf Laboratories GmbH
Several international studies on the influence of electromagnetic fields from mobile communications on cognitive performance and brain function during wakefulness and sleep have been performed during the last years. No health relevant effects were found below the maximum exposure of 2 Watt per kilogram (W/kg), which applies for the use of mobile devices by the public.
In Germany, the construction of a new digital radio communication network for security authorities and organisations based on the TETRA standard has been finished at the end of 2015. TETRA (Terrestrial Trunked Radio) uses a frequency band around 400 MHz and has been much less investigated than public mobile communications. The results of the German Mobile Telecommunications Research Programme showed a higher temperature increase of the exposed tissue at 400 MHz than at the frequencies used by mobile phones. For occupational groups using mobile TETRA devices (such as for example policemen and firemen), a local exposure up to 10 W/kg is permitted. Possible effects of electromagnetic fields of mobile TETRA devices on humans were investigated to further reduce scientific uncertainties concerning the impact of the digital radio for security authorities.
In the present study, possible effects of an exposure with TETRA signals (sham, SAR values of 1.5 W/kg and 6 W/kg) on the brain activity of humans were investigated. The volunteer study was performed on healthy young men, preferentially from the group of potential users who were likely to be occupationally exposed.
- Tests were performed which allowed for conclusions on reaction speed and accuracy, processing of acoustic and visual information, the ability to concentrate, memory and mental state.
- In parallel, the waking EEG (electroencephalogram, examination of brain activity) under different conditions (rest, processing of tests) was recorded and evaluated.
- Furthermore, the influence of TETRA exposure on sleep quality and sleep EEG, as well as performance and well being on the following day were investigated.
The results were evaluated in relation to their health relevance for occupationally exposed users.
For study participation, 32 male volunteers (policemen, police trainees, firefighters, emergency medical staff) at the age of 18 – 30 years were recruited, who were not active in night service, right-handed and non-smokers.
Each of the 32 volunteers filled in a questionnaire and underwent a medical examination at the beginning of the study. Then, everybody spent one afternoon and one night in the test room to get adapted. During daytime, computer-based cognition tests were performed; during nighttime, sleep was investigated.
After this starting period, all volunteers alternately spent nine afternoons and nine nights in the laboratory, with a rest period of one week in each case. Every volunteer was exposed three times to 1.5 and 6 W/kg and three times sham exposed (the antenna was worn on the head, but no exposure took place). The study duration was 20 weeks per person.
Neither the volunteers nor the scientists who were examining the volunteers and evaluating the data were aware of the actual exposure (double-blind study design). The sequence of exposures for a particular person was randomized.
After evaluating all the data, the results were merged with the relevant exposure. These measures serve quality assurance.
Literature study: scientific knowledgeshow / hide
In other European countries, security authorities have already been using TETRA radio networks for some time. Similar to Germany, other European countries are currently setting up their nationwide networks. In some of these countries, the introduction of the TETRA standard was accompanied by scientific research. Within the framework of the volunteer study to investigate the effects of the TETRA radio signal on cognitive functions, scientists of the Berlin Charité's "Competence Center Sleep Medicine" performed a literature review on health effects of digital radio, bringing together data from publications and reports on the various national scientific results. Overall, there is much less data for TETRA than for public mobile communications.
The few results published previously do not show any health-relevant effects of TETRA. In one study, a slight influence on memory was found. However, because of the high number of tests performed in the study, this observation might as well be purely coincidental. Therefore, this result has to be verified.
Exposure setupshow / hide
In this study, volunteers were exposed in the head region to a TETRA signal at SAR values of 1.5 W/kg and 6 W/kg.
A corresponding exposure setup was constructed and characterised by IMST GmbH (Kamp Lintfort).
It consisted of a flat antenna worn on the left side of the head, which was supposed to simulate the exposure to a TETRA mobile device.
It can be worn comfortably for up to eight hours, even during sleep.
The actual exposure of individual brain regions was calculated in detail by Seibersdorf Laboratories GmbH.
Perception of warmingshow / hide
At the highest level of radiated power, which leads to an exposure of 6 watt per kilogramme, the exposure setup causes the temperature on the head’s surface to increase by almost 1 °C. Since the study had to be performed in a blinded way (neither the volunteer nor the directly involved scientist knew the actual exposure situation), it was important to prove whether the volunteers were able to perceive this warming.
Therefore, a pilot study was performed. It could be shown that the volunteers were not able to judge correctly the actual temperature increase. Therefore, there was no risk of unblinding (the volunteers were not able to discover the specific exposure situation).
