Blood MeHg Research Articles

Postnatal exposure to methyl mercury and neuropsychological development in 7-year-old urban inner-city children exposed to lead in the United States

Background: The most common route for general population exposure to methyl mercury (MeHg) is fish consumption. Recommendations to pregnant women about consuming fish contaminated with MeHg are also applied to children, but there are few studies available about the effects of low-level postnatal MeHg exposure in them.Objectives: To investigate the association between postnatal methyl mercury exposure and neuropsychological development in a study of children also exposed to lead, both measured at 7 years.Methods: We measured MeHg concentrations in blood samples from the Treatment of Lead-Exposed Children (TLC) trial in which 780 children with elevated concentrations of lead in blood were followed with neuropsychological tests from ages 12–33 months through 7 years. Here we examine blood MeHg concentration and neuropsychological test scores, both measured at age 7 years. We used a maximum likelihood method to estimate geometric mean MeHg concentration and generalized linear regression models to analyze MeHg and neuropsychological test scores.Results: Geometric mean MeHg concentration was 0.56 (95% confidence interval: 0.52, 0.59) μg/L. A 1 μg/L increase in MeHg was associated with a 2.1 (95% confidence interval: 0.4, 3.8) point increase in Full-Scale IQ and 0.2 (95% confidence interval: 0.02, 0.4) point increase in Learning Slopeindex T-score on a test of verbal memory.Conclusions: Our results suggest that the relatively low MeHg exposure in US school-aged children from this population has no detectable adverse effect on neuropsychological development. The positive associations observed between MeHg and neurodevelopment may indirectly reflect consumption of beneficial polyunsaturated fatty acids from seafood.

Four Cases of Abnormal Neuropsychological Findings in Children with High Blood Methylmercury Concentrations

BackgroundMethylmercury (MeHg) easily crosses the blood–brain barrier and accumulates in the brain. Accumulated MeHg will cause neurological symptoms. We report four pediatric cases of neuropsychological findings with high blood MeHg concentrations.Case presentationFour children were admitted for follow-up study because their total mercury (THg) concentration in the blood was found to be high during a national survey. Case 1 was a 9-year-old female with a 16.6 μg/ℓ blood THg concentration in the survey. During admission, the blood THg, hair THg, and blood MeHg concentration(mercury indices) were 21.4 μg/ℓ, 7.2 μg/g, and 20.1 μg/ℓ, respectively. In our neuropsychological examination, cognitive impairment and attention deficit were observed. Her diet included fish intake 2–3 times per week, and she had been diagnosed with epilepsy at 3 years of age. Case 2 was a 12-year-old male with blood THg of 15.4 μg/ℓ in the survey and the mercury indices were 12.7 μg/ℓ, 5.7 μg/g, and 11.8 μg/ℓ, respectively, on admission. He was also observed to have attention-deficit/hyperactivity disorder. Case 3 was a 10-year-old male child with blood THg of 17.4 μg/ℓ in the survey, and the mercury indices on admission were 21.6 μg/ℓ, 7.5 μg/g and 21.5 μg/ℓ, respectively. In his case, mild attention deficit was observed. Case 4 was a 9-year-old male with blood THg of 20.6 μg/ℓ in the survey and the mercury indices were 18.9 μg/ℓ, 8.3 μg/g, and 14.4 μg/ℓ, respectively, on admission. Mild attention difficulty was observed.ConclusionWe suggest that fish consumption may be the main source of MeHg exposure, and that MeHg may have been the cause of the neuropsychological deficits in these cases.

Fish consumption, omega-3 fatty acids, and environmental contaminants in relation to low-grade inflammation and early atherosclerosis

