Irradiation of rats by 918‐MHz microwaves at 2.5 mW/cm2: Delineating the dose‐response relationship

Eight male rats were exposed for 13 weeks to 918-MHz CW microwaves at an averaged power density of 2.5 mW/cm2. The rats were exposed ten hours every night for a total of 910 hours of irradiation. The exposure system consisted of (1) cylindrical waveguides that were capable of delivering guided, circularly polarized waves (TE11 mode); and (2) Plexiglas living chambers that provided standard laboratory conditions for the rodents. The waveguides allowed for easy quantification of incident and absorbed energy in each chamber independent of the number of rodents being simultaneously exposed. Daily measures of body mass and of intake of food and water revealed no significant differences between the eight irradiated and the eight sham-irradiated controls. Blood sampled after 4, 8, and 12 weeks showed no differences in most parameters of serum chemistry (e.g., calcium, sodium, potassium, chlorine, blood urea nitrogen, carbon dioxide, ion gap and glucose). During the 11th week, serial assessments were made of colonic temperature and behavioral repertoire but neither demonstrated a significant effect of the microwave exposures. Serum corticosterone levels sampled after 910 hours of radiation gave no indication of stress. Finally, neither one- nor two-bottle preference tests for a saccharin solution suggested the presence of radiation-related malaise. The significance of these results is discussed with respect to comparable exposures of rats to 10 mW/cm2, which do influence several of the assessed parameters.