Content uploaded by G. Mark Richardson
Author content
All content in this area was uploaded by G. Mark Richardson on Mar 26, 2015
Content may be subject to copyright.
A preview of the PDF is not available
Assessment of mercury exposure and risks from dental amalgam
Figures
Figures - uploaded by G. Mark Richardson
Author content
All figure content in this area was uploaded by G. Mark Richardson
Content may be subject to copyright.
... The portion of persons in the general public is about 1 to 4% [52]. Richardson concludes that approximately 20% of the general public may experience subclinical central nervous system and/or kidney function impairment due to amalgam fillings [53]. ...
... Cysteine and glutathione synthesis are crucial for mercury detoxification, and are reduced in autistic children, possibly due to genetic polymorphisms [53,75]. Therefore, autistic children have 20% lower levels of cysteine and 54% lower levels of glutathione, which adversely affect their ability to detoxify and excrete metals like mercury [53,76]. ...
... Cysteine and glutathione synthesis are crucial for mercury detoxification, and are reduced in autistic children, possibly due to genetic polymorphisms [53,75]. Therefore, autistic children have 20% lower levels of cysteine and 54% lower levels of glutathione, which adversely affect their ability to detoxify and excrete metals like mercury [53,76]. This leads to a higher concentration of free mercury in blood, which then transfers into tissues and increases the half-life of mercury in the body, as compared to children with normal levels of cysteine and glutathione [54]. ...
... An assessment of mercury (Hg) exposure and risks from dental amalgam was completed for Canada in 1995 (Richardson and Allan 1996; also released as Health Canada 1995a). Dental amalgam fillings are a major source of Hg exposure in Canada, compared to food (including fish), indoor and outdoor air, drinking water and soil (Health Canada 1995a, 1996 Richardson and Allan 1996; Richardson et al. 1995). The primary route of exposure to Hg from amalgam is via inhalation of Hg 0 vapor emanating from in-place amalgam fillings (Richardson et al. 2011; USFDA 2009; Richardson and Allan 1996; Health Canada 1995a; WHO 1991). ...
... Dental amalgam fillings are a major source of Hg exposure in Canada, compared to food (including fish), indoor and outdoor air, drinking water and soil (Health Canada 1995a, 1996 Richardson and Allan 1996; Richardson et al. 1995). The primary route of exposure to Hg from amalgam is via inhalation of Hg 0 vapor emanating from in-place amalgam fillings (Richardson et al. 2011; USFDA 2009; Richardson and Allan 1996; Health Canada 1995a; WHO 1991). Increasing dental amalgam load has been associated with altered urinary porphyrin profiles indicative of alteration of the heme synthesis pathway (Geier et al. 2011; Woods et al. 2012). ...
... The Guidelines for Canadian Drinking Water Quality, which are used to regulate municipal drinking water quality across the country, are derived to deliver a dose via tap water consumption that does not exceed Canadian RELs (Health Canada 1995b). The previous assessment by Health Canada (Richardson and Allan 1996 ) employed Canadian dental health data collected between 1970 and 1972 and assumed that all in-place fillings were composed of dental amalgam. The trend in dental care since that time has been away from dental amalgam and toward aesthetic (toothcolored ) dental restorative materials. ...
Dental amalgam is 50% metallic mercury (Hg0) by weight and causes Hg exposure. The first assessment of Hg exposure and risk from dental amalgam in Canada was published in 1996. Recent data provided the opportunity to update that assessment. During the Canadian Health Measures Survey (CHMS; 2007 to 2009) the number of tooth surfaces specifically restored with dental amalgam was recorded. Data were also collected on the concentration of Hg in urine of survey participants. These data were employed to determine Hg exposures in the Canadian population. Also determined was the number of amalgam-restored tooth surfaces that would not result in exposure exceeding the dose associated with Canada's reference exposure level (REL) for Hg0. Based on the CHMS data, 17.7 million Canadians aged ≥6 years collectively carry 191.1 million amalgam surfaces, representing 76.4 million amalgam-restored teeth. Average Hg exposures were: Children—0.065 μg Hg/kg-day; Teens—0.032 μg/kg-day; Adults—0.033 μg/kg-day; and Seniors—0.041 μg/kg-day. Of Canadians with dental amalgam restorations, 80.4% experience a daily dose of Hg that exceeds the Canadian REL-associated dose. The number of amalgam surfaces that will not result in exceeding the REL-associated dose varied from two amalgam surfaces (children, both sexes) to seven surfaces (adult males).