BackgroundFish consumption and omega-3 polyunsaturated fatty acid (PUFA) intake are shown to protect from cardiovascular diseases (CVD). However, most fish contain environmental contaminants such as dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and methylmercury (MeHg) that may have adverse effects on cardiovascular health. ObjectiveOur aim was to elucidate the associations of fish consumption, omega-3 PUFAs, environmental contaminants with low-grade inflammation, early atherosclerosis, and traditional CVD risk factors. MethodsThe Health 2000 survey participants (n=1173) represented the general Finnish population and the Fishermen study participants (n=255) represented a population with high fish consumption and high exposure to environmental contaminants. Model-adjusted geometric means and tests for linear trend were calculated for CVD risk factors by tertiles of fish consumption and serum omega-3 PUFAs, and additionally in the Fishermen study only, by tertiles of serum PCDD/F+PCB, and blood MeHg. ResultsSerum triglyceride decreased across omega-3 PUFA tertiles in both sexes and studies. Insulin resistance, C-reactive protein, tumour necrosis factor α, and interleukin 6 decreased across omega-3 PUFA tertiles among the Health 2000 survey participants. Among the Fishermen study men, insulin resistance and arterial stiffness indicated by β-stiffness index tended to increase and the RR estimate for carotid artery plaque tended to decrease across tertiles of PCDD/F+PCB and MeHg. ConclusionPreviously established hypotriglyceridemic and anti-inflammatory effects of omega-3 PUFAs were seen also in this study. The hypothesised favourable effect on insulin sensitivity and arterial elasticity was suggested to be counteracted by high exposure to environmental contaminants but the effect on plaque prevalence appeared not to be harmful.

Association between methylmercury and cardiovascular risk factors in a native population of Quebec (Canada): A retrospective evaluation

BackgroundEpidemiological evidence suggests a negative impact of methylmercury (MeHg) on cardiovascular risk factors such as blood pressure (BP) and heart rate (HR). This issue is of concern in Arctic populations such as in the Inuit of Nunavik since this contaminant is accumulated in fish and marine mammals, which still represent the subsistence diet of this population. ObjectiveWe examined the associations between MeHg and BP and resting HR among Inuit adults. MethodsThe “Santé Quebec” health survey was conducted in 1992 in the 14 villages of Nunavik and a complete set of data was obtained for 313 Inuit adults≥18 years. Blood samples were collected in order to determine total mercury, lead, total polychlorinated biphenyls (PCBs), n−3 polyunsaturated fatty acids (PUFAs), fasting glucose and lipid profile while socio-demographic variables were obtained through questionnaires. Anthropometric measurements as well as BP and resting HR were obtained using standardised protocols. Pulse pressure (PP: systolic BP minus diastolic BP) was also calculated. Multiple linear regression was used in order to determine the change in the dependent variables associated with the quartiles of MeHg concentration, taking the quartile 1 as reference. ResultsThe mean age of the participants was 38±14 years and the sample was composed of 132 men (42.2%) and 181 women (57.8%). MeHg geometric mean was 15.4μg/L (95%CI: 13.9–17.0) and levels ranged from 0.8 to 112.0μg/L. Resting HR increased linearly across quartiles of blood MeHg concentration after adjusting for confounders (p for trend=0.02). An increase of 6.9 beats per minute (bpm) between the 4th and 1st quartile was observed after adjusting for confounders. No significant association was observed between blood MeHg and systolic BP, diastolic BP or PP. ConclusionsMeHg was associated with increasing resting HR after considering traditional risk factors as well as other contaminants (lead and total PCBs) and n−3 PUFAs. In contrast, no significant association with blood pressure was observed in this study.

The relationship between the fish consumption and blood total/methyl-mercury concentration of costal area in Korea

The purpose of this study was to evaluate the relationship between fish consumption and blood THg/MeHg concentration in Korean adults by measuring MeHg concentration in blood directly. The study subjects consisted of 400 adults aged 20 or older from 30 subareas in Busan, Ulsan and Gyeongsangnam-do province in Korea from August to October, 2010. We tried to recruit the same number of male and female participants in different age groups (20s, 30s, 40s, 50s and 60s) and allocated 13–16 subjects by district to represent Hg concentration in the research areas. The geometric means of THg and MeHg concentration in blood were 5.27μg/L (5.00–5.57) and 4.05μg/L (3.81–4.32), respectively. The proportion of MeHg/THg concentration was 78.53% (77.09–79.97). MeHg concentration was higher in coastal areas (4.26μg/L) than in inland areas (3.52μg/L) and was higher in men (4.68μg/L) than in women (3.52μg/L). In male participants, blood MeHg concentration increased with increasing annual fish consumption, and the proportion of MeHg/THg concentration showed an upward trend as THg concentration increased.However, none of the measures of the proportion of MeHg/THg showed significant differences. This is the first report in Korea about the relationship between blood MeHg concentration and related factors. Our findings suggest that MeHg concentration is affected by fish consumption as well as by gender difference and drinking status. Since the pathological mechanism has not been clarified, additional studies are needed for explaining the biological and lifestyle differences in the risk of adverse health effects by Hg exposure.

