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Ethylmercury vs. Methylmercury in Mass Poisonings

The revolutionary conclusions of the new CDC study actually reflect decades of work by mainstream independent scientists outside the agency. A rich scientific literature that emerged from accidental poisoning events has consistently documented—despite CDC's official claims—that ethylmercury and methylmercury are equally toxic. In addition to the well-known Minamata and Iraq methylmercury-poisoning, many other large-scale food poisonings have occurred involving ethylmercury fungicides in Iraq in 1956 and 1960, in Pakistan in 1961, and in Russia in the 1960s as well. These episodes resulted in maladies ranging from basic tissue injury to heart and brain injury and even death.

Derban reported in 1974 on 144 cases of mercury poisoning from the use of ethylmercury fungicide on a southern Ghana state farm. Multiple other studies based on these poisoning events showed, as stated in a 1977 study by David Fagan, that the long-term neurological consequences produced by the "ingestion of either methyl or ethyl mercury-based fungicides are indistinguishable."

A 1979 case report concerned a fifteen-year-old boy who had eaten the meat of a pig that had fed on ethylmercury fungicide−treated seed. Documented effects on the boy included debilitating brain damage and loss of coordination, with high toxicity for the brain as well as the spinal motor neurons, peripheral nerves, skeletal muscles, and heart muscle. The boy died about one month after becoming ill.

Ethylmercury's use as pesticide was eventually banned in many countries, including the United States and those in the European Union, and for good reason: A 1977 study gauged ethylmercury chloride's relative toxicity as a pesticide as the fifth most toxic of thirty substances tested, with a score of 12.7. That grade score almost matched that of DDT, at 14.2, an infamous pesticide banned in 1972.

In 1977 Fagan reported on 13 children suffering from exomphalos (a rare abdominal wall defect that allows the intestines to protrude from the abdomen) treated with gauze soaked applications of thimerosal to prevent infection. Of thirteen patients treated with thimerosal, 9 died. The authors tested mercury levels in the tissue of 8 of the children who died. They reported that "blood and tissue levels of mercury well above the threshold at which damage occurs in all other age groups, it is extremely unlikely that these infants escape neurological damage, which may be subtle." One infant exposed to thimerosal and survived was later reported as being "restless, easily distracted, and not interested in schoolwork." The authors recommended that "organic mercurial antiseptics should be heavily restricted or withdrawn from hospital use, as the fact that mercury readily penetrates intact membranes and is highly toxic seems to have been forgotten."

Why Does the US EPA only Provide Guidelines for Exposure to Methylmercury and not Ethylmercury?

In 1995, based on research from outbreaks of poisonings and other research from the Faroe Islands and the Seychelles, the EPA established a safe "reference dose" for methyl mercury (RfD). An RfD is defined as "an estimate of a daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of adverse effects when experienced during a lifetime," according to the EPA.

The EPA adopted for methylmercury an RfD of 0.1 microgram of mercury per kilogram of the individual's body weight per day. Other health agencies set their own recommended limits for methylmercury exposure, including the FDA in 1979, the World Health Organization in 1989 and the US Agency for Toxic Substances and Disease Registry (ATSDR) in 1999. The highest of these limits was the WHO's, at 0.47 microgram per kilogram of body weight per day.

In 1999 the US Congress directed the EPA to contract with the nonprofit, independent National Research Council (NRC) to prepare recommendations on an updated and appropriate RfD. The EPA commissioned the National Academy of Sciences (NAS) and the NRC to carry out a study on toxicological effects of methylmercury compounds. The goal was to review the process used by the EPA to establish national safety standards. The committee evaluated the literature, which demonstrated methylmercury compounds' high toxicity to brain tissue, even at minute levels. The NAS ultimately agreed with the EPA's originally conceived RfD, which remains in place today. An RfD has never been established for ethylmercury.

The CDC has crossed ethical and perhaps even legal boundaries by purposefully blocking efforts by the National Institute of Environmental Health Science's (NIEHS) National Toxicology Program (NTP) to test ethylmercury for toxicity – a process that would have lead to maximum exposure guidelines. In 2000, the FDA nominated thimerosal to the NTP for toxicity testing. However, CDC officials derailed the review telling the NTP committee that "There is a great concern within CDC about continued attacks from anti-vaccine groups questioning the integrity of CDC activities and recommendations regarding the use of thimerosal-containing vaccine." In response to CDC pressure, the NTP put thimerosal on permanent deferred status. Thimerosal has, therefore, never been tested for safety or toxicity.

Ethyl Mercury Exposure Levels Based on Methyl Mercury Guidelines

A single Thimerosal-preserved flu vaccine contains 25 micrograms of ethylmercury. If the EPA RfD for ingested methylmercury is applied to this injected ethylmercury figure, an individual would have to weigh more than 250 kilograms (551 pounds) for the 25 microgram exposure to be considered safe. Back in the 1990s, a two-month-old child could have received 62.5 micrograms from three vaccines in a single doctor's visit. Assuming the child weighed about 5 kilograms (11 pounds), he or she would have received 125 times the EPA RfD for methylmercury.

At least one study has suggested that the methylmercury RfD should be set lower for infants and also for fetuses. In 1995, Steven Gilbert and Kimberly Grant-Webster wrote: "Available information on the developmental neurotoxic effects of MeHg [methylmercury], particularly the neurobehavioral effects, indicates that the fetus and infant are more sensitive to adverse effects of MeHg. It is therefore recommended that pregnant women and women of childbearing age be strongly advised to limit their exposure to potential sources of MeHg. Based on results from human and animal studies on the developmental neurotoxic effects of methylmercury, the accepted reference dose should be lowered to 0.025 to 0.06 MeHg [microgram]/kg/day."

What might this mean for a fetus today? We'll take the low end of that estimate and apply it to an average 1.15-kilogram (2.54-pound) fetus at the start of the third trimester. A fetus exposed to 25 micrograms of mercury via a Thimerosal-preserved flu shot administered to its pregnant mother could be subject to 870 times the proposed lower reference dose.

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