Mercury

“OBJECTIVES:

The purpose of this study was to evaluate the systemic mercury levels in urine of patients and dental school students caused by exposure to silver amalgam. It is currently believed that occupational exposure shows the highest rate of potential for poisoning by mercury. Dental professionals are part of that quota, introducing concerns regarding the handling of dental amalgam.

MATERIALS AND METHODS:

The study comprised 40 urine samples from 20 subjects, which were divided into four sampling groups: G1A (n = 10) composed of students before their first occupational contact; G1B (n = 10) composed of the same G1 students after their first contact; G2A (n = 10) composed of patients who needed to have dental restorations before amalgam removal; and G2B (n = 10) composed of patients who needed to have dental restoration after amalgam removal. Cold-vapor atomic absorption spectrophotometry (CVAAS) was used as the evaluation method.

RESULTS:

A statistically significant difference was found among dependent groups 1 and 2 (p = 0.0038), whereas mercury levels increased considerably after the first occupational contact of all subjects.

CONCLUSIONS:

Occupational exposure to dental amalgam poses a potential risk of increasing systemic mercury levels, although urine mercury levels in all the sample participants were below the limits of biologic tolerance.”

“Neuroligins are postsynaptic cell adhesion proteins that bind specifically to presynaptic membrane proteins called neurexins. Mutations in human neuroligin genes are associated with autism spectrum disorders in some families. The nematode Caenorhabditis elegans has a single neuroligin gene (nlg-1), and approximately a sixth of C. elegans neurons, including some sensory neurons, interneurons and a subset of cholinergic motor neurons, express a neuroligin transcriptional reporter. Neuroligin-deficient mutants of C. elegans are viable, and they do not appear deficient in any major motor functions. However, neuroligin mutants are defective in a subset of sensory behaviors and sensory processing, and are hypersensitive to oxidative stress and mercury compounds; the behavioral deficits are strikingly similar to traits frequently associated with autism spectrum disorders. Our results suggest a possible link between genetic defects in synapse formation or function, and sensitivity to environmental factors in the development of autism spectrum disorders.”

“This longitudinal, case-control pilot study examined amygdala growth in rhesus macaque infants receiving the complete US childhood vaccine schedule (1994-1999). Longitudinal structural and functional neuroimaging was undertaken to examine central effects of the vaccine regimen on the developing brain. Vaccine-exposed and saline-injected control infants underwent MRI and PET imaging at approximately 4 and 6 months of age, representing two specific timeframes within the vaccination schedule. Volumetric analyses showed that exposed animals did not undergo the maturational changes over time in amygdala volume that was observed in unexposed animals. After controlling for left amygdala volume, the binding of the opioid antagonist [(11)C]diprenorphine (DPN) in exposed animals remained relatively constant over time, compared with unexposed animals, in which a significant decrease in [(11)C]DPN binding occurred. These results suggest that maturational changes in amygdala volume and the binding capacity of [(11)C]DPN in the amygdala was significantly altered in infant macaques receiving the vaccine schedule. The macaque infant is a relevant animal model in which to investigate specific environmental exposures and structural/functional neuroimaging during neurodevelopment.”

“This study examined whether acquisition of neonatal reflexes in newborn rhesus macaques was influenced by receipt of a single neonatal dose of hepatitis B vaccine containing the preservative thimerosal (Th). Hepatitis B vaccine containing a weight-adjusted Th dose was administered to male macaques within 24 h of birth (n = 13). Unexposed animals received saline placebo (n = 4) or no injection (n = 3). Infants were tested daily for acquisition of nine survival, motor, and sensorimotor reflexes. In exposed animals there was a significant delay in the acquisition of root, snout, and suck reflexes, compared with unexposed animals. No neonatal responses were significantly delayed in unexposed animals. Gestational age (GA) and birth weight (BW) were not significantly correlated. Cox regression models were used to evaluate main effects and interactions of exposure with BW and GA as independent predictors and time-invariant covariates. Significant main effects remained for exposure on root and suck when controlling for GA and BW, such that exposed animals were relatively delayed in time-to-criterion. Interaction models indicated there were various interactions between exposure, GA, and BW and that inclusion of the relevant interaction terms significantly improved model fit. This, in turn, indicated that lower BW and/or lower GA exacerbated the adverse effects following vaccine exposure. This primate model provides a possible means of assessing adverse neurodevelopmental outcomes from neonatal Th-containing hepatitis B vaccine exposure, particularly in infants of lower GA or BW. The mechanisms underlying these effects and the requirements for Th requires further study.”

