Riddervold IS, Kjærgaard SK, Pedersen GF, Andersen NT, Franek O, Pedersen AD, Sigsgaard T, Zachariae R, Mølhave L, Andersen JB. No effect of TETRA hand portable transmission signals on human cognitive function and symptoms. Bioelectromagnetics. March 8, 2010. Ahead of print.
Terrestrial Trunked Radio (TETRA) is a European standard digital mobile radio communication system that has primarily been developed for use by public safety and emergency services. The system is specified to work in the frequency range 150-900 MHz, and most often operates at around 400 MHz. The lower frequency of operation makes the system less vulnerable to interference, which is very important for emergency services. The signal in TETRA is transmitted in bursts, which results in a power modulation of the signals at a frequency of 17.6 Hz. This pulsing is the subject of concern in terms of its potential health effects. Previous research on potential effects of radiofrequency radiation on nervous system function has produced inconsistent findings, which may be related to methodological limitations of some studies. Not much is currently known about the effects of exposure to TETRA signals.
The objective of this study was to determine whether brief TETRA radiofrequency exposure can produce acute effects on cognitive performance and an increase in self-reported symptoms.
This was a randomized double-blind cross-over study with random allocation of the participants to the two possible exposure orders. The exposure was controlled by a remotely placed (more than 100 km away) engineer who set the equipment according to the randomization and who had no contact with either the participants or the investigators. The two exposure sessions (sham and TETRA) were conducted on separate days with at least 24 hours between them. For TETRA exposure, the target SAR value was 2 W/kg averaged over 10 g of tissue (the ICNIRP general public exposure limit). Each session included completion of a computer based questionnaire at baseline followed by 45 minutes exposure. During exposure, participants completed four standardized cognitive test and also the questionnaire for the second time to measure self-reported psychological and physical symptoms at the end of exposure. The primary cognitive outcome was the Trail Making B (TMB) test. The participants were 53 male volunteers aged between 25 and 49 years with no history of head injuries, neurological or psychiatric diseases.
There were no significant differences in test performance for any of the cognitive tasks between TETRA exposure and sham exposure. Neither were there significant differences in self-reported symptoms.
Interpretation and Conclusion
The results of this study do not provide evidence for an effect of exposure to TETRA signal on cognitive performance. The authors note, however, that they only assessed the acute affect of short-term exposure from TETRA handset; therefore, no conclusions can be drawn about possible effects of long-term exposure.