Factors influencing blood mercury levels of inhabitants living near fishing areas

Methylmercury (MeHg), a well-known neuro-toxicant, is usually emitted by industrial and other man-made activities; it is ingested with seafood and shellfish, and accumulates in the human body. The aim of this study was to compare the differences in blood levels of total mercury (T-Hg) and MeHg in residents of 4 coastal sites and 4 inland sites around Taiwan. Meanwhile, the potential question is warranted to find out the association between dietary intake and MeHg accumulation. We found that coastal residents had significantly higher mean blood T-Hg levels (mean: 16.1μg/L, range: 0.9–184.9μg/L) than inland residents (mean: 11.8μg/L, range: 0.8–146.6μg/L). The same was for blood MeHg levels: coastal residents (mean: 16.5μg/L, range: 0.9–184.9μg/L), inland residents (mean: 11.8μg/L, range: 2.1–133.4μg/L). These elevated levels were positively associated with seafood and shellfish consumption. However, the nature of their residential area may also be an important factor, because the highest T-Hg and MeHg levels were found in residents of a relatively non-industrialized area. To protect vulnerable population—especially children and pregnant women—it is important to know whether locally caught or raised and consumed fish has any source of Hg and MeHg pollution.

Biomarkers of low-level mercury exposure through fish consumption in pregnant and lactating Slovenian women

In order to assess the mercury exposure of pregnant and lactating women in Slovenia, levels of total mercury (THg) and methylmercury (MeHg) were determined in hair, cord blood and breast milk. In addition, the frequency of fish consumption was estimated, because fish is generally the main pathway for human exposure to MeHg. Hair samples were collected from 574 women participating in this study, while cord blood and breast milk samples were collected from 446 and 284 women, respectively. As expected, the levels of THg in hair (median (Med)=297ng/g, 10th percentile (P10)=73ng/g, 90th percentile (P90)=781ng/g), cord blood (Med=1.5ng/g, P10=0.5ng/g, P90=4.2ng/g) and breast milk (Med=0.2ng/g, P10=0.06ng/g, P90=0.6ng/g) were low, due to low consumption of fish (X=25g/day). A significant linear correlation was found between levels of lnTHg in hair and lnTHg in cord blood (r=0.87, 95% confidence interval (CI): 0.84–0.89), between levels of lnTHg in hair and lnMeHg in cord blood (r=0.94, 95% CI: 0.90–0.96) and between lnTHg levels in cord blood and lnTHg levels in breast milk (r=0.36, 95% CI: 0.25–0.47). Spearman's rank correlations between the frequency of fish consumption and THg in hair (rs=0.35, 95% CI: 0.28–0.42), and between the frequency of fish consumption and THg in cord blood (rs=0.43, 95% CI: 0.36–0.51) or MeHg in cord blood (rs=0.31, 95% CI: 0.06–0.52) were weak. This could be due to the approximate information on fish consumption obtained from the questionnaires, the high variability of MeHg concentrations in fish and a relatively high proportion of inorganic mercury in the biomarkers which originates from sources other than fish. In conclusion, THg levels in cord blood, THg levels in hair and MeHg levels in cord blood are suitable biomarkers of low-level Hg exposure through fish consumption. Compared to cord blood, hair samples are easy to collect, store and analyse.

Evaluation of Background Mercury Level From the Residents Living in Vicinity of Fishing Area Around Taiwan

