Longitudinal study of methylmercury and inorganic mercury in blood and urine of pregnant and lactating women, as well as in umbilical cord blood

Early exposure to mercury and cardiovascular function of seven-year old children in Guadeloupe (French West Indies)

BACKGROUND

The cardiotoxicity of prenatal exposure to mercury has been suggested in populations having regular contaminated seafood intake, though replications in the literature are inconsistent.

METHODS

The Timoun Mother-Child Cohort Study was set up in Guadeloupe, an island in the Caribbean Sea where seafood consumption is regular. At seven years of age, 592 children underwent a medical examination, including cardiac function assessment. Blood pressure (BP) was taken using an automated blood pressure monitor, heart rate variability (HRV, 9 parameters) and electrocardiogram (ECG) characteristics (QT, T-wave parameters) were measured using Holter cardiac monitoring during the examination. Total mercury concentrations were measured in cord blood at birth (median = 6.6 μg/L, N = 399) and in the children's blood at age 7 (median = 1.7 μg/L, N = 310). Adjusted linear and non-linear modelling was used to study the association of each cardiac parameter with prenatal and childhood exposures. Sensitivity analyses included co-exposures to lead and cadmium, adjustment for maternal seafood consumption, selenium and polyunsaturated fatty acids (n3-PUFAs), and for sporting activity.

RESULTS

Higher prenatal mercury was associated with higher systolic BP at 7 years of age (βlog2 = 1.02; 95% Confidence Interval (CI) = 0.10, 1.19). In boys, intermediate prenatal exposure was associated with reduced overall HRV and parasympathetic activity, and longer QT was observed with increasing prenatal mercury (βlog2 = 4.02; CI = 0.48, 7.56). In girls, HRV tended to increase linearly with prenatal exposure, and no association was observed with QT-wave related parameters. Mercury exposure at 7 years was associated with decreased BP in girls (βlog2 = -1.13; CI = -2.22, -0.004 for diastolic BP). In boys, the low/high-frequency (LF/HF) ratio increased for intermediate levels of exposure.

CONCLUSION

Our study suggests sex-specific and non-monotonic modifications in some cardiac health parameters following prenatal exposure to mercury in pre-pubertal children from an insular fish-consuming population.

Association of blood metal exposure with age at menarche in Korean women: KNHANES (2008-2017)

Humans are exposed to metals in their daily lives and this metal exposure is responsible for various adverse health effects. Delayed pubertal development has been suggested as an adverse outcome of metal exposure; however, evidence in nationally representative populations, especially in Asia, is limited. We evaluated the association of blood cadmium (Cd), lead (Pb), and mercury (Hg) levels with the age at menarche in Korean females whose blood heavy metals were measured as part of the Korean National Health and Nutrition Examination Survey (KNHANES) 2008-2017. Among the females 16 years of age or older, all measured heavy metals in blood, i.e., Cd, Pb, and Hg, were positively associated with age at menarche. These associations remained significant in a model adjusted for age, survey year, income, education, body mass index, smoking history, and menopausal status as covariates (β: 0.10, 95% confidence interval (CI): 0.03-0.18 for Cd; β: 0.17, 95%CI: 0.06-0.27 for Pb; β: 0.12, 95%CI: 0.05-0.19 for Hg). When the population was separated by age group at the time of the survey, the significance between heavy metal levels and age at menarche became inconsistent, but the general trends were similar. Among those in their 20s and 40s, blood Cd showed a significant association, while Pb was significant among those in their 40s and 50s. A similar trend was observed in the sensitivity analysis in the girls aged 10-15 years at the time of the survey. Blood Cd levels were associated with decreased odds of precocious menarche (OR: 0.57, 95%CI: 0.31-1.03). Delayed menarche is a risk factor for cardiovascular and chronic kidney diseases in later life; hence, public health implication of heavy metal exposure warrants a public health attention.

A SYBR Green I-based aptasensor for the label-free, fluorometric, and anti-interference detection of MeHg. Anal Bioanal Chem 2024;416:299-311. [PMID: 37932512 DOI: 10.1007/s00216-023-05018-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Methylmercury (MeHg+) is a common form of organic mercury that is substantially more toxic than inorganic mercury and is more likely to accumulate in organisms through biological enrichment. Therefore, developing a method to enable the specific and rapid detection of MeHg+ in seafood is important and remains challenging to accomplish. Herein, a rapid, label-free fluorescence detection method for MeHg+ determination was developed based on SYBR Green I. The detection system implemented "add and measure" detection mode can be completed in 10 min. Under optimal assay conditions, the detection platform showed a linear relationship with the concentration of MeHg+ within 1-50 nM (Y = 8.573x + 42.89, R2 = 0.9928), with a detection limit of 0.3218 nM. The results obtained for competitive substances, such as inorganic mercury ions and anions, show a high specificity of the method. In addition, this method successfully detected MeHg+ in seawater and marine products, with an accompanying spike recovery rate of 96.45-105.1%.

