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The Alberta Occupational Health and Safety threshold limit value for mercury vapor over an eight-hour time-weighted period is 25.0 mug/m3. The absolute ceiling for mercury vapor, not to be exceeded at any time, is 125.0 mug/m3. When both water spray and suction were used, mercury vapor levels were consistently below this threshold. When suction without water spray was used, mercury vapor levels exceeded the safety threshold 8% of the time. When neither water spray nor suction was used, 36% of the mercury vapor readings exceeded the absolute ceiling value. To maximize safety, dental schools should train students to remove amalgam only while using water spray and high volume suction. Alternatively, students should use appropriate occupational hygiene personal protective equipment during amalgam removals.”

“The mercury contained in dental amalgam fillings contributes to overall human exposure to this toxic metal. According to the World Health Organization, there is uncertainty as to how much mercury in your body can cause harm. Cremation of bodies with dental amalgams is a significant source of mercury release to the Vermont environment. For these reasons, the Advisory Committee has recommended to the Legislature that dental amalgam use be discontinued in the future in most instances, and that dental patients be provided with unbiased information on the health and environmental concerns with dental amalgam. The purpose of this fact sheet is to provide such information to the general public on health and environmental concerns.”

“References documenting symptoms to mercury exposure”

"Male, 34 years old, European ethnic. He started having symptoms in 1999 while the Relapsing-Remitting MS was diagnosed in 2004. In May 2007, the patient underwent his first Hair Mineral Analysis, showing mercury and aluminium excess. After the first 6 months of dietary integration based on Hair Mineral Analysis (HMA) results, the patient noticed increasing of the strength, physical endurance, more energy, beside the disappearance of headache and other symptoms. Evaluation by MRI reported the reduction of the 'amount of encephalic lesions' and of the 'extension of the lesion located in the left near-trigonous white matter'; as well, 'numerous plaques within the periventricular white matter in front-parietal region, bilaterally' disappeared. To date, symptoms are slowly but constantly decreasing. Concomitant HMA control shown a clear decreasing of mercury."

"A 17-year-old African American male had recurrent emergency department (ED) visits or hypertension resistant to initial treatment, which resulted in multiple hospital admissions.  Hypertension was associated with significant weight loss, peripheral neuropathy and night sweats. An extensive laboratory and imaging workup ruled out renal, cardiac, rheumatologic and endocrine causes for his symptoms. Ultimately, a more detailed history and toxicology consultation lead to the cause for his persistent symptoms: mercury poisoning."

"The purpose of this review is to examine the evidence for a relationship between mercury (Hg) exposure from dental amalgams and certain idiopathic chronic illnesses–chronic fatigue syndrome (CFS), fibromyalgia (FM), depression, anxiety, and suicide. Dental amalgam is a commonly used dental restorative material that contains approximately 50% elemental mercury (Hg0) by weight and releases Hg0 vapor. Studies have shown that chronic Hg exposure from various sources including dental amalgams is associated with numerous health complaints, including fatigue, anxiety, and depression–and these are among the main symptoms that are associated with CFS and FM. In addition, several studies have shown that the removal of amalgams is associated with improvement in these symptoms. Although the issue of amalgam safety is still under debate, the preponderance of evidence suggests that Hg exposure from dental amalgams may cause or contribute to many chronic conditions. Thus, consideration of Hg toxicity may be central to the effective clinical investigation of many chronic illnesses, particularly those involving fatigue and depression."

"BACKGROUND:
Autism spectrum disorder (ASD) is defined by standardized criteria of qualitative impairments in social interaction, qualitative impairments in communication, and restricted and stereotyped patterns of behavior, interests, and activities. A significant number of children diagnosed with ASD suffer a loss of previously-acquired skills, which is suggestive of neurodegeneration or a type of progressive encephalopathy with an etiological pathogenic basis occurring after birth. To date, the etiology of ASD remains under debate, however, many studies suggest toxicity, especially from mercury (Hg), in individuals diagnosed with an ASD. The present study evaluated concerns about the toxic effects of organic-Hg exposure from Thimerosal (49.55% Hg by weight) in childhood vaccines by conducting a two-phased (hypothesis generating/hypothesis testing) study with documented exposure to varying levels of Thimerosal from vaccinations.

METHODS:
A hypothesis generating cohort study was undertaken to evaluate the relationship between exposure to organic-Hg from a Thimerosal-containing Diphtheria-Tetanus-acellular-Pertussis (DTaP) vaccine in comparison to a Thimerosal-free DTaP vaccine administered, from 1998 through 2000, for the risk of ASD as reported in the Vaccine Adverse Event Reporting System (VAERS) database (phase I). A hypothesis testing case-control study was undertaken to evaluate the relationship between organic-Hg exposure from Thimerosal-containing hepatitis B vaccines administered at specific intervals in the first six months of life among cases diagnosed with an ASD and controls born between 1991 through 1999 in the Vaccine Safety Datalink (VSD) database (phase II).

RESULTS:
In phase I, it was observed that there was a significantly increased risk ratio for the incidence of ASD reported following the Thimerosal-containing DTaP vaccine in comparison to the Thimerosal-free DTaP vaccine. In phase II, it was observed that cases diagnosed with an ASD were significantly more likely than controls to receive increased organic-Hg from Thimerosal-containing hepatitis B vaccine administered within the first, second, and sixth month of life.

