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Influence of high frequency electromagnetic fields of mobile telecommunications on sensory organs A. The auditory system |
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Topic Influence of high frequency electromagnetic fields of mobile telecommunications on sensory organs Start 01.07.2004 End 30.04.2007 Project Management University of Tübingen Objective Microwave hearing in the field of radar radiation is a known phenomenon caused by thermoelastic waves in the brain. However, only a few studies explore the effects of high frequency electromagnetic fields of mobile phones on the auditory system. These studies suggest possible physiological effects. Their mode of action is not known in detail. The influence of pulsed (GSM) and non-pulsed fields (UMTS) on a delicate sensory organ such as the ear, which is particularly exposed during a phone call, will be investigated. The ear and, respectively, the cochlea with its hair cells, will be exposed to various intensities above and below approved partial body SAR values (2 W/kg). The possible influence of high frequency fields on physiological parameters of the sensory cells and interneurons and their synaptic communication can be studied, for example, using neuro-physiological methods. Threshold values of these biological effects will be determined. If possible, the mechanism of action is to be explained. The objective of this project is to describe the possible physiological effects of high frequency electromagnetic fields on the auditory system and to investigate their mechanisms of action in order to evaluate their relevance to health. Results As a first result a review on possible influences of high frequency electromagnetic fields on the hearing system of humans and animals has been provided. At the beginning of the project (2004) the data situation was unsatisfactory, there were only very few contradictory publications. The situation has substantially improved due to the EU projects GUARD (influence of GSM on the hearing system, http://www.guard.polimi.it/home/home.html) and EMFnEAR (a similar project on UMTS, http://ec.europa.eu/health/ph_projects/2004/action1/docs/action1_2004_07_frep_a2_en.pdf). The results show that electromagnetic fields of mobile phones have no influence on the physiological parameters of hair cells and on acoustically evoked brain stem potentials of humans and laboratory rodents. All investigations mentioned were performed in vivo, therefore a detailed investigation of the electrical processes within the sensory cells was not possible. This gap was closed by the present project. The activity of the voltage-dependent calcium channels of the inner hair cells from the cochlea of mice was measured by means of the patch clamp method using glass electrodes. These calcium channels forward the acoustic signal registered by the hair cells and transformed to an electrical signal to the downstream nerve cells. The exposure setup designed by the university Wuppertal was based on the principle of a finline. The exposure occurred with the signals UMTS, GSM 900 and GSM 1800 at 0.02, 0.2, 2 and 20 W/kg. A sham exposure took place in a blinded design. Sixteen cells per exposure group were investigated. The temperature of the physiological solution containing the preparation varied by maximally 0.2 °C. Measurements took place before, during and after an exposure of 20 min duration. Altogether six electrophysiological parameters (resistances, voltage-current relationship) as well as the temperature were measured and statistically evaluated by means of a covariance analysis. The temperature showed consistently a significant dependence on the SAR value. All electrophysiological parameters of the hair cells depended on the time course of the experiments – this is a phenomenon well-known from the literature and depends on the life time of the isolated hair cells. In the present study the life time was 40 min, a very good value. Altogether 36 statistic tests were performed to evaluate the dependence of the physiological parameters of the ion channels on the SAR value, and a total of five of the tests were statistically significant. However, the results showed no consistent association between the SAR value, the type of the signal and any of the evaluated parameters. They were rather distributed between two SAR values (2 and 20 W/kg), all three signal types and three different cell parameters. Simple paired statistic tests showed no significant associations between SAR and any of the physiological parameters. For this reason the statistical significant tests were rated as statistical coincidences. Since they arose only at the two highest SAR values, a thermal influence cannot be excluded as well. All measured parameters are within the normal physiological range, as estimated on the basis of the data obtained from the 47 sham exposed cells. Based on the presented data the authors conclude, that there is no indication that a systematic, biologically relevant effect of an acute exposure of a mobile phone field at SAR-values of up to 20 W/kg on the function of calcium channels in inner hair cells exists. The final report can be downloaded as a PDF-file in German (3.909 kB) with English abstract. References
Conclusions The results of this project do not show any negative health influence of EMF exposure from mobile phones on the hearing system. The few statistical significant associations are due to the high number of comparisons and thus most likely a statistical coincidence. However, a thermal influence cannot be excluded completely. The minor changes found remain within the normal physiological range and do not represent a health impairment. This is in accordance with the results of the international projects GUARD and EMFnEAR as well as further published work. |