The US National Toxicology Program (NTP) conducted a 2-year experimental research design on the carcinogenic impacts of cell phone radiofrequency radiation (RFR) on Harlan Sprague Dawley rats. The experiment included a control group and two experimental groups. The controls were not exposed to any radio frequency radiation while the experimental groups were exposed to RFR of the two types currently used in the US wireless network systems (NTP, 2016). The Code Division Multiple Access (CDMA) and Global System for Mobile Communication (GSM) were the primary RFR predictor/exposure variables implicated in the study (NTP, 2016). For each of the experimental/exposed rat groups (GSM and CDMA-modulated cell radio frequency), the levels of the RFR exposure were grouped into three emission categories of RFR of 1.5W/kg, 3 W/kg, and 6 W/kg (NTP, 2016).
The purpose of the research inquiry was intended to explore the toxicity of the current RFR used in cell phone transmission and its link to gliomas of the brain and schwannomas of the heart. Prior studies have shown correlational associations between brain tumor or gliomas and heavy cell phone uses (NCI, 2011). Gliomas and schwannomas affect glial cells, and the Schwann cells are classified as glial cells (NTP, 2016). Glial cells are specialized, non-neural, support cells involved but are not limited to maintaining homoeostasis, the formation of myelin, and provision of support and protection of peripheral nervous system (PNS) and central nervous system (CNS) neurons (NTP, 2016). In the PNS, Schwann cells produce myelin which is analogous to the oligodendrocytes of the CNS (NTP, 2016).
In the experimental groups or the exposure groups, rats’ exposure to the RFR began from the in utero stage (pregnant dams or pregnant stage) throughout their life course perspective or over the 2-years period of the study. Both the rats in the control/non-exposure and the experimental/exposure groups were housed in identical reverberation chambers throughout the study period and were provided ad libitum (at the rats’ discretion) access to feed and water (NTP, 2016). Rats were exposed to GSM or CDMA-modulated RFR at 900 MHz with whole-body specific absorption rate (SAR) of 0 for the control groups and 1.5 or 3 or 6 W/kg for the exposed groups. Based on the changes in the body weight, the RFR magnitudes or strengths were frequently adjusted to maintain the desired SAR levels (NTP, 2016). For the experimental/exposure groups, all the RFR exposures were conducted over a period of 18 hours with a continuous cycle of 10 minutes on exposure and 10 minutes of non-exposure for a total duration of exposure or dose time of approximately 9 hours a day, 7 days per week (NTP, 2016). Also, the reverberation chambers’ environmental conditions were maintained on a 12-hour light/dark cycle, within a temperature range of 72oF plus or minus 3oF, a humidity range of 50% plus or minus 15%, and with a minimum of 10 changes per hour (NTP, 2016). The health impacts associated with the RFR exposures were evaluated and stratified based on sex (male and female rats).
The primary health outcomes evaluated in the study are the incidence of ‘malignant glioma’ and ‘glial cell hyperplasia’ in the ‘brain’ (brain tumors), and ‘schwannomas’ and ‘Schwann cell hyperplasia’ in the ‘heart’ (heart tumors). Among male rats exposed to GSM-Modulated RFR, all the exposure levels (1.5 or 3 or 6 W/kg RFR levels) had low incidence rate of brain malignant glioma (3.3%, 3.3%, and 2.2% respectively) and glial cell hyperplasia (2.2%, 3.3%, and 1.1% respectively) while the rats in the control groups had no incidence of malignant glioma and glial cell hyperplasia (NTP, 2016). Also, male rats exposed to CDMA-modulated RFR had an incidence of malignant glioma only at the 6 W/kg RFR level of exposure at the rate of 3.3%, and the incidence rate of glial cell hyperplasia at the 1.5 and 6 W/kg RFR levels of exposures was 2.2% each. Overall, there was a statistically significant positive trend in the incidence of the malignant glioma (p<0.05) for CDMA-modulated RFR exposures (NTP, 2016).
On the other hand, among female rats exposed to GSM-modulated RFR, a malignant glioma (1.1%) was observed only in a single rat exposed to 6 W/kg RFR level, and glial cell hyperplasia (1.1%) was observed in a single rat exposed to 3 W/kg RFR over the course of the study (NTP, 2016). Female rats exposed to CDMA-modulated RFR had incidence of malignant glioma in the brain only at the exposure level of 1.5 W/kg RFR at the rate of 2.2% and the incidence rate of glial cell hyperplasia at the 1.5, 3, and 6 W/kg RFR levels of exposures at the rate of 1.1% each (NTP, 2016).
