Chronic toxicity oncogenicity evaluation of 60 Hz (power frequency) magnetic fields in F344/N rats

A 2-yr whole-body exposure study was conducted to evaluate the chronic toxi city and possible oncogenicity of 60 Hz (power frequency) magnetic fields i n rats. Groups of 100 male and 100 female F344/N rats were exposed continuo usly to pure, linearly polarized, transient-free 60 Hz magnetic fields at f lux densities of 0 Gauss (G) (sham control), 20 milligauss (mG), 2 G, and 1 0 G; an additional group of 100 male and 100 female F344/N rats received in termittent (1 hr on/1 hr off) exposure to 10 G fields. Mortality patterns, body weight,gains throughout the study, and the total incidence and number of malignant and benign tumors in all groups exposed to magnetic fields wer e similar to those found in sex-matched sham controls. Statistically signif icant increases in the combined incidence of C-cell adenomas and carcinomas of the thyroid were seen in male rats chronically exposed to 20 mG and 2 G magnetic fields. These increases were not seen in male rats exposed contin uously or intermittently to 10 G fields or in female rats at any magnetic f ield exposure level. No increases in the incidence of neoplasms, which have been identified in epidemiology studies as possible targets of magnetic fi eld action (leukemia, breast cancer, and brain cancer), were found in any g roup exposed to magnetic fields. There was a decrease in leukemia in male r ats exposed to 10 G intermittent fields. The occurrence of C-cell tumors at the 2 lower field intensities in male rats is interpreted as equivocal evi dence of carcinogenicity; data from female rats provides no evidence of car cinogenicity in that sex. These data, when considered as a whole, are inter preted as indicating that chronic exposure to pure linearly polarized 60 Hz magnetic fields has little or no effect on cancer development in the F344/ N rat.