PP-30-091 Background/Aims: The chemicals form of mercury (T-Hg) that is of primary methylmercury (MeHg), a well-known neurotoxicant. The primary public health significance is MeHg, which was usually emitted from industrial and man-made activities and final bioaccumulated to people. This study aims to investigate the blood Hg and MeHg concentration in people living in the vicinity of 4 coastal sites and 4 suburban sites around Taiwan. Meanwhile, the fish consumption and dietary habits are also been included to evaluate the association between dietary intake and MeHg accumulation. Methods: For measurement of human blood T-Hg and MeHg levels, 4 areas, 8 sampling sites around 4 areas, in east, south, west, and north of Taiwan were selected. In each area, one town was selected as coastal sites and other one was reference site. A total of 565 T-Hg measurements and 414 MeHg measurements were completed in this study. Results: Significantly higher average blood T-Hg level was found in coastal area (16.1 ng/L) than in reference site (11.8 ng/L), as well as significantly higher blood MeHg level was found in coastal area (16.5 ng/L) than in reference site (11.8 ng/L). Meanwhile, significantly higher T-Hg level was found in east, following in south, and the lower was in north and centre Taiwan. Multiple liner regression also showed the positive associations for fish consumption, age, whether living in coastal or suburban areas, and locations of where they lived around Taiwan. Conclusion: Fish consumption is the popular food in Taiwanese. The present showed fish consumption was a significant influence factor for people's T-Hg and MeHg accumulation. However, the highest T-Hg and MeHg levels were found in some area, such as east, an unpolluted area in Taiwan. The considerable strong point and local mercury sources need to be concerned.

Mercury Concentration of Whole Blood and Red Blood Cell in Taiwan Residents

PP-31-151 Background/Aims: People are exposed to different forms of mercury (Hg), and about 80% of methylmercury (MeHg) in blood is associated with red blood cells (RBC), where it is largely bound to hemoglobin. We aimed at measuring the Hg concentration in whole blood (WB) and RBC and evaluating their correlation in Taiwan residents. Methods: We recruited 43 volunteers (18 male and 23 female) aged between 19 and 48 years who were not exposed to Hg. Samples of blood (5 mL) were collected and 3 mL RBC was obtained at the same time. The amount of total Hg in WB and RBC is determined by using cold vapor atomic absorption spectroscopy. The WB and RBC samples were treated by microwave-assisted digestion to reach complete solubilization before determination. Results: We found 95% of Hg kept in RBC, the concentration of Hg in WB and RBC was 5.91 ± 2.81 and 11.22 ± 5.68 ng/g, respectively. A high correlation of Hg concentration between WB and RBC was observed (r = 0.93, P < 0.001), this correlation was higher in males (r = 0.95) than that in females (r = 0.90). We divided volunteers into 2 groups by median of age; both WB and RBC Hg concentrations were found almost the same in these 2 metrics. The Hg concentration of WB observed in males was higher than in females (6.14 vs. 5.72 ng/g, P = 0.34), however, in RBC, the results showed adverse direction (10.47 vs. 11.80, P = 0.28). Conclusion: We found the WB and RBC Hg concentrations in Taiwan residents were 5.91 ± 2.81 and 11.22 ± 5.68 ng/g, respectively, this level was higher as compared with the residents of United States and European countries.

Blood concentration of methylmercury in relation to food consumption

Dietary fish is the main source of methylmercury (MeHg) for man, and fish consumption has been used as a measure of MeHg exposure. However, other dietary sources of exposure exist and MeHg metabolism may also be modified by nutritional factors. The aim of the present study was to examine the association between blood MeHg concentration and consumption of different foods in a Finnish population with high fish consumption. Blood samples, a detailed FFQ and additional frequency data on fish consumption were collected. MeHg was analysed from whole blood by the isotope dilution method with high-resolution MS. The consumption of different foods was calculated by MeHg quartiles and tested for linear trend. Finnish southern and south-western coast of the Baltic Sea. Two hundred and ninety-nine professional fishermen, their spouses and other family members. Mean (range) blood MeHg concentration was 4·6 (0·21-22) μg/l among men and 2·8 (<0·15-20) μg/l among women. Fish had the strongest positive association with MeHg (P for linear trend <0·001 among both men and women). Among men, positive associations were also observed for fruit vegetables, wheat and wine. Among women, positive associations were observed for root vegetables, legumes, potato and game, but adjustment for fish consumption attenuated these trends. The study shows that, besides fish, MeHg may have other dietary sources that should be taken into account in risk assessment studies. Due to the observed high blood MeHg concentration, a thorough exposure assessment among the general Finnish population is recommended.

Does background postnatal methyl mercury exposure in toddlers affect cognition and behavior?

