Mercury

“OBJECTIVES:

This project was conducted to examine whether the computerised analysis of psychomotor responses available from Cognitive Drug Research is appropriate for measuring an effect of low level exposure to mercury in dentists.

METHODS:

A computerised battery of psychomotor tests was given to two groups of dentists (older dentists and trainees) and to two age matched control groups. As well as the psychomotor tests, volunteers were required to complete a questionnaire to identify potential influences on psychomotor performance and to provide a sample for analysis of urinary mercury.

RESULTS:

Statistical analysis of the results showed that the older dentists had slightly higher concentrations of urinary mercury although most were around background levels and they were all within occupational limits. Five of the psychomotor tests showed no differences between the performance of the four groups. The older dentists showed significantly better performance on the simple reaction time test and significantly poorer performance in the immediate word recall and delayed word recall tests.

CONCLUSIONS:

Poorer performance in memory recall tests confirms previously reported studies. This together with the confirmation that this test system is a practical tool in the occupational setting suggests that a larger study of the effects of mercury exposure on dentists would be appropriate.”

“The authors determined the number and surface area of occlusal dental amalgams in a group of 129 Roman Catholic sisters who were 75 to 102 years of age. Findings from this study of women with relatively homogeneous adult lifestyles and environments suggest that existing amalgams are not associated with lower performance on eight different tests of cognitive function.”

“The new fields of behavioral toxicology and behavioral teratology investigate the outcome of specific toxic exposures in humans and animals on learning, memory, and behavioral characteristics. Three important classes of behavioral neurotoxicants are metals, solvents, and pesticides. The clearest data on the deleterious effects of prenatal exposure to toxicants comes from the study of two metals, lead and mercury, and from epidemiological investigations of the effects of alcohol taken during pregnancy. Less complete data are available for two other groups of agents, solvents and pesticides. What we do know about their effects on the fetal brain is convincing enough to make us demand caution in their distribution.”

“Amalgam fillings constitute, after food, the main source of exposure to mercury for the general population. An evaluation of potential health risks has to be based on the dose of mercury released from the fillings. This dose is estimated by a new procedure of mercury speciation which elutes the released elemental and inorganic mercury with solvents of different polarity (paraffin and saline). In vitro tests with spherical amalgam pellets have shown that mercury release into the solvents is linearily correlated to time and amalgam surface area. Doses estimated in volunteers by this method average 4.5 micrograms/day (range 0.3-13.9), as compared to a dose of 3.4 micrograms/day (range 0.1-11.8) measured conventionally in the oral air. The aforementioned dose, combined with the nearly equal mercury uptake from food, is below the acceptable daily intake of 40 micrograms for all forms of mercury.”

Thirteen patients with symptomatic oral lichen planus had been shown by patch testing to be allergic to ammoniated mercuric chloride. Replacement of amalgam restorations in these patients effected an improvement in all but one case. In some cases the resolution of symptoms was dramatic following the replacement of one or two fillings. The authors feel that the removal of all amalgam fillings need not be necessary except in the most intractable case.

The corresponding systemic uptake of Hg was estimated to 12 µg/d based on external data relating air Hg°-exposures to urinary Hg-excretions. The worst case individual showed a gross mass balance of 200 µg Hg/d connected to a systemic uptake of 70 µg Hg/d. These values were compared to the average intake of to al-Hg by a Swedish diet (2 µg/d) and to the WHO’s tolerable value for intake of total-Hg by food (45 µg/d). Upscaled to the entire Swedish population (8 mill.), the data suggests a fecal/urinary emission to the environment of 100 kg Hg yearly originating from a population load of amalgam fillings containing 90,000 kg of Hg.

“Exposure thresholds for health effects associated with elemental mercury (Hg degree) exposure were examined by comparing behavioral test scores of 19 exposed (mean urinary Hg = 36 micrograms/l) with those of 20 unexposed dentists. Thirty-six micrograms Hg/l is 7 times greater than the 5 micrograms Hg/l mean level measured in a national sample of dentists. To improve the distinction between recent and cumulative effects, the study also evaluated porphyrin concentrations in urine, which are correlated with renal Hg content (a measure of cumulative body burden). Subjects provided an on-site spot urine sample, were administered a 1-h assessment consisting of a consent form, the Profile of Mood Scales, a symptom and medical questionnaire, and 6 behavioral tests: digit-span, symbol-digit substitution, simple reaction time, the ability to switch between tasks, vocabulary, and the One Hole Test. Multivariate regression techniques were used to evaluate dose-effects controlling for the effects of age, race, gender and alcohol consumption. A dose-effect was considered statistically significant below a p value of 0.05. Significant urinary Hg dose-effects were found for poor mental concentration, emotional lability, somatosensory irritation, and mood scores. Individual tests evaluating cognitive and motor function changed in the expected directions but were not significantly associated with urinary Hg. However, the pooled sum of rank scores for combinations of tests within domains were significantly associated with urinary Hg, providing evidence of subtle preclinical changes in behavior associated with Hg exposure. Coproporphyrin, one of three urinary porphyrins altered by mercury exposure, was significantly associated with deficits in digit span and simple reaction time.”(ABSTRACT TRUNCATED AT 250 WORDS)

