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Chronic Toxicity/Oncogenicity Evaluation of 60 Hz (Power Frequency) Magnetic Fields in F344/N Rats

National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, Boorman{at}niehs.nih.gov.

David L. McCormick

Illinois Institute of Toxicology Research Institute, Chicago, Illinois 60616-3799

John C. Findlay

Illinois Institute of Toxicology Research Institute, Chicago, Illinois 60616-3799

James R. Hailey

National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709

James R. Gauger

Illinois Institute of Toxicology Research Institute, Chicago, Illinois 60616-3799

Tim R. Johnson

Illinois Institute of Toxicology Research Institute, Chicago, Illinois 60616-3799

Robert M. Kovatch

Pathology Associates International, Frederick, Maryland 21701

Robert C. Sills

National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709

Joseph K. Haseman

National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709

A 2-yr whole-body exposure study was conducted to evaluate the chronic toxicity and possible oncogenicity of 60 Hz (power frequency) magnetic fields in rats. Groups of 100 male and 100 female F344/N rats were exposed continuously to pure, linearly polarized, transient-free 60 Hz magnetic fields at flux densities of 0 Gauss (G) (sham control), 20 milligauss (mG), 2 G, and 10 G; an additional group of 100 male and 100 female F344/N rats received intermittent (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 were similar to those found in sex-matched sham controls. Statistically significant 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 continuously or intermittently to 10 G fields or in female rats at any magnetic field exposure level. No increases in the incidence of neoplasms, which have been identified in epidemiology studies as possible targets of magnetic field action (leukemia, breast cancer, and brain cancer), were found in any group exposed to magnetic fields. There was a decrease in leukemia in male rats 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 evidence of carcinogenicity; data from female rats provides no evidence of carcinogenicity in that sex. These data, when considered as a whole, are interpreted 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.

Key Words: Rodent carcinogenicity studies • electromagnetic fields • extremely low frequency (ELF) • alternating fields • cancer • bioassay • thyroid C-cell tumors

Toxicologic Pathology, Vol. 27, No. 3, 267-278 (1999)
DOI: 10.1177/019262339902700301


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