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National Toxicology Program releases final reports on rat and mouse studies of radio frequency radiation like that used in 2G and 3G cell phone technologies
The National Toxicology Program (NTP) concluded there is clear evidence that male rats exposed to high levels of radio frequency radiation (RFR) like that used in 2G and 3G cell phones developed cancerous heart tumors, according to final reports released today. There was also some evidence of tumors in the brain and adrenal gland of exposed male rats. For female rats, and male and female mice, the evidence was equivocal as to whether cancers observed were associated with exposure to RFR. The final reports represent the consensus of NTP and a panel of external scientific experts who reviewed the studies in March after draft reports were issued in February.
“The exposures used in the studies cannot be compared directly to the exposure that humans experience when using a cell phone,” said John Bucher, Ph.D., NTP senior scientist. “In our studies, rats and mice received radio frequency radiation across their whole bodies. By contrast, people are mostly exposed in specific local tissues close to where they hold the phone. In addition, the exposure levels and durations in our studies were greater than what people experience.”
The lowest exposure level used in the studies was equal to the maximum local tissue exposure currently allowed for cell phone users. This power level rarely occurs with typical cell phone use. The highest exposure level in the studies was four times higher than the maximum power level permitted.
“We believe that the link between radio frequency radiation and tumors in male rats is real, and the external experts agreed,” said Bucher.
The $30 million NTP studies took more than 10 years to complete and are the most comprehensive assessment, to date, of health effects in animals exposed to RFR with modulations used in 2G and 3G cell phones. 2G and 3G networks were standard when the studies were designed and are still used for phone calls and texting.
“A major strength of our studies is that we were able to control exactly how much radio frequency radiation the animals received — something that’s not possible when studying human cell phone use, which has often relied on questionnaires,” said Michael Wyde, Ph.D., lead toxicologist on the studies.
He also noted the unexpected finding of longer lifespans among the exposed male rats. “This may be explained by an observed decrease in chronic kidney problems that are often the cause of death in older rats,” Wyde said.
The animals were housed in chambers specifically designed and built for these studies. Exposure to RFR began in the womb for rats and at 5 to 6 weeks old for mice, and continued for up to two years, or most of their natural lifetime. The RFR exposure was intermittent, 10 minutes on and 10 minutes off, totaling about nine hours each day. RFR levels ranged from 1.5-6 watts per kilogram in rats, and 2.5-10 watts per kilogram in mice.
These studies did not investigate the types of RFR used for Wi-Fi or 5G networks.
“5G is an emerging technology that hasn’t really been defined yet. From what we currently understand, it likely differs dramatically from what we studied,” said Wyde.
For future studies, NTP is building smaller RFR exposure chambers that will make it easier to evaluate newer telecommunications technologies in weeks or months, rather than years. These studies will focus on developing measurable physical indicators, or biomarkers, of potential effects from RFR. These may include changes in metrics like DNA damage in exposed tissues, which can be detected much sooner than cancer.
The U.S. Food and Drug Administration nominated cell phone RFR for study by NTP because of widespread public use of cell phones and limited knowledge about potential health effects from long-term exposure. NTP will provide the results of these studies to FDA and the Federal Communications Commission, who will review the information as they continue to monitor new research on the potential effects of RFR.
NTP uses four categories to summarize the evidence that a substance may cause cancer:
- Clear evidence (highest)
- Some evidence
- Equivocal evidence
- No evidence (lowest)
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Dr Paul Gardner-Stephen is a Senior Lecturer in the College of Science and Engineering at Flinders University
This report provides an incremental contribution to understanding of the interaction between radio frequency radiation and cancer, although it is not at all clear that the results have applicability to humans using mobile phones in any realistic manner. Of course, people who are concerned about the risk can always choose to use a headset or similar device when using a mobile phone, so that any possible risk -- however small or unlikely -- can be completely avoided. In short, this is a potential risk -- and it is important to stress that the risk is still not proven -- that if people are worried about it, they are fully in control of, and are able to completely avoid if they wish to.
Professor Rodney Croft is Chief Investigator at the Australian Centre for Electromagnetic Bioeffects Research and Professor of Health Psychology in the School of Psychology at the University of Wollongong
Mobile phones and associated technologies use ‘radiofrequency’ electromagnetic fields to operate. To determine whether these radiofrequency fields might pose a problem for public health, a substantial literature has tested for effects of radiofrequency fields on cancer and cancer-related biological processes. The NTP study is the latest such study, and has many advantages over previous studies in terms of the number of animals tested and the use of exposure over the whole of the animals’ lives. However, consistent with previous research, the NTP study does not provide evidence of a link between radiofrequency fields and cancer, nor any evidence that mobile phone use can adversely affect health.
There are a number of key issues that need to be considered when interpreting the NTP press release and research publications:
1. The animals exposed to radiofrequency fields lived significantly longer than the controls (and cancer risk increases as you get older).
2. The radiofrequency fields are not relevant to mobile phone use (they were strong enough to increase body temperature in the rats by over 0.5 degrees, whereas a mobile phone can’t increase body temperature at all).
3. The results were only reported for male rats, but not female rats, or male or female mice (which makes the relevance of any results to humans questionable).
And most importantly...
4. There is no indication that any of the results are statistically significant (i.e. not merely due to chance).
This is particularly important as sensible patterns were not observed within or across rodent groups, and also because the reported findings are inconsistent with previous research findings. If chance was ruled out using statistical techniques, the reported ‘evidence’ of carcinogenicity would vanish.
The NTP rodent carcinogenicity study does not provide evidence that the radiofrequency fields relevant to mobile telecommunications can cause cancer.
Bruce Armstrong is a consultant for Cancer Causes and Prevention, and Adjunct Professor in the School of Global and Population Health at the University of Western Australia
In a nutshell, the present results serve only to add a little strength to the evidence available following the first report on the rat studies. That report has stood up to very careful scrutiny. The new results from the mice studies serve to strengthen the findings from the rat studies only a little. I remain of the view that IARC classification of 'possibly carcinogenic to humans' remains correct for the present.
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