Mice of the parental generation (P1 mice) were randomly divided into an exposure and a control group. P1 mice in the exposure group were exposed to the magnetic field for 14 weeks, then mating was induced. Pregnancy with the first filial generation (F1 mice) as well as birth, lactation, weaning and development until the end of the experiment took place under exposure conditions. The same procedure was conducted with the control group but without exposure to the magnetic field. Only F1 mice were investigated.
F1 mice were divided into 4 groups: 1) exposure to the magnetic field for 14-15 weeks after birth (medium-term exposure, young adults; n=30), 2) control group for group 1 without exposure (n=30), 3) exposure to the magnetic field for 50-52 weeks after birth (chronic exposure, adults; n=20), 4) control group for group 3 without exposure (n=20).
|Chamber||standard macrolon cages with methacrylate plastic cover|
|Setup||set of Helmholtz coils oriented in east-west direction, each with a radius of 0.375 m and 220 turns of 1.2 mm copper wire; temperature was maintained at a daily mean of 22 ± 2°C|
|Sham exposure||A sham exposure was conducted.|
The relative risk for mice exposed to the magnetic field for 50-52 weeks (group 3) to develop a chronic leukemia was significantly increased compared to the control group.
Individual hematologic diagnosis revealed a significantly higher risk for proliferative disorders of leukocytes in 14- to 15-week-old exposed mice (group 1) compared to the control group. The incidence for chronic lymphocytic leukemia was significantly higher in exposed animals after 14-15 and 50-52 weeks compared to the respective control groups.
After 50-52 weeks of exposure, the mortality of exposed mice was 30% versus 0% in the control group. 67% of these dead mice showed malignant alterations associated with leukemia. The mean life span of surviving animals was significantly shorter in exposed animals compared to the control group.
The authors conclude that a chronic exposure of mice to a 50 Hz magnetic field could be related to the development of leukemia and that this result agrees with the results of numerous epidemiological studies.