Associations of methylmercury and inorganic mercury between human cord blood and maternal blood: a meta-analysis and its application

Prenatal mercury exposure and body mass index at 2 and 4 years: The Japan Environment and Children's Study

Whether prenatal mercury (Hg) exposure may increase obesity among children remains unclear. We here investigated the association between cord blood methylmercury (MeHg) and inorganic mercury (IHg) concentration and body mass index (BMI) z-scores, as well as overweight or obesity at the ages of 2 and 4 years. We used 3147 mother-child pairs data from the Japan Environment and Children's Study. The levels of MeHg and IHg in cord blood were quantified by liquid chromatography coupled with inductively coupled plasma mass spectrometry. Pediatric physicians examined the children's height and weight at ages 2 and 4, and BMI z-scores were calculated. Linear or logistic regression models were employed to examine the association between Hg concentrations and BMI outcomes. After adjusting for potential confounders, our findings indicated that a 2-fold increase in IHg concentrations was associated with increases in BMI z-scores of 0.05 (95% CI: 0.01, 0.09; p = 0.021) and 0.05 (95% CI: 0.02, 0.09; p = 0.0046) at ages 2 and 4, respectively. Conversely, no significant associations were observed for MeHg. When overweight or obesity was employed as an outcome, we did not observe consistent associations for either MeHg or IHg. In this birth cohort study, an increase in cord blood IHg, but not MeHg, was associated with a slight increase in BMI z-score in children at 2 and 4 years of age. However, the observed associations were weak and inconsistent, suggesting that the results might be due to residual confounding or mere chance rather than indicative of a causal relationship.

Temporal changes of blood mercury concentrations in Chinese newborns and the general public from 1980s to 2020s

Mercury (Hg) is a global pollutant that threatens the environment and human health. As a major producer, emitter and consumer of Hg, China is currently taking different measures to curb mercury pollution in accordance with the requirements of the Minamata Convention on Mercury. Blood Hg can reflect the human body's recent exposure to Hg. This review summarized the temporal changes in blood Hg concentrations in newborns and the general public in China from 1980 s to 2020 s. It was shown that the blood Hg concentrations of newborns showed the downward trend, although it was not significant. The general public Hg concentrations showed a trend of first increase and then decrease trend. Most of the cord blood Hg and venous blood Hg concentrations in China were lower than the USEPA reference concentration of 5.8 µg/L. Since low-dose prenatal Hg exposure can affect fetal and neonatal development, continuous attention needs to be paid to reduce maternal and neonatal Hg exposure. The information provided in this review may lay a basis for the effectiveness evaluation on the implementation of Minamata Convention on Mercury.

Effects of mercury exposure on fetal body burden and its association with infant growth

Several studies have been conducted among South Korean to investigate effects of high blood mercury (Hg) levels. In this study fetal body burden of Hg in 344 pregnant women were estimated using a physiologically-based pharmacokinetic model (PBPK) and its associative effects on the growth of infants were analyzed. The association between cord blood Hg and growth variables at birth was analyzed based on parameters such as the sex of the newborn, living area, maternal age group, gestation day, maternal body mass index . We investigated the effects of Hg on infant growth through follow-ups, using a non-linear mixed model. The mean Hg levels in maternal and cord blood were 4.47 μg/L and 7.35 μg/L, respectively. Among the subjects, the corresponding fetal body burden for Methylmercury ranged between 26.3-86.9 mg. Cord blood Hg levels positively correlated with length at birth. Furthermore, the high cord blood group showed greater growth rates compared to the low cord blood group. Therefore, we suggest that pregnant women should make efforts to mitigate exposures to Hg, specifically from diet. Further research is suggested to investigate the relationship between the follow-up growth of the infants and Hg levels, considering fish consumption, diet information, and other environmental pollutants.

