The National Toxicology Program and a panel of external scientific experts have concluded that high exposure to the kind of radio frequency radiation generated by older cell phones is associated with heart tumors in male rats, according to final reports of NTP studies released in November. NTP Senior Scientist John Bucher cautioned that the results are not directly applicable to humans. “The exposures used in the studies cannot be compared directly to the exposure that humans experience when using a cell phone,” Bucher said in an NTP press release. “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 studies subjected rats and mice to radiation similar to that used in 2G and 3G cell phones, which were standard technologies when the studies were conceived in the 1990s. Two common technologies for transmitting cell phone signals were tested: Code Division Multiple Access, or CDMA; and Global System for Mobile Communications, or GSM. The animals were exposed to radio frequency radiation intermittently, nine hours a day, for a period of two years. According to NTP, the lowest exposure level used in the studies was equal to the maximum local tissue exposure currently allowed for cell phone users.  In addition to showing clear evidence related to heart tumors, the studies also showed some evidence of a link between radio frequency radiation and tumors in the brains and adrenal glands of male rats. Results were inconclusive for female rats and for both male and female mice. The studies did not address the types of radio frequency radiation used in today’s wireless networks and in 4G and 5G cell phones. While the studies subjected animals to radiation across their entire bodies at exposure levels and durations greater than those experienced by humans from normal cell phone use, an NTP fact sheet says that the studies “question the long-held assumption that radio frequency radiation is of no concern as long as the energy level is low and does not significantly heat the tissues.” NTP plans to collaborate with the National Institute of Standards and Technology and the IT’IS Foundation on future studies of cell phone radiation. According to NTP, these shorter-term studies will investigate the possibility of DNA damage in exposed tissues and will attempt to identify biomarkers of damage from radio frequency radiation. The new studies will reportedly be designed to keep pace with changing cell phone technologies. More information about the studies is available from the NTP and from the agency's and fact sheet ().