Also among the rats used in the study, cardiac schwannomas and Schwann cell hyperplasia were observed in both male and female rats exposed to GSM and CDMA-modulated RFR, while none was observed in control/unexposed groups (NTP, 2016). The cardiac schwannomas outcomes observed among male rats for both RFR modulations (GSM and CDMA) were statistically significant with a positive trend associated with the SAR levels. The cardiac schwannomas for GSM-modulation exposures-1.5 Wkg, 3 W/kg, and 6 W/kg are 2.2%, 1.1%, and 5.5% respectively (NTP, 2016). The Schwann cell hyperplasia outcomes for GSM-modulation exposures-1.5 Wkg, 3 W/kg, and 6W/kg are 1.1%, 0%, and 2.2% respectively (NTP, 2016). On the other hand, the cardiac schwannomas for CDMA-modulation driven exposures-1.5 Wkg, 3 W/kg, and 6W/kg are 2.2%, 3.3%, and 6.6% respectively (NTP, 2016). The Schwann cell hyperplasia outcomes incidence observed in the study for CDMA-modulation driven exposures -1.5 Wkg, 3 W/kg, and 6W/kg are 0%, 0%, and 3.3% respectively (NTP, 2016).
Cardiac schwannomas outcomes were observed among female rats for both GSM and CDMA-modulations. The incidence rate for the cardiac schwannomas for GSM-modulation exposures-1.5 Wkg, 3 W/kg, and 6W/kg are 0%, 0%, and 2.2% respectively (NTP, 2016). There were no Schwann cell hyperplasia outcomes observed for GSM-modulation exposures-1.5 Wkg, 3 W/kg, and 6W/kg (NTP, 2016). On the other hand, the cardiac schwannomas observed for CDMA-modulation driven-exposures-1.5 Wkg, 3 W/kg, and 6 W/kg are 2.2%, 0%, and 2.2% respectively. The Schwann cell hyperplasia outcomes for CDMA-modulation driven exposures-1.5 Wkg, 3 W/kg, and 6W/kg was approximately 1.1% for each level of exposure (NTP, 2016). Overall, in female rats, the observed incidence of cardiac schwannomas was not statistically significant.
The observed historical incidence rate of cardiac schwannomas in non-exposed or control Harlan Sprague Dawley male rats was 1.30%, which is approximately 1 in 77 rats. Also, for individual NTP studies, the highest historical incidence rate of cardiac schwannomas in control/unexposed rats ranges from 0-6% (NTP, 2016). Apparently, the 5.5-6.6% incidence rate observed in the 6W/kg experimental/exposed group (GSM- and CDMA-modulated RFR levels) exceeded the historical incidence rate of cardiac schwannomas (NTP, 2016). Hence, the investigators concluded that the increase in the incidence rate of cardiac schwannomas among male rats in the study was likely due to whole-body exposure of rats to GSM- or CDMA-modulated RFR. Furthermore, to support this conclusion stated in the study, none of the rats in the control groups were observed with a brain tumor or cardiac schwannomas during the duration of the study, under investigation.
In addition, the historical incidence rate of malignant glioma in male rats in past studies was 2%, which is approximately 1 in 50 and could range from 0-8% for individual studies (NTP, 2016). As a result, the 2.2-3.3% observed in all of the GSM-modulation groups, and the 6 W/kg CDMA-modulated RFR group slightly exceeded the mean historical incidence rate observed in the control rats (NTP, 2016). More so, the researchers emphasized that most of the gliomas were found in rats that died late in the study or at the terminal stage (NTP, 2016). Moreover, they indicated that relatively high number of cardiac schwannomas in exposed groups were observed by 90 weeks (~22.5 months) into the study, a time of which approximately 60 of the 90 control male remained alive and at risk of developing a tumor (NTP, 2016). The investigators also suggested that if malignant gliomas or schwannomas are late-developing tumors, the absence of the tumor lesions in control males in the study under investigation could be related to the shorter longevity among rats in the control groups. Overall, the investigators/researchers demonstrated the need for more epidemiological studies on the link between cell phone RFR and brain tumor and cardiac schwannomas, which could drive meaningful health promotion measures.
National Cancer Institute. (NCI). (2011). NCI Statement: International Agency for Research on Cancer classification of cell phones as “possible carcinogen”. Retrieved from http://www.cancer.gov/news-events/press-releases/2011/IARCcellphoneMay2011
National toxicology Program. (NTP). (2016). Report of partial findings from the national toxicology program carcinogenesis studies of cell phone radiofrequency radiation in Hsd. Sprague Dawley SD rats (whole-body exposures). Retrieved from http://biorxiv.org/content/biorxiv/early/2016/05/26/055699.full.pdf