Effects of heavy metal exposure during pregnancy on birth outcomes

Exposure to heavy metals such as lead, cadmium, and mercury poses serious health risks to pregnant women because of their high toxicity. In this study, we investigated the associations of heavy metal exposure with birth outcomes of Korean infants. Data of 5,215 women between 2015 and 2019 were analyzed. This study was part of the Korean Children's Environmental Health (Ko-CHENS) study. Linear regression and logistic regression analyses were used to examine effects of concentrations of lead, cadmium, and mercury on birth weight, small for gestational age, and large for gestational age after adjusting for maternal age groups, parity, infant sex, education, income, smoking, drinking, body mass index, stillbirth, premature birth, diabetes, hypertension, and gestational diabetes. Besides adjusting for these covariates, each metal was mutually adjusted to estimate birth weight and large for gestational age status. Maternal cadmium concentrations during early pregnancy (β =  - 39.96; 95% confidence interval (CI): - 63.76, - 16.17) and late pregnancy (β =  - 37.24; 95% CI - 61.63, - 12.84) were significantly associated with birth weight. Cadmium levels during early pregnancy (adjusted OR = 0.637; 95% CI 0.444, 0.912) were also associated with large for gestational age status. Our findings suggest that prenatal cadmium exposure, even at a low level of exposure, is significantly associated with low birth weight.

A State-of-the-Science Review on Metal Biomarkers

PURPOSE OF REVIEW

Biomarkers are commonly used in epidemiological studies to assess metals and metalloid exposure and estimate internal dose, as they integrate multiple sources and routes of exposure. Researchers are increasingly using multi-metal panels and innovative statistical methods to understand how exposure to real-world metal mixtures affects human health. Metals have both common and unique sources and routes of exposure, as well as biotransformation and elimination pathways. The development of multi-element analytical technology allows researchers to examine a broad spectrum of metals in their studies; however, their interpretation is complex as they can reflect different windows of exposure and several biomarkers have critical limitations. This review elaborates on more than 500 scientific publications to discuss major sources of exposure, biotransformation and elimination, and biomarkers of exposure and internal dose for 12 metals/metalloids, including 8 non-essential elements (arsenic, barium, cadmium, lead, mercury, nickel, tin, uranium) and 4 essential elements (manganese, molybdenum, selenium, and zinc) commonly used in multi-element analyses.

RECENT FINDINGS

We conclude that not all metal biomarkers are adequate measures of exposure and that understanding the metabolic biotransformation and elimination of metals is key to metal biomarker interpretation. For example, whole blood is a good biomarker of exposure to arsenic, cadmium, lead, mercury, and tin, but it is not a good indicator for barium, nickel, and uranium. For some essential metals, the interpretation of whole blood biomarkers is unclear. Urine is the most commonly used biomarker of exposure across metals but it should not be used to assess lead exposure. Essential metals such as zinc and manganese are tightly regulated by homeostatic processes; thus, elevated levels in urine may reflect body loss and metabolic processes rather than excess exposure. Total urinary arsenic may reflect exposure to both organic and inorganic arsenic, thus, arsenic speciation and adjustment for arsebonetaine are needed in populations with dietary seafood consumption. Hair and nails primarily reflect exposure to organic mercury, except in populations exposed to high levels of inorganic mercury such as in occupational and environmental settings. When selecting biomarkers, it is also critical to consider the exposure window of interest. Most populations are chronically exposed to metals in the low-to-moderate range, yet many biomarkers reflect recent exposures. Toenails are emerging biomarkers in this regard. They are reliable biomarkers of long-term exposure for arsenic, mercury, manganese, and selenium. However, more research is needed to understand the role of nails as a biomarker of exposure to other metals. Similarly, teeth are increasingly used to assess lifelong exposures to several essential and non-essential metals such as lead, including during the prenatal window. As metals epidemiology moves towards embracing a multi-metal/mixtures approach and expanding metal panels to include less commonly studied metals, it is important for researchers to have a strong knowledge base about the metal biomarkers included in their research. This review aims to aid metals researchers in their analysis planning, facilitate sound analytical decision-making, as well as appropriate understanding and interpretation of results.

