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Thimerosal is a preservative that has been used in manufacturing vaccines since the 1930s. Reports have indicated that infants can receive ethylmercury (in the form of thimerosal) at or above the U.S. Environmental Protection Agency guidelines for methylmercury exposure, depending on the exact vaccinations, schedule, and size of the infant. In this study we compared the systemic disposition and brain distribution of total and inorganic mercury in infant monkeys after thimerosal exposure with those exposed to MeHg. Monkeys were exposed to MeHg (via oral gavage) or vaccines containing thimerosal (via intramuscular injection) at birth and 1, 2, and 3 weeks of age. Total blood Hg levels were determined 2, 4, and 7 days after each exposure. Total and inorganic brain Hg levels were assessed 2, 4, 7, or 28 days after the last exposure. The initial and terminal half-life of Hg in blood after thimerosal exposure was 2.1 and 8.6 days, respectively, which are significantly shorter than the elimination half-life of Hg after MeHg exposure at 21.5 days. Brain concentrations of total Hg were significantly lower by approximately 3-fold for the thimerosal-exposed monkeys when compared with the MeHg infants, whereas the average brain-to-blood concentration ratio was slightly higher for the thimerosal-exposed monkeys (3.5 ± 0.5 vs. 2.5 ± 0.3). A higher percentage of the total Hg in the brain was in the form of inorganic Hg for the thimerosal-exposed monkeys (34% vs. 7%). The results indicate that MeHg is not a suitable reference for risk assessment from exposure to thimerosal-derived Hg. Knowledge of the toxicokinetics and developmental toxicity of thimerosal is needed to afford a meaningful assessment of the developmental effects of thimerosal-containing vaccines.

Exposure to methylmercury (MeHg) before birth can adversely affect children's neurodevelopment. The most common form of prenatal exposure is aternal fish consumption, but whether such exposure harms the fetus is unknown. We aimed to identify adverse neurodevelopmental effects in a fish-consuming population. We investigated 779 mother-infant pairs residing in the Republic of Seychelles. Mothers reported consuming fish on average 12 meals per week. Fish in Seychelles contain much the same concentrations of MeHg as commercial ocean fish elsewhere. Prenatal MeHg exposure was determined from maternal hair growing during pregnancy. We assessed neurocognitive, language, memory, motor, perceptual-motor, and behavioural functions in children at age 9 years. The ssociation between prenatal MeHg exposure and the primary endpoints was investigated with multiple linear regression with adjustment for covariates that affect child development. Mean prenatal MeHg exposure was 6·9 parts per million (SD 4·5ppm). Only two endpoints were associated with prenatal MeHg exposure. Increased exposure as associated with decreased performance in the grooved pegboard using the non-dominant hand in males and improved scores in the hyperactivity index of the Conner's teacher rating scale. Covariates affecting child development were appropriately associated with endpoints. These data do not support the hypothesis that there is a neurodevelopmental risk from prenatal MeHg exposure resulting solely from ocean fish consumption.

Thiomersal is a preservative containing small amounts of ethylmercury that is used in routine vaccines for infants and children. The effect of vaccines containing thiomersal on concentrations of mercury in infants’ blood has not been extensively assessed, and the metabolism of ethylmercury in infants is unknown. We aimed to measure concentrations of mercury in blood, urine, and stools of infants who received such vaccines. 40 full-term infants aged 6 months and younger were given vaccines that contained thiomersal (diptheria-tetanus-acellular pertussis vaccine, hepatitis B vaccine, and in some children Haemophilus influenzae type b vaccine). 21 control infants received thiomersal-free vaccines. We obtained samples of blood, urine, and stools 3–28 days after vaccination. Total mercury (organic and inorganic) in the samples was measured by cold vapour atomic absorption. Mean mercury doses in infants exposed to thiomersal were 45·6 μg (range 37·5-62·5) for 2-month-olds and 111·3 μg (range 87·5-175·0) for 6-month-olds. Blood mercury in thiomersal-exposed 2-month-olds ranged from less than 3·75 to 20·55 nmol/L (parts per billion); in 6-month-olds all values were lower than 7·50 nmol/L. Only one of 15 blood samples from controls contained quantifiable mercury. Concentrations of mercury were low in urine after vaccination but were high in stools of thiomersal-exposed 2-month-olds (mean 82 ng/g dry weight) and in 6-month-olds (mean 58 ng/g dry weight). Estimated blood half-life of ethylmercury was 7 days (95% Cl 4–10 days). Administration of vaccines containing thiomersal does not seem to raise blood concentrations of mercury above safe values in infants. Ethylmercury seems to be eliminated from blood rapidly via the stools after parenteral administration of thiomersal in vaccines.

