G14 (I) Health effects of mercury

Persistent pollutants in the Arctic have received much attention. It is well known that these contaminants accumulate in food webs and potentially can cause severe physiological damages to top level predators, including humans. People in Arctic regions tend to be more exposed to these pollutants due to a potential high intake of wild fish and animals. In most Norwegian studies, focus has been on persistent organic pollutants (POPs), rather than mercury, although food consumption limits for fish often are driven by Hg. The present study assesses mercury exposure and seriousness of Hg in a population in northern Norway.

Through a large epidemiological public health survey in the municipality of Tromsø, Northern Norway, around 13 000 people aged 30 to 87 delivered hair samples as well as blood and supporting health information. In addition two questionnaires related to potential contaminant exposure and other health related issues has been answered by each participant.

Over 5000 hair samples have been analysed for mercury in order to evaluate the levels and seriousness of Hg exposure in the general Tromsø population in relation to diet. Additionally, the connection to the Tromsø health survey eventually will enable assessment of links between mercury exposure and possible health impacts of mercury in the adult population.

Tromsø is a coastal town with high access to high quality fresh fish and seafood. The dietary patterns show that many participants have a high intake of fish and seafood. However, due to relatively low Hg concentrations in the most commonly consumed fish species, few participants exceed the JECFA PTWI of 1.6 µg/kg bw/week. Hg concentration levels in this Norwegian population are low compared to values reported for other populations in the Arctic, especially indigenous populations in Greenland and Arctic Canada.

The association between mercury exposure and neuropsychological outcomes such as IQ has been demonstrated in several cohort studies with individual-level measurements, and provides the basis for current mercury regulation. The extent to which contemporary mercury exposure is associated with clinically-relevant neurological disorders (e.g., autistic spectrum disorders) is less well studied, although associations have been reported in a several studies with group-level outcome measurements ("ecological studies") and/or group-level exposure measurements. Although the results of these studies are viewed with caution by most scientists due to the fact that group-level associations often differ from individual-level associations, group-level studies do influence public perception. Published studies on mercury have used surrogate or group-level variables for exposure (e.g. proximity to coal fired power plants, regional precipitation patterns, wood smoke particulate) and group-level data on special education services to characterize disability prevalence. For example, we reanalyzed data examining the effect of using different group-level mercury exposure surrogates (e.g., reported emissions levels, downwind status from a power plant, local fish consumption advisories) on autism prevalence in school districts in the U.S. State of Texas. Using multilevel Poisson regression analysis we found associations between air mercury emissions and autism prevalence in some years, but not consistently over time. Results were sensitive to assumptions about presumed lag time between mercury emissions and autism development. Evaluations using other surrogate exposure variables did not yield statistically significant associations. We also observed that the treatment of censored data (due to privacy protections in reporting of low special education enrollment counts) had an important effect on the analysis; associations that were large when censored data were handed as zeros (RR=4.44, 95% CI: 4.16-4.74) became much smaller when censored data were treated as the mid-point of the censored range (RR=1.28, 95% CI: 1.00-1.63). Mercury health effects are most appropriately assessed through well controlled case-control or cohort studies with appropriate individual-level measurements; government agencies, advocacy groups and mercury emitting industries should consider supporting such studies so that emerging questions concerning the health effects of mercury can be reliably addressed.

Methylmercury (MeHg) exposure assessments among average fish consumers in the United States may underestimate exposures among U.S. subpopulations with high intakes of region­ally specific fish. To address this, we examined relationships among fish consumption, estimated mercury (Hg) intake, and measured Hg exposure within one such potentially highly exposed group, recreational anglers in the state of Louisiana, USA. We surveyed 534 anglers in 2006 using interviews at boat launches and fishing tourna­ments combined with an Internet-based survey method. Hair samples from 402 of these anglers were collected and analyzed for total Hg. Questionnaires provided information on species-specific fish consumption during the 3 months before the survey. Anglers’ median hair Hg concentration was 0.81 µg/g (n = 398; range, 0.02–10.7 µg/g); 40% of participants had levels >1 µg/g, which approximately corresponds to the U.S. Environmental Protection Agency’s reference dose. Fish consumption and Hg intake were significantly positively associated with hair Hg. Participants reported consuming nearly 80 different fish types, many of which are specific to the region. Unlike the general U.S. population, which acquires most of its Hg from commercial seafood sources, approximately 64% of participants’ fish meals and 74% of their estimated Hg intake came from recreationally caught seafood. In conclusion, study participants had relatively elevated hair Hg concentrations and reported con­sumption of a wide variety of fish, particularly locally caught fish. This group represents a highly exposed subpopulation with an exposure profile that differs from fish consumers in other regions of the United States, suggesting a need for more regionally specific exposure estimates and public health advisories.

