The predominant source of human exposure to radio frequency radiation (RFR) occurs through the use of cellular phone handsets. The Food and Drug Administration nominated cell phone RFR emission for toxicology and carcinogenicity testing in 1999. At that time, animal experiments were deemed crucial because meaningful human exposure data from epidemiological studies were not available. Male and female Hsd:Sprague Dawley SD rats were exposed to time-averaged whole-body specific absorption rates of Global System for Mobile Communications (GSM)- or Code Division Multiple Access (CDMA)-modulated cell phone RFR at frequencies of 900 MHz (herein referred to as “cell phone RFR”) in utero, during lactation, and after weaning for 28 days or 2 years. Genetic toxicology studies were conducted in rat peripheral blood erythrocytes and leukocytes, brain cells, and liver cells.
Study Design
28-Day Studies
Beginning on gestation day (GD) 6, groups of 20 time-mated F0 female rats were housed in specially-designed reverberation chambers and received whole-body exposures to GSM- or CDMA-modulated cell phone RFR at power levels of 0 (sham control), 3, 6 or 9 W/kg for 5 to 7 days per week, continuing throughout gestation and lactation. The daily exposure duration was 9 hours and 10 minutes over an 18-hour and 20-minute period, as exposures cycled between modulations every 10 minutes. There were seven exposure groups per sex, including a shared sham control and three exposure groups for each modulation. At weaning, 10 males and 10 females per group were selected across four litters for continuation. Weaning occurred on the day the last litter reached postnatal day (PND) 21, marking the beginning of the 28-day study. Male and female F1 offspring continued to receive whole-body exposures to GSM- or CDMA-modulated cell phone RFR at the same power levels and under the same exposure paradigm, 5 to 7 days per week for up to 28 days.
2-Year Studies
Beginning on GD 5, groups of 56 time-mated F0 female rats were housed in reverberation chambers and received whole-body exposures to GSM- or CDMA-modulated cell phone RFR at power levels of 0 (sham control), 1.5, 3, or 6 W/kg for 7 days per week, continuing throughout gestation and lactation. The daily exposure duration was 9 hours and 10 minutes over an 18-hour and 20-minute period, as exposures cycled between modulations every 10 minutes. There were seven exposure groups per sex, including a shared sham control and three exposure groups for each modulation. At weaning, three males and three females per litter from 35 litters were randomly selected per exposure group for continuation. Weaning occurred on the day the last litter reached PND 21, marking the beginning of the 2-year studies. Groups of 105 male and 105 female F1 offspring continued to receive whole-body exposures to GSM- or CDMA-modulated cell phone RFR at the same power levels and under the same exposure paradigm, 7 days per week for up to 104 weeks. After 14 weeks of exposure, 10 rats per group were randomly selected for interim histopathologic evaluation and five were designated for genetic toxicity evaluation.
Perinatal Findings and Thermal Effects
Consistent perinatal effects were observed between modulations, and in both the 28-day and 2-year studies, including lower dam body weights in late gestation and lactation, lower pup body weights and lower pup survival rates. Whole-body exposure to GSM- or CDMA-modulated cell phone RFR had no effect on survival of dams during gestation or lactation and no effect on littering, litter size or live litter pup numbers on PND 1. Lower body weight gains were observed during gestation in dams exposed to GSM during the 28-day and 2-year studies and the CDMA 28-day studies, with body weight effects becoming more pronounced and persisting throughout lactation for both modulations and studies. Lower pup survival was observed for GSM exposure at 9 W/kg in early lactation (before PND 4) and at 6 and 9 W/kg in CDMA-exposed animals, in early and late (after PND 4) lactation. Lower male and female pup body weights were observed beginning in early lactation following exposure to ≥ 6 W/kg of either GSM- or CDMA-modulated cell phone RFR.
Body weight decreases in RFR exposed groups persisted throughout the post-weaning period in the 28-day studies, were observed at the 14-week interim evaluation in the 2-year studies, but eventually resolved and were not observed at later time points in the 2-year studies. There were no clinical observations associated with exposures to either modulation.