“To assess amalgam use and waste management protocols practised by Pakistani dentists, a cross-sectional study was made of 239 dentists in Islamabad and Rawalpindi, recruited by convenience and cluster sampling. Amalgam was the most frequently used restorative material, with the choice dictated by patients’ financial constraints. While 90.4% of dentists perceived amalgam as a health risk, only 46.4% considered it an environmental hazard. The majority disposed of amalgam waste in the trash, down the sink or as hospital waste. Very few (5.9%) had an amalgam separator installed in their dental office. Amalgam waste management protocols and mercury recycling should be introduced in Pakistan.”

“BACKGROUND & OBJECTIVES:
The US Agency for Toxic Substances and Disease Registry (ATSDR) reports that mercury (Hg) is a known endocrine disruptor and it adversely affects the steroid synthesis pathway in animals and humans, and may interact to enhance the risk for a child developing premature puberty. An association between premature puberty and exposure to Hg from thimerosal-containing vaccines (TCVs) was evaluated in computerized medical records within the Vaccine Safety Datalink (VSD).

METHODS:
A total of 278,624 subjects were identified in birth cohorts from 1990-1996. The birth cohort prevalence rates of medically diagnosed International Classification of Disease, 9(th) revision (ICD-9) premature puberty and control outcomes were calculated. Exposures to Hg from TCVs were calculated by birth cohort for specific exposure windows from birth-7 months and birth-13 months of age. Poisson regression analysis was used to model the association between the prevalence of outcomes and Hg doses from TCVs.

RESULTS:
Significantly increased (P<0.0001) rate ratios were observed for premature puberty for a 100 microg difference in Hg exposure from TCVs in the birth-7 months (rate ratio=5.58) and birth-13 months (rate ratio=6.45) of age exposure windows. By contrast, none of the control outcomes had significantly increased rate ratios with Hg exposure from TCVs.

INTERPRETATION & CONCLUSIONS:
Routine childhood vaccination should be continued to help reduce the morbidity and mortality associated with infectious diseases, but efforts should be undertaken to remove Hg from vaccines. Additional studies should be done to evaluate the relationship between Hg exposure and premature puberty.”

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“The study described here was comprised of 100 pregnant females from two prenatal care units at the cities of Hassleholm and Simrishamn in southern Sweden. It included a questionnaire as well as whole blood (total mercury, cadmium, and lead) and hair (total mercury) sampling (collection period 2002-2003). The median values of total mercury (B-Hg 0.70 microg/L; range 0.27-2.1 microg/L), cadmium (0.30 microg/L, 0.05-4.8 microg/L) and lead (11.0 microg/L, 4.2-79 microg/L) in whole blood were low in the total material, as were the hair mercury concentrations (Hair-Hg 0.22 microg/g, 0.04-0.83 microg/g). In a multiple linear regression model, B-Hg was related to the number of fish meals per week and to the number of occlusal amalgam fillings (multiple r = 0.51; p < .001). The levels of mercury, cadmium, and lead in whole blood were lower than suggested biological reference intervals, and did not indicate risks for adverse health effects.”

“The Dental Products Panel met on December 14 and 15, 2010, to discuss and make recommendations on scientific issues raised in petitions received by FDA concerning the final rule on the classification of dental amalgam, which published in the Federal Register on August 4, 2009 (74 FR 38686). The Panel deliberated on the exposure to mercury from dental amalgam, reference exposure levels, human clinical studies and the strength and weaknesses of the available evidence.”