Science - the story so far

Science cannot prove categorically that something is safe; the only certainty in science is that there is no certainty. It is not possible to prove a negative, so no-one can prove conclusively that a product or technology is not harmful. Scientific methodology is empirical. Knowledge develops from observation and measurement, producing theories that can be used to predict what might happen under certain conditions, testing those theories through experiments and studies, peer-reviewing the findings, methodology, and conclusions, and attempting to replicate the results. In this way a body of robust scientific evidence builds up. If, after many years, a number of studies find no harmful effects, scientists can say with growing confidence that a product is probably safe.

The World Health Organisation holds a database of hundreds of studies into the impact of radio frequency emissions, including some at the frequencies used by the TETRA standard. The balance of evidence has demonstrated no adverse impact on health. While uncertainties remain about the potential effects of long-term use of radio-based technologies, advisory bodies like the World Health Organisation advocate a precautionary approach. However, this does not mean that radio technologies should not be used and it reaffirms the importance of science-based standards.

The Independent Experts Group on Mobile Phones (the "Stewart Inquiry") published a report in 2001 which considered the potential health impact of review the radio frequencies at which the mobile phone networks operated. The committee did not examine TETRA in detail and so did not make any specific recommendations about TETRA technology.

However it did mention scientific work, dating back to the 1970s, that implied that radio signals with modulations around 16Hz might have an impact on release of cellular calcium. The report acknowledged that this evidence was inconclusive but suggested that “as a precautionary measure, amplitude modulation around 16Hz should be avoided if possible in future development of signal coding”. Professor Lawrie Challis, who was the vice chairman of the Stewart Inquiry, has explained publicly that this recommendation was made not because of any worries about health, but merely to acknowledge the existence of unreplicated research dating back to the 1970s.

During the years since then both industry and Government have responded to the recommendations made by the Stewart Report, in particular:

• The Government adopted the ICNIRP safety guidelines as recommended by the Stewart Inquiry. These ICNIRP standards were already being used for TETRA systems. (Click here to find out more about ICNIRP.)
  
  

• Operators and carriers established guidance to help them identify potential transmitter sites which might be of concern to communities and devised a communications and communications and consultation model to help ensure that the appropriate amount and nature of communications takes place.
  
  

• The Mobile Telecommunications and Health Research (MTHR) programme as set up, co-funded by industry and Government and independently managed under the Chairmanship of Professor Lawrie Challis until 2008 and then Professor David Coggon. The purpose of the programme is to make sure that high quality independent studies into health aspects of mobile phone use take place. This programme includes a number of TETRA studies which can be found on our Science - Research Studies page.
  
  

• Studies on the release of cellular calcium, commissioned by the Home Office, have been completed by the Defence Science and Technology Laboratory. The results have been published and the study found that the TETRA signal had no effect on cellular calcium.

The Stewart team conducted an update inquiry in 2004 and published a further report (Mobile Phones and Health, 2004), known as “Stewart 2”. This included a section on TETRA which reaffirmed the conclusions of the 2001 report by the Advisory Group on Non-Ionising Radiation. AGNIR had said “it is notable that the signals from TETRA base stations are not pulsed, whereas those from mobile terminals and repeaters are. Although areas of uncertainty remain about the biological effects of low level RF radiation in general, including modulated signals, current evidence suggests that it is unlikely that the special features of the signals from TETRA terminals and repeaters pose a hazard to health."

In 2007 MTHR published a report on progress with the research programme. To download a copy of the complete report click here.

The MTHR press release accompanying that report said:

“Mobile phones have not been found to be associated with any biological or adverse health effects according to the UK’s largest investigation into the possible health risks from mobile telephone technology. The Mobile Telecommunications and Health Research (MTHR) Programme has published their conclusions today as part of its 2007 Report.

The six year research programme has found no association between short term mobile phone use and brain cancer. Studies on volunteers also showed no evidence that brain function was affected by mobile phone signals or the signals used by the emergency services (TETRA). The MTHR programme management committee believes there is no need to support further work in this area.

The research programme also included the largest and most robust studies of electrical hypersensitivity undertaken anywhere in the world. These studies have found no evidence that the unpleasant symptoms experienced by sufferers are the result of exposure to signals from mobile phones or base stations.

The situation for longer term exposure is less clear as studies have so far only included a limited number of participants who have used their phones for 10 years or more. The committee recommends more research be conducted in this area.