In the midst of research focusing on the neurodevelopmental effects of mercury vapor in rats, we detected significant levels of mercury (30-60 ng/g) in the blood of nonexposed control subjects. We determined that the dominant form of the mercury was organic and that the standard laboratory chow we used in our vivarium was the source of the contamination. The dietary levels were deemed of potential biologic significance, even though they might have fallen below the limits of measurement specified by the supplier. All investigators employing animals in research must assess such potential contamination because dietary agents may alter a) conclusions based on intentionally administered doses, b) outcomes by interacting with other agents that are the primary focus of the research, and c) outcomes of research unrelated to the toxic effects of experimentally administered agents.

Nine children and their mother were exposed to vapors of metallic mercury. The source of the exposure appears to have been a 6-oz vial of mercury taken from a neighbor's home. The neighbor reportedly operated a business preparing mercury-filled amulets for practitioners of the Afro-Caribbean religion Santeria. At diagnosis, urinary mercury levels in the children ranged from 61 to 1,213 μg/g creatinine, with a geometric mean of 214.3 μg/m creatinine. All of the children were asymptomatic. To prevent development of neurotoxicity, we treated the children with oral meso-2,3-dimercaptosuccinic acid (DMSA). During chelation, the geometric mean urine level rose initially by 268% to 573.2 μg mercury/g creatinine (p < 0.0005). At the 6-week follow-up examination after treatment, the geometric mean urine mercury level had fallen to 102.1 μg/g creatinine, which was 17.8% of the geometric mean level observed during treatment (p < 0.0005) and 47.6% of the original baseline level (p < 0.001). Thus, oral chelation with DMSA produced a significant mercury diuresis in these children. We observed no adverse side effects of treatment. DMSA appears to be an effective and safe chelating agent for treatment of pediatric overexposure to metallic mercury.

The sym biotic algae (zoochlorellae) of Hydra viridis live inside the gastrodermal cells. When isolated into pure suspension free of animal tissue, zoochlorellae liberate maltose to the medium during photosynthesis. Maltose synthesis and excretion are very sensitive to external pH. At pH 4.0, about 40 to 50 % of the carbon fixed in photosynthesis may be released from the cells as maltose, and a further 4 to 6 % as other compounds (including alanine, glycollie acid, glucose, and an oligosaccharide provisionally identified as maltotriose). As the pH rises, excretion progressively diminishes, and at pH 7.0, only about 1% of the photo synthetically fixed carbon is excreted, about half as maltose. Only traces of maltose are ever found within the cells, and sucrose is always the predominant intracellular soluble sugar. When cells previously labelled with 14C at pH 7.0 are transferred to non-radioactive media in the dark at pH 4.0, they immediately begin to synthesize and excrete [14C ]maltose; the increase of [14C]maltose is closely correlated with a decrease of 14C-labelled hexose monophosphates and is not accompanied by any loss of 14C from the insoluble fraction. This suggests that maltose is synthesized from hexose monophosphates by a process which is not directly light dependent. In short-term photosynthesis experiments at pH 4.0, fixed 14C appears in sucrose within 20s, but none appears in maltose until 60 s. This, together with the near absence of intracellular maltose and the marked sensitivity of maltose synthesis to external pH, suggests that the mechanism of synthesis is at or near the cell surface. The experimental results were consistent with the hypothesis that maltose synthesis is UDPG -dependent, but direct proof of this was n o t obtained. Although excretion of photosynthetically fixed 14C at pH 4.0 diminishes in the presence of external maltose, it could still continue at an appreciable rate when the external maltose concentration was as high as 10% (w/v). In 10% maltose media, some of the excreted 14C was still in maltose, but most was in compounds provisionally identified as maltotriose and maltotetrose, suggesting that a mechanism for transglycosylation may exist on the surface of the cells. Unlike symbiotic zooxanthellae and lichen algae, Hydra zoochlorellae show no signs of losing their ability of excreting carbohydrate during the first 24 h after isolation from the symbiosis. In the case of Hydra, it is suggested that the host might be able to control maltose excretion from its zoochlorellae by variations in the intracellular pH of the gastrodermal cells, but evidence for such changes is still lacking.

In order to establish guidelines for exposure of astronauts to iodine, used as a water disinfectant in space, we studied the usefulness of hair, saliva, and urine for biological monitoring in humans and in the human hair/nude mouse model. The monitoring of iodine in patients that received 150 mCi of Na131I (carrier-free) showed similar patterns of elimination for blood, saliva, and urine. The mean correlation coefficient (r) between iodine elimination for blood/saliva was 0.99, for blood/urine, 0.95, and for saliva/urine, 0.97. The absolute value of iodine concentrations in urine revealed marked variability, which was corrected by adjusting for creatinine levels. The autoradiographic studies of human hair demonstrated that iodine is rapidly incorporated into external layers of the hair root and can be removed easily during washing. These data were confirmed after iodine exposure using the human hair/nude mouse model. Hair does not provide satisfactory information about exposure due to unstable incorporation of iodine. The most useful medium for biological monitoring of astronauts exposed to high doses of iodine in drinking water is urine, when adjusted for creatinine, and saliva, if quantitative evaluation of flow rate is provided.