Mercury

AIMS:

To establish and analyse reference data for the mercury burden of patients with and without amalgam fillings.

METHODS:

Atomic absorption spectroscopy was used to quantify Hg concentrations in the scalp hair and urine (before and after application of dimercaptopropane sulphonate), and Hg release from dental amalgams (using a newly developed, amalgam specific chew test), in 2223 subjects.

RESULTS:

50th centiles were 1.3 microg Hg/g creatinine in basal urine, 32 microg Hg/g creatinine after DMPS application, 454 ng Hg/g in hair, and 27 microg Hg per g of chewing gum, which corresponds to about 1 micro g Hg released per minute of chewing. Total Hg intake (from ambient air, drinking water, food, and amalgams) of most patients is well below the provisioned tolerable weekly intake (PTWI) defined by the WHO, unless extremely Hg rich food is consumed on a regular basis. However, for patients exceeding the 75th centile in chew tests, total Hg intake exceeds the PTWI by about 50%, even at the low limit of intake from food. In the absence of occupational exposure, significant Hg release from dental amalgams is a necessary but insufficient condition to obtain a high long term body burden. After removal of dental amalgams, chew tests no longer exhibit oral Hg exposure, while basal urine Hg content and DMPS induced excretion display a exponential decrease (half life about 2 months in both cases).

CONCLUSIONS:

A standardised procedure for evaluation of the magnitude and origin of the Hg burden of individuals has been developed, which, by comparison with the database presented here for the first time, can serve as a diagnostic tool.”

“The extensive use of fish meal as a source of protein for poultry and swine may lead to additional exposure to methylmercury (MeHg). We determined the concentration of MeHg and inorganic mercury (I-Hg) in blood and total mercury (T-Hg) in hair in 27 persons (9 men and 18 women, 20-58 years of age) who stated that they had consumed no fish for a period of 2 years or more. The participants answered a food frequency questionnaire and reported their number of dental amalgam fillings. The MeHg concentrations in blood (median, 0.10 microg/L; range, 0.0-1.0 microg/L) were very low and did not constitute a concern for health effects. We also analyzed selenium (Se) in serum. The median concentration was 76 microg/L (range, 53-103 microg/L), which is in agreement with previous studies of the Swedish general population, indicating that the Se status of non-fish-eating individuals is not substantially lower than that of people who include fish in their diet. We found a significant association (P=0.002) between the number of dental amalgam fillings and the I-Hg concentration in blood (median, 0.09 microg/L; range, 0.03-0.57 microg/L). The T-Hg in hair (median, 0.06 mg/kg; range, 0.04-0.32 mg/kg) was significantly associated (R2=0.89; P<0.001) with the MeHg in blood, but not with the I-Hg in blood. Therefore, the T-Hg in hair seems to reflect MeHg exposure and not I-Hg exposure even in persons with no intake of fish.”

Mercury has been used in both medicine and dentistry for centuries. Recent media attention regarding the increased levels of mercury in dietary fish, high levels of mercury in air emissions, and conjecture that certain diseases may be caused by mercury exposure has increased public awareness of the potential adverse health effects of high doses of mercury. Dentistry has been criticized for its continued use of mercury in dental amalgam for both public health and environmental reasons. To address these concerns, dental professionals should understand the impact of the various levels and types of mercury on the environment and human health. Mercury is unique in its ability to form amalgams with other metals. Dental amalgam–consisting of silver, copper, tin, and mercury–has been used as a safe, stable, and cost-effective restorative material for more than 150 years. As a result of this use, the dental profession has been confronted by the public on two separate health issues concerning the mercury content in amalgam. The first issue is whether the mercury amalgamated with the various metals to create dental restorations poses a health issue for patients. The second is whether the scraps associated with amalgam placement and the removal of amalgam restorations poses environmental hazards which may eventually have an impact on human health. Despite the lack of scientific evidence for such hazards, there is growing pressure for the dental profession to address these health issues. In this article, the toxicology of mercury will be reviewed and the impact of amalgam on health and the environment will be examined.

