In the UK, the Stewart Report expressed concern about the potential health impact of RF emissions. What has happened since then?
The original Stewart committee report, published in 2001, reviewed the frequencies at which the mobile phone networks operated. It 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 that this recommendation was made not because of any worries about health, but merely to acknowledge the existence of this unreplicated research.
Since then, both industry and Government have responded to the recommendations made by the report, in particular:
- The Government adopted the ICNIRP safety guidelines, which were already in use for TETRA systems (see our Standards page for more information.)
- Operators and carriers established guidance to help them identify potential transmitter sites which may be of concern to communities and devised a communications and consultation best practice model.
- The Mobile Telecommunications and Health Research (MTHR) programme – co-funded by industry and Government but independently managed – was established to direct further high quality research into health aspects of mobile phone and TETRA use. More information can be found on our Science page.
The Stewart team conducted an update inquiry in 2004 and published a further report (Mobile Phones and Health, 2004), known as “Stewart 2”. This report included a section on TETRA reaffirming the conclusions of a 2001 report by the Advisory Group on Non-Ionising Radiation, which 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.”
The MTHR published a report in 2007 that concluded that no association had been found between use of mobile phones and biological or adverse health effects. In particular the report highlighted that a six year research programme had found no association between short term mobile phone use and brain cancer and that volunteer studies using a TETRA signal showed no evidence that brain function by TETRA signals. The MTHR programme management committee said they believed there was no need to support further work in this area. The MTHR programme also investigated whether mobile phones might affect cells and tissue beyond simply heating them and concluded that results so far showed no evidence for this and said that the committee believed there was no need to support further work in this area either.
However, the MTHR report recognised that the situation for longer term exposure is less clear as studies have so far only included a limited number of participants who have used phones for 10 years or more and recommended more research in potential impact of long-term use.
To read the MTHR 2007 report in full, click here
Who are the experts and why?
The expertise needed to conduct studies into the potential impact of radio frequency emissions on human biology and health is multi-disciplinary – the scientists involved include physicians, physicists, cell biologists, chemists, bio-engineers and psychologists. Reputable scientists have in common a commitment to rigorous testing of a hypothesis through carefully planned and executed experiments and studies. They submit their work for independent peer-review before publishing their results in a reputable journal, rather than releasing their results through the media. They also accept that the weight of scientific evidence builds up over time, through the completion of many studies and do not give undue weight to the findings of any single study.
Those who are acknowledged by their peers to be experts in the field of RF naturally tend to be the scientists who are asked to undertake reviews of the whole body of scientific evidence and to sit on Government advisory bodies. In so doing they are careful to weigh both positive and negative evidence on any issue, and produce a balanced report. These scientists rightly remain absolutely independent of both Government and industry.
To read some perspectives about the quality of the scientific process, look at the IET Positioning Statement in the “Who are the experts” section on our Science page and visit the Sense about Science web site.
What recent scientific studies have been completed on possible biological effects and what have they found?
A list of current and completed studies on TETRA can be found on our Science page, Brief summaries of those that relate to potential biological effects, and some more general RF studies and reviews on biological effects are summarised below.
A double blind provocation study, using both GSM and TETRA signals, was undertaken by a team at the University of Sheffield led by Professor Tony Barker. The study investigated whether exposure to the signals caused changes in heart rate or blood pressure and also measured levels of adrenaline in the bloodstream, Neither changes in heart rate and blood pressure nor in blood chemistry were observed as a result of exposure. The work was published in Bioelectromagnetics 2007 28(6):433-438.
The biomedical sciences department of the Defence Science and Technology Laboratories (DSTL) completed an investigation of the effects of TETRA signals on cellular calcium. As well as reproducing the maximum exposure that can arise from TETRA handsets, the researchers used several lower power levels to see if there could be “power windows” where TETRA signals could cause a reaction. No effects of TETRA on calcium efflux were found at any of the power levels used.
The results were published in the International Journal of Radiation Biology in December 2006 (click here to view, please note that this is not a free document).
Another DSTL team led by Dr Sarah Bowditch examined the effects of TETRA signal exposure on cognitive function and assessed the results of a self assessment of mood, workload and anxiety. No effects on mood or anxiety measures or reported symptoms were observed, and no impact of signal exposure was observed on 21 of 22 cognitive tasks. The work was submitted for publication to the Bioelectromagnetics Journal.
In June 2002 the Swedish Radiation Protection Authority (SSI) appointed an International Expert Team to analyse and evaluate the research on EME (electromagnetic emissions) and its potential effect on health, specifically biological effects. To view the team’s various reports click the relevant year (all open in a new window): 1st & 2nd Reports (2003-04), 3rd Report (2005), 4th Report (2006), 5th Report (2007), 6th Report (2009), 7th Report (2010), 8th Report (2013), 9th Report (2014), 10th Report (2015).
Work by Dr Alan Preece at the University of Bristol, presented at the Bioelectromagnetics Society Conference in June 2002, based on a study of TETRA users, found no effect on cognitive brain function.
