Bucher said the effect likely only showed up in the male rats because they were larger, and likely absorbed more radiation than the female rats or mice.
The team subjected rats to high levels of radiation at 2G and 3G frequencies, the type still used in voice calls and texting in the United Kingdom and US, for ten minute periods for over nine hours each day. The amount of radiation to which the laboratory animals were exposed included the levels emitted by cellphones millions of people use everyday. But the radiofrequency radiation from a cellphone doesn't work that way - and today's results support that. There are additional unusual findings from the study, such as the exposed rats living longer than the control group rats, that we are assessing to understand how that may be relevant to the results.
Unlike ionising radiation such as that from gamma rays, radon and X-rays, which can break chemical bonds in the body and are known to cause cancer, radiofrequency devices such as cellphones and microwaves emit radiofrequency energy, a form of non-ionising radiation.
The Food and Drug Administration (FDA) has issued a statement saying it respects the research by the toxicology program, has reviewed many other studies on cellphone safety, and has "not found sufficient evidence that there are adverse health effects in humans caused by exposures at or under the current radio-frequency exposure limits".
In 2011, a working group of the International Agency for Research on Cancer said cellphones are possibly carcinogenic. During that time, there have been no shortage of studies looking at the mobile phones and cancer - with evidence both supporting and contradicting a connection between the two - and still more research is ongoing.
Male rats exposed to very high levels of the kind of radiation emitted by cellphones developed tumours in the tissues around their hearts, according to a draft report by USA government researchers on the potential health risks of the devices. The first is that the studies involved 2G and 3G signals, not the current generation 4G or upcoming 5G signals, so any risk specific to LTE will not have been noted.
The draft reports are set to be reviewed by outside experts in March. "So, these findings should not be directly extrapolated to human cell phone usage", he says. Various tumors were also observed in mice exposed to radio-frequency radiation. The earlier report showed a hint of increased brain tumours in male rats, but the final results did not bear that out. And just because researchers discover an association in rodents does not mean they translate to humans.
The American Cancer Society was in agreement with the assessment that cellphones were safe to use. To make his point, he pointed out in a later interview, "I am actually holding my cellphone up to my ear".