Because the toxicological effects of mercury (Hg) are more serious in the developing central nervous system of children than adults, there are growing concerns about prenatal and early childhood Hg exposure. This study examined postnatal methylmercury (MeHg) exposure and cognition and behavior in 780 children enrolled in the Treatment of Lead (Pb)-exposed Children clinical trial (TLC) with 396 children allocated to the succimer and 384 to the placebo groups. Mercury exposure was determined from analyses of blood drawn 1 week before randomization and 1 week after treatment began when succimer had its maximal effect on blood Pb (PbB). The baseline MeHg concentrations were 0.54 μg/L and 0.52 μg/L and post-treatment concentrations were 0.51 μg/L and 0.48 μg/L for placebo and succimer groups, respectively. Because the baseline characteristics in the two groups were balanced and because succimer had little effect on MeHg concentration and no effect on the cognitive or behavioral test scores, the groups were combined in the analysis of MeHg and neurodevelopment. The children's IQ and neurobehavioral performance were tested at age 2, 5 and 7 years. We saw weak, non-significant but consistently positive associations between blood MeHg and IQ test scores in stratified, spline regression and generalized linear model data analyses. The behavioral problem scores were constant or decreased slightly with increasing MeHg concentration. Additional adjustment for PbB levels in multivariable models did not alter the conclusion for MeHg and IQ scores, but did confirm that concurrent PbB was strongly associated with IQ and behavior in TLC children. The effects of MeHg on neurodevelopmental indices did not substantially differ by PbB strata. We conclude that at the present background postnatal MeHg exposure levels of US children, adverse effects on children's IQ and behavior are not detectable.

Longitudinal Cohort Study of Prenatal Exposure to Mercury in the Mediterranean Region

ISEE-0667 Background/Objectives: Neurotoxicity from prenatal exposure to methylmercury has been studied but no firm conclusions have been reached on the dose-response relationship, especially at levels of exposure less than 10 ppm. This study has enrolled a total of 1700 pregnant women and their children in Slovenia, Croatia, Italy and Greece to assess the impact of mercury exposure through fish consumption during pregnancy on child neurodevelopment. We present here results at baseline on levels of total mercury (THg) and methylmercury (MeHg) in maternal hair in relation to fish consumption patterns during pregnancy and estimate correlations between THg and MeHg concentrations in maternal hair and between maternal and cord blood. Methods: Maternal hair, blood, and cord blood samples are collected at different times during pregnancy and after delivery. THg in hair is analysed by CV-AAS and, in subjects whose hair THg exceeds 1 ppm, MeHg in hair and blood samples is determined by gas chromatography. We assessed fish consumption through food frequency questionnaires administered during pregnancy and 1–3 months after delivery, respectively. Results: Mean THg in hair is 0.94 ppm, with 69% <1 ppm and 10% >2 ppm. Less than one serving/week of fresh fish is consumed by 45% of mothers and >3 servings/week by 8%, with a correlation between hair THg and fresh fish consumption (rs = 0.45, P < .0001) during pregnancy. In paired samples, THg in maternal hair and maternal blood are highly correlated (r = 0.88, P < .0001) as well as MeHg in maternal blood and THg in maternal hair (r = 0.78, P < .0001). There is a moderate correlation between THg in maternal hair and MeHg in cord blood (r = 0.57, P < .0001). In maternal hair samples with THg >1ppm, 98% of total mercury is methylmercury. Conclusion: Current mercury levels in hair are low, but there is a correlation between consumption of fresh fish and hair THg levels.

Cognitive function and blood methylmercury in adults living near a deserted chloralkali factory

We assessed the association between blood methylmercury (MeHg) and cognitive function in 240 adult residents living near a deserted chloralkali plant. Total mercury (T-Hg) in the blood, MeHg, and health and dietary related questionnaire were examined for all participants. The Cognitive Abilities Screening Instrument (CASI C-2.0) and Mini-Mental State Examination (MMSE) were used to assess the participants’ cognitive functions. We found a significantly high correlation ( r=0.979; p<0.001) between blood T-Hg (17.3±10.9 μg/L) and MeHg (15.3±9.2 μg/L). We also found significantly higher blood MeHg levels in participants with high local fish and seafood consumption, which revealed that dietary intake was the major exposure route of MeHg. All the participants were assigned to the high-MeHg (H-MeHg, 27.0±10.4 μg/L) or low-MeHg (L-MeHg, 11.6±4.7 μg/L) groups based on the 75th percentile of their blood MeHg (19.2 μg/L), and then matched for cognitive function confounders: age, gender, and education levels. Higher abnormality rates for remote memory ( p=0.036), mental manipulation ( p=0.013), and orientation ( p=0.005) were found in the H-MeHg group than in the L-MeHg group. Long-term consumption of MeHg-contaminated fish and seafood by residents living near this contaminated area may have persistent effects on their cognitive function. We suggest a follow-up study to monitor the long-term health effects on the residents living near this deserted plant.

