Recent experimental data on Extremely Low Frequency (ELF) magnetic field carcinogenic risk: open questions.

The NTP experimental studies on Extremely Low Frequency (ELF) magnetic fields (two-year studies in rats and mice and magnetic field promotion/DMBA initiation in female rats studies, NTP 1999) are of main interest because of the value and completeness of the information produced on neoplastic and non-neoplastic effects. Ajoint evaluation of the two-year study data indicates a thyroid C-cell focal hyperplasia increase in female rats at the same exposures at which the neoplasm increment of the same cells has been observed only in male rats (on which the "equivocal evidence" NTP classification is based). The significant exposure-related trichoepithelioma and trichoepithelioma plus other skin neoplasms reported for male rats in the two year studies finds some support in the female rat data relative to trichoepithelioma reported in incidence summary of the NTP 26-week initiation/promotion study, even if the experimental designs of the two studies are different. An indication of exposure-related increase of single mammary carcinomas emerges from the summary of neoplasm incidence, together with a dose-related decrease of mammary gland multiple carcinomas. A significant decrease of lung alveolar/bronchiolar adenoma incidence was observed in exposed groups in both mouse genders. It seems improbable to attribute the above effects only to chance. The present debate, dividing science in two opposite fields: one of them denying any appreciable carcinogenic effect of magnetic fields, and the other one hypothesising their dramatic effects, are presently devoid of reliable and exhaustive scientific support, which could only be provided by further research.