Mercury

“Eighty-seven teeth were diagnosed with a cracked tooth (81.3%), 14 were diagnosed with vertical root fracture (VRF, 13.1%), 4 had a split tooth (3.7%), and 2 had a fractured cusp (1.9%); 82.2% showed a sensitive reaction on the bite test. Longitudinal tooth fractures were observed most frequently in patient in their 40s. The upper first molar (28.0%) was most frequently cracked, followed by the lower first molar (25.2%), the lower second molar (20.6%), and the upper second molar (16.8%). Most longitudinal tooth fractures (72.0%) occurred mainly in restored teeth, whereas only 28.0% were found in intact teeth. Compared with resin (4.7%) or porcelain (0.9%), the use of nonbonded inlay restoration materials such as gold (20.5%) or amalgam (18.7%) increased the occurrence of longitudinal tooth fractures. Out of 107 of longitudinal fractured teeth, 33 (30.8%) were treated endodontically and 74 (69.2%) were not. VRF was associated with endodontic treatment.”

“The number of amalgam fillings present will determine just how much Hg exposure arises from those fillings. It is obvious that a person with no amalgam (and thus no amalgam-related Hg exposure) will receive greater Hg exposure from eating a tuna fish sandwich. Likewise, however, a person with one or more amalgam fillings will receive more Hg from that source than from tuna fish if that person does not eat tuna fish sandwiches.”

“Little agreement exists as to whether low-level mercury (Hg) exposure causes damage to the central nervous system in adults. Although eating fish is associated with intake of methylmercury, researchers in this field have generally thought that the beneficial effects of a diet rich in long-chain, n-3 fatty acids (N3FA) can outweigh the cognitive neurotoxicity of mercury.
Objective: This study intended to clarify the impact of Hg and intake of seafood on cognition.
Design: The study was a retrospective, cross-sectional analysis.
Setting: The research team performed the study at the Carillon Outpatient Center in St Petersburg, Florida.
Participants: Participants were 384 men and women, primarily corporate executives, who were attending an all-day comprehensive physical evaluation.”

“Due to the facts that thiomersal-containing vaccine is still in use in many developing countries, and all forms of mercury have recognised neurotoxic, nephrotoxic, and other toxic effects, studies on disposition of ethylmercury and other mercury forms are still justified, especially at young age. Our investigation aimed at comparing mercury distribution and rate of excretion in the early period of life following exposure to either thiomersal (TM) or mercuric chloride (HgCl2) in suckling rats. Three experimental groups were studied: control, TM, and HgCl2, with 12 to18 pups in each. Both forms of mercury were administered subcutaneously in equimolar quantities (0.81 μmol/kg b.w.) three times during the suckling period (on the days of birth 7, 9, and 11) to mimic the vaccination regimen in infants. After the last administration of TM or HgCl2, total mercury retention and excretion was assessed during following six days. In TM-exposed group mercury retention was higher in the brain, enteral excretion was similar, and urinary excretion was much lower compared to HgCl2-exposed sucklings. More research is still needed to elucidate all aspects of toxicokinetics and most harmful neurotoxic potential of various forms of mercury, especially in the earliest period of life.”

“OBJECTIVE: The authors used a public use data set to investigate associations between the receipt of thimerosal-containing vaccines and immune globulins early in life and neuropsychological outcomes assessed at 7-10 years.

METHODS:
The data were originally created by evaluating 1,047 children ages 7-10 years and their biological mothers. This study developed seven latent neuropsychological factors and regressed them on a comprehensive set of covariates and thimerosal exposure variables.

RESULTS:
The authors found no statistically significant associations between thimerosal exposure from vaccines early in life and six of the seven latent constructs. There was a small, but statistically significant association between early thimerosal exposure and the presence of tics in boys.

CONCLUSIONS:
This finding should be interpreted with caution due to limitations in the measurement of tics and the limited biological plausibility regarding a causal relationship.”

BACKGROUND:

Mercury is known to be neurotoxic at high levels. There have been few studies of potential peripheral neurotoxicity among persons with exposure to elemental mercury at or near background levels.

OBJECTIVES:

The present study sought to examine the association between urinary mercury concentration and peripheral nerve function as assessed by sensory nerve conduction studies in a large group of dental professionals.

METHODS:

From 1997 through 2006 urine mercury measurements and sensory nerve conduction of the median and ulnar nerves in the dominant hand were performed, and questionnaires were completed, on the same day in a convenience sample of dental professionals who attended annual conventions of the American Dental Association. Linear regression models, including repeated measures models, were used to assess the association of urine mercury with measured nerve function.

RESULTS:

3594 observations from 2656 subjects were available for analyses. Urine mercury levels in our study population were higher than, but substantially overlap with, the general population. The only stable significant positive association involved median (not ulnar) sensory peak latency, and only for the model that was based on initial observations and exclusion of subjects with imputed BMI. The present study found no significant association between median or ulnar amplitudes and urine mercury concentration.

