Preliminary dose-finding studies investigated the ability of various radiofrequency irradiation conditions and doses of 2-methoxyethanol to produce external malformations when administered on gestation day 13. Based on these preliminary studies, radiofrequency irradiation (sufficient to elevate rectal temperature to 42°C for 30 min) and 150 mg/kg 2-methoxyethanol administration were selected for the main study.
In the main study, pregnant rats were administered radiofrequency irradiation and distilled water gavage, 2-methoxyethanol gavage and sham exposure, radiofrequency exposure and 2-methoxyethanol gavage concurrently, or sham exposure and distilled water gavage. Pregnant animals were sacrificed on gestation day 20, and the offspring were examined for external malformations.
|Chamber||Forma scientific enviromental chamber maintained at 24°C and 50% humidity|
|Setup||rats were exposed without anesthesia in cylindrical plexiglas holders with 12 mm holes; each rat was oriented with its long axis parallel to the incident electric field|
|Sham exposure||A sham exposure was conducted.|
Combined exposures enhanced the adverse effects produced by either experimental agent alone. Mean fetal malformations/litter increased from 14% after 2-methoxyethanol and sham exposure and 30% after radiofrequency irradiation and water gavage, to 76% after the combined treatment. In addition to a significant increase in the frequency of malformations, the severity of malformations also was enhanced by the combination treatment.
The study provided evidence of synergism between radiofrequency irradiation and 2-methoxyethanol administration, but additional research will be required to characterize the extent of synergism between these two agents. Potential interactive effects between chemical and physical agents need to be studied to determine the extent to which such interactions should impact occupational exposure standards.