Repeated exposure to nanosecond high power pulsed microwaves increases cancer incidence in rat

High-power microwaves are used to inhibit electronics of threatening military or civilian vehicles. This work aims to assess health hazards of high-power microwaves and helps define hazard threshold levels of modulated radiofrequency exposures such as those emitted by the first generations of mobile phones. Rats were exposed to the highest possible field levels, under single acute or repetitive exposures for eight weeks. Intense microwave electric fields at 1 MV/m of nanoseconds duration were applied from two sources at different carrier frequencies of 10 and 3.7 GHz. The repetition rate was 100 pps, and the duration of train pulses lasted from 10 s to twice 8 min. The effects were studied on the central nervous system, by labelling brain inflammation marker GFAP and by performing different behavioural tests: rotarod, T-maze, beam-walking, open-field, and avoidance test. Long-time survival was measured in animals repeatedly exposed, and anatomopathological analysis was performed on animals sacrificed at two years of life or at death if earlier. One group was sham exposed. Few effects were observed on behaviour. With acute exposure, an avoidance reflex was shown at very high, thermal level (22 W/kg); GFAP was increased some days after exposure. Most importantly, with repeated exposures, survival time was 4-month shorter in the exposed group, with eleven animals exhibiting a large sub-cutaneous tumour, compared to two in the sham group. A residual X-ray exposure was also present in the beam (0.8 Gy), which is not a bias for the observed result. High power microwaves below thermal level in average, can increase cancer incidence and decrease survival time in rats, without clear effects on behaviour. The parameters of this effect need to be explored further, and a more precise dosimetry to be performed.