EFFECTS OF PRENATAL METHYLMERCURY EXPOSURE FROM A HIGH FISH DIET ON DEVELOPMENTAL MILESTONES IN THE SEYCHELLES CHILD-DEVELOPMENT STUDY

Mercury is widespread in the environment and exists in several physica l and chemical forms. Prenatal exposure to methylmercury disrupts brai n development. The most common mode of prenatal methylmercury exposure is maternal fish consumption. Studies of human prenatal exposure in I raq following maternal ingestion of methylmercury treated grain sugges ted that maternal hair mercury concentrations above 10 ppm may be rela ted to delayed developmental milestones and neurological abnormalities . This level of exposure can be achieved by frequent consumption of fi sh. The Seychelles Child Development Study analyzed developmental mile stones similar to those determined in Iraq in a large controlled, pros pective study of children exposed prenatally to methylmercury when the ir mothers ate fish. As part of this ongoing study, cohort children we re evaluated at 6.5, 19, 29, and 66 months of age. At 19 months care-g ivers were asked at what age the child walked (n = 720 out of 738) and talked (n = 680). Prenatal mercury exposure was determined by atomic absorption analysis of maternal hair segments corresponding to hair gr owth during the pregnancy. The median mercury level in maternal hair w as 5.8 ppm with a range of 0.5 - 26.7 ppm. The mean age (in months) at walking was 10.7 (SD = 1.9) for females and 10.6 (SD = 2.0) for males . The mean age at talking (in months) was 10.5 (SD = 2.6) for females, and 11.0 (SD = 2.9) for males. After adjusting for covariates and sta tistical outliers, no association was found between the age at which S eychellois children walked or talked and prenatal exposure to mercury. Normal ages at achievement of the developmental milestones walking an d talking were found in Seychellois toddlers following prenatal exposu re to methylmercury from a maternal fish diet. These results do not su pport the lowest effect levels in young children following prenatal me thylmercury exposure predicted by the dose response analysis of the Ir aq data. More detailed studies in older children are needed to determi ne if there are adverse effects in fish eating populations. (C) 1997 I ntox Press, Inc.