Long-term monitoring of mercury in young German adults: Time trend analyses from the German Environmental Specimen Bank, 1995-2018

As highlighted in the Minamata Convention, Mercury (Hg) in its various forms poses a substantial risk to human health and the environment. The health relevance of Hg is also recognized by the European Human Biomonitoring Initiative (HBM4EU), which classifies Hg as a priority substance, since considerable knowledge and data gaps on Hg exposure levels and their changes over time still exist in Europe. The German Environmental Specimen Bank (German ESB) provides valuable policy relevant data and long-term trends of substance exposure on a national level for international comparison and evaluation. In this study we analysed data of the German ESB on Hg exposure of young adults aged 20 to 29 including data on urinary Hg levels from 1995 to 2018 and whole blood Hg levels from 2001 to 2010. Results show a clear decrease in both, about 86% in urine total daily Hg excretion from 1995 (0.76 μg/L) to 2018 (0.11 μg/L) (n = 10,069) and about 57% in blood concentrations of Hg from 2001 (1.76 μg/L) to 2010 (0.77 μg/L) (n = 4085). Over the investigated timeframe only a few values exceeded the toxicologically derived health based guidance value HBM I for blood and urine, with these exceedances decreasing over time in line with the general trend. The factors mostly influencing Hg excretion identified in this study are dental amalgam as well as fish and seafood consumption. Besides other factors (e.g. age and sex), also airborne Hg exposure appears to be a low but evident influencing factor in Germany. Although a considerable decrease in internal Hg exposure is recognized in the last decades, the current low-level exposure may cause adverse health effects especially to vulnerable groups such as pregnant women and children. To further elucidate and evaluate current exposure sources and to reduce human exposure to Hg, continuous environmental and human biomonitoring is needed.

Serum cytokines are associated with n-3 polyunsaturated fatty acids and not with methylmercury measured in infant cord blood in the Seychelles child development study

BACKGROUND

Maternal fish consumption increases infant methylmercury (MeHg) exposure and polyunsaturated fatty acid (PUFA) concentrations. The n-3 PUFA are regulators of inflammation while MeHg may impact the cord cytokine profile and, subsequently, contribute to immune mediated outcomes. This study aimed to investigate associations between infant MeHg exposure and cord cytokine concentrations while adjusting for cord PUFA.

METHODS

We studied participants in the Seychelles Child Development Study (SCDS) Nutrition Cohort 2 (NC2), a large birth cohort in a high fish-eating population. Whole blood MeHg, serum PUFA and serum cytokine concentrations (IFN-γ, IL-1β, IL-2, IL-12p70, TNF-α, IL-4, IL-10, IL-13, IL-6 and IL-8) were measured in cord blood collected at delivery (n = 878). Linear regression examined associations between infant MeHg exposure and cord cytokines concentrations, with and without adjustment for cord PUFA. An interaction model examined cord MeHg, cytokines and tertiles of the n-6:n-3 ratio (low/medium/high).

RESULTS

There was no overall association between cord MeHg (34.08 ± 19.98 μg/L) and cytokine concentrations, with or without adjustment for PUFA. Increased total n-3 PUFA (DHA, EPA and ALA) was significantly associated with lower IL-10 (β = -0.667; p = 0.007) and lower total Th2 (IL-4, IL-10 and IL-13) (β = -0.715; p = 0.036). In the interaction model, MeHg and IL-1β was positive and significantly different from zero in the lowest n-6:n-3 ratio tertile (β = 0.002, p = 0.03).

CONCLUSION

Methylmercury exposure from fish consumption does not appear to impact markers of inflammation in cord blood. The association of cord n-3 PUFA with lower IL-10 and total Th2 cytokines suggests that they may have a beneficial influence on the regulation of the inflammatory milieu. These findings are important for public health advice and deserve to be investigated in follow up studies.

