Studies of possible genetic effects in bacteria of high frequency electromagnetic fields

Possible non-thermal mutagenic effects of high frequency electromagnetic fields on Salmonella typhimurium and Escherichia coli were investigated. Bacteria were exposed to the following fields: 27.12 MHz CW electric field, 27.12 MHz CW magnetic field, 2.45 GHz CW electromagnetic far field, and 3.07 GHz pulsed electromagnetic far field. The temperature of the treated sample as well as of the non-exposed control sample was kept constant at 37.0°C (temperature differences between exposed and control samples were less than ± 0.3°C). In eleven different strains of bacteria, forward, backmutation or prophage induction were measured. Exponentially growing bacteria in nutrient medium were exposed to microwaves (SAR 35–100 W/kg) and RF fields (SAR up to 4 W/kg) during 1–7 hours. The cellular growth was measured for all strains. A conspicuous stimulation of growth was observed, especially under certain treatment conditions and in certain bacterium strains. Possible temperature changes might explain only a minor part of this effect. The relative increase in bacterium count was most marked towards the end of exponential growth. Bacteria exhibited an increased metabolic rate during exposure, illustrated by an increased rate of RNA synthesis. The pooled mutation frequency (for all exposures and strains) did not differ from that of the controls. A weak prophage-inducing capacity and a certain ability to modify the response to UV-irradiation were noted, possibly indicating a mobilization of “SOS-functions”. The upper confidence limit of the accepted hypothesis of no mutagenic action corresponds to the response that, in the bacterium strains studied, is elicited by about 10 rad of γ-radiation. Applying the radiation-dose equivalent for risk estimation, and using a risk coefficient of 2·10-4 rad-1 for cancer death, the ratio of absorbed doses due to occupational exposure in Sweden (about 1010 J year-1) and in the present experiments (about 106 J kg-1) gives an estimated cancer risk of less than one case annually.