Sublethal effect of a weak intermittent magnetic field on the development of Xenopus laevis (Daudin) tadpoles

In three repeated experiments with three different litters of Xenopus laevis (Daudin) tadpoles, three cohorts were reared in an aquarium under the "saw-tooth" magnetic field produced by a television set. Their maturation times are compared with those of three corresponding control cohorts grown in an unexposed aquarium. In the exposed aquarium, the magnetic field amplitude was less than 25 ?T and the frequency in the extremely-low- frequency and very-low-frequency wave-bands. Neither the exposed nor the unexposed cohorts suffered significant mortality and malformations. However, the exposed tadpoles took about 5 days more than the unexposed ones to reach metamorphosis. The differences in mean maturation times between the exposed and control cohorts were extremely significant (P < 0.001). The results show that a biological population can suffer a sublethal effect when exposed to the magnetic field of a TV set for a long time in the course of juvenile life stages, and that this effect can consist of a delay in reaching the adult stage.