Uma revisão de escopo de revisões sistemáticas sobre exposição humana ao mercúrio

Resumo: Introdução: a promulgação da Convenção de Minamata no Brasil em 2018 incentivou o cumprimento dos seus objetivos em reduzir o uso e a poluição por mercúrio. Objetivo: caracterizar a produção científica sobre exposição humana ao mercúrio e identificar lacunas de conhecimento a fim de subsidiar a tomada de decisão em saúde. Métodos: revisão de escopo de revisões sistemáticas e metanálises, sem restrição de idioma ou data de publicação, utilizando as bases PubMed, BVS e Cochrane Library. Resultados: 71 estudos atenderam aos critérios de elegibilidade, com 40 revisões sistemáticas, 30 metanálises e 1 overview. Amálgama dentário e contaminação alimentar e ambiental por atividades que utilizam mercúrio foram as fontes de exposição mais mencionadas. Os temas mais estudados contaram com transtornos mentais e comportamentais, assim como uso de biomarcadores e testes neurocomportamentais relacionados à exposição ao mercúrio. Discussão: lacunas como a exposição ocupacional ao mercúrio, uso em práticas tradicionais e em cosméticos apontam para a necessidade de mais estudos. As revisões identificadas podem oferecer subsídios para sínteses de evidências e protocolos de atenção à saúde de populações expostas, assim como para a elaboração de políticas públicas que visem o controle do uso e da exposição ao mercúrio.

Comparison of Simultaneous Quantitative Analysis of Methylmercury and Inorganic Mercury in Cord Blood Using LC-ICP-MS and LC-CVAFS: The Pilot Study of the Japan Environment and Children's Study

Prenatal exposure to methylmercury (MeHg) affects child development after birth. However, many epidemiological studies have evaluated total mercury levels without analyzing speciation. Biomonitoring of MeHg and inorganic mercury (IHg) is essential to reveal each exposure level. In this study, we compared a high-throughput analysis for mercury speciation in blood using liquid chromatography-inductively coupled plasma-mass spectrometry (LC-ICP-MS) and liquid chromatography-cold vapor atomic fluorescence spectrometry (LC-CVAFS). The validated LC-ICP-MS method was applied to 101 maternal blood and 366 cord blood samples in the pilot study of the Japan Environment and Children’s Study (JECS). The accuracy of the LC-CVAFS method ranged 90–115% determined by reference material analysis. To evaluate the reliability of 366 cord blood samples, fifty cord blood samples were randomly selected and analyzed using LC-CVAFS. The median (5th–95th percentile) concentrations of MeHg and IHg were 5.4 (1.9–15) and 0.33 (0.12–0.86) ng/mL, respectively, in maternal blood, and 6.3 (2.5–15) and 0.21 (0.08–0.49) ng/mL, respectively, in cord blood. Inter-laboratory comparison showed a relatively good agreement between LC-ICP-MS and LC-CVAFS. The median cord blood:maternal blood ratios of MeHg and IHg were 1.3 and 0.5, respectively. By analyzing speciation, we could focus on the health effects of each chemical form.

Amino Acid Transporter LAT1 (SLC7A5) Mediates MeHg-Induced Oxidative Stress Defense in the Human Placental Cell Line HTR-8/SVneo

The placental barrier can protect the fetus from contact with harmful substances. The potent neurotoxin methylmercury (MeHg), however, is very efficiently transported across the placenta. Our previous data suggested that L-type amino acid transporter (LAT)1 is involved in placental MeHg uptake, accepting MeHg-L-cysteine conjugates as substrate due to structural similarity to methionine. The aim of the present study was to investigate the antioxidant defense of placental cells to MeHg exposure and the role of LAT1 in this response. When trophoblast-derived HTR-8/SVneo cells were LAT1 depleted by siRNA-mediated knockdown, they accumulated less MeHg. However, they were more susceptible to MeHg-induced toxicity. This was evidenced in decreased cell viability at a usually noncytotoxic concentration of 0.03 µM MeHg (~6 µg/L). Treatment with ≥0.3 µM MeHg increased cytotoxicity, apoptosis rate, and oxidative stress of HTR-8/SVneo cells. These effects were enhanced under LAT1 knockdown. Reduced cell number was seen when MeHg-exposed cells were cultured in medium low in cysteine, a constituent of the tripeptide glutathione (GSH). Because LAT1-deficient HTR-8/SVneo cells have lower GSH levels than control cells (independent of MeHg treatment), we conclude that LAT1 is essential for de novo synthesis of GSH, required to counteract oxidative stress. Genetic predisposition to decreased LAT1 function combined with MeHg exposure could increase the risk of placental damage.

