Bo Holmberg

MAGNETIC FIELDS AND CANCER : ANIMAL AND CELLULAR EVIDENCE : AN OVERVIEW

A few animal studies on the possible carcinogenic effect of magnetic fields have been published. They have been designed to reveal a possible tumor promotion obtained by applying continuous or pulsed alternating fields at flux densities varying between 0.5 microT and 30 mT on mice or rats initiated with different initiators. One study with 2 mT applied on DMBA-initiated mice may suggest a copromotive effect together with the promoter TPA. Another study on rats suggests an inhibitory effect by a magnetic field on rat liver foci formation, induced with DENA. Cell studies show that magnetic fields at some frequencies, amplitudes, and wave forms interact with biological systems. Thus effects have been seen, e.g., on enzymes related to growth regulation, on calcium balance in the cell, on gene expression, and on pineal metabolism and its excretion of the oncostatic melatonin. Cellular and physiologic studies thus suggest effects that may be related to cell multiplication and tumor promotion.

Consensus Report: Mutagenicity and Carcinogenicity of Car Exhausts and Coal Combustion Emissions

Car exhausts and coal combustion emissions may cause a spectrum of health effects, varying from annoyance reactions, to bronchitis, to cancer in the respiratory organs and possibly also other organs. Deaths in cardiovascular diseases in particularly sensitive individuals have furthermore, under certain circumstances, been associated with ambient air pollution. The objective of the meeting was to examine the relevance of short-term and long-term biological tests for mutagenicity and carcinogenicity to the assessment of human carcinogenic risk that may arise from exposure to air pollution from motor vehicle exhausts and coal combustion products. (135 refs.)

Three industrial solvents investigated for tumor promoting activity in the rat liver

Dioxane, perchloroethylene, and trichloroethylene were investigated as rat liver altered foci promoters in an initiation/promotion protocol. Animals were initiated with diethylnitrosamine, 30 mg/kg, injected i.p. 24 h after 2/3 partial hepatectomy. The chemical under study was administered by gavage once a day, 5 times a week for 7 weeks. Ten days after the last administration the animals were killed. Liver sections were stained for gamma-glutamyl-transpeptidase (GGT) and the number and total volume of GGT-positive foci was studied. Dioxane (1000 mg/kg) significantly increased the number and total volume of foci while a marginal effect was noted for the high dose of trichloroethylene (1100 mg/kg). A high dose of perchloroethylene (1100 mg/kg) had no effect.

Mammary tumours in Sprague-Dawley rats after initiation with DMBA followed by exposure to 50 Hz electromagnetic fields in a promotional scheme.

In order to test whether a transient-producing intermittent magnetic field (MF) acts as a promoter in rat mammary tumour development, a study of a 50 Hz sinusoidal MF with flux densities of 0.25 and 0.5 mT was performed on female Sprague-Dawley rats. A single administration of 7 mg of 7,12-dimethyl-benz[a]anthracene (DMBA) was given by gavage to 52-day-old animals. After 1 week, exposure to an intermittent (15 s on/15 s off) transient-associated magnetic field was started. MF exposure was performed for 19 or 21 h per day up to 25 weeks, when the study was terminated. Twice a week a careful examination with palpation for tumours was done. Tumour incidence, the number of tumours per animal, tumour volume and tumour weight were recorded. A total of 70% of MF-exposed animals developed tumours. For animals exposed to DMBA alone the correspondent figure was 71.7%. No statistical differences were seen either for tumour-bearing animals or for the total number of tumours. A slightly larger total tumour weight and tumour volume was seen for animals exposed to 0.25 mT MF. These differences were not statistically significant.

The effects of long-term oral administration of ethanol on Sprague-Dawley rats — a condensed report

For a period of 2 years Sprague-Dawley rats received 3% and 1% ethyl alcohol or an equicaloric amount of glucose in a semisynthetic liquid diet. Thereafter the tumour incidence was recorded. For male rats no neoplastic lesions were observed to be related to ethanol exposure. For females, when individual group comparisons were made, an increase in mammary gland tumours was seen for females receiving the low ethanol containing diet. In some tumour frequency comparisons the opposite, namely a decrease in the rate of incidence, was obtained. The overall information seems to indicate the absence of a carcinogenic activity of ethyl alcohol per se after long-term oral administration. Liver and bile duct injury was seen among males. Inflammatory reactions were seen among males in pancreas and for females in the clitoral gland. Hyperplasia was observed in the thyroid gland in both sexes and in the adrenal glands among females. Peripheral nerve degeneration was common in both sexes.

Magnetic fields and cancer development in animal models

Several laboratory animal studies have been up to July 1993 published with the aim to investigate possible carcinogenic or cocarcinogenic effects of magnetic fields. No large-scale study of complete carcinogenicity, considering tumor as an endpoint, has been performed. Nor has any study on tumor initiation only been performed. In studies designed for tumor promotion, small parallel series for complete carcinogenicity have also been included in some experiments. These small series do not permit an evaluation of the possible complete carcinogenicity or noncarcinogenicity of magnetic fields. Studies designed to illuminate the possibility of a tumor-promotive effect of magnetic fields seem not to support the hypothesis that continuous magnetic fields act as promoters in rats or mice. Observations on skin tumors in mice seem to indicate a possible copromotional effect of a 2-mT 60-Hz magnetic field and a simultaneous treatment with a known skin tumor promoter in the sensitive Sencar mouse strain.