Two federal lawmakers are raising concerns about whether new 5G technologies will cause cancer.

Specifically, Sen. Richard Blumenthal, D-Conn., and Rep. Anna Eshoo, D-Calif., sent a letter (PDF) to FCC Commissioner Brendan Carr asking for guidance on the topic.

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“To ensure we communicate accurate information to our constituents … we respectfully request you provide to our offices the 5G safety determination from FCC and relevant health agencies,” they wrote. “Most of our current regulations regarding radiofrequency safety were adopted in 1996 and have not yet been updated.”

They added that the FCC's specific absorption rate (SAR) limits do not apply to devices operating above 6 GHz and pointed out that some 5G communications occur at 24 GHz or above.

“Furthermore, the final results of the world's largest and most expensive study to date on the link between radiofrequency radiation and cancer were only just released on November 1, 2018 by the National Toxicology Program (NTP),” the legislators wrote. “As you know, this study found evidence of cancerous heart tumors, as well as some evidence of cancerous brain tumors, in male rats exposed to exposed to high levels of radiofrequency radiation like that used in 2G and 3G cell phones. However. researchers have cautioned that findings ‘do not apply to 4G or 5G technologies.’”

A representative from Commissioner Carr’s office did not immediately respond to questions about the letter.

Others rallied around the request by Blumenthal and Eshoo.

“We strongly support Senator Blumenthal’s request of FCC Commissioner Carr to provide the documentation evidencing the FCC’s ‘safety determination for 5G,’ along with the supporting scientific citations used in making that determination,” wrote Jim Turner, president of the National Institute for Science, Law & Public Policy (NISLAPP), in a release. “NISLAPP considers it a mistake to place new high-frequency radiating antennas in local communities, in very close proximity to homes, offices and schools, when no pre-market health testing at scale has been conducted on the effects of the radiation emitted, to our knowledge, and when much safer hard-wired internet access technologies are readily available.”

Such concerns are not new. The cellular industry for years has been working to address concerns about possible health effects from wireless transmissions. Indeed, the main trade association for wireless operators like AT&T and Verizon, CTIA, issued a prompt statement in response to the letter from Blumenthal and Eshoo:

“The safety of cellphone consumers is important to CTIA and the wireless industry,” the association wrote in a statement to FierceWireless. “We follow the guidance of the experts when it comes to antennas and health effects. Following numerous scientific studies conducted over several decades, the FCC, the FDA, the World Health Organization, the American Cancer Society and numerous other international and U.S. organizations and health experts continue to say that the scientific evidence shows no known health risk to humans due to the RF energy emitted by antennas and cellphones. The evidence includes analysis of official federal brain tumor statistics showing that since the introduction of cellphones in the mid-1980s, the rate of brain tumors in the United States has decreased.”

Notably, Vox recently published a lengthy and detailed look at all of the research conducted around the health effects of cellular communications. The publication reviewed a number of different studies on the topic and detailed the different methods involved in each of the studies, as well as the conclusions each of the studies reached.

Importantly, the publication also cited the recently concluded NTP study, noting that it cost fully $30 million and was mainly based on studies on animals. Vox reported that it found “clear evidence” that male rats exposed to high levels of radio frequency radiation—typical of 2G and 3G networks when the study was designed—developed heart schwannomas.

However, the publication also noted that animal studies are a poor way to understand human health, and that there is no conclusive evidence of adverse health effects from cellular communications, particularly with 5G communications.