... For example, if an individual's amalgam restorations have a collective Hg release rate of 0.4 ng/s, and a 20-sec- ond intra-oral Hg vapor sample is collected at a flow rate of 0.75 L/min, the total amount of mercury collected will be 0.4 ng/s x 20 s = 8 ng, and the Hg vapor concentration in the air collected will be: This example illustrates why the quantity that must be determined in intra-oral Hg vapor measurements is the release rate, not the Hg vapor concentration. This fact has been almost universally recognized in recent papers on the subject (Berglund, 1990; Bjorkman and Lind, 1992; Olsson and Bergman, 1992; Skare and Engqvist, 1994; Halbach, 1995; Berdouses et al., 1995; Richardson, 1995; Berglund and Molin, 1996). Occasionally, however, intra-oral mercury vapor measurements are treated as though they are equivalent to room air measurements. ...
... When a model of mercury intake from dental amalgam is based upon a baseline (unstimulated) value and a magnification factor by which this baseline value is multiplied to obtain the stimulated value as in the case of the Health Canada assessment (Richardson, 1995)-an error in the baseline value is directly reflected in the final estimate. The Health Canada assessment predicted that an adult with approximately 8 amalgam fillings would have an absorbed dose of 3.6 jig Hg/day. ...
... The Health Canada assessment predicted that an adult with approximately 8 amalgam fillings would have an absorbed dose of 3.6 jig Hg/day. By the mere substitution of a more realistic unstimulated baseline value (0.4 jg/day per surface) rather than the Skare and Engqvist (1994) stimulated value, the daily absorbed dose estimate obtained by Richardson (1995) would be reduced to 2.0 ,ug Hg/day. The other primary correction that must be made to the Richardson model is the selection of a stimulation magnification factor that more accurately reflects the increase in mercury vapor release that occurs during the chewing of ordinary food. ...
This review examines the question of whether adverse health effects are attributable to amalgam-derived mercury. The issue of absorbed dose of mercury from amalgam is addressed first. The use of intra-oral Hg vapor measurements to estimate daily uptake must take into account the differences between the collection volume and flow rate of the measuring instrument and the inspiratory volume and flow rate of air through the mouth during inhalation of a single breath. Failure to account for these differences will result in substantial overestimation of the absorbed dose. Other factors that mus be considered when making estimates of Hg uptake from amalgam include the accurate measurement of baseline (unstimulated) mercury release rates and the greater stimulation of Hgrelease afforded by chewing gum relative to ordinary food. The measured levels of amalgam-derived mercury in brain, blood, and urine are shown to be consistent with low absorbed doses (1-3 pLg/day). Published relationships between thenumber ofamalgam surfaces andurine levels areusedtoestimate thenumber ofamal- gamsurfaces that wouldberequired toproduce the30plg/g creatinine urine mercury level stated by WHO to be associated with the most subtle, pre-clinical effects in the most sensitive individuals. From 450 to 530 amalgam surfaces would be required to produce the 30 pg/g creatinine urine mercury level for people without any excessive gum-chewing habits. The potential for adverse health effects and for improvement in health following amalgam removal is also addressed. Finally, the issue of whether any material can ever be completely exonerated of claims of producing adverse health effects is considered.
... It also means that exposure and tolerable daily intake levels applied to dental mercury amalgam should be adjusted by accounting for the age and weight of the subject. To demonstrate that such an exposure assessment is possible and feasible, the Canadian government, in its risk assessment of dental amalgam (Richardson 1995 ), was open and transparent about the prevalence of mercury fi llings in the Canadian population, with adults having up to 25 fi lled teeth and children as young as 3 years of age having fi lled teeth. Richardson ( 1995 ) was explicit in incorporating this data into the methods used to estimate exposures, and as such, Health Canada was provided with estimates of mercury vapor exposure per fi lled tooth for each of fi ve separate age groups (toddlers, children, teens, adults, and seniors). ...
... To demonstrate that such an exposure assessment is possible and feasible, the Canadian government, in its risk assessment of dental amalgam (Richardson 1995 ), was open and transparent about the prevalence of mercury fi llings in the Canadian population, with adults having up to 25 fi lled teeth and children as young as 3 years of age having fi lled teeth. Richardson ( 1995 ) was explicit in incorporating this data into the methods used to estimate exposures, and as such, Health Canada was provided with estimates of mercury vapor exposure per fi lled tooth for each of fi ve separate age groups (toddlers, children, teens, adults, and seniors). ...
