Characterization of the Core Temperature Response of Free-Moving Rats to 1.95 GHz Electromagnetic Fields

Abstract

The present study investigated the core body temperature (CBT) response of free-moving adult male and female Sprague Dawley rats, during and following a 3-h exposure to 1.95 GHz radiofrequency electromagnetic fields (RF-EMFs) within custom-built reverberation chambers, using temperature capsules implanted within the intraperitoneal cavity and data transmitted via radiotelemetry. Comparing RF-EMF exposures (at Whole-Body Average-Specific Absorption Rate [WBA-SAR] levels of 0.1, 0.4, and 4 W/kg) to the sham exposed condition, we identified a statistically significant peak increase in CBT after 26 min of RF-EMF exposure at 4 W/kg (+0.49°C), but not in the 0.1 or 0.4 W/kg conditions at the same timepoint. In the last 30 min of the RF-EMF exposure, temperature was significantly increased in both the 4 W/kg (0.62°C) and 0.4 W/kg (0.14°C) conditions, but not 0.1 W/kg, when compared to sham. After 20 min following cessation of exposure, post temperature was still significantly higher in the 4 W/kg condition when compared to the sham (0.37°C), but not in either 0.1 or 0.4 W/kg. Based on our findings, it is apparent that rats can effectively compensate for increased thermal loads of up to 4 W/kg as the maximum temperature rise was substantially lower than 1°C. In addition, the elevated CBT during exposure in the 4 W/kg condition was significantly reduced immediately after exposure cessation, indicating that measures of CBT following RF-EMF exposure cessation may not reflect maximum RF-EMF-mediated changes in the CBT of rats. Bioelectromagnetics. 00:00-00, 2025. © 2025 Bioelectromagnetics Society.

Keywords: body temperature; radiofrequency electromagnetic fields; radiotelemetry; rat.

Figure 1

Bodyweight of rats of Batch 1 and Batch 2, data presented as mean ± SEM. There was a total of 24 rats used in this experiment. Batch 1 consisted of 8 male rats and 8 female rats, Batch 2 consisted of 4 male rats and 4 female rats for a total 12 male and 12 female rats.

Figure 2

Data analysis of temperature measurements. This is the average of both male rats (n = 11) and female rats (n = 12) combined. Baseline was determined as the last 10 min before the start of the RF‐EMF exposure. “InPeak” was the average of a 20‐min period that started 26 min after RF‐EMF exposure begun. “End” was the average of the last 30 min before the end of the 3‐h RF‐EMF exposure. “Post” was the average of a 20‐min period after the end of the RF‐EMF exposure.

Figure 3

Change in temperature (relative to baseline) in rat phantoms (n = 2) during and following exposure cessation from 3‐h exposure to 1.95 GHz RF‐EMF at 0 W/kg (sham), 0.1, 0.4, and 4 W/kg WBA‐SAR. RF‐EMF exposure starts at 0 min; shaded area indicates RF‐EMF exposure is ON. Relative to the sham, each of the RF‐EMF exposures resulted in significant temperature rises at last 30‐min interval of the exposure; 4 W/kg was the only strength to cause a significant decrease at the 30‐min interval immediately after exposure cessation.

Figure 4

Change in temperature from baseline in rats (11 males and 12 females averaged) during 3‐h exposure to 1.95 GHz RF‐EMF at 0 W/kg (sham), 0.1, 0.4, and 4 W/kg WBA‐SAR. Shaded areas indicated RF‐EMF exposure is ON; error bars represent ± standard error of the mean. Relative to the sham, only 4 W/kg significantly increased CBT after a 26‐min interval of exposure, both 0.4 and 4 W/kg caused a significant increase within the last 30‐min interval. In the 20 min following post cessation, only 4 W/kg significantly increased CBT when compared to sham.