Mercury Exposure Assessment in Mother-Infant Pairs from Continental and Coastal Croatia

The main source of mercury (Hg) exposure in the general population is fish. Another possible source is dental amalgam. Here, we compare the levels of Hg and selenium (Se) in samples of maternal and fetal origin collected shortly after childbirth of healthy postpartum women in the coastal (n = 96) and continental (n = 185) areas of Croatia related to maternal seafood/fish consumption. We also evaluated Hg concentrations and maternal serum metallothionein (MT2) concentrations in relation to the number of dental amalgam fillings, and MT2A-5A/G (rs28366003) polymorphism. The levels of Hg and Se in maternal hair and blood/serum, placenta and cord blood/serum increased in relation to increasing fish consumption with the highest values in subjects from the coast. The concentrations of each element and between elements correlated across the matrices. Increasing amalgam number correlated linearly with increased Hg levels in maternal and cord serum and was not associated with serum MT2. No association of MT2A-5A/G polymorphism and Hg or Se levels were found. The results confirmed higher fish consumption in coastal vs. continental Croatia and increases of both Hg and Se related to fish consumption in all analyzed samples. Increased blood Hg reflected the predominant MeHg share from seafood, while increased serum Hg matched exposure from dental amalgams.

Methylmercury and long chain polyunsaturated fatty acids are associated with immune dysregulation in young adults from the Seychelles child development study

BACKGROUND

Exposure to the environmental toxicant mercury (Hg) has been associated with immune dysregulation, including autoimmune disease, but few human studies have examined methylmercury (MeHg) exposure from fish consumption.

OBJECTIVES

We examined associations between MeHg exposure and biological markers of autoimmunity and inflammation while adjusting for long chain polyunsaturated fatty acids (LCPUFA).

METHOD

At age 19 years, hair total Hg (Y19Hg), LCPUFA status, a panel of 13 antinuclear antibodies (ANA), total serum immunoglobulins (Ig) IgG, IgA, and IgM and serum markers of inflammation (IL-1, IL-2, IL-6, IL-10, C-reactive protein (CRP), IFN-γ, TNF-α) were measured in the Seychelles Child Development Study (SCDS) Main Cohort (n = 497). Multivariable regression models investigated the association between Y19Hg and biomarkers, adjusting for prenatal total hair Hg (MatHg) and other relevant covariates, and with and without adjustment for LCPUFA.

RESULTS

With each 1 ppm increase in Y19Hg (mean 10.23 (SD 6.02) ppm) we observed a 4% increased odds in a positive Combined ANA following adjustment for the n6:n3 LCPUFA ratio (β = 0.036, 95%; CI: 0.001, 0.073). IgM was negatively associated with Y19Hg (β = -0.016, 95%CI: 0.016, -0.002) in models adjusted for n-3, n-6 LCPUFA and when separately adjusted for the n-6:n-3 LCPUFA ratio. No associations were observed with MatHg. Total n-3 LCPUFA status was associated with reduced odds of a positive anti-ribonuclear protein (RNP) A. The n-3 LCPUFA were negatively associated with IL-6, IL-10, CRP, IFN-γ, TNF-α and positively with TNF-α:IL-10. There were positive associations between the n-6:n-3 ratio and IL-6, IL-10, CRP, IFN-γ, TNF-α and a negative association with TNF-α:IL-10.