All dental amalgam fillings contain approximately 50 % elemental mercury by weight. Concerns about health risks due to continual emissions of mercury vapor from this tooth restorative material have been addressed by dentists, scientists, and government authorities worldwide and have resulted in a range of recommended practices and regulations. By reviewing articles collected by a literature search of the International Academy of Oral Medicine and Toxicology (IAOMT) database and the PubMed database, we identify health risks associated with dental mercury amalgam. We present the science of potential harm as applicable to the general population, pregnant women, fetuses, children, and dental professionals. We specifically address genetic predispositions, mercury allergies, Alzheimer’s disease, multiple sclerosis, amyotrophic lateral sclerosis, and other health conditions pertinent to dental mercury exposure. We conclude that reviews and studies of dental amalgam mercury risk should assess biocompatibility with special consideration for all populations and all risk factors.
... The general side effects could potentially be related to the release of mercury from dental amalgam [1,6,15,16]. However, the effects from individual behaviors (e.g., bruxism and chewing which is associated with increased release of mercury from dental amalgam restorations [8,17]) and possible effect modifiers like genetic polymorphisms are not known in detail [16,18]. ...
Objective: Health complaints attributed to dental amalgam fillings comprise both intraoral and general health complaints. There are data suggesting that patients with medically unexplained physical symptoms (MUPS) attributed to amalgam fillings show improvement in symptoms after removal of all amalgam fillings. However, data indicating changes of specific health complaints are limited. This study evaluated the changes of health complaints after removal of amalgam restorations in patients with health complaints attributed to dental amalgam fillings. Method: Patients with MUPS attributed to dental amalgam (Amalgam cohort) had all their amalgam fillings removed. The participants indicated an intensity of 11 local and 12 general health complaints on numeric rating scales before the treatment and at follow-up after 1 and 5 years. The comparison groups comprising a group of healthy individuals and a group of patients with MUPS without symptom attribution to dental amalgam did not have their amalgam restorations removed. Results: In the Amalgam cohort, mean symptom intensity was lower for all 23 health complaints at follow-up at 1 year compared to baseline. Statistically significant changes were observed for specific health complaints with effect sizes between 0.36 and 0.68. At the 5-year follow-up, the intensity of symptoms remained consistently lower compared to before the amalgam removal. In the comparison groups, no significant changes of intensity of symptoms of health complaints were observed. Conclusion: After removal of all amalgam restorations, both local and general health complaints were reduced. Since blinding of the treatment was not possible, specific and non-specific treatment effects cannot be separated.
... The issue of mercury and dental amalgam in dentistry revolves around the proposition that mercury leaching out of amalgam fillings may have an adverse effect on health. Richardson, [1995] concluded that the likely daily intake of mercury from dental amalgam fillings encroached substantially on a prudent safety margin between exposures and identified adverse effects. According to Fan et al., [1997] the use of dental amalgam has been discouraged In Scandinavia and elsewhere in Europe because of environmental concerns despite the apparent consistency of these findings the individual studies are very variable in terms of the strength of the conclusions that can be drawn from them. ...
Aim: The aim of the present study was to investigate children and parents preferences for den- tal restorative materials for both anterior and posterior teeth and the main reason for their selection.
Study Design: This descriptive cross sectional study recruited 71 children aged 6 to 12 years and their parents attending the dental clinics at Faculty of Dentistry, King Abdulaziz University, Jeddah - Saudi Arabia.
Methods: Parent-child pairs completed a questionnaire and viewed dental typodont models containing different dental restorations. The participants were asked to indicate their preferred type of dental restoration and give reasons for their preferences.
Results: the majority of participants favored composite and esthetic crowns for small resto- rations and esthetic crowns for large restorations. Child’s age signi cantly in uenced their rea- son of selecting anterior teeth small restoration (p=0.04). More seven years and younger children (88.10%) reported that shape and color were the main reason for their selection. The reason for parents selection of anterior teeth small restoration was signi cantly in uenced by parent’s level of education (p=0.049).
Conclusions: composite and esthetic crowns are the most preferred for small restorations while amalgam and glass ionomer were the least preferred. Shape and color are the main reason for chil- dren and parents preferences of certain restorative material.
... Richardson's report, released in 1995, was the first comprehensive risk assessment in Canada of mercury exposure from amalgam. 277 Richardson's study did not include laboratory research or clinical investigations but relied instead on sophisticated computer modelling techniques to arrive at a tolerable daily intake level for mercury. His initial simulations and calculations indicated that amalgam contributes about 50% of the daily mercury exposure for the average Canadian. ...