The use of mercury in dentistry (Source: WorlDental.org):

• Silver Fillings – also called amalgams – are compromised of 50% mercury and 30% silver, with the remaining amounts of copper, tin and zinc
• The American Dental Association (“ADA”) reports that 76% of their members use amalgams with their patients
• A poll of U.S. dental patients found that 72% were not aware that mercury was the main component of dental amalgam, and 92% wished to be told about mercury before receiving it in a filling
• In 2008 silver (amalgam) dental fillings were banned in Sweden, Denmark and Norway - three of the top ten countries globally with the greatest number of dentists per capita

• Points of view and recommendations from the U.S. Agency for Toxic Substances and Disease Registry, and Health Canada
• Discussion that mercury remains chemically locked within “extremely stable” dental fillings
• Mercury’s role in electromagnetic – galvanic interaction with other dental materials such as silver, copper, tin and zinc – even gold
• Safe protocols for amalgam removal and restoring the mouth with biocompatible materials

  Dr. Colson works with an integrative approach and practices minimally invasive dentistry. Dr. Colson’s practice has been mercury-free for more than 25 years, and she is an accredited memner of the I.A.O.M.T. She studies biological dentistry and utilizes acupuncture, homeopathy and reflexology and works with other health care practitioners to help patients become metal free using safe removal protocols. State of the art technologies - such as lasers, ozone and digital radiography - are hallmarks of her practice. Dr. Colson’s new book, Your Mouth, Your Health and You - is a yoga-based approach to exploring the connections between oral health, whole body wellness and longevity.

Although the toxicity of mercury is species dependent, most studies only measure total and not speciated mercury. In this cross-sectional study, we measured speciated mercury in umbilical cord blood among 300 newborns and compared these concentrations with birth outcomes. Methyl mercury (MeHg), inorganic mercury (IHg) and ethyl mercury (EtHg) were measured using inductively coupled plasma mass spectrometry (ICP-MS). Only 2 out of 300 individuals had observable levels of EtHg. MeHg and IHg were both lognormally distributed. We used values above the detection limit (MeHg: 84%, IHg: 22%) and observable values below the detection limit (MeHg: 8%, IHg: 46.7%). We imputed lower values using the lowest observed measurement divided by √2. Geometric means for MeHg and IHg were 0.94 µg/L (95% confidence interval: 0.84, 1.06) and 0.12 µg/L (0.09, 1.45) respectively. A multivariable linear regression model for ponderal index included both MeHg and IHg and controlled for maternal age, primiparity, prepregnancy body mass index, race, smoking, hypertension, diabetes, infant gestational age as well as umbilical cord serum selenium and fatty acids (n=271). Each unit increase of ln(MeHg) was related to a statistically significant decrease in ponderal index of -0.04 g/cm³*100 (-0.08, -0.003), whereas each unit increase of ln(IHg) was related to an statistically significant increase in ponderal index of 0.02 (0.001, 0.04). Limiting the analysis to values that were above the detection limit or observable for MeHg and IHg (n=182) strengthened the relationship of MeHg and attenuated the relationship of IHg with ponderal index. The direction of the relationship of MeHg or IHg with ponderal index was the same when only one mercury species was present in the model, but the relationships were no longer statistically significant. There was no indication of interaction between selenium and mercury in this analysis. These results suggest the relationship of mercury with ponderal index could be dependent on mercury species.

In 1986-1987, a birth cohort of 1022 subjects was formed in the Faroe Islands, and the prenatal exposure to methylmercury was assessed by analysis of the mercury concentration in cord blood and in maternal hair. Follow-up took place at age 7 and 14 years, and most recently at age 22 years, where 846 (84%) cohort members underwent detailed examinations by clinical specialists. Mercury-associated neurodevelopmental delays have been documented in regard to language, attention, verbal memory and other functions, and these findings have now been extended into young adulthood. In addition, cord blood from cohort members has now been analyzed for polychlorinated biphenyls (PCBs) to address the possible, though weak, confounding from concomitant PCB exposure, originating from pilot whale blubber. Although the marine diet in the Faroes includes copious mounts of fish, most of the methylmercury exposure in this population comes from traditional pilot whale consumption. Adjustment for maternal fish intake during pregnancy results only in a small increase in the point estimates for mercury associated deficits. Further, selenium is present in much higher concentrations in cord blood than mercury, and adjustment for selenium does not affect the results. Similar findings have been reported in subsequent studies of human methylmercury toxicity, where negative confounding from fish intake was controlled for. Based on the new data from the Faroes, the developmental neurotoxicity caused by this pollutant must be considered to be permanent.

