No abstract

In a five-year longitudinal study of mothers and infants exposed to methylmercury during the Iraq epidemic of 1972, the frequencies of signs and symptoms exhibited by the mothers were typical of methylmercury poisoning. When blood concentrations of mercury are corrected to 1 March 1972, mothers with the most severe signs and symptoms had an average blood mercury concentration significantly higher (p less than 0.01) than either the milder or asymptomatic groups. Analytical data indicate that the predominant route of exposure for the infant was through breast milk in which approximately 60% of total mercury was determined, by cold vapor atomic absorption, to be organic mercury. Abnormal neurological signs in these infants became more obvious with time: hyperreflexia was observed in 8 of 22 infants at first examination, and in 17 of 22 at second examination. Delayed motor development became evident at the second and third examinations. The frequency of pathological reflexes and delayed motor developmental milestones was so high as to be considered significant even in the absence of a controlled study. There was no increase in mortality as compared to a control group.

A disastrous epidemic of methylmercury poisoning occurred in rural Iraq early in 1972, due to the ingestion of home-made bread prepared from wheat treated with a methylmercury fungicide. We report the clinical and laboratory evaluation of 15 infant-mother pairs exposed to methylmercury during pregnancy, including mercury determinations in blood samples of mothers and infants, and in milk samples from mothers, during the first seven months following the epidemic. In all cases except one, the infants' blood mercury levels were higher than their mothers' during the first four months after birth. Our results indicate that methylmercury passes readily from mother to fetus and that neonatal blood mercury levels are maintained through ingestion of mercury in mothers' milk. Clinical manifestations of methylmercury poisoning were evident in six of 15 mothers and in at least six of 15 infants. In five severely affected infants there was gross impairment of motor and mental development. However, in only one infant-mother pair was the infant affected and the mother free of signs and symptoms–a marked contrast to the reports of Japanese mother-infant pairs from Minamata. Careful follow-up studies of these and other Iraqi infants will determined where signs and symptoms of methylmercury poisoning will appear as these children continue to develop. Studies of these and additional infant-mother pairs may allow determination of the prenatal period of greatest fetal sensitivity to methylmercury poisoning.