The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings may not have been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. For more information, see the Explanation of Levels of Evidence for Developmental Toxicity. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.
Four groups of 55 sperm-positive rats were exposed to 60 Hz magnetic fields, three groups to continuous field strengths of 0.02, 2, and 10 gauss, while a fourth group received intermittent exposure to 10 G (i.e., intermittent exposure was accomplished by turning the exposure fields on for one hour, then off for one hour, repeatedly). A fifth group of equal size received sham exposure. In addition, another group of 15 sperm-positive rats served as a positive control and received oral administration of ethylenethiourea. The rats were exposed to electromagnetic fields or sham treatment for 18.5 hours per day, 7 days per week on gestation days 6 through 19, for a total of thirteen 18.5 hour exposure periods within 14 consecutive days, while the positive controls received 85 mg/kg of ETU suspended in water on gestation days 11, 12 and 13.
The field strengths during exposure (i.e., when the fields were energized) for the low, medium, high intermittent and high continuous exposure levels averaged 0.020, 2.00, 9.93 and 9.89 gauss, respectively; average field strength in the sham control exposure room was 0.0004 gauss. When the fields were deenergized the levels were negligible and ranged from 0.0003 to 0.0009 gauss.
No deaths occurred during the study. No statistically significant differences in dam body, uterus or liver and kidney weights were evident between the EMF-exposed rats and the sham controls at any time during the study. However, a slight but statistically significant reduction in body weight gain between gestation days 15-12 was observed in the 10 G intermittent group. In addition, the positive control dams gained slightly less over gestation days 12-9. Cumulative body weight gain was also reduced in the 10 G intermittent group dams on gestation day 15 and in the positive control group dams on gestation days 12 and 15. Dams in these groups rebounded from this effect by gestation day 18. Food consumption was minimally and sporadically affected in the 2 and 10 G continuous groups and the positive control group during the study.
The percentage of males/litter was increased significantly in the 2 G exposure group. In addition, concomitant slight reductions in mean male and female fetal weights were observed in the 2 G exposed group. These changes were not considered to be biologically significant. No biologically significant difference in pup viability was detected in the EMF-exposed fetuses compared to sham controls. Gross external, visceral and skeletal examinations failed to show any biologically significant increase in the incidence of fetal malformations or anomalies in the EMF-exposed offspring, while 100% of the fetuses from dams treated with ETU were malformed and had significantly reduced fetal weights. Accordingly, exposure of pregnant rats to 60 Hz magnetic fields of 0.02, 2, 10 G continuous or 10 G intermittent during gestation days 6 through 19 did not produce any biologically relevant changes in the dam or fetus.