In the 28-day studies, subcutaneously implanted microchips were used to record body temperatures of animals within 3 to 5 minutes of exposure pauses. Body temperatures were recorded in F0 females during gestation and lactation and in F1 offspring during the post-weaning phase. Higher body temperatures were observed during gestation in 9 W/kg GSM dams and during lactation in ≥ 6 W/kg GSM dams and 9 W/kg CDMA dams. At power levels selected for the 2-year studies (up to 6 W/kg), body temperature elevations did not exceed 1° C in the 28-day study measurements. No exposure-related temperature effects were observed in F1 offspring.
2-Year Studies
In the 2-year studies, there was significantly lower survival in the shared male sham control group compared to almost all exposed groups, for both modulations. Survival began to decline at a faster rate than in exposed groups after week 75. In the sham control group, 28% of animals survived to study termination, compared to 48% to 68% for exposed groups across both modulations. Lower survival in sham control male rats was largely attributed to higher severity of chronic progressive nephropathy and there was a spectrum of lesions in other organs considered secondary to chronic progressive nephropathy that occurred at higher incidences in male sham controls. Survival in the shared female sham control group was significantly lower than the 6 W/kg CDMA-exposed group; however, it was similar to all other exposure groups, across modulations. At study termination, there was no effect on body weight in male or female rats, and there were no exposure-related clinical observations.
At the 14-week interim evaluation, there were increased incidences of right ventricular cardiomyopathy in the heart of male rats following exposure to GSM- and CDMA-modulated cell phone RFR compared to sham controls.
At 14 weeks, sperm motility and counts were evaluated in male rats exposed to GSM or CDMA. Exposure to whole-body GSM- or CDMA-modulated cell phone RFR, up to 6 W/kg, did not result in significant changes/differences in reproductive organ histopathology or sperm parameters in male rats compared to the sham controls.
At 2 years, there were similarities in neoplastic and nonneoplastic responses between modulations. Following exposure to GSM- or CDMA-modulated cell phone RFR, there were increases in the incidences of malignant schwannoma in the heart of male rats, with a significant positive trend in the incidences in GSM- and CDMA-exposed males and a significant pairwise increased incidence in CDMA 6 W/kg males. Also observed in the heart were significantly increased incidences of right ventricular cardiomyopathy in 3 and 6 W/kg GSM male and female rats and 6 W/kg CDMA male rats.
Several other, weaker, responses were observed in both modulations including malignant glioma in the brain, adenomas in the pituitary gland (pars distalis), and pheochromocytomas of the adrenal medulla. Additionally, in GSM male rats there were marginal responses in the prostate gland, granular cell tumors of the brain, and in pancreatic islets that were not observed in CDMA-exposed rats, and in CDMA-exposed male rats, there was a response in the liver. The relationship between these responses and exposure to GSM or CDMA RFR was uncertain.
In the brain, there were incidences (not statistically significant) of malignant glioma in all groups of GSM male rats, in 6 W/kg CDMA male rats, and in 1.5 W/kg CDMA females, compared to no incidences in either the male or female sham control groups. There were also occurrences of glial cell hyperplasia in the brain of GSM and CDMA male rats and CDMA female rats that were not observed in sham control animals.
In the pituitary gland (pars distalis) of male rats, there were increased (not statistically significant) incidences of adenoma in all GSM-exposed groups and significantly increased incidences in 3 W/kg CDMA males compared to the sham controls.
There were significantly increased incidences of benign, malignant or complex pheochromocytoma (combined) in the adrenal medulla of the 1.5 and 3 W/kg GSM male rats and 1.5 W/kg CDMA female rats. In GSM female rats, there were increased incidences of hyperplasia in the adrenal medulla at 6 W/kg.
There were increased incidences (not statistically significant) of prostate gland adenoma in 3 W/kg rats, and a single incidence of prostate gland carcinoma in the same group. The incidence and severity of prostate epithelial hyperplasia was slightly higher in all exposed groups of GSM male rats. An exposure-related increase in the incidence of prostate gland epithelial hyperplasia was also observed in CDMA male rats.
