Pregnancy mercury exposure during

Human pharmacokinetic studies indicate that methylmercury has a half-life in blood and the whole body of about 50 days (CDC 2005). Hair grows at about 1 cm/month with a delay of around 20 days between current blood concentration and appearance of mercury in hair (Myers et al. 2003). Thus, postnatal maternal hair can be analyzed sequentially to evaluate timing of methylmercury exposure during pregnancy. However, the potential that this affords to document critical periods of prenatal methylmercury exposure has yet to be realized. 

Analyses of methyl mercury in scalp hair can be used to make a retrospective estimation of maternal exposure during pregnancy. It has been found that children born to mothers, whose hair mercury concentrations ranged between 70 and 640 pg Hg/ g, show a considerably higher prevalence of developmental changes than controls. Scalp hair levels exceeding 6 pg/ g are considered elevated and should be confirmed by a 24-hour urine collection. 

In critical periods of development before they are born, and in the early months after birth, children and fetuses are particularly sensitive to the harmful effects of metallic mercury and methylmercury on the nervous system. Harmful developmental effects may occur when a pregnant woman is exposed to metallic mercury and some of the mercury is transferred into her developing child. Thus, women who are normally exposed to mercury vapors in the workplace (such as those working in thermometer/barometer or fluorescent light manufacturing or the chlor-alkali industry) should take measures to avoid mercury vapor exposures during pregnancy. Exposures to mercury vapors are relatively rare outside of the workplace, unless metallic mercury is present in the home. 

Myers et al. (1997) evaluated the population of the SCDS for developmental milestones similar to those determined in Iraq. As part of this ongoing study, cohort children were evaluated at 6.5, 19, 29, and 66 months of age. At 19 months care-givers 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 growth during the pregnancy. 

Girard M, Dumont C. 1995. Exposure of James Bay Cree to methylmercury during pregnancy for the years 1983-91. In Porcella DB, Wheatley B, eds. Mercury as a global pollutant. Proceedings of the Third International Conference Whistler, British Columbia, July 10-14, 1994. Boston, MA Kluwer Academic Publishers, 13-19. 

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