Nieto-Hernandez R, Williams J, Cleare AJ, Landau S, Wessely S, Rubin GJ. Can exposure to a terrestrial trunked radio (TETRA)-like signal cause symptoms? A randomised double-blind provocation study. Occup Environ Med. Sep 23, 2010. Ahead of print.
Terrestrial trunked radio (TETRA) has been used by the UK police since 2000. This communication system employs signals pulsing at 17.6 Hz. Some police officers reported symptoms (nausea and headaches) which they attributed to their use of the radio.
The objective was three-fold: 1) to test whether exposure to TETRA-like signals can cause acute subjective symptoms; 2) to assess if the pulsing nature of the TETRA signal is important; 3) to test whether effects of exposure (if any) are more pronounced in subjects who attributed subjective symptoms to TETRA than in subjects who did not.
The design of the study was double-blind. A total of 60 sensitive (53 male, mean age ~36 years) and 60 non-sensitive subjects (50 male, mean age ~38 years) were exposed to 3 different conditions (50 minutes each) in a randomized order. These conditions were a TETRA-like pulsed signal (SAR averaged over 10 g =1.3 W/kg), a continuous wave signal, and sham-exposure. During and after each session, the participants rated the severity of 8 symptoms and at the end of each session – their mood state. After each session, the participants stated whether they thought the session involved exposure or not, and rated the degree of their confidence about this.
Results and Interpretation
Exposure to continuous wave signal was associated with an increased likelihood of headache in all subjects, difficulty concentrating in sensitive subjects, and fatigue in non-sensitive subjects. In sensitive participants, this exposure condition was associated with reduced ratings of itching sensation. Exposure to a TETRA-like signal was associated only with increased likelihood of difficulty concentrating in sensitive subjects. When analyses were adjusted for multiple comparisons, only the effect of continuous wave exposure on itching remained significant. Exposure to a TETRA-like signal was associated with an increased likelihood of a high positive mood score in the non-sensitive group. Neither sensitive nor non-sensitive subjects could discriminate between the real and sham exposure. The reasons for a larger effect of continuous wave exposure compared to pulsed exposure and for reduction of skin itching by continuous wave exposure are unclear.
The authors conclude that their results “should be relatively reassuring for users of TETRA radios. Not only did our TETRA-like exposure have no specific adverse effects in comparison to continuous wave, if anything inclusion of a 16 Hz component appeared to make our signal less biologically active.” The authors point out that it would be beneficial to replicate their unexpected findings.