The United States Air Force reported at the Electromagnetic Fields and Human Health seminar in Russia in September 2002 an attempt to replicate the 1970s studies on calcium efflux. Its studies failed to show any effect. It also conducted some very high pulse power tests looking at calcium channels that were reported at the Second International Workshop on Biological Effects of Electro Magnetic Emissions in Rhodes in October 2002, and again saw no effects.
The Report by the Expert Panel of the Royal Society of Canada (1999) and the subsequent Report from the French Ministry of Health (Zmirou Report, 2001) both backed the extensive research reported in a UNEP/WHO/IRPA Report of 1993, which concluded that there was no strong reason to believe that 16Hz modulation has special effects.
To obtain more detailed information on RF studies and reviews, you can visit the sites listed on our Links page.
If TETRA is safe why is research continuing?
Scientific evidence on any topic builds up over time as research studies are completed and replicated. Replication of the results of individual studies is an important element of quality control in the scientific process.
The use of radio frequency emissions has already been subject to a far greater number of scientific studies and risk assessments than many of the chemicals in our food. The MTHR Report of 2007 did indicate that it saw no need for further research in some areas, but did call for continued studies on potential long-term effects.
Science can never guarantee that anything is absolutely safe. But as the number of completed studies grows the stronger the reassurance that it can offer that any risk from a technology is small, particularly when set against the many more mundane risks – like driving or crossing roads – we accept in our daily lives.
Why is the Home Office sponsoring a major epidemiological study of police officers?
Following publication of the Stewart report, the Home Office asked AGNIR to produce a report about the use of TETRA in the UK. AGNIR published a report in July 2001, which included 8 recommendations for a long-term research programme. The Imperial College long-term study, monitoring user health and patterns of usage, was established in response to one of these recommendations. The study involves a cohort of around 100,000 police users, and will go on for some fifteen years. A description of the Imperial College study, from a presentation at a THG seminar in 2006, can be found by clicking here (opens in a new window).
Advances in all technologies carry a small degree of risk, but no products or services reach the market without appropriate studies, testing and assessment having been conducted. TETRA equipment complies with all the relevant safety standards and exposes officers to less RF than their old communications systems.
What is the long term monitoring study trying to do?
The study will monitor the health of a large number of users of TETRA over a long period looking in particular at the incidence of mortality for diseases such as cancer and Parkinson’s, sick absence levels and trends for retirement on health grounds. Health screening is offered to participants. A cognitive study is taking place in parallel, looking at whether exposure to a TETRA signal has any impact on the ability of the volunteer to undertake a range of computer tests to test speed of reaction, short term memory and so on.
What is the ’16Hz issue’ and why does it matter?
TETRA handsets pulse at 17.6Hz and it has been suggested that this could cause a biological effect. Experiments back in the 1970s had suggested that pulsed RF close to 16Hz affected the rate at which calcium, which plays an important role in the human nervous system, leaks out of cells.
Although the results had been replicated by the same group of people who originally conducted them, other groups who tried to replicate the findings were unable to do so. AGNIR and WHO looked in detail at how the work had been carried out and found the early experiments had been flawed in their technique, design and analysis. In 2001 AGNIR stated that current evidence suggested it was unlikely that the special features of the TETRA signal were hazardous but recommended further studies.
In 2005 two groups of carefully designed and executed studies were commissioned by the Home Office and found that TETRA signals had no effect on calcium efflux. The DSTL study is outlined on the Science page of our website.
Professor Colin Blakemore, who was a member of Stewart Inquiry, has spoken and written extensively on this issue, and, talking about the 1970s calcium efflux studies, has said “…..there is a much greater danger to life associated with poor communications than that implied by a questionable investigation [some 30 years ago]……”.
Professor Lawrie Challis, Vice-Chairman of the Stewart Inquiry, has said that absorption from [TETRA] handsets would generally be “appreciably less than from current police radios“, that the handsets operate “way below the guidelines” and that there is “no evidence that 17.65Hz pulsing has an effect nor any known biological mechanisms that suggest it should”.
Does TETRA impact on efflux of cellular calcium?
The most recent study, carried out recently by a team at the Defence Science and Technology Laboratories found no evidence of calcium efflux. The results of this study were published in the International Journal of Radiation Biology in December 2005. To see a summary of a presentation at a THG seminar in 2007 by Dr John Tattersall, who conducted the studies, click here (opens in a new window). (See also “16Hz issue” answer above).
Is radio frequency radiation dangerous?
There is a wide range of types of radiation. Ionising radiation like X-rays and gamma rays is dangerous as it can break chemical bonds and damage DNA. RF radiation is low frequency and non-ionising so it cannot do that. The only known effect is heating. The heating effect from a TETRA handset is very small, and much less than the natural variation in body temperature that occurs throughout the day. Larger heating effects can be dangerous – for example microwave ovens emit non-ionising radiation but clearly have a substantial heating effect to cook. ICNIRP sets exposure limits designed to protect against heating effects and TETRA handsets operate well within these limits.