DISCUSSION

The Y19Hg exposure was associated with higher ANA and lower IgM albeit only following adjustment for the n-3 LCPUFA or the n-6:n-3 LCPUFA ratio. The clinical significance of these findings is unclear, but warrant follow up at an older age to determine any relationship to the onset of autoimmune disease.

Mercury speciation in meconium and associated factors

Meconium is formed early in gestation and it is normally not excreted until after birth. Thus it may provide a longer and cumulative record of exposure to mercury (Hg). The present study aims to speciate Hg in meconium samples (N = 488) from Slovenian and Croatian new-borns prenatally exposed to low levels of methyl-Hg (MeHg) from maternal seafood intake and to Hg⁰ from maternal dental amalgam fillings. We had complete data of total Hg (THg) and MeHg in meconium and THg in maternal hair (MH), while THg and MeHg in maternal blood (MB) were available only for Croatian mothers. Personal data namely maternal seafood intake, age, pre-pregnancy BMI, parity, smoking, estimated gestational age at birth, sex, and birth weight were available for the majority of participants, except the number of dental amalgams which was in most cases missing for Croatian mothers. The median THg concentration in meconium was 11.1 (range: 0.41-375.2) ng/g and inorganic Hg (Hg(II)) presented 98.8% (range: 82%-100%, CV: 2%) of THg. We observed significant correlation between meconium and MH Hg levels, with the highest correlation between hair THg and meconium MeHg. Correlation analysis including MB (available only for Croatian population) showed a significant positive correlation between THg in meconium and THg in MB (R_s = 0.642). Additionally, MeHg from MB was correlated with MeHg in meconium (R_s = 0.898), while the correlation between Hg(II) in MB and meconium was positive, but not significant. Maternal seafood intake was significantly correlated with meconium MeHg (R_s = 0.498) and Hg(II) (R_s = 0.201). Multiple linear regression (performed on the Slovenian population, N = 143) confirmed a positive association between meconium MeHg and seafood intake. Furthermore, meconium Hg(II) was positively associated with the number of maternal dental amalgam fillings, but linear regression models did not confirm correlation between seafood intake and meconium Hg(II) levels. We assume that Hg⁰ released from maternal dental amalgam fillings and MeHg from seafood intake were both transported through the placental barrier and portioned between different foetal compartments including meconium. Weak correlation between maternal seafood intake and Hg(II) levels in meconium suggests that there is certain evidence of MeHg demethylation. However, because this correlation was not confirmed by the multiple regression, MeHg demethylation during prenatal life cannot be neither confirmed nor excluded. Further investigations at higher level of exposure are needed to confirm this observations. We can conclude that meconium is a suitable biomarker for MeHg and Hg⁰ exposure during pregnancy. However, comparability of the results reported in meconium in different studies is hindered by a lack of standardized sampling protocols, storage, and analysis.

Neurodevelopmental and Metabolomic Responses from Prenatal Coexposure to Perfluorooctanesulfonate (PFOS) and Methylmercury (MeHg) in Sprague-Dawley Rats

