Independent Expert Group on Mobile Phones

Summaries of Oral Evidence

Dr A Preece, University of Bristol


Summary of Oral Evidence presented to IEGMP by Dr A Preece, University of Bristol, on Friday 10 December 1999

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Dr Preece described his earlier work with 50 hertz (Hz) magnetic fields, which at high flux densities has produced deficits of attention and impairment to working memory. He then explained his work on effects of exposure to mobile phone frequencies. Volunteers were exposed to 915 MHz continuous wave or pulsed at 217 Hz. Subjects completed a battery of tests designed by Cognitive Drug Research Ltd, Reading. There were two groups of exposed individuals consisting of hospital staff and medical/dental students. When data from the two groups were combined it was found there was a 15 millisecond (ms) reduction in choice reaction time in exposed groups. Dr Preece believes that this is an effect on the angular gyrus which is an interface between the visual and speech centres and is normally located on the left side of the head; an alternative explanation is based on the possible production of heat shock proteins. This work has been repeated by a Finnish group led by Dr Koivisto (published as Koivisto, M, Revonsuo, A, Krause, C M, Haarala, C, Sillanmäki, L, Laine, M and Hämäläinen, H, Effects of 902 MHz electromagnetic field emitted by cellular phones on response times in humans. NeuroReport, 11, 413–15 (2000)). The Finnish study, which was somewhat larger than the Preece work, has detected a decrease in simple reaction time, together with a speeding up of the vigilance response, and an improvement in accuracy of performance. Although the two studies are broadly similar there were a number of differences between them including the position of the antenna and the range of tests employed.

Dr Preece feels that it is important to perform this type of study in humans. Penetration of the field into the human brain is extremely limited (2 cm), leading to exposure of very specific areas of the cortex. In small rodents, such as rats and mice, the same penetration would result in exposure of the entire brain. He believes that one explanation of his results might be a small heating effect resulting in changes in blood flow within the brain. He is examining this possibility in a double-blind crossover trial. Dr Preece has also been engaged in work to assess specific energy absorption rate (SAR) values in the brain using a realistic phantom. For this work he has used dielectric values taken from surgical and cadaver measurements. Although broadly similar, SARs produced using these dielectric values are generally higher than those produced by Niels Kuster (Swiss Federal Institute of Technology) and Camelia Gabriel (Microwave Consultants); Kuster uses simpler models, so that differences are more apparent in complex situations. He has found that there is considerable variation between the SARs produced by different models of mobile phone and suggests that consumers should be given this information to enable them to make informed choices, regardless of whether or not there may be an adverse health effect. He believes that some Global System for Mobiles (GSM) phones may result in exposures only just inside the guidelines from the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Dr Preece would like to examine possible long-term effects of mobile phone exposure on brain function. He suggested that this could be done by means of a freefone online cognitive test, which is currently under evaluation. The Group is concerned, however, that it may be difficult to distinguish acute from chronic effects using this approach and it might be difficult to allow for any confounding factors.

Dr Preece noted that there are identified effects on pacemakers and some equipment used in intensive care units and these effects need to be considered. He also noted the reports of sleep disturbance and changes in blood pressure. He has received many anecdotal comments relating to cerebro-vascular accidents, dysphonia, auditory disturbances, testicular cancer and neurological tumours, as a result of being named in media presentations. He believes that reports from a study of changes in electroencephalography (EEG) during sleep are evidence of an electrophysiological effect; he is not aware of similar studies on subjects who were awake. Exposure during the EEG sleep study was intermittent (15 minutes on/15 minutes off).

Dr Preece said that the electricity industry had attempted to stop his power frequency work by applying pressure via the vice-chancellor of his university. The Department of Health, which provided funding for this study, is aware of the situation and agreed to provide members of the Group with copies of correspondence relating to the incident. In response to a question from the Group, Dr Preece indicated that he does not have difficulty in obtaining funding for his work; he agreed to provide a written summary of his experiences with the media.

Dr Preece agreed that as the angular gyrus is usually located on the left hand side of the brain, his theory could be tested by comparing effects on the left- and right-hand sides of the head. He noted that it is difficult to rule out thermal mechanisms causing changes in blood flow when using microwaves. However he considers that the maximum temperature rises induced in the brains of his subjects are likely to be quite small and it is uncertain whether blood flow would be affected. He intends to examine this by performing measurements of blood flow using a magnetc resonance imaging (MRI) machine in conjunction with a simulated phone constructed from non-ferrous materials. There was some concern about possible interactions between the mobile phone signals and radiofrequency fields (RF) used in MRI machines. Dr Preece suggested that as ordinary MRI machines operate at around 40–50 MHz this is unlikely to be a problem, although there could be some interaction in functional MRI machines which operate at around 400–500 MHz. Ultrasound was a good technique for measuring blood flow, but was unsuitable for highly localised responses. Another option might be to use positron emission tomography scans which would be sensitive enough to detect changes in brain blood flow.

Dr Preece was asked whether he considered that existing guidelines, which are based on avoiding a temperature rise of greater than 1°C, were appropriate. He believes that the value for whole body exposure is based on the avoidance of discomfort in people and behavioural changes in animals and that it is probably reasonable given the ten-fold margin of safety incorporated in the guidelines. He is less comfortable with the basic restriction of 10 watts per kilogram (W/kg), averaged over any 10 g in the head; he feels that this should be less than the metabolic load of the brain. Dr Preece believes that the best way to set guidelines would be to get neuro-physiologists to assess the effects of RF on the brain and to combine this with the knowledge of energy deposition. It should then be possible to reduce exposures until no effect is observed. It was agreed that Sir David Cox would write to Dr Preece with more detailed questions respecting the statistical analysis of his work. Further questions from the Group would also be forwarded.

Dr Preece said that his current work includes evaluation of an implantable electric field probe, development of a phantom head for use in intercomparison of modelling and measurement, a risk perception study around cell phone masts and power lines, tests of the cognitive effects of cell phone exposure, dielectric measurements, and a student project on driving performance during exposure to mobile phone signals.


First issued 19 April 2000