“Alongside food, emissions from amalgam fillings are an essential contribution to man’s mercury burden. Previous methods for the determination of intraoral mercury vapor (Hg degrees ) release used principally some form of preconcentration of Hg on gold (film or wool), allowing relatively few measurements with unknown precision and sensitivity at selected times. Recently available computer-controlled Hg detectors operating on Zeeman atomic absorption spectroscopy (ZAAS) facilitate the direct real-time measurement of Hg degrees concentrations. It was the aim to adapt this method for a comparative investigation of emission processes from fillings in situ and from amalgam specimens in vitro. In addition to the ZAAS instrument, the apparatus consisted of a pump, magnetic valves, an electronic flow controller and a handle with a disposable mouth piece for aspiration of oral air. A programmable timer integrated the computer-controlled instrument operation and the data collection into a standard sampling protocol. A fast exponential decay of the emission was found after stimulation of amalgam specimens and of fillings in situ (halftimes 8.6 and 10.7 min). Precision was evaluated by a series of measurements on a single patient which indicated a consistently low coefficient of variation between 18% and 25%. After insertion of a few new fillings, sensitivity was high enough to detect a significant increase in emission against the background emission from the majority of old fillings. Zeeman-AAS in connection with a semi-automated sampling protocol and data storage provides precise in-situ measurements of Hg degrees emission from dental amalgam with real-time resolution. This facilitates the detailed exploration of the Hg degrees release kinetics and the applicability to large-scale studies.”

“Mercury (Hg) release from dental offices has become an acute issue for the dental profession and has resulted in efforts by regulators to mandate both the use of Best Management Practices (BMPs) as well as the installation of amalgam separators. Concern has been expressed by some regarding the efficacy of amalgam separators in reducing the Hg loads to wastewater treatment plants (WWTPs). Data from several Publicly Owned Treatment Works (POTWs) serving areas with installed bases of separators suggest these devices can substantially reduce Hg burdens to WWTPs. The data consists of Hg levels in sewer sludge (biosolids) and in some cases includes Hg concentrations in WWTP influent and effluent. Data comes from various geographical locations, and suggest separators can have a positive effect in reducing the amount of Hg reaching WWTPs.”

“AIM:

A study of 180 dentists in the West of Scotland was conducted to determine their exposure to mercury during the course of their work and the effects on their health and cognitive function.
DESIGN:

Data were obtained from questionnaires distributed to dentists and by visiting their surgeries to take measurements of environmental mercury.

METHODS:

Dentists were asked to complete a questionnaire including items on handling of amalgam, symptoms experienced, diet and possible influences on psychomotor function such as levels of stress and alcohol intake. They also completed the 12-item General Health Questionnaire. Dentists were asked to complete a dental chart of their own mouths and to give samples of urine, hair and nails for mercury analysis. The dentists were visited at their surgeries where environmental measurements were made in eight areas of the surgery and they undertook a computerised package of psychomotor tests. One hundred and eighty control subjects underwent a similar procedure, completing a questionnaire, having their amalgam surfaces counted, giving urine, hair and nail samples and undergoing the psychomotor test procedure.

RESULTS:

Dentists were found to have, on average, urinary mercury levels over 4 times that of control subjects although all but one dentist had urinary mercury below the Health and Safety Executive health guidance value of 20 mumol mmol(-1) creatinine. Urine was found to be a better biological marker for mercury exposure than hair or nails.Dentists were significantly more likely than control subjects to have suffered from disorders of the kidney but these symptoms were not significantly associated with their level of mercury exposure as measured in urine. One hundred and twenty two (67.8%) of the 180 surgeries visited had environmental mercury measurements in one or more areas above the Occupational Exposure Standard (OES) set by the Health and Safety Executive. In the majority of these surgeries the high levels of mercury were found at the skirting and around the base of the dental chair. In 45 surgeries (25%) the personal dosimetry measurement (ie in the breathing zone of dental staff) was above the OES.

CONCLUSION:

On the basis of these findings, it is recommended that greater emphasis should be made relating to safe handling of amalgam in the training and continuing professional development of dentists, that further studies are carried out on levels of mercury exposure of dental team members during the course of their working day, and that periodic health surveillance, including urinary mercury monitoring, of dental personnel should be conducted to identify possible effects of practising dentistry.”

“Recent reports have described neurobehavioral impairments in human subjects carrying a V66M polymorphism in the gene encoding brain-derived neurotrophic factor (BDNF). Inasmuch as ventral nervous system (CNS) deficits associated with this BDNF polymorphism are similar to those observed among subjects with chronic exposure to elemental mercury (Hg degrees ), we examined the potential effect of this BDNF polymorphism on symptoms and mood in an established cohort of dental practitioners with chronic low-level Hg degrees exposure. Self-reported symptoms and mood were obtained by computerized questionnaire from 193 male dentists (DTs) and 230 female dental assistants (DAs). Spot urine samples were analyzed for mercury concentrations to evaluate recent exposure. Detailed work histories were obtained to calculate chronic indices of Hg degrees exposure. Buccal cell samples were obtained to identify the V66M polymorphism of BDNF. Scores for 11 current and 12 recent and chronic symptom groups, along with six mood factors, were evaluated with respect to recent and chronic Hg degrees exposure and BDNF polymorphism. Multiple regression analysis controlled for age, race, socioeconomic status, tobacco and alcohol use, self-reported health problems, and medications. Separate evaluations were conducted for DTs and DAs. Twenty-three associations between recent or chronic Hg degrees exposure and BDNF status and self-reported symptoms were observed with p < 0.10. All but three were in the expected direction (symptom scores increasing with Hg degrees exposure or BDNF polymorphism), and all but six were among DAs. All eight correlations between chronic exposure indices and recent and chronic symptoms among DAs were in the expected direction. All seven associations between BDNF and symptoms were in the expected direction and split between DTs and DAs. All three associations with mood factors were among DAs and in the expected direction. These results indicate that among DAs very low levels of occupational Hg degrees exposure are associated with increased symptoms. The BDNF polymorphism is also associated with increased symptom and mood scores. Notably, Hg degrees and BDNF polymorphism were additive with respect to their associations with the same symptom group.”

