When exposed to radio frequency radiation like that used in 2G and 3G cellphones, male rats developed heart tumors, and there was also evidence of tumors in the brain and adrenal gland. Instead, the National Toxicology Program dialed up its concerns about a link to heart and brain cancer from a study of male rats that was made public last winter.
Scientists also studied radiation effects on female rats and mice, and found equivocal evidence as to whether cancers observed were associated with exposure.
In addition, the entire bodies of the mice were exposed to RFR during the study, as compared to the localized exposure that humans get while using their gadgets.
According to Bacher and his colleagues, animals that were irradiated by radio waves with a frequency of 900 and 1900 megahertz "clearly showed that these forms of radiation, encoded in the "mobile format", have carcinogenic activity". By contrast, people are mostly exposed in specific local tissues close to where they hold the phone.
The levels the rodents experienced were far higher than people are typically exposed to.
"We do believe that the tumor responses that we have seen in our studies is real and they are associated with radiofrequency radiation", Bucher said. The highest exposure level used in the studies was four times greater than the maximum power level allowed.
Scientists have divided these rodents into several groups, each of which received a different dose of irradiation, since the maximum allowed for mobile phones and ending levels exceeding this figure by about 3-4 times.
The result came after 10-years of study that says that it causes various types of cancers from heart to the brain. The studies didn't look into the kinds of RFR used for WiFi or 5G networks.
One of the strengths of the studies was that scientists could control how much radiation the rats and mice were getting, which isn't possible when studying how humans use cell phones, Wyde said.
"The study was not created to test the safety of cell phone use in humans, so we can not draw conclusions about the risks of cell phone use from it", Shuren said.
This may be because the male rats exposed to radiation were less likely to develop chronic kidney problems, which are a common cause of death among older rats, the researchers said.
For the study, the team housed the animals in chambers specifically designed for the study. The animals were exposed for up to two years, for about nine hours a day (with 10 minutes of exposure and 10-minute breaks in between). The RFR levels in the studies ranged from 1.5-6 watts per kilogram in rats, and 2.5-10 watts per kilogram in mice.
Future studies will focus on developing measurable physical indicators, or biomarkers, of potential effects from RFR.
The Food and Drug Administration (FDA), which oversees cellphone safety, disagreed with the risk upgrade.
But the results of the study do need proper context.
Tina Pelkey, a FCC spokeswoman, said, "Scientific evidence always informs FCC rules on these issues, and we will continue to follow all recommendations from federal health and safety experts".
While this suggestion has been dismissed by a number of researchers, studies undertaken over a number of years by the US National Institute of Environmental Health Sciences appears to have found evidence that, at the outset, would appear to confirm these fears.
About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services.