Reproduction and growth following prenatal methylmercuric chloride exposure in mice

Reproductive effects of the environmental pollutant methylmercuric chloride administered as a single dose per os during pregnancy were studied both in treated mice (G0 generation) and in their prenatally exposed offspring (G1). Treatment at 9.5 days postfertilization caused no observed effects at doses as high as 12-18 mg Hg+/kg. In contrast, treatment at 12.5 and 15.5 days produced toxicity; results were similar and were combined for analysis. Among G0 mice, the percentage capable of delivering one or more viable pups showed an estimated threshold level response at 8.0 mg/kg. The percentage of G1 pups that were viable at 1 day post partum was significantly dose-related, with an approximate threshold exposure level of 4.3 mg/kg. Among the surviving G1 offspring, body weight in adulthood (8 months) showed a statistically significant reduction that was also dose-related. Fertility testing of G1 offspring revealed no treatment effects on mating behavior judged by time interval between pairing and parturition. However, there was a trend (statistically nonsignificant) toward a dose effect on sizes of females' litters. Sterility (inability to produce offspring) did not occur either among G1 males at 4 months of age (N = 30; dose 8-12 mg/kg) or among females up to the advanced reproductive age of 14 months (N = 29; dose 5.3-12 mg/kg). We conclude that mice exposed prenatally to methylmercuric chloride revealed no greater susceptibility to sterility than to perinatal mortality.