Executive Summary
Issue
Amalgam is a restorative material that has been widely used to treat dental caries for more
than 150 years. But because dental amalgam is partly composed of mercury (Hg), its use
has fuelled concern for decades about risks to human health. Composite resin is the most
common alternative to dental amalgam; although data indicate that rates of restoration
failure and secondary caries — as well as costs — are higher compared with amalgam. As
well, the potential for toxicity to human health from composite resin restorations vis-à-vis
compounds such as bisphenol A, for instance, remain uncertain.
Given longstanding debate around the use of dental amalgam, alongside a global impetus
to phase down its use, a comprehensive evaluation of its benefits, harms, and other
consequences is necessary to inform Canadian decision-makers. Specifically, this health
technology assessment (HTA) sought to inform the following policy question:
Should dental amalgam continue to be used in Canada?
Objectives and Research Questions
Clinical Review 1.
2.
Economic Review 3.
Patient Perspectives and Experience 4.
Implementation Issues 5.
6.
This HTA aims to inform the policy question through a comparative assessment of dental
amalgam and composite resin restorations, including investigation into the efficacy, safety,
cost-consequence, patient perspectives and experiences, implementation issues,
environmental impact, and ethical considerations.
What is the comparative efficacy of direct dental restorations made of composite resin
versus amalgam for the treatment of dental caries in permanent posterior teeth?
What is the comparative safety of dental restorations made of composite resin versus
amalgam in children and adults?
What are the comparative consequences and costs of using dental restorations made
of composite resin or amalgam for permanent teeth in Canada?
What are the perspectives and experiences of patients (adults or children), parents of
children patients, or caregivers around dental amalgam and composite resin
restorations?
What is the current use of amalgam restorations in Canadian dental practices or
programs?
What is the current use of composite resin restorations in Canadian dental practices or
programs?
HEALTH TECHNOLOGY ASSESSMENT REPORT Composite Resin Versus Amalgam for Dental Restorations: A Health Technology Assessment 12
7.
Environmental Assessment 8.
Ethics 9.
... Eine Exposition ge-genüber beiden Hg-Formen zeigt dabei einen synergistischen Effekt. Auf ähnliche Zusammenhänge deuten Untersuchungen von Drasch et al. [78]: Arbeiter in einer Goldmine, welche neben Methyl-Hg aus Fisch zusätzlich Quecksilberdampf exponiert waren, wiesen deutlich mehr neurologische Auffälligkeiten auf als eine Kontrollgruppe, deren Exposition zum größten Teil nur aus Methyl-Hg aus Fisch bestand und deren Hg-Werte im Haar und Blut im Vergleich zu den zusätzlich quecksilberdampfexponierten Personen höher waren (Mediane: Blut: 9,0 vs. 7,0 g/l; Haar: 2,65 vs. 1,71 g/l) [78,79] [111]. ...
Amalgam, welches weltweit seit 150 Jahren als Zahnfllmateri- al verwendet wird, besteht aus etwa 50 % elementarem Queck- silber und einer Mischung aus Silber, Zinn, Kupfer und Zink. Aus fertigen Amalgamfllungen werden kontinuierlich kleine Men- gen an Quecksilberdampf freigesetzt. Amalgam trgt dabei sig- nifikant zur menschlichen Quecksilberbelastung bei. Quecksil- ber kann in Organen, insbesondere im Gehirn akkumulieren, da die Bindung zu Proteinen strker als die von anderen Schwer- metallen (z. B. Blei, Kadmium) ist. Im Gehirn werden Halb- wertszeiten von 1 - 18 Jahren angenommen. Quecksilber gilt als eines der giftigsten nichtradioaktiven Elemente. Es bestehen Hinweise darauf, dass Quecksilberdampf strker neurotoxisch wirkt als Methyl-Quecksilber aus Fisch. Neuere Publikationen weisen auf das Risiko von Nierenschdigungen, neuropsycholo- gischen Beeintrchtigungen, Induktion von Autoimmuner- krankungen oder Sensibilisierungen, gesteigerte oxidative Be- lastung, Autismus, Haut- und Schleimhautreaktionen und unspezifische Beschwerden durch Amalgamexposition hin. Auch die Alzheimer-Erkrankung oder die Entwicklung einer MS wird z. T. mit einer Quecksilberexposition in Zusammen- hang gebracht. Es bestehen, mglicherweise erblich bedingt oder erworben, unterschiedliche interindividuelle Empfind- lichkeiten zur Entstehung von negativen Effekten durch Amal- gambelastungen. Quecksilbermessungen in Biomarkern sind aufgrund fehlender Korrelation zu den Quecksilberkonzentra- tionen in den Organen nur bedingt zur Abschtzung der Queck- silberbelastung der kritischen Organe geeignet. Wegen metho- discher Mngel sind manche Amalgamstudien in ihren Aussagen nur bedingt verwertbar. Eine Amalgamentfernung Abstract
