Experimental studies of brain tumour development during exposure to continuous and pulsed 915 MHz radiofrequency radiation

• It has been suggested that electromagnetic fields (EMFs) act as a promoter late in the carcinogenesis process. To date, however, noconvincing laboratory evidence has been obtained indicating that EMFs cause tumour promotion at non-thermal exposure levels. The effects of EMF exposure in a rat brain glioma model were investigated. The exposure consisted of 915 MHz microwaves, both as continuous waves (1 W), and modulated with 4, 8, 16 and 200 Hz in 0.5 ms pulses and 50 Hz in 6 ms pulses (2 W per pulse). Fischer 344 rats of both sexes, weighing 150-250 g, were used in the experiments. 5000 RG2 cells in 5 μ1 nutrient solution were injected by the stereotaxic technique into the head of the right caudate nucleus in 37 experimental rats and 37 matched controls. The exposed animals were kept unanaesthetized in well ventilated transverse electromagnetic (TEM) cells producing 915 MHz continuous or modulated microwaves. Exposure was started on day five after inoculation. The animals were exposed for 7 hd d-1 for 5 d per week during two to three weeks. The controls were kept in an identical TEM cell without EMF exposure. All brains were examined histopathologically and the tumour size was determined. Our study does not show a significant difference in tumour size between animals exposed to 915 MHz microwaves, and those not exposed. Our preliminary results do not support that even an extensive daily exposure to EMF promotes tumour growth when given from the fifth day after the start of tumour growth in the rat brain until the death of the animal which by then has a large brain tumour. Further studies with higher specific absorption rate levels are in progress.

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