It is known that perinatal exposure to methylmercury (MeHg) affects child neurodevelopment adversely. MeHg accumulates in humans mostly through consumption of fish and shellfish. From the nutritional point of view, fish is beneficial for pregnant women and unborn babies because it is rich in nutrients such as polyunsaturated fatty acids (PUFA), especially docosahexaenoic acid (DHA) and selenium (Se). Several cohort studies reported that maternal fish intake was associated with higher scores in neurodevelopmental tests, though there has been disagreement concerning the adverse effect of prenatal exposure to MeHg on child neurodevelopment. Therefore, these health hazard issues are particularly important in fish-eating populations. We have conducted Tohoku Study of Child Development (TSCD), focusing on both the potential risks and benefits of fish intake during pregnancy. The research is being conducted of two areas, an urban area and a coastal area, in the northeastern area of Japan. In the urban area, prenatal exposure to MeHg was found to adversely affect the motor cluster of the Neonatal Behavioral Assessment Scale (NBAS) that was assessed at three days after birth. In contrast, maternal seafood intake appears to be beneficial. In this study, we examined the associations of neurodevelopment of neonates registered in the coastal area with the cord blood total mercury (THg), maternal plasma DHA and cord plasma Se. The NBAS was used to assess the neurodevelopment in 657 neonates three days after birth whose confounders were completely available. The associations of THg, DHA and Se with the NBAS were examined by multivariate analyses with adjustment for confounders. The median THg level was 15.7 ng/g (2.7-96.1) in cord blood. The median levels were 169.7µg/ml (56.1-464.7) for DHA in maternal plasma, and 66.3 ng/g (42.5-103.3) for Se in cord plasma. A negative relation was found between THg in cord blood and the Regulation of State cluster of the NBAS, even after adjusting for possible confounders such as birth weight, birth order and gender. Se in cord blood was positively associated with the Autonomic Stability cluster of the NBAS, but the significant correlation disappeared when entering birth weight. No significant correlation was seen between any NBAS cluster and DHA in maternal blood. In conclusion, perinatal exposure to MeHg adversely affects the Regulation of State. A positive effect of Se on the Autonomic Stability was suggested, though such neurobehavioral function, assessed by the NBAS, appears to be associated with confounders like birth weight.

Methylmercury-associated effects on the cardiovascular system have been documented though discrepancies exist. Most studied populations experience elevated methylmercury exposures. Further, few have investigated the impact of low-level elemental mercury exposure. This study explored the association between mercury exposure (methylmercury via hair and blood, elemental mercury via urine) and blood pressure measures using the U.S. National Health and Nutrition Examination Survey (NHANES, 1999-2006) and a cohort of dental professionals that experience background exposures to both mercury forms. Information on demographics, occupational practices, medical history, and fish consumption was collected from dental professionals recruited during the 2010 Michigan Dental Association (MDA) Annual Convention. Hair and urine samples were analyzed for mercury, and blood pressure (systolic, SBP; diastolic, DBP) was measured in the dental cohort (n=262). Hair mercury levels were available for female NHANES participants (n=1150), and urine and blood mercury, SBP and DBP were obtained from male (n=1377) and female (n=3932) NHANES subjects. Distribution of mercury in hair in the dental cohort (median, range: 0.28, 0.02-5.18 µg/g) and urine (0.63, 0.03-5.54 µg/L) correspond well with the NHANES data. Linear regression models adjusting for potential confounders (BMI, age, gender) in the MDA cohort revealed a significant positive association between DBP and hair mercury (ß (standard error, SE)=2.76 (1.17) mm Hg, p=0.02). An association of the same direction was observed between SBP and hair mercury, though this was not significant (ß (SE)=2.67 (1.68) mm Hg, p=0.11).Urine mercury results opposed hair mercury in many ways. Notably, elemental mercury exposure was associated with a significant SBP decrease driven by the male population (ß (SE) for males: -3.26 (1.23) mm Hg, p=0.01; for females: 0.71 (1.35) mm Hg, p=0.6). Linear regression modeling of the NHANES data revealed a positive relationship between total mercury in blood and DBP after adjusting for confounders (ß (SE)=0.14 (0.05), p<0.05). Urine mercury was inversely associated with SBP in both males and females, and the association was stronger in males (ß (SE): -1.17 (0.41) vs. -0.28 (0.1) mm Hg; p<0.01). Overall, this study found associations between blood pressure and two forms of mercury in two cohorts at exposure levels relevant to the general population. These relationships varied according to gender and type of mercury exposure.