1.1.1 Objectives Amalgam is used since 150 years as a dental filling material. Although the use of amalgam is decreasing nowadays, preexisting fillings are frequently encountered. A recent article with the caption “Ex Vivo Mercury Release from Dental Amalgam after 7.0-T and 1.5-T MRI“, published in the magazine Radiology, studied the subject of mercury release from amalgam fillings due to magnetic resonance imaging (MRI). The authors Yilmaz and Adisen found in an ex-vivo study that artificial saliva containing amalgam filled teeth displayed significantly increased mercury concentrations after being exposed to an MRI with a field strength of 7 Tesla (T). The mean mercury levels in the artificial saliva were 673 µg/L in the 7.0-T-MRI-group, 172 µg/L in the 1.5-T-MRI-group and 141 µg/L in the control group. Due to the potential health implications of these results the objective was to reproduce the study. The mercury release from dental amalgam after 7.0-T-MRI, 3.0-T-MRI and 1.5-T-MRI should be analyzed and the topic should be researched further. 1.1.2 Design and Methods 20 well-preserved, caries-free extracted teeth, as well as 60 extracted teeth filled with amalgam were collected. The untreated teeth were prepared ex-vivo and filled with amalgam. Two-sided cavities were opened in 20 caries-free teeth and amalgam fillings were applied. The other 60 extracted teeth were already filled with amalgam. The teeth were randomly divided into four groups and placed in 20 ml of artificial saliva. MRI-exposures were carried out for 20 minutes with a magnetic field strength of 1.5-T, 3.0-T and 7.0-T. A control group was not subjected to a scan. Each group was exposed to the various MRI-scans in a rotating order and mercury release was analyzed after each scan. Mercury levels of the saliva samples were measured using inductively coupled plasma mass spectrometry 24 hours after the scan. A total of 320 measurements of the saliva were carried out. The mean values ± the standard error were calculated using SPSS Statistics®. One way analysis of variance (ANOVA) was applied to test whether the mean difference between the individual groups are significant or not. In addition, Tukey‘s test was used to identify the group combinations which produced a significant difference. 1.1.3 Observations and Results The mean value of the mercury concentrations in the artificial saliva without exposure to an MRI was 1,4 ± 3,6 µg/L. After exposure to the 1,5-T-MRI the mean value of the mercury concentrations was 1,3 ± 3,0 µg/L, after exposure to the 3,0-T-MRI it was 0,9 ± 2,0 µg/L and after exposure to the 7,0-T-MRI it was 1,4 ± 3,5 µg/L. The mean value of the 7,0-T-MRI thus was not higher than that of the control group. The statistical analysis showed no significant differences in the measured mercury concentrations after exposure to the various magnetic field strengths and control groups. No significant association was found between increased mercury concentrations from amalgam fillings and MRI-scans. In the control group without a scan, no significantly lower values were measured. The mercury release in the group of the old filled teeth was significantly greater than that in the group of the newly filled teeth. The mean value of the preexisting fillings was 1,7 ± 3,5 µg/L and of the newly applied fillings 0,0 ± 0,3 µg/L. 1.1.4 Conclusions In summary, the results of our study showed that neither the exposure of a 7.0-T-MRI, 3.0-T-MRI nor 1.5-T-MRI resulted in an increased release of mercury from amalgam fillings in human ex-vivo teeth. The mercury concentrations measured in saliva did not differ depending on the influencing factor magnetic field strength. The outcome of the present investigation therefore does not support the results of Yilmaz and Adisen. Further studies are needed to examine the correlation between ultra-high-field-MRI and the release of mercury from amalgam fillings.