CONCLUSIONS:
Routine childhood vaccination is an important public health tool to reduce the morbidity and mortality associated with infectious diseases, but the present study provides new epidemiological evidence supporting an association between increasing organic-Hg exposure from Thimerosal-containing childhood vaccines and the subsequent risk of an ASD diagnosis."

Mercury is a potent toxicant of concern to both the general public and occupationally exposed workers (e.g., dentists). Recent studies suggest that several genes mediating the toxicokinetics of mercury are polymorphic in humans and may influence inter-individual variability in mercury accumulation. This work hypothesizes that polymorphisms in key glutathione synthesizing enzyme, glutathione S-transferase, andselenoprotein genes underlie inter-individual differences in mercury body burden as assessed by analyticalmercury measurement in urine and hair, biomarkers of elemental mercury and methylmercury, respectively. Urine and hair samples were collected from a population of dental professionals (n=515), and total mercurycontent was measured. Average urine (1.06±1.24 microg/L) and hair mercury levels (0.49±0.63 microg/g) were similar to national U.S. population averages. Taqman assays were used to genotype DNA from buccal swab samples at 15 polymorphic sites in genes implicated in mercury metabolism. Linear regression modeling assessed the ability of polymorphisms to modify the relationship between mercury biomarkerlevels and exposure sources (e.g., amalgams, fish consumption). Five polymorphisms were significantly associated with urine mercury levels (GSTT1 deletion), hair mercury levels (GSTP1-105, GSTP1-114, GSS 5'), or both (SEPP1 3'UTR). Overall, this study suggests that polymorphisms in selenoproteins andglutathione-related genes may influence elimination of mercury in the urine and hair or mercury retention following exposures to elemental mercury (via dental amalgams) and methylmercury (via fish consumption).

"Modification of the epigenome may be a mechanism underlying toxicity and disease following chemical exposure. Animal and human data suggest that mercury (Hg) impacts DNA methylation. We hypothesize that methylmercury and inorganic Hg exposures from fish consumption and dental amalgams, respectively, may be associated with altered DNA methylation at global repetitive elements (long interspersed elements, LINE-1) and candidate genes related to epigenetic processes (DNMT1) and protection against Hg toxicity (SEPW1, SEPP1). Dental professionals were recruited at Michigan Dental Association (MDA) meetings in 2009 and 2010. Subjects (n=131) provided survey data (e.g. exposure sources, demographics) and biological samples for Hg measurement and epigenetic analysis. Total Hg was quantified via atomic absorption spectrophotometry in hair and urine, indicative of methylmercury and inorganic Hg exposures, respectively. Global repetitive and candidate gene methylation was quantified via pyrosequencing of bisulfite converted DNA isolated from buccal mucosa. Hair Hg (geometric mean (95% CI): 0.37 (0.31-0.44) µg/g) and urine Hg (0.70 (0.60-0.83) µg/L) were associated with sources of exposure (fish consumption anddental amalgams, respectively). Multivariable linear regression revealed a trend of SEPP1 hypomethylation with increasing hair Hg levels, and this was significant (P<0.05) among males. The trend remained when excluding non-dentists. No significant relationships between urine Hg and DNA methylation were observed. Thus, in a limited cohort, we identified an association between methylmercury exposure and hypomethylation of a potentially labile region of the genome (SEPP1 promoter), and this relationship was gender specific."

"Background: Recent studies have suggested that several genes that mediate mercury metabolism are polymorphic in humans.

Objective: We hypothesized that single-nucleotide polymorphisms (SNPs) in metallothionein (MT) genes may underlie interindividual differences in mercury biomarker levels. We studied the potential modifying effects of MT SNPs on mercury exposure–biomarker relationships.

Methods: We measured total mercury in urine and hair samples of 515 dental professionals. We also surveyed occupational and personal exposures to dental amalgam and dietary fish consumption, from which daily methylmercury (MeHg) intake was estimated. Log-transformed urine and hair levels were modeled in multivariable linear regression separately against respective exposure surrogates, and the effect modification of 13 MT SNPs on exposure was investigated.

Results: The mean mercury levels in urine (1.06 μg/L) and hair (0.51 μg/g) were not significantly different from the U.S. general population (0.95 μg/L and 0.47 μg/g, respectively). The mean estimated daily MeHg intake was 0.084 μg/kg/day (range, 0–0.98 μg/kg/day), with 25% of study population intakes exceeding the current U.S. Environmental Protection Agency reference dose of 0.1 μg/kg/day. Multivariate regression analysis showed that subjects with the MT1M (rs2270837) AA genotype (n = 10) or the MT2A (rs10636) CC genotype (n = 42) had lower urinary mercury levels than did those with the MT1M or MT2AGG genotype (n = 329 and 251, respectively) after controlling for exposure and potential confounders. After controlling for MeHg intake, subjects with MT1A (rs8052394) GA and GG genotypes (n = 24) or the MT1M (rs9936741) TT genotype (n = 459) had lower hair mercury levels than did subjects with MT1A AA (n = 113) or MT1M TC and CC genotypes (n = 15), respectively.

Conclusion: Our findings suggest that some MT genetic polymorphisms may influence mercury biomarker concentrations at levels of exposure relevant to the general population."