Methylmercury poisoning in the Iraqi suckling infant: a longitudinal study over five years.

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.