There were increased incidences (not statistically significant) of benign granular cell tumor in the brain of all exposed groups of GSM male rats compared to the sham controls, and a single incidence of malignant granular cell tumor in the 3 W/kg GSM group.
There was a significantly increased incidence of adenoma or carcinoma (combined) in pancreatic islets in 1.5 W/kg GSM male rats.
In CDMA male rats, there were incidences of hepatocellular adenoma in all exposed groups, and one incidence of carcinoma each in the 3 and 6 W/kg groups. These neoplasms were not statistically significant, but were not observed in the sham control group.
A few nonneoplastic lesions that were not associated with any of the neoplastic responses were also observed. There were increased incidences of thyroid gland C-cell hyperplasia in all groups of GSM-exposed female rats.
Genetic Toxicology
As part of the 14-week interim evaluation, samples of frontal cortex, hippocampus, cerebellum, liver, and blood leukocytes were evaluated for DNA damage using the comet assay (two sexes, two cell phone RFR modulations, and five tissues per animal). Samples of peripheral blood were also evaluated for chromosome damage in the micronucleus assay. Results are based on the 100-cell scoring approach that was standard at the time of the studies; data obtained using a second, 150-cell scoring approach recommended in a recently adopted international guideline for the in vivo comet assay, are noted for the few instances where results differed between the two methods. A significant increase in DNA damage (% tail DNA) was observed in hippocampus cells of male rats exposed to the CDMA modulation. Although the levels of DNA damage in hippocampus cells were also increased in an exposure-related fashion using the 150-cell scoring approach, the increases were not statistically significant. An exposure-related increase in DNA damage seen in the cells of the frontal cortex of male rats exposed to the CDMA modulation was judged to be equivocal based on a significant trend test. Although results from scoring 100 cells were negative for male rat blood leukocytes exposed to either CDMA or GSM modulations, the results (both CDMA and GSM) were judged to be equivocal when evaluated using the 150-cell scoring method. No statistically significant increases in DNA damage were observed in any of the female rat samples scored with the 100-cell approach; with the 150-cell approach, results in peripheral blood leukocytes of female rats (CDMA) were judged to be equivocal.
No significant increases in micronucleated red blood cells or changes in the percentage of immature erythrocytes among total erythrocytes were observed in peripheral blood of rats of either sex exposed to either modulation of cell phone RFR.
Conclusions
Under the conditions of this 2-year whole-body exposure study, there was some evidence of carcinogenic activity of GSM-modulated cell phone RFR at 900 MHz in male Hsd:Sprague Dawley SD rats based on the incidences of malignant schwannoma in the heart. The incidences of adenoma or carcinoma (combined) in the prostate gland, malignant glioma and benign or malignant granular cell tumors in the brain, adenoma of the pars distalis in the pituitary gland, pheochromocytoma (benign, malignant, or complex combined) in the adrenal medulla, and pancreatic islet cell adenoma or carcinoma (combined) may have been related to cell phone RFR exposure. There was no evidence of carcinogenic activity of GSM-modulated cell phone RFR at 900 MHz in female Hsd:Sprague Dawley SD rats administered 1.5, 3, or 6 W/kg. There was some evidence of carcinogenic activity of CDMA modulated cell phone RFR at 900 MHz in male Hsd:Sprague Dawley SD rats based on the incidences of malignant schwannoma in the heart. The incidences of malignant glioma in the brain, adenoma of the pars distalis in the pituitary gland, and adenoma or carcinoma (combined) of the liver may have been related to cell phone RFR exposure. There was equivocal evidence of carcinogenic activity of CDMA-modulated cell phone RFR at 900 MHz in female Hsd:Sprague Dawley SD rats based on the incidences of malignant glioma in the brain and pheochromocytoma (benign, malignant, or complex combined) in the adrenal medulla.
Increases in nonneoplastic lesions in the heart, brain, and prostate gland of male rats, and of the heart, thyroid gland, and adrenal gland in female rats occurred with exposures to GSM cell phone RFR at 900 MHz. Increases in nonneoplastic lesions of the heart, brain, and prostate gland occurred in males, and of the brain in females exposed to CDMA cell phone RFR at 900 MHz.