Methylmercury (MeHg) and perfluorooctanesulfonate (PFOS) are major contaminants of human blood that are both common in dietary fish, thereby raising questions about their combined impact on human development. Here, pregnant Sprague-Dawley rats ingested a daily dose, from gestational day 1 through to weaning, of either 1 mg/kg bw PFOS (PFOS-only), 1 mg/kg MeHg (MeHg-only), a mixture of 0.1 mg/kg PFOS and 1 mg/kg MeHg (Low-Mix), or of 1 mg/kg of PFOS and 1 mg/kg MeHg (High-Mix). Newborns were monitored for physical milestones and reflexive developmental responses, and in juveniles the spontaneous activity, anxiety, memory, and cognition were assessed. Targeted metabolomics of 199 analytes was applied to sectioned brain regions of juvenile offspring. Newborns in the High-Mix group had decreased weight gain as well as delayed reflexes and innate behavioral responses compared to controls and individual chemical groups indicating a toxicological interaction on early development. In juveniles, cumulative mixture effects increased in a dose-dependent manner in tests of anxiety-like behavior. However, other developmental test results suggested antagonism, as PFOS-only and MeHg-only juveniles had increased hyperactivity and thigmotaxic behavior, respectively, but fewer effects in Low-Mix and High-Mix groups. Consistent with these behavioral observations, a pattern of antagonism was also observed in neurochemicals measured in rat cortex, as PFOS-only and MeHg-only juveniles had altered concentrations of metabolites (e.g., lipids, amino acids, and biogenic amines), while no changes were evident in the combined exposures. The cortical metabolites altered in PFOS-only and MeHg-only exposed groups are involved in inhibitory and excitatory neurotransmission. These proof-of-principle findings at relatively high doses indicate the potential for toxicological interaction between PFOS and MeHg, with developmental-stage specific effects. Future mixture studies at lower doses are warranted, and prospective human birth cohorts should consider possible confounding effects from PFOS and mercury exposure on neurodevelopment.

Associations of maternal immune response with MeHg exposure at 28 weeks' gestation in the Seychelles Child Development Study

PROBLEM

Maternal methylmercury (MeHg) exposure may be associated with immune response during pregnancy.

METHOD OF STUDY

In the high fish-eating Seychelles Child Development Study Nutrition Cohort 2, we examined the association between maternal MeHg, polyunsaturated fatty acids (PUFA), and immune markers (Th1:Th2; TNF-α, IL-1β, IFN-γ, IL-2, IL-4, IL-5, IL-10, MCP-1, TARC, sFlt-1, VEGF-D, CRP and IL-6) at 28 weeks' gestation. Linear regression examined associations between MeHg exposure and immune markers with and without adjustment for PUFA.

RESULTS

In all models, as MeHg concentrations increased, the Th1:Th2 ratio, total Th1 and individual Th1 (IL-1β, IL-2, TNF-α) concentrations decreased. MeHg was not associated with total Th2 cytokines but was associated with a decrease in IL-4 and IL-10. MeHg was positively associated with TARC and VEGF-D and negatively associated with CRP. There was a significant interaction between MeHg and the n-6:n-3 ratio, with MeHg associated with a larger decrease in Th1:Th2 at higher n-6:n-3 PUFA ratios. The n-3 PUFA were associated with lower CRP, IL-4 and higher IFN-γ. The n-6 PUFA were associated with higher IL-1β, IL-2, TNF-α, IL-4, IL-10, CRP and IL-6.

CONCLUSION

Maternal MeHg was associated with markers of immune function at 28 weeks' gestation. A significant interaction between MeHg and the n-6:n-3 ratio on the Th1:Th2 ratio suggests that the n-3 PUFA may mitigate any immunosuppressive associations of MeHg. The n-3 and n-6 PUFA were associated with suppressive and stimulatory immune responses, respectively. Overall, the associations were of small magnitude, and further research is required to determine the clinical significance.

Maternal and fetal exposure to cadmium, lead, manganese and mercury: The MIREC study

