Young Children Rapidly Excrete Vaccine Mercury

Blood half-life of parenteral ethyl mercury is shorter than that of oral methyl mercury; may be less toxic

THURSDAY, Jan. 31 (HealthDay News) -- A recent prospective observational study of mercury concentration in blood, urine and stool of neonates and infants recently vaccinated with thimerosal-containing vaccines showed that ethyl mercury had a short half-life in these children and was primarily excreted rapidly in feces. This differs from oral methyl mercury from fish, which has a longer half-life in humans and toxicity at low concentrations, researchers report in the February issue of Pediatrics.

Michael E. Pichichero, M.D., and colleagues at the University of Rochester in Rochester, N.Y., took blood, stool and urine samples both before and after normally administered childhood vaccinations, from three groups of 72 children each: neonates, 2-month-olds and 6-month-olds. All children were recruited from Children's Hospital in Buenos Aires, Argentina. Samples were taken at various times, up to 30 days post-vaccination, and tested for ethyl and methyl mercury content.

In all groups, blood half-life of ethyl mercury was 3.7 days after vaccine administration. Ethyl mercury (unlike methyl mercury ingested from fish) did not appear to accumulate in blood. All stool samples contained mercury; stool concentrations of inorganic mercury leveled off during the sampling time. Urine contained almost no mercury. Experiment limitations include the unexplained presence of methyl mercury in some blood samples, and the inability to trace the fate of the ethyl mercury. Thimerosal elimination kinetics studies continue.

Pichichero and colleague conclude, "The low levels of mercury detected in this study suggests relatively low risk for toxicity from this exposure."

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