Dougherty, WJ; Coulston, F; Golberg, L
An evaluation of the toxic and possible teratogenic effects of methylmercury chloride (MMC) was carried out in 40 mature pregnant rhesus monkeys (M. mulatta). Following diagnosis of pregnancy, the monkeys were assigned either to the control group or to 1 of the test groups receiving MMC in doses of 0.05, 0.16 or 0.5 mg Hg/kg. The MMC (K & K Laboratories, Plainview, N.J., Lot No. 98443), dissolved in 5.0 mM Na2CO3, was administered by stomach tube daily from day 20 through day 38 of pregnancy; the controls received the Na2CO3 solution. All animals were observed daily for indications of toxicity, predominantly those ascribable to methylmercury poisoning, i.e., loss of weight and reduced spontaneous activity followed by signs of progressive ataxia. Monkeys developing these signs became moribund and were killed. An autopsy was performed on all animals that died or were killed, including fetuses, as well as two infants from each group and examined histopathologically, total Hg being measured in blood and selected organs. Of the 10 control monkeys, 9 delivered live offspring and 1 aborted. (The spontaneous abortion rate among untreated females in our colony is approximately 12%). Of the 9 monkeys receiving 0.05 mg/kg MMC, there were 7 live births and 2 abortions, no adult deaths and no apparent effect of MMC. In 10 monkeys given 0.16 mg/kg, there were 7 live births and 1 abortion in a female exhibiting no sign of toxicity; 2 additional monkeys aborted after the appearance of MMC intoxication. Nine of 11 monkeys given 0.5 mg/kg MMC aborted subsequent to the development of MMC toxicity. One monkey aborted and died without showing evidence of MMC poisoning. Four fetuses were recovered from this group. In affected groups, the time of first appearance of toxic manifestations varied from day 35 to day 95 of gestation. Malformations were not observed in any infant or fetus. Infants still living appear clinically normal and are being evaluated for possible behavioral decrement. (Supported by Research Grant 2P0I-ES00226-07 from the National Institute of Environmental Health Sciences, NIH, by National Institutes of Health Training Grant 2T0I-ES00103-07, and by the New York State Department of Health.)