Rats were exposed to radiation with a frequency of 900 megahertz, typical of the cellphones in use when the study was conceived in the 90s, for about nine hours per day for two years, The New York Times reports. The lowest levels of radiation used in the study were equivalent to the maximum exposure a phone can cause and still receive federal regulatory approval; the highest levels to which the animals were exposed were four times that.
The FCC has yet to implement GAO’s recommendations to more closely reflect real-life use. For a narrow subset of smartphones – those sold with lanyards or straps – the FCC advises manufacturers to test phones at a distance of no more than 5 mm from the body (FCC 2014). Yet the FCC has done nothing to ensure more realistic testing of most other smartphones or to account for the widespread use of accessories such as cases, which many different manufacturers produce with both metallic and non-metallic components.
A few epidemiology studies have reported higher rates of tumors inside the skull among people who use cell phones heavily for 10 years or more. Of particular concern are benign Schwann cell tumors called acoustic neuromas, which affect nerve cells connecting the inner ear with structures inside the brain. These growths can in some instances progress to malignant cancer with time. But other studies have found no evidence of acoustic neuromas or brain tumors in heavy cell phone users.
The study specifically used 2G and 3G frequencies — not the frequencies used on more advanced 4G or 5G networks. Researchers exposed the rodents’ entire bodies to the radiowaves for more than nine hours per day, for up to two years. (“A rat that is 2 years old is roughly equivalent to a 70-year-old person,” STAT News reports.) These exposure levels were much higher than what people would experience, John Bucher, senior scientist with the NTP, says in a statement. “So, these findings should not be directly extrapolated to human cell phone usage,” he says.
Because of inconsistent findings from epidemiologic studies in humans and the lack of clear data from previous experimental studies in animals, in 1999 the Food and Drug Administration nominated radiofrequency radiation exposure associated with cell phone exposures for study in animal models by the U.S. National Toxicology Program (NTP), an interagency program that coordinates toxicology research and testing across the U.S. Department of Health and Human Services and is headquartered at the National Institute of Environmental Health Sciences, part of NIH.
Taken together, the findings “confirm that RF radiation exposure has biological effects” in rats, some of them “relevant to carcinogenesis,” says Jon Samet, a professor of preventive medicine and dean of the Colorado School of Public Health, who did not participate in either study. Samet, however, cautioned the jury is still out as to whether wireless technology is similarly risky to people. Indeed, heart schwannomas are exceedingly rare in humans; only a handful of cases have ever been documented in the medical literature.
The base station is equipped with antennas for reception and transmission. In order to communicate, the mobile phones and the antennas at the base station emit radiowave radiation (see below). The mobile phone instrument transmits a lower amount of radiation than the one transmitted by the transmission center (cell site), but because the instrument is near the body, the body directly absorbs the energy from the instrument’s antenna.
But, dear reader, don’t think we’ve reached a “case closed” moment: Unfortunately, even the best evidence on cellphones and brain tumors is far from ideal. Remember, these cohort studies are still observational research — not experimental studies like RCTs. That means they can’t tell us about causation, and there are still many ways they could be biased.
The next scientific step will be to determine what this means for humans. The peer-reviewed papers will be passed on to the US Food and Drug Administration, which is responsible for determining human risk and issuing any guidelines to the public, and the Federal Communications Commission, which develops safety standards for cell phones. The FDA was part of the group of federal agencies who commissioned the studies back in the early 2000s.
In subsequent analyses of Interphone data, investigators addressed issues of risk according to specific location of the tumor and estimated exposures. One analysis of data from seven of the countries in the Interphone study found no relationship between brain tumor location and regions of the brain that were exposed to the highest level of radiofrequency radiation from cell phones (9). However, another study, using data from five of the countries, reported suggestions of an increased risk of glioma and, to a lesser extent, of meningioma developing in areas of the brain experiencing the highest exposure (10).