Methylmercury exposure assessment using dietary and biomarker data among frequent seafood consumers in France: CALIPSO study

Background Seafood is considered by toxicologists as the main source of methylmercury (MeHg), but little data is available concerning contamination of seafood and MeHg status of French frequent consumers. Objectives The objectives were to assess food exposure and biomarker of exposure of MeHg from a group of frequent consumers of seafood. Methods Two approaches to exposure assessment were used: the currently used food intake and the biomarker of exposure. A validated food frequency questionnaire (FFQ) was used to assess seafood consumptions for 80 products of 385 frequent consumers aged 18 and over in four French coastal areas. Seafood samples were collected in each region considering preservation methods and supply habits according to a total diet study sampling. Food samples were analyzed for MeHg. Exposure was assessed by combining consumptions with contamination data. Whole blood samples were collected from the volunteers and analyzed for MeHg. Results The mean dietary exposure to MeHg or weekly intake (WI FFQ) was 1.51±1.17 μg/kg bw/wk. Thirty-five percent of the subjects exceed the Joint Expert Committee on Food Additives (JECFA) provisional tolerable weekly intake (PTWI), whereas the use of the biological results with the JECFA/Environmental Protection Agency (EPA) one-compartment pharmacokinetic model to calculate weekly intake (WI PKM) shows that only 2% of subjects exceed the PTWI. The mean of the individual ratios WI FFQ/WI PKM is 4.3 and the higher the WI FFQ and the blood MeHg level, the lower is the ratio, close to 1–2. Conclusions These analyses support the assumption that the calculated dose of methylmercury is overestimated with the FFQ-based method used in this study. Since FFQ are commonly used in risk assessments, the overestimate of dose is public health protective and this finding is somewhat reassuring from a public health point of view, especially since the JECFA or EPA have applied uncertainty factors of 3.2 or 3, respectively, to take into account the inter-individual pharmacokinetic variability.

Mercury in human brain, blood, muscle and toenails in relation to exposure: an autopsy study

BackgroundThe main forms of mercury (Hg) exposure in the general population are methylmercury (MeHg) from seafood, inorganic mercury (I-Hg) from food, and mercury vapor (Hg0) from dental amalgam restorations. While the distribution of MeHg in the body is described by a one compartment model, the distribution of I-Hg after exposure to elemental mercury is more complex, and there is no biomarker for I-Hg in the brain. The aim of this study was to elucidate the relationships between on the one hand MeHg and I-Hg in human brain and other tissues, including blood, and on the other Hg exposure via dental amalgam in a fish-eating population. In addition, the use of blood and toenails as biological indicator media for inorganic and organic mercury (MeHg) in the tissues was evaluated.MethodsSamples of blood, brain (occipital lobe cortex), pituitary, thyroid, abdominal muscle and toenails were collected at autopsy of 30 deceased individuals, age from 47 to 91 years of age. Concentrations of total-Hg and I-Hg in blood and brain cortex were determined by cold vapor atomic fluorescence spectrometry and total-Hg in other tissues by sector field inductively coupled plasma-mass spectrometry (ICP-SFMS).ResultsThe median concentrations of MeHg (total-Hg minus I-Hg) and I-Hg in blood were 2.2 and 1.0 μg/L, and in occipital lobe cortex 4 and 5 μg/kg, respectively. There was a significant correlation between MeHg in blood and occipital cortex. Also, total-Hg in toenails correlated with MeHg in both blood and occipital lobe. I-Hg in both blood and occipital cortex, as well as total-Hg in pituitary and thyroid were strongly associated with the number of dental amalgam surfaces at the time of death.ConclusionIn a fish-eating population, intake of MeHg via the diet has a marked impact on the MeHg concentration in the brain, while exposure to dental amalgam restorations increases the I-Hg concentrations in the brain. Discrimination between mercury species is necessary to evaluate the impact on Hg in the brain of various sources of exposure, in particular, dental amalgam exposure.

