Methylmercury infant

Monkeys, Macaca fascicularis adults age 7-10 years Monkeys, Macaca fascicularis female adults Monkeys, Macaca spp. Exposed in utero maternal doses of 0, 50, 70, or 90 pg methylmercury/ kg BW daily resulted in blood mercury levels in treated infants of 1.0-2.5 mg/L offspring were conditioned and tested for ability to respond to a lit button for an apple juice reward and other tasks Daily dose of methylmercury chloride in apple juice for 150 days equivalent to daily doses of 0.0, 0.4, 4.0, or 50.0 pg methylmercury/kg BW Various... 

Pregnant or nursing women exposed to methylmercury through their diet or otherwise also expose their developing fetus or breast-fed infant to the chemical, since methylmercury passes through placental membranes and enters the fetal bloodstream, and also enters breast milk. This is particularly problematic since fetuses and infants (and toddlers) are more susceptible and sensitive to the neurotoxic properties of mercury than are adults. 

The second prospective study of in utero exposure to methylmercury was initiated in the Republic of Seychelles and enrolled about 800 mother-infant pairs (Myers et al., 1995). In contrast to the Faroe Islands study, the investigation in the Seychelles did not find evidence of methylmercury-related adverse effects on the neuro-behavioural development of children through nine years of age (Myers et al., 2003). In some instances, prenatal mercury exposure was actually associated with precocious behaviour, and important developmental milestones were reached more quickly in the most highly exposed subjects. 

Finally, lipid-soluble chemicals like the insecticide DDT, polychlorinated biphenyls, and methylmercury are excreted readily as dissolved chemicals into milk fat droplets. Lead is secreted into milk using the same transport system as calcium. Nursing mothers may therefore transfer environmental contaminants to their infants - not to the point, however, of negating the well-established benefits of breastfeeding. 

Methylmercury causes subtle to severe neurologic effects depending on dose and individual susceptibility. EPA considers methylmercury to have sufficient human and animal data to be classified as a developmental toxicant. Methylmercury accumulates in body tissue consequently, maternal exposure occurring prior to pregnancy can contribute to the overall maternal body burden and result in exposure to the developing fetus. In addition, infants may be exposed to methylmercury through breast milk. 

Methylmercury crosses the placental barrier. Pregnant women who have not displayed any signs of mercury toxicity have given birth to infants with birth defects. Some infants were mentally retarded some had palsy. 

Methylmercury is the form of mercury most commonly associated with a risk for developmental effects. Exposure can come from foods contaminated with mercury on the surface (for example, from seed grain treated with methylmercury to kill fungus) or from foods that contain toxic levels of methylmercury (as in some fish, wild game, and marine mammals). Mothers who are exposed to methylmercury and breast-feed their infant may also expose the child through the milk. The... 

Organic Mercury. Limited information was located regarding respiratory effects in humans after oral exposure to organic mercury. Two boys who died after eating meat from a hog that had eaten seed treated with ethylmercuric chloride developed bronchopneumonia and edematous alveolitis, and required artificial ventilation (Cinca et al. 1979). Bronchopneumonia was also identified as the cause of death in four adults and one infant who died as the result of methylmercury poisoning in Iraq during 1972 (Al-Saleem and the Clinical Committee on Mercury Poisoning 1976). It is unclear whether these respiratory effects were the result of direct effects on the respiratory system or were secondary to other effects. 

Methylmercury levels vary considerably between species and within species of fish (depending on water conditions and size), so there are wide ranges in estimates of the average exposure levels to mercury in the general population from consumption of fish. Some researchers estimate that the typical daily exposure to mercury is 0.49 g/day for infants (aged 6-11 months), 1.3 g/d for 2-year-old children,... 

The chronic oral MRL for methylmercury is based upon the Seychelles Child Development Study (SCDS), in which over 700 mother-infant pairs have, to date, been followed and tested from parturition through 66 months of age (Davidson et al. 1998). The SCDS was conducted as a double-blind study and... 

For the Swedish population in the study, Oskarsson et al. (1996) reports that there was an efficient transfer of inorganic mercury from blood to breast milk and that mercury from amalgam fillings was probably the main source of mercury in breast milk, while methylmercury levels in blood did not appear to be efficiently transferred to breast milk. Exposure of the infant to mercury in breast milk was calculated to range up to 0.3 g/kg/day of which approximately one-half was inorganic mercury. This exposure corresponds to approximately one-half the tolerable daily intake of total mercury for adults recommended by the World Health organization. The authors concluded that efforts should be made to decrease total mercury burden in women of reproductive age Oskarsson et al. (1996). 

Infants and developing fetuses may be exposed to methylmercury if their mothers consume certain methylmercury-contaminated fish, shellfish, or wildlife species from contaminated waters prior to their pregnancy, during their pregnancy, or while nursing. Older children also may be exposed to methylmercury by eating contaminated fish and wildlife species. Certain states, Native American tribes, and U.S. Territories have issued fish and wildlife advisories for mercury in fresh water, estuarine, and saltwater fish and in freshwater turtles (see Section 5.7). 

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