Given the susceptibility of the fetus to toxicants, it is important to estimate their exposure. Approximately 2000 pregnant women were recruited in 2008-2011 from 10 cities across Canada. Cd, Pb, Mn and total Hg were measured in maternal blood from the 1st and 3rd trimesters, umbilical cord blood, and infant meconium. Nutrient intakes of vitamin D, iron, and calcium (Ca) were assessed using a food frequency questionnaire and a dietary supplement questionnaire. Median concentrations in 1st trimester maternal blood (n = 1938) were 0.20, 8.79 and 0.70 μg/L for Cd, Mn and Hg, respectively, and 0.60 μg/dL for Pb. While the median difference between the paired 1st and 3rd trimester concentrations of Cd was 0, there was a significant decrease in Pb (0.04 μg/dL) and Hg (0.12 μg/L) and an increase in Mn (3.30 μg/L) concentrations over the course of the pregnancy. While Cd was rarely detected in cord blood (19%) or meconium (3%), median Pb (0.77 μg/dL), Mn (31.87 μg/L) and Hg (0.80 μg/L) concentrations in cord blood were significantly higher than in maternal blood. Significant negative associations were observed between estimated Ca intake and maternal Cd, Pb, Mn and Hg, as well as cord blood Pb. Vitamin D intake was associated with lower maternal Cd, Pb, and Mn as well as Pb in cord blood. Even at current metal exposure levels, increasing dietary Ca and vitamin D intake during pregnancy may be associated with lower maternal blood Pb and Cd concentrations and lower Pb in cord blood.

Prenatal low-level mercury exposure and infant neurodevelopment at 12 months in rural northern China

Although MeHg is a confirmed neurotoxin at sufficiently high dosages, the effect of prenatal low-level Hg exposure on infant neurodevelopment is still unknown. Four hundred ten mother-infant pairs were recruited in rural northern China from September 2010 to September 2012. We investigated maternal diet during pregnancy, collected maternal and umbilical blood samples, and tested infant neurodevelopment using Gesell developmental schedules (GDS) at the age of 1 year old. The geometric means (GM) of Hg exposure in maternal and umbilical blood were 0.72 and 1.2 μg/L, respectively. Positive associations between Hg levels and the frequency of total fish consumption were found (Spearman's correlation, r = 0.09 for maternal Hg, r = 0.14 for umbilical Hg, p < 0.01). After adjusting for confounding factors, we found a log-unit increase in umbilical blood Hg levels was associated with a 4.22-point (95 % confidence interval (95 %CI) 0.77 to 7.67) increase in the adaptive domain and a 4.06-point (95 %CI 0.51 to 7.62) increase in the social domain. No significant association has been found between other domains and Hg levels in our study. In further analysis, we noticed the positive correlation between the developmental quotient (DQ) scores of the adaptive domain and frequencies of total fish consumption (p = 0.04). Our results failed to indicate the adverse effects between prenatal Hg exposure and infant neurodevelopment. However, given the low-level Hg exposure and its predominant source, the potential positive associations in our study may be attributed to the beneficial nutrients of fish consumption.

Cord Blood Methylmercury and Fetal Growth Outcomes in Baltimore Newborns: Potential Confounding and Effect Modification by Omega-3 Fatty Acids, Selenium, and Sex

BACKGROUND

Methylmercury (MeHg) may affect fetal growth; however, prior research often lacked assessment of mercury speciation, confounders, and interactions.

OBJECTIVE

Our objective was to assess the relationship between MeHg and fetal growth as well as the potential for confounding or interaction of this relationship from speciated mercury, fatty acids, selenium, and sex.

METHODS

This cross-sectional study includes 271 singletons born in Baltimore, Maryland, 2004-2005. Umbilical cord blood was analyzed for speciated mercury, serum omega-3 highly unsaturated fatty acids (n-3 HUFAs), and selenium. Multivariable linear regression models controlled for gestational age, birth weight, maternal age, parity, prepregnancy body mass index, smoking, hypertension, diabetes, selenium, n-3 HUFAs, and inorganic mercury (IHg).

