the combined field exposure. Developmental delays did not result in abnormal development or decreases in survival through hatching.
The chicken embryo has been used to study potential effects of electric fields. Blackman et al. (1988a,b) studied brain tissue from embryos in chicken eggs exposed to 50- or 60-Hz fields at 10 V/m rms. The associated magnetic field was less than 70 nT (1 nT = 10-9 T) rms. Brain tissue was removed 1.5 days after hatching. The tissue was placed in a physiologic salt solution containing radioactive calcium and then placed in the same solution with no radioactive calcium and exposed to 50- or 60-Hz fields at 15.9 V/m rms and 73 nT rms for 20 min. The calcium efflux from the brain tissue of chicks exposed as embryos to 60-Hz fields was affected (see the description and analysis of these experiments in Chapter 3). The same phenomenon was not observed with embryos exposed to 50-Hz fields. Three replicates of the Blackman study by other laboratories have not produced consistent results.
Male and female mice were exposed to either horizontal or vertical electric fields in two studies by Marino et al. (1976, 1980). In the first study, mice were exposed to electric fields at 10 and 15 kV/m that led to effects attributed by the authors to microshocks. The second study involved three generations of mice. Although the postnatal-weight gains were similar in exposed and unexposed mice, a higher mortality was observed in the exposed mice. This is the only report of that phenomenon, and the results have not been supported by data from studies conducted at other laboratories.
Unlike the work of Marino and co-workers, Fam (1980) was unable to identify an exposure-related change in mortality of the progeny of mice exposed to 60-Hz electric fields at 240 kV/m. In this study, mice were exposed throughout gestation, the offspring were bred, and their litters were monitored for growth, blood histologic and biochemical changes, and histologic changes of major organs. In agreement with the results of Marino et al. (1980) except those on mortality, no changes were observed in growth or in any of the other measurements as a result of exposure.
Kowalczuk and Saunders (1990) were unable to detect any exposure-related dominant lethal mutations in male mice exposed to 50-Hz electric fields at 20 kV/m. Males were exposed for 2 weeks before breeding, and no exposure-related effects in offspring were detected in in utero death, litter size, or viability of offspring. Females were not exposed.