Simultaneous determination of trace levels of ethylmercury and methylmercury in biological samples and vaccines using sodium tetra(n-propyl)borate as derivatizing agent

Because of increasing awareness of the potential neurotoxicity of even low levels of organomercury compounds, analytical techniques are required for determination of low concentrations of ethylmercury (EtHg) and methylmercury (MeHg) in biological samples. An accurate and sensitive method has been developed for simultaneous determination of methylmercury and ethylmercury in vaccines and biological samples. MeHg and EtHg were isolated by acid leaching (H2SO4-KBr-CuSO4), extraction of MeHg and EtHg bromides into an organic solvent (CH2Cl2), then back-extraction into Milli-Q water. MeHg and EtHg bromides were derivatized with sodium tetrapropylborate (NaBPr4), collected at room temperature on Tenax, separated by isothermal gas chromatography (GC), pyrolysed, and detected by cold-vapour atomic fluorescence spectrometry (CV AFS). The repeatability of results from the method was approximately 5-10% for EtHg and 5-15% for MeHg. Detection limits achieved were 0.01 ng g-1 for EtHg and MeHg in blood, saliva, and vaccines and 5 ng g-1 for EtHg and MeHg in hair. The method presented has been shown to be suitable for determination of background levels of these contaminants in biological samples and can be used in studies related to the health effects of mercury and its species in man. This work illustrates the possibility of using hair and blood as potential biomarkers of exposure to thiomersal.

Correlations between mercury concentrations in umbilical cord tissue and other biomarkers of fetal exposure to methylmercury in the Japanese population

Methylmercury (MeHg) is one of the most risky substances to affect humans through fish consumption, and the fetus is known to be in the most susceptible group. Our objective in this study is to examine the relationships of total mercury (THg) and MeHg concentrations between umbilical cord tissue and other tissues as biomarkers of fetal exposure to MeHg in the Japanese population. In total, 116 paired samples were collected in three Japanese districts, the Tsushima Islands, Fukuoka City, and Katsushika ward of metropolitan Tokyo. THg was measured for hair and THg and MeHg were measured in cord tissues, maternal blood, and cord blood. The relationships among tissues in Hg concentrations were similar among districts. Therefore, we analyzed the relationships using all the samples. More than 90% of Hg in cord tissue, cord blood, and maternal blood was MeHg. THg and MeHg in cord blood was about two times higher than in maternal blood. A strong correlation was found between THg and MeHg in cord tissue. The cord tissue THg and MeHg showed a strong correlation with cord blood Hg, which is recognized as the best biomarker for fetal exposure to MeHg. The findings of this study indicate the significance of cord tissue THg and MeHg as biomarkers for fetal exposure to MeHg at parturition.

Transport of methylmercury and inorganic mercury to the fetus and breast-fed infant.

It is well established that methylmercury (MeHg) and mercury vapor pass the placenta, but little is known about infant exposure via breast milk. We measured MeHg and inorganic mercury (I-Hg) in blood of Swedish mothers (n = 20) and their infants, as well as total mercury (T-Hg) in breast milk up to 13 weeks postpartum. Infant blood MeHg was highly associated with maternal blood MeHg at delivery, although more than twice as high. Infant MeHg decreased markedly until 13 weeks of age. Infant blood I-Hg was associated with, and about as high as, maternal blood I-Hg at delivery. Infant I-Hg decreased until 13 weeks. In breast milk, T-Hg decreased significantly from day 4 to 6 weeks after delivery but remained unchanged thereafter. At 13 weeks, T-Hg in breast milk was associated with infant MeHg but not with maternal MeHg. Conversely, T-Hg in breast milk was associated with maternal I-Hg but not with infant I-Hg. From the findings of the present study in which the exposure to both MeHg and I-Hg was low, we conclude that the exposure to both forms of mercury is higher before birth than during the breast-feeding period, and that MeHg seems to contribute more than I-Hg to infant exposure postnatally via breast milk.

