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Mercury, a potent toxic metal that targets the developing brain and nervous system, is challenging lead as the number one environmental health threat to American children. According to the EPA's top mercury scientist, one out of every six children born in the United States is exposed to levels of methyl mercury during pregnancy that exceed what the Agency considers safe (Mahaffey 2004). The principal source of high fetal methyl mercury exposure is maternal consumption of contaminated seafood, primarily canned tuna. Pregnant women who eat significant quantities of large ocean-going fish could expose their babies to amounts of mercury that are well above the government's recommended safe levels.

In March, 2004, the Food and Drug Administration revised their mercury seafood advisory to include a specific warning about consumption of canned albacore tuna. Pregnant women and children are advised to eat no more than one six ounce can of albacore tuna per week. The advisory, however, provides no consumption advice for a number of fish where high mercury levels are a concern, including tuna steaks, sea bass, halibut, and many others. The Environmental Working Group has filed a legal challenge to the FDA mercury seafood advisory, charging that it is not based on the best available science on seafood contamination and mercury risk levels to the developing fetus.

But contaminated seafood is not the only source of mercury exposure for the developing fetus or infant. Mercury amalgam dental fillings are a potentially significant source of fetal mercury exposure, although precise amounts are not well characterized. And from 1988 through about 2002, children were exposed to significant doses of mercury from birth through six months of age in the form of a mercury-based preservative, thimerosal, used in routine childhood immunizations. Children born to Rh negative mothers were also exposed to mercury in-utero when their mothers received a mercury-containing RhoGAM shot. The flu shot is another source of fetal and infant mercury exposure. The health impact of mercury exposure through vaccinations has been the source of intense debate because of significant changes in the vaccination regimen from 1988 through 1991 that increased neonatal and infant exposure to mercury.

In 1988, the Centers for Disease Control (CDC) recommended important new additions to the nation's infant immunization program, including three Hepatitis B immunizations (one injected at birth), and three Haemophilis B shots—all delivered by six months of age. Drug companies responded with vaccinations supplied in multiple dose containers preserved with the mercury-based antibacterial thimerosal. Neither the CDC, nor the Food and Drug Administration (FDA), which monitors the safety of vaccinations, expressed concerns at that time about the relatively high doses of mercury that newborn babies and infants would be exposed to through these shots.

Drug companies were similarly silent on the matter, although internal company documents show that they were aware of the potent neurotoxic effects of mercury as early as the 1940s. Notably, the FDA banned the sale of topically applied thimerosal antibiotics in the 1980s due to severe, even crippling, adverse skin reactions in sensitive individuals.

The amount of mercury in the standard battery of childhood immunizations more than doubled between 1988 and 1991 when these additional shots were added to the early childhood vaccination regimen. Throughout the 1990s, children received nine mercury-containing vaccinations within their first six months of life, including the unprecedented injection of a mercury-containing vaccine at birth, and up to three shots given in a single day at 2-, 4-, and 6-months. The average two-month old baby vaccinated with thimerosal-containing shots in the 1990s received a single day dose of mercury that was between 100 and 125 times the government's long-term safe exposure level.

Drug companies used thimerosal as a vaccine preservative to allow multiple injections to be shipped and stored in single containers. Thimerosal is 49 percent ethyl mercury, a widely recognized and potent neurotoxin. After more than a decade of nationwide, high childhood exposures, it was removed from childhood vaccinations between 1999 and 2002, at the urging of the Public Health Service and the American Academy of Pediatrics, but is still present in most flu vaccines. California and Iowa have banned mercury-containing thimerosal from all vaccinations, and Missouri and Nebraska have legislation in progress.

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