Results of sleep investigationshow / hide
The exposure had no substantial effects on the sleep macrostructure (sleep latency, duration and structure of particular sleep stages). The same holds true for sleep spindles (characteristic signs of sleep in the EEG).
The power spectra of the EEG changed under exposure, the power in the beta frequency range (13 – 22 Hz) was reduced. The observed effects occurred primarily after a longer exposure (at the end of the night) and did not show any dependence on the exposure intensity.
Well-being and subjectively perceived sleep quality were not influenced by the exposure.
Results of daytime testsshow / hide
The power spectra of the waking EEG modulated under exposure as well. The power in the beta frequency range increased (not dose-dependent) during exposure at one location. Additionally, the theta frequency range (4.0 – 7.75 Hz) of the waking EEG modulated at three locations. The power of these slow waves was higher under exposure. These results did not reflect in behavior or well-being.
Slow brain potentials evoked by acoustic and visual stimuli modulated only in one of several tests during exposure. Daytime tiredness or alertness, as measured by EEG as well as by the diameter of the pupil, were not influenced by the exposure.
The results of visual and acoustic tests on attention (precision, reaction times) did not show any influence of the exposure. In memory tests with various degrees of difficulty, the tests with intermediate difficulty showed deviations in both directions under exposure - during an exposure of 1.5 Watt per kilogramme, the number of correct responses was higher and during an exposure of 6 Watt per kilogramme it was lower than during sham exposure. At the highest and the lowest degree of difficulty, there were no exposure-dependent differences. These results are probably coincidental.
Well-being, anxiety, depression and the occurrence of symptoms were not influenced by exposure during the day.
Evaluation of the results
Exposure with TETRA up to 6 W/kg did not influence sleep quality and well-being in the morning after an 8-hour exposure. Alertness and cognitive performance, well-being and occurrence of various symptoms during the day were also independent from the exposure by a simulated signal of a TETRA mobile device.
Concerning the extent, the slight variations in sleep and waking EEG are comparable to the known observations from public mobile phones (GSM, UMTS, 2 watt per kilogram). The effects were not pronounced more at 6 watt per kilogram than at 1.5 watt per kilogram. They were not subjectively perceived, a possible health relevance is not known.
Altogether, it can be assumed that TETRA mobile devices do not pose health risks for the users. The degree of brain activity during wakefulness and sleep is age and sex dependent. Therefore, results obtained from young, healthy men are not representative for other population groups.
The statistics performed here at group level can show only relatively strong effects. Individual analyses could deliver further information about possible effects at a personal level.
Questions and Answers to the Study
Many employees in security authorities and organizations are women; why were only men investigated?show / hide
The study duration was 20 weeks per person. Among women, sleep as well as cognitive performance are strongly influenced by the menstrual cycle. During data collection, it would have been necessary to account for the phase of the menstrual cycle. This would have had to result in an even more comprehensive planning of the study design.
Many members of security authorities and organizations are older; why were only young volunteers tested?show / hide
In sleep research, the group of young men at the age of 18 – 30 years is an established homogeneous reference group which has already been investigated intensively.
Sleep structure as well as cognitive performance depend strongly on age. Therefore, different age groups should not be mixed up within one investigation.
Separate studies on older individuals of both sexes are desirable and planned by the BfS.
Nobody makes phone calls while sleeping; why is the influence of the exposure to a mobile device on sleep investigated?show / hide
Sleep is a very complex biological process controlled by the central nervous system. It is a very well defined biological state, which reacts sensitively to external influences. Therefore, sleep is a suitable model for the investigation of possible effects on the brain.
Sleep EEG can be described very precisely and is much more suitable for the investigation of minor effects than the waking EEG, which is very variable and depends strongly on sensory perception and other factors like, for example, the degree of alertness (sleepiness).
Furthermore, it is not clear whether an exposure immediately before falling asleep might influence the sleep. For this reason, exposure started before sleep began.
Why are the limit values higher for occupationally exposed persons than for the general public?show / hide
Limit values generally provide sufficient protection against known health impact due to electromagnetic fields. There is always a safety factor between thresholds for proven health consequences and limit values.
For the general public this safety factor is higher in order to protect especially sensitive individuals (children, adolescents, old and sick persons) as well.
Occupationally exposed persons normally are healthy adults, especially sensitive population groups do not need to be considered. Occupational exposure is not permanent, but restricted to working time. For these two reasons, a lower safety factor is used for occupationally exposed persons.
State of 2018.01.08
- Investigation of the effects of the TETRA radio signal on cognitive functions of volunteers
- Modelling of the SAR-distribution within the whole body, in particular within the head region especially considering the eye, when exposed to electromagnetic fields from TETRA terminals deployed in Germany