Mercury Concentrations in Bicknell?s Thrush and Other Insectivorous Passerines in Montane Forests of Northeastern North America

Anthropogenic input of mercury (Hg) into the environment has elevated risk to fish and wildlife, particularly in northeastern North America. Investigations into the transfer and fate of Hg have focused on inhabitants of freshwater aquatic ecosystems, as these are the habitats at greatest risk for methylmercury (MeHg) biomagnification. Deviating from such an approach, we documented MeHg availability in a terrestrial montane ecosystem using a suite of insectivorous passerines. Intensive and extensive sampling of Bicknell's thrush (Catharus bicknelli) indicated significant heterogeneity in MeHg availability across 21 mountaintops in northeastern North America. Southern parts of the breeding range tended to be at greater risk than northern parts. Mean blood Hg concentrations for Bicknell's thrush at 21 distinct breeding sites ranged from 0.08 to 0.38 ug/g (ww) and at seven Greater Antillean wintering sites ranged from 0.03 to 0.42 ug/g (ww). Overall concentrations were significantly greater in wintering than in breeding areas. Mercury exposure profiles for four passerine species on Mt. Mansfield, Vermont indicated greatest MeHg uptake in Bicknell's thrush and yellow-rumped warbler (Dendroica coronata) and lowest in blackpoll warbler (Dendroica striata) and white-throated sparrow (Zonotrichia albicollis). The MeHg and total Hg ratio in blood in these four species was nearly 1:1. There was no correlation between blood and feather Hg concentrations in breeding Bicknell's thrush, in part because of apparent retention of winter Hg body burdens, within-season variation of MeHg availability, and confounding factors such as influences from age. Adult thrushes had significantly higher concentrations of feather Hg than did young-of-the-year. Although individual patterns of inter-year feather Hg concentrations were disordered, some individuals exhibited bioaccumulation of MeHg. Female blood Hg concentrations were significantly lower than males', in part because females have additional depurating mechanisms through eggs. Older male Bicknell's thrushes that breed in New England are therefore likely at greatest risk. Mechanisms for Hg methylation in montane areas without standing water are not yet fully understood. However, recent studies indicate that MeHg is present in forest tree leaves and leaf detritus; saturated soils and other moist microhabitats may also contribute to MeHg availability. Our finding of a correlation between regional litterfall Hg flux patterns and Bicknell's thrush blood Hg concentrations demonstrates on-site availability of MeHg. Further investigations into MeHg availability in montane environments are recommended to assess risk to insectivorous passerines, particularly the Bicknell's thrush.

Methyl mercury exposure in Swedish women with high fish consumption

We studied the exposure to methyl mercury (MeHg) in 127 Swedish women of childbearing age with high consumption of various types of fish, using total mercury (T-Hg) in hair and MeHg in blood as biomarkers. Fish consumption was assessed using a food frequency questionnaire (FFQ), including detailed information about consumption of different fish species, reflecting average intake during 1 year. We also determined inorganic mercury (I-Hg) in blood, and selenium (Se) in serum. The average total fish consumption, as reported in the food frequency questionnaire, was approximately 4 times/week (range 1.6–19 times/week). Fish species potentially high in MeHg, included in the Swedish dietary advisories, was consumed by 79% of the women. About 10% consumed such species more than once a week, i.e., more than what is recommended. Other fish species potentially high in MeHg, not included in the Swedish dietary advisories, was consumed by 54% of the women. Eleven percent never consumed fish species potentially high in MeHg. T-Hg in hair (median 0.70 mg/kg; range 0.08–6.6 mg/kg) was associated with MeHg in blood (median 1.7 μg/L; range 0.30–14 μg/L; r s=0.78; p<0.001). Hair T-Hg, blood MeHg and serum Se (median 70 μg/L; range 46–154 μg/L) increased with increasing total fish consumption ( r s=0.32; p<0.001, r s=0.37; p<0.001 and r s=0.35; p=0.002, respectively). I-Hg in blood (median 0.24 μg/L; range 0.01–1.6 μg/L) increased with increasing number of dental amalgam fillings. We found no statistical significant associations between the various mercury species measured and the Se concentration in serum. Hair mercury levels exceeded the levels corresponding to the EPA reference dose (RfD) of 0.1 μg MeHg/kg b.w. per day in 20% of the women. Thus, there seems to be no margin of safety for neurodevelopmental effects in fetus, for women with high fish consumption unless they decrease their intake of certain fish species.