The MTHR programme also investigated whether mobile phones might affect cells and tissue beyond simply heating them. The results so far show no evidence for this and the committee believes there is no need to support further work in this area.

Professor Lawrie Challis, Chairman of MTHR, said “This is a very substantial report from a large research programme. The work reported today has all been published in respected peer-reviewed scientific or medical journals. The results are so far re-assuring but there is still a need for more research, especially to check that no effects emerge from longer-term phone use from adults and from use by children”.

The research programme has also funded some basic measurements of radio signals from microcell and picocell base stations such as those found in airports, railway stations and shopping malls. These have shown that exposures are well below international guidelines.

Additional studies also confirmed that the use of a mobile phone while driving, whether hand-held or hands-free, causes impairment to performance comparable to that from other in-car distractions. There are however indications that the demand on cognitive resources from mobile phones may be greater.”

The MTHR report refers to some studies that have been or are being carried out on TETRA signals. The main references to TETRA in the body of the 2007 report are summarised here for ease of reference:

Standard Exposure System

Dr Phil Chadwick of MCL was commissioned to design a system to produce RF exposures representative of those to real phone and TETRA radio users. (Report page 7.)

Brain Function

The roll-out of the TETRA-based network for the emergency services prompted concern about the possible effects of exposure to pulse-modulated fields from the handsets.

• MTHR supported work by Dr Peter Dimbylow, HPA, to characterise the way energy is absorbed in the head from a TETRA handset (published in Phys Med Biol, 48, 3911-26)
  
  

• MTHR supported work by Dr Stuart Butler at the Burden Neurological Institute in Bristol to assess cognitive and electro-physiological effects TETRA signals in healthy volunteers (submitted for publication)
  
  

• Home Office-funded work by Dr Sarah Bowditch at DSTL examined the effects of TETRA signal exposure on cognitive function and the results of a self assessment of mood, workload and anxiety (submitted for publication)
  
  

• Prof Tony Barker at Sheffield assessed impact of RF exposure (including a TETRA signal) on blood pressure and heart rate. (published in Bioelectromagnetics, 26(2), 102 – 8)

Hypersensitivity

A small proportion of users of electrical equipment, including mobile phones and TETRA handsets, report unpleasant symptoms such as headaches and tingling and this is sometimes described as ‘electrical hypersensitivity’.

• Work by Prof Elaine Fox at University of Essex concluded that self-reported hypersensitivity is between around 1% and 4% of the population.
  
  

• Previous provocation studies (using an electromagnetic source and sham signal to see if symptoms can be provoked) were reviewed by Dr James Rubin at King’s College London, who reported that the great majority of studies failed to find any evidence that symptoms of hypersensitivity are caused by exposure to electromagnetic fields (published in Psychosom Med, 67, 224-32)

MTHR noted that exposure to TETRA signals had not been adequately investigated, and further studies are now underway. These are:

• Prof Adrian Burgess at Imperial College London and University of Swansea are undertaking a Home Office supported study with a group of police officers, including both those who report symptoms when using TETRA radios and those who do not, using a battery of cognitive tests, recording measures of brain activity and completion of a well-being questionnaire.
  
  

• Prof Simon Wellesley at King’s College is working on an MTHR2- supported study with groups of police officers, some who report symptoms and some who do not, using sham, continuous, and modulated RF signal exposures.
  
  

• Prof Elaine Fox at University of Essex is undertaking an MTHR2-supported study on exposure to base station signals, with a group that attributes symptoms to base station exposure and one that does not. Users will be exposed to sham or TETRA base station signals and asked to self-assess severity of symptoms.

Current and planned work on TETRA and hypersensitivity is summarised on page 33 of the MTHR report.

Biological Mechanisms

A study by Dr Sienkiewicz at HPA, with colleagues at University of Bristol and DSTL, searched for evidence that RF fields could cause changes in brain function, using TETRA, GSM, and UMTS signals. The work has not yet been published.

In June 2008, MTHR announced a new cohort study to investigate whether the use of mobile phones is linked to long term health affects such as brain cancer and neurodegenerative diseases. The study will be carried out by a team at Imperial College London and will monitor the health of 200,000 mobile phone users over a number of years. Imperial College is already conducting a long term health monitoring cohort study with police users of TETRA.