The use of dental amalgam as a restorative material has long been a contentious issue because of its elemental mercury component. While microleakage of mercury from amalgam has been conclusively confirmed over the past 30 years intensive research has failed to identify deleterious health outcomes. Mercury, as with other metals entering the body tissues, appears to be tolerated at low levels. Nevertheless, a contrary opinion is held by some professional and lay groups who advocate a zero tolerance for inhaled or ingested elemental mercury. They identify dental amalgam as an aetiological factor for neurological conditions such as chronic fatigue syndrome, multiple sclerosis and Alzheimer's disease resulting from chronic mercury poisoning. Epidemiological and clinical evidence of widespread chronic mercury toxicity associated with a body burden of amalgam has consistently failed to be established even in populations with a high prevalence of dental amalgam restorations. On current evidence, international consensus heavily supports the statement that amalgam does not constitute a health risk to patients. However, exposure to volatile free mercury in dental clinics should be controlled to eliminate occupational risk. This paper provides a general review of the current situation and issues. It offers a consensus viewpoint for practitioners and lay people in reaching an informed decision on dental amalgam restorations.
Mercury vapors are released from paint containing mercury compounds used to prolong the shelf-life of interior latex paint. To determine whether homes recently painted with paint containing mercury had elevated indoor-air mercury concentrations, we studied 37 Ohio homes. Twenty-one homes painted with mercury-containing paint a median of 86 days earlier were compared with 16 homes not recently painted with mercury-containing paint. Paint samples from the exposed homes contained a median of 210 mg Hg/L (range 120-610 mg/L). The median air mercury concentration was higher in the exposed homes (0.3 ixg/m3; range nondetectable-l,5 p,g/m 3) than in the unexposed homes (nondetectable; range nondetectable-0.3 fxg/m 3, P < 0.0001). Among the exposed homes there were seven in which paint containing <200 mg/L had been applied. In these homes, the median air mercury concentration was 0.2 Ixg/m 3 (range nondetectable
Mercury retention and distribution in organs of fetal and neonatal guinea pigs after in utero exposure to mercury vapor was investigated. Guinea pigs near term were exposed to mercury vapor at approximately 10 mg/m 3 for 150 min. Two hours after exposure, the highest mercury concentration among fetal organs was found in the liver. In the other organs, such as the kidney, brain, heart, and lung, mercury concentrations were not markedly elevated. The neonates were fostered by nonexposed mothers to minimize possible mercury intake through the maternal milk. On days 5 and 10 postpartum, the highest concentration was found in the kidney, followed by the liver, lung, and brain. All the concentrations, except the liver, were clearly elevated when compared with the concentrations in fetuses. Sephadex G-75 gel chromatography showed that a substantial portion of the mercury in the fetal liver soluble fraction was associated with metallothionein. During the neonatal development period, metallothionein levels in the liver decreased and the mercury in the fetal liver soluble fraction was eluted in the high-molecular-weight region. These results suggested that mercury initially bound to hepatic metallothionein is further distributed. Studies on the toxicological significance of mercury, thus distributed, are necessary.
In the population, there is uptake of mercury (Hg) as inorganic (mainly elemental Hg vapor, Hgo), and organic (mainly methyl-Hg, MeHg)Hg. We have monitored biologically the uptake of inorganic Hg through measurements of the Hg level in urine (U-Hg) and of MeHg through the Hg level in blood (B-Hg).
Hg exposure may occur from occupational and non-occupational sources. The most prevalent occupational exposure is to Hgo among dental personnel. However, with use of adequate methods, the exposure is low. Thus, in a recent study of 244 dentists and dental nurses, we found that the average U-Hg was only 3.3 μg/g creatinine (range up to 23), which was only slightly higher than the level found in a reference population, 2.0 μg/g crea (up to 10). Considerably higher occupational exposure to Hgo occurs in workers in chloralkali plants and fluorescent-tube factories. Such workers had U-Hg levels up to 78 μg/g crea.
In the general population, without occupational Hg exposure, the main source of exposure to Hgo is usually dental amalgam. In a recent study of 81 subjects, we found that there was a pronounced, and exponential, increase of U-Hg with a rising number of amalgam fillings. In subjects with no fillings, the level corresponded to less than 0.5 μg/g crea, in those with many fillings to 5 μg/g crea. Also, removal of all fillings resulted in a dramatic decrease of U-Hg; after one year, the level was only about 25% of that before removal.
In Sweden, the main source of exposure of MeHg is fish. All fish contain MeHg. However, the levels are particularly high in fish from lakes, rivers, and coastal waters contaminated with Hg. We have recently studied the association between fish intake and Hg exposure in a population of 396 subjects. In subjects who never had fish, the average B-Hg was 1.8 ng/g, in those who had at least two fish meals per week 6.7 ng/g. The importance of fish was also clearly demonstrated by a close association between levels of marine n-3 polyunsaturated fatty acids in serum and B-Hgs. The situation will deteriorate, as acid rain increases the fish MeHg level.