“Methylation events play a critical role in the ability of growth factors to promote normal development. Neurodevelopmental toxins, such as ethanol and heavy metals, interrupt growth factor signaling, raising the possibility that they might exert adverse effects on methylation. We found that insulin-like growth factor-1 (IGF-1)- and dopamine-stimulated methionine synthase (MS) activity and folate-dependent methylation of phospholipids in SH-SY5Y human neuroblastoma cells, via a PI3-kinase- and MAP-kinase-dependent mechanism. The stimulation of this pathway increased DNA methylation, while its inhibition increased methylation-sensitive gene expression. Ethanol potently interfered with IGF-1 activation of MS and blocked its effect on DNA methylation, whereas it did not inhibit the effects of dopamine. Metal ions potently affected IGF-1 and dopamine-stimulated MS activity, as well as folate-dependent phospholipid methylation: Cu(2+) promoted enzyme activity and methylation, while Cu(+), Pb(2+), Hg(2+) and Al(3+) were inhibitory. The ethylmercury-containing preservative thimerosal inhibited both IGF-1- and dopamine-stimulated methylation with an IC(50) of 1 nM and eliminated MS activity. Our findings outline a novel growth factor signaling pathway that regulates MS activity and thereby modulates methylation reactions, including DNA methylation. The potent inhibition of this pathway by ethanol, lead, mercury, aluminum and thimerosal suggests that it may be an important target of neurodevelopmental toxins.”

“There is a concern on the part of public health community that adverse health consequences by thimerosal, a preservative in vaccines for infants, may occur among infants during immunization schedule. Therefore, the effect of thimerosal on cellular content of glutathione was examined on thymocytes obtained from 4-week-old rats using a flow cytometer and 5-chloromethylfluorescein diacetate. Thimerosal at concentrations ranging from 1 to 10 microM reduced the cellular content of glutathione in a concentration-dependent manner, and the complete depletion of cellular glutathione was observed when the cells were treated with 30 microM thimerosal. L-Cysteine significantly attenuated the actions of thimerosal to reduce the glutathione content and to increase the intracellular Ca2+ concentration. Prolonged incubation (24 h) with 1-3 microM thimerosal induced the apoptosis. The cytotoxic action of thimerosal was greatly augmented when the cells suffered oxidative stress induced by H2O2. It may be unlikely that thimerosal exerts potent cytotoxic action under the in vivo condition because the blood concentration of thimerosal after receiving vaccines does not seem to reach micromolar range and nonprotein thiols at micromolar concentrations are present in the blood.”

“The effect of thimerosal, an organomercurial preservative in vaccines, on cerebellar neurons dissociated from 2-week-old rats was compared with those of methylmercury using a flow cytometer with appropriate fluorescent dyes. Thimerosal and methylmercury at concentrations ranging from 0.3 to 10 microM increased the intracellular concentration of Ca2+ ([Ca2+]i) in a concentration-dependent manner. The potency of 10 microM thimerosal to increase the [Ca2+]i was less than that of 10 microM methylmercury. Their effects on the [Ca2+]i were greatly attenuated, but not completely suppressed, under external Ca(2+)-free condition, suggesting a possibility that both agents increase membrane Ca2+ permeability and release Ca2+ from intracellular calcium stores. The effect of 10 microM thimerosal was not affected by simultaneous application of 30 microM L-cysteine whereas that of 10 microM methylmercury was significantly suppressed. The potency of thimerosal was similar to that of methylmercury in the presence of L-cysteine. Both agents at 1 microM or more similarly decreased the cellular content of glutathione in a concentration-dependent manner, suggesting an increase in oxidative stress. Results indicate that thimerosal exerts some cytotoxic actions on cerebellar granule neurons dissociated from 2-week-old rats and its potency is almost similar to that of methylmercury.”