“Mercury is released from amalgam fillings in several forms, i.e. as elemental vapour, ions and in fine particles. Despite many investigations there is still considerable uncertainty concerning the uptake of such mercury. Most available estimates have calculated the pulmonary uptake of mercury vapour based on measurements of concentrations intra-orally or in expired breath. Presented estimates vary by an order of magnitude from approximately 1 to 20 micrograms/day. The possibility of estimating this uptake based on levels of mercury in a biological index medium has received comparatively little attention. The purpose of the present work is to estimate the uptake of mercury from amalgam fillings based on urinary concentrations of mercury. It is estimated that the average uptake of mercury from amalgam fillings in Swedish subjects is within the interval 4-19 micrograms/day. This interval was arrived at after a detailed evaluation of the uncertainties in the data used and in the different assumptions. Notwithstanding the considerable range of this estimate it indicates a higher uptake than several other estimates, some of which have had a large impact on the scientific debate concerning this issue.”

“Six groups of genetically mercury-susceptible female SJL/N (H-2s) mice were exposed to mercury vapor at a concentration of 0.3-1.0 mg Hg/m3 air for 0.5-19 hr/day 5 days a week for 10 weeks. The absorbed doses were calculated to be between 75 and 2365 micrograms Hg/week/kg body wt (micrograms Hg/week/kg). The correlation between the dose and the concentration of Hg in kidney, spleen, and thymus was highly significant (p < 0.0001; Spearman’s rank correlation test). The lowest observed adverse effect level (LOAEL) for serum IgG antinucleolar antibodies (ANoA) was 170 micrograms Hg/week/kg, corresponding to a renal mercury concentration of 4.0 +/- 0.76 micrograms Hg/g wet wt. The correlation between the absorbed dose and the ANoA titer was highly significant (p < 0.0001; Spearman’s rank correlation test), and all mice were ANoA-positive at a dose of 480 micrograms Hg/week/kg. High-titer ANoA targeted the nucleolar 34-kDa protein fibrillarin. The LOAEL for B-cell stimulation, measured as an increase in serum IgG2a and IgG1 concentrations, was 360 micrograms Hg/week/kg, but the increase was fivefold higher and also included IgE at a dose of 690 and 2365 micrograms Hg/week/kg. The serum Ig concentrations peaked after 2-4 weeks and then slowly declined but, except for IgE, remained significantly increased during the entire exposure time. Glomerular, mesangial IgG immune complex (IC) deposits, accompanied by systemic vessel wall IC deposits, were first detected at a dose of 480 micrograms Hg/week/kg. The mesangium also showed increased titers of IgM IC deposits and complement factor C3c. The correlation between the absorbed dose, and the individual titer of IgG, IgM, and C3c, was highly significant (p < 0.0001; Spearman’s rank correlation test). In conclusion, mercury vapor efficiently induced an autoimmune syndrome in genetically susceptible mice, and the LOAEL for the adverse effects varied in the order ANoA < B-cell stimulation < IC deposits. Comparing the body burden of mercury in mice at the LOAEL for autoantibodies with the body burden in populations of occupationally exposed humans suggests that the safety margin may be narrow for genetically susceptible individuals.”

“There are insufficient published data on the potential health effects of dental amalgam specifically to support or refute the diverse variety of health effects attributed to it. Numerous studies constantly report effects on the central nervous system (CNS) in persons occupationally exposed to Hg. Virtually all studies failed to detect a threshold for the effects CNS measured. A tolerable daily intake (TDI) of 0.014 µg Hg/kg body weight/day was proposed for mercury vapour, the principal form of mercury to which bearers of amalgam fillings are exposed. This TDI was based on a published account of sub-clinical (i.e. not resulting in overt symptoms or medical care) CNS effects in occupationally exposed men, expressed as slight tremor of the forearm. An uncertainty factor of 100 was applied to these data, to derive a reference dose (TDI) which should, in all probability, prevent the occurrence of CNS effects in non-occupationally-exposed individuals bearing amalgam fillings.”

Author: Richardson GM and Canada.