Placenta mercury

Ilback NG, Sundberg J, Oskarsson A. 1991. Methyl mercury exposure via placenta and milk impahs natural killer (NK) cell function in newborn rats. Toxicol Left 58 149-158. 

Roels HA, Hubermont G, Buchet J-P, et al. 1978. Placental transfer of lead, mercury, cadmium, and carbon monoxide in women III. Factors influencing the accumulation of heavy metals in the placenta and the relationship between metal concentration in the placenta and in maternal and cord blood. 

Mercuric salts weakly penetrate the placenta barrier however, they can accumulate in placenta [26-29], foetal membranes and amniotic fluid [30], In mice, mercuric chloride (1.5 mg per kg) injected on day 14 of gestation resulted in 0.14% of the injected mercury being transferred to foetal tissues 4 days later [27],... 

Elemental mercury in the form of mercury vapor is readily and rapidly absorbed into the bloodstream when inhaled and easily crosses the blood-brain barrier and the placenta. Oral ingestion of elemental mercury is far less hazardous than inhalation of mercury vapor due to its poor absorption in the gut. Acute, high level exposure to mercury vapor can result in respiratory, cardiovascular, neurological, and gastrointestinal effects, and even death. 

Mercury accumulates in the muscle of the fish, which makes it all but impossible to avoid consumption of the methyl mercury. Methyl mercury is readily absorbed from the intestine and crosses the blood-brain barrier and the placenta. 

Genetic and Neonatal Toxicity. The ability of heavy metals readily to cross the placenta and disrupt nucleic acids coupled with the high sensitivity of the fetus and neonate increases the potential dangers of congenital and neonatal toxicity. In mammalian leukocyte cultures, chromosomal aberrations have been reported with lead (112), arsenic (113), mercury (114), and methylmercury (115). Charbonneau, et al. (116) reported a lack of mutagenic effect for methylmercury. 

Biomethylation of Elements. The biomethylation of elements is carried out principally by microorganisms and is important in environmental toxicology, particularly in the case of heavy metals, because the methylated compounds are absorbed through the membranes of the gut, the blood-brain barrier, and the placenta more readily than are the inorganic forms. For example, inorganic mercury can be methylated first to monomethylmercury and subsequently, to dimethylmercury ... 

Creatures of the sea present a real conundrum for pregnant women. Fish is so good for you. We read it over and over again in the newspaper s science section. Unfortunately, it is also one of the most contaminated foods out there—the biggest source of exposure to mercury, which can cross the placenta and mess with fetal brain development. 

The regeneration of the activity of the enzyme by cobalt differs from the behaviour of an alkaline phosphatase isolated from human placenta.228 This enzyme is reported to be re-activated by replacement of the native zinc ion by either zinc, magnesium, or mercury. No other metal is active. 

Mercury contaminated foodstuffs and water supplies are a concern because of the extreme toxicity of the element and its compounds. Elemental mercury is used in the production of chlorine gas, and organomercury compounds formerly found use as pesticides and fungicides. Alkyl mercury compounds are of greatest concern since they do not degrade readily, and methyl mercury compounds concentrate in fish lipid tissue [9]. Pregnant women are at greatest risk since methyl mercury readily crosses the placenta, affecting the fetus [6]. 

Gastrointestinal absorption of mercuric chloride from food is less than 15% in mice and 7% in a study of human volunteers. In humans and other mammals, the kidneys are the primary targets where mercuric ions accumulate. Renal uptake and accumulation of mercury in vivo are rapid. As much as 50% of low dose of mercuric chloride (0.5pmolkg ) has been shown to be present in the kidney of rats within a few hours after exposure. Within the kidney it accumulates primarily in the cortex and outer stripe of outer medulla. Mercuric chloride does not readily cross the blood-brain barrier but will accumulate in the placenta. Urinary and fecal excretion of mercury is the principal means by which humans and other mammals eliminate the different forms of mercury from the body. Under most circumstances, a greater fraction of a dose of mercury is excreted in the feces than in the urine early after exposure to a nonne-phrotoxic dose of mercuric chloride. 

Inorganic salts of mercury do not readily cross the blood-brain barrier or the placenta. They are, therefore, ultimately less toxic to the central nervous system and the developing fetus than either absorbed metallic mercury or organic mercury compounds. Metallic mercury is more readily oxidized to... 

Absorbed metallic mercury crosses the placenta, and the fetal blood may concentrate mercury to levels 10 or more times the levels found in the maternal blood. Therefore, the developing fetal nervous system may be quite sensitive to maternal exposures to mercury vapors. 

Pitkin RM, Bahns JA, Filer LJ, et al. 1976. Mercury in human maternal and cord blood, placenta, and milk. Proceedings of the Society for Experimental Biology and Medicine 151 565-567. 

Soria ML, Sanz P, Martinez D, et al. 1992. Total mercury and methylmercury in hair maternal and umbilical blood and placenta from women in the Seville area. Bull Environ Contain Toxicol 48(4) 494-501. 

A variety of effects have been observed in animals treated with toxic doses, but some of these, such as renal damage and anorexia, have not been observed in humans exposed to high doses. The primary tissues of concern in humans are the nervous system and particularly the developing brain, and these have been the main reason for the wide range of epidemiologial studies. Methylmercury passes about ten times more readily through the placenta than other mercury compounds. The dermal absorption of methylmercury is similar to that of inorganic mercury salts. 

Organic mercury is the most readily absorbed (90-95% from the gastrointestinal tract), and after absorption distributes especially to the brain, particularly the posterior cortex. All the forms of mercury will cross the placenta and gain access to the foetus, although elemental mercury and organic mercury show greater uptake. The concentrations in certain foetal tissues, such as red blood cells, are greater than in maternal tissue. 

Schramel P, Hasse S and Ovcar-Pavlu J (1988) Selenium, cadmium, lead, and mercury concentrations in human breast milk, in placenta, maternal blood, and the blood of the newborn. Biol Trace Elem Res 15 111-124. 

Because of its hpophilicity, absorbed mercury vapor quickly crosses the blood-brain barrier in humans (Hursh et al. 1976, Aschner and Aschner 1990) and the placenta in animals (Clarkson etal. 1972, Vimy etal. 1997, Yoshida etal. 1989) and humans (Drasch et al. 1994, Yang et al. 1997). 

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