RESULTS

Geometric mean cord blood MeHg was 0.94 μg/L (95% CI: 0.84, 1.07). In adjusted models for ponderal index, βln(MeHg) = -0.045 (g/cm(3)) × 100 (95% CI: -0.084, -0.005). There was no evidence of a MeHg × sex interaction with ponderal index. Contrastingly, there was evidence of a MeHg × n-3 HUFAs interaction with birth length [among low n-3 HUFAs, βln(MeHg) = 0.40 cm, 95% CI: -0.02, 0.81; among high n-3 HUFAs, βln(MeHg) = -0.15, 95% CI: -0.54, 0.25; p-interaction = 0.048] and head circumference [among low n-3 HUFAs, βln(MeHg) = 0.01 cm, 95% CI: -0.27, 0.29; among high n-3 HUFAs, βln(MeHg) = -0.37, 95% CI: -0.63, -0.10; p-interaction = 0.042]. The association of MeHg with birth weight and ponderal index was affected by n-3 HUFAs, selenium, and IHg. For birth weight, βln(MeHg) without these variables was -16.8 g (95% CI: -75.0, 41.3) versus -29.7 (95% CI: -93.9, 34.6) with all covariates. Corresponding values for ponderal index were -0.030 (g/cm(3)) × 100 (95% CI: -0.065, 0.005) and -0.045 (95% CI: -0.084, -0005).

CONCLUSION

We observed an association of increased MeHg with decreased ponderal index. There is evidence for interaction between MeHg and n-3 HUFAs; infants with higher MeHg and n-3 HUFAs had lower birth length and head circumference. These results should be verified with additional studies.

Metallic mercury use by South African traditional health practitioners: perceptions and practices

BACKGROUND

Mercury is a toxic metal however its use in traditional healthcare systems remains widespread. The aim of this study was to determine the prevalence of mercury use by South African Traditional Health Practitioners (THP) and to document reasons for use and administration methods.

METHODS

A cross-sectional study design was employed. A total of 201 THPs were enrolled from two main metropolitan areas of KwaZulu-Natal (South Africa), and 198 were included in the final analysis. Information on demographic characteristics, reasons for using or not using mercury as well as mercury administration methods were collected.

RESULTS

Of the 198 THPs, 78 (39%) used mercury for healing purposes and 74 (95%) of the mercury users stated that they were taught to use it by another THP. The two main routes of administration were oral and sub-cutaneous implantations (ukugcaba) at 85% (n = 66) and 59% (n = 46), respectively. The most common responses for mercury administration were for child birth (n = 70; 90%) and protection against guns (n = 39; 50%).

CONCLUSION

This is the first study to describe the prevalence and practice of mercury use in South African traditional medicine. Socio-cultural mercury use is a potential source of exposure to both THPs and their patients. In light of such findings, public education messages and regulatory measures need to be effected.

Real and potential mercury accumulation in human scalp of adolescents: a case study

Mercury (Hg) concentration in human hair is used to estimate methylmercury (MeHg) exposure and establish a reference dose for MeHg intake. In this study, Hg accumulation and MeHg intake were evaluated in relation to fish consumption habits in adolescents from two coastal areas: Angra do Heroísmo (Azores archipelago) and Murtosa (Portuguese mainland). Results showed that Hg concentration and MeHg intake increased with increasing fish consumption. In spite of that, Hg concentrations remained relatively low when compared with World Health Organization "no observed adversary effect level"; therefore, risk for mercury exposure should not be considered. Adolescents revealed a similar range of Hg concentrations (0.03-2.60 μg g(-1)) in scalp hair, apart from being exposed to natural or anthropogenic Hg source (Azores and Mainland, respectively). Nevertheless, Mainland volunteers generally exhibited higher values of Hg accumulation, being approximately 50 % of the results above 1 μg g(-1). Hg concentrations increased in both adolescent groups according to the weekly rate of fish meals, however, not linearly in the highest fish consumption rates. In fact, considering the adolescents' group having over one fish meal per week, the Hg bioaccumulation pattern found in the respective scalp hair suggests the ability of the human body to induce a self-protection response, probably mitigating Hg levels in the blood when experiencing increasing Hg exposure due to fish uptake. Actual and potential mercury levels in human scalp of adolescents probably diverge as fish consumption increases, the effective Hg uptake being lower than the expected, reducing risk to human health.