CONCLUSIONS:

At levels of urine mercury that overlap with the general population we found no consistent effect of urine mercury concentration on objectively measured sensory nerve function.”

“This report begins the process of risk assessment by evaluating the clinical, environmental, and occupational exposures and the toxicity of the alternatives to mercury containing dental amalgam. It uses the fourstep human health risk assessment approach used by U.S. federal agencies. Basing itself on the primary literature, this four-step paradigm includes hazard identification, exposure assessment, toxicity assessment, and risk characterization. Material Safety Data Sheets were secured for the various composite, glass ionomer, and compomer formulations along with preparation and application formulations (etchants, primers, activators, coupling agents, adhesives, and bonding agents). Seventy-eight constituents were identified, organized, and summarized for the different formulations.”

“Birth weight is a strong determinant of attained weight at early ages. Until now, many studies have reported that low birth weight corresponds with high mercury levels. However, the relationship between mercury exposure and attained weight of infant has not been well studied. Therefore, the aim of the present study was to assess the degree of prenatal exposure to mercury by measuring the total mercury levels in maternal and cord blood, and examine the relationship between the mercury level during pregnancy and the attained weight of infant during the first 24 months of life. The prospective cohort study of Mothers and Children’s Environmental Health (MOCEH) was built up in 2006, and 921 mother-infant pairs were recruited. Information on the socio-demographic characteristics, health behavior and environmental exposure were collected from an interview with trained nurses. After delivery, infants and mothers were followed up at 6, 12 and 24 months and the weights of the infants were measured. The mercury concentrations in the late maternal blood (?=-0.19. p=0.05) and cord blood (?=-0.36. p=0.01) were negatively associated with the infants’ attained weight over the first 24 months of age. The infants’ attained weight in the small for their gestational age (SGA) group was lower than the normal birth weight group at the highest quartile of the mercury level. Therefore, efforts should be made to reduce the mercury level in the maternal blood at late pregnancy and cord blood. Further research on the possible harmful effects of prenatal mercury exposure on postnatal growth is recommended.”

“Autism is defined by a behavioral set of stereotypic and repetitious behavioral patterns in combination with social and communication deficits. There is emerging evidence supporting the hypothesis that autism may result from a combination of genetic susceptibility and exposure to environmental toxins at critical moments in development. Mercury (Hg) is recognized as a ubiquitous environmental neurotoxin and there is mounting evidence linking it to neurodevelopmental disorders, including autism. Of course, the evidence is not derived from experimental trials with humans but rather from methods focusing on biomarkers of Hg damage, measurements of Hg exposure, epidemiological data, and animal studies. For ethical reasons, controlled Hg exposure in humans will never be conducted. Therefore, to properly evaluate the Hg-autism etiological hypothesis, it is essential to first establish the biological plausibility of the hypothesis. This review examines the plausibility of Hg as the primary etiological agent driving the cellular mechanisms by which Hg-induced neurotoxicity may result in the physiological attributes of autism. Key areas of focus include: (1) route and cellular mechanisms of Hg exposure in autism; (2) current research and examples of possible genetic variables that are linked to both Hg sensitivity and autism; (3) the role Hg may play as an environmental toxin fueling the oxidative stress found in autism; (4) role of mitochondrial dysfunction; and (5) possible role of Hg in abnormal neuroexcitory and excitotoxity that may play a role in the immune dysregulation found in autism. Future research directions that would assist in addressing the gaps in our knowledge are proposed.”

“BACKGROUND:

Recent studies suggest that children diagnosed with an autism spectrum disorder (ASD) have significantly increased levels of urinary porphyrins associated with mercury (Hg) toxicity, including pentacarboxyporphyrin (5cxP), precoproporphyrin (prcP), and coproporphyrin (cP), compared to typically developing controls. However, these initial studies were criticized because the controls were not age- and gender-matched to the children diagnosed with an ASD.

METHODS:

Urinary porphyrin biomarkers in a group of children (2-13 years of age) diagnosed with an ASD (n= 20) were compared to matched (age, gender, race, location, and year tested) group of typically developing controls (n= 20).

RESULTS:

Participants diagnosed with an ASD had significantly increased levels of 5cxP, prcP, and cP in comparison to controls. No significant differences were found in non-Hg associated urinary porphyrins (uroporphyrins, hexacarboxyporphyrin, and heptacarboxyporphyrin). There was a significantly increased odds ratio for an ASD diagnosis relative to controls among study participants with precoproporphyrin (odds ratio = 15.5, P < 0.01) and coproporphyrin (odds ratio = 15.5, P < 0.01) levels in the second through fourth quartiles in comparison to the first quartile.

CONCLUSION:

These results suggest that the levels of Hg-toxicity-associated porphyrins are higher in children with an ASD diagnosis than controls. Although the pattern seen (increased 5cxP, prcP, and cP) is characteristic of Hg toxicity, the influence of other factors, such as genetics and other metals cannot be completely ruled out.”