Optimisation of distillation as an isolation method for the determination of low methylmercury concentrations in urine samples

Methylmercury (MeHg) speciation in urine requires a robust, reproducible and sensitive technique that enables reliable measurements in limited sample volumes. Conventional MeHg extraction by acid digestion allows for processing of only small amounts of urine digest, making accurate MeHg determination in low-concentration samples virtually impossible. Distillation has been proven as an efficient isolation method with very low detection limits for measuring MeHg in water samples; therefore, in this study, it was optimised for urine samples. Combined with aqueous phase ethylation, purging with nitrogen, preconcentration on Tenax trap, isothermal gas chromatography and cold vapour atomic fluorescence detection, distillation achieved high and repeatable urine spike recoveries of 94% ± 7%. Larger measured aliquot volume led to a significantly lower limit of detection (LOD) for distillation compared with acid digestion (1.1 versus 5.5 pg g^-1 urine). Thirty-two general population urine samples were analysed using both methods, and the results were compared. Distillation led to better separation of MeHg from inorganic Hg and the matrix. Good correlation was observed between the results obtained by the two methods for samples with MeHg concentrations above 10 pg g^-1 urine (slope = 0.9492, R² = 0.9879). For samples below this MeHg concentration, distillation was superior, enabling the measurement of MeHg in 9 out of 12 urine samples that were below the LOD of acid digestion. Distillation had significantly lower measurement uncertainty, particularly in the low-concentration samples, where the expanded combined standard uncertainty of the acid digestion method reached as high as 43.2% (k = 2), predominantly owing to poor sample repeatability.

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.

Total Blood Mercury Predicts Methylmercury Exposure in Fish and Shellfish Consumers

Many studies evaluating methylmercury (MeHg) toxicity rely on whole blood total mercury (THg) measurements to estimate MeHg exposure. However, whole blood THg includes other forms of mercury (Hg), such as inorganic Hg, which have different exposure sources and toxicological effects than MeHg. Therefore, estimating the whole blood MeHg/THg ratio is critical to predicting MeHg exposure and, subsequently, efforts to establish an exposure-response relationship for use in risk assessment. A large, representative dataset (National Health and Nutrition Examination Survey (NHANES) 2011-2016) was used to determine the whole blood MeHg/THg ratio among (a) self-reported fish and shellfish consumers, ≥ 15 years of age (the "full adult" population (N = 5268 training dataset; N = 2336 test dataset)) and (b) female fish and shellfish consumers, 15-44 years of age (the "women of reproductive age" population (N = 1285 training dataset; N = 560 test dataset)). Unadjusted and adjusted linear and spline models with direct measurements for both THg and MeHg were evaluated. The mean whole blood MeHg/THg ratio was 0.75 (95% confidence interval (CI): 0.74, 0.75). This ratio was significantly higher among those with higher THg concentrations. All models exhibited excellent fit (adjusted R² from 0.957 to 0.982). Performance was slightly improved in spline versus linear models. For the full adult population and women of reproductive age, the unadjusted spline model predicted whole blood MeHg concentrations of 5.65 µg/L and 5.55 µg/L, respectively, when the THg concentration was 5.80 µg/L. These results suggest that whole blood THg is a good predictor of whole blood MeHg among fish and shellfish consumers.

Thyroid hormones in relation to toxic metal exposure in pregnancy, and potential interactions with iodine and selenium

BACKGROUND

Several endocrine-disrupting metals may affect thyroid function, but the few available studies of exposure during pregnancy and thyroid hormones are inconclusive.

OBJECTIVE

To explore if environmental exposure to cadmium (Cd), lead (Pb), and methylmercury (MeHg) impacts thyroid function in pregnancy, and interacts with iodine and selenium status.

METHODS

Women in a Swedish birth cohort provided blood and urine samples in early third trimester. Concentrations of erythrocyte Cd, Pb, and Hg (n = 544), urinary Cd and iodine (n = 542) and plasma selenium (n = 548) were measured using inductively coupled plasma-mass spectrometry.Free and total thyroxine (fT4, tT4) and triiodothyronine (fT3, tT3), and thyroid stimulating hormone (TSH), were measured in plasma (n = 548) with electrochemiluminescence immunoassays. Metal-hormone associations were assessed in regression models, and metal mixture effects and metal-nutrient interactions were explored in Bayesian kernel machine regression (BKMR).

RESULTS

In multivariable-adjusted regression models, a doubling of urinary Cd was associated with a mean increase in tT4 of 2.7 nmol/L (95% CI: 0.78, 4.6), and in fT3 and tT3 of 0.06 pmol/L (0.02, 0.10) and 0.09 nmol/L (0.05, 0.13), respectively. A doubling of urinary Cd was associated with a -0.002 (-0.003, -0.001) and -0.03 (-0.05, -0.02) decrease in the fT4:tT4 and fT3:tT3 ratio, respectively. A doubling of erythrocyte Hg (>1 µg/kg) was associated with a decrease in fT3 and tT3 by -0.11 pmol/L (-0.16, -0.05) and -0.11 nmol/L (-0.16, -0.06), respectively, and a -0.013 (-0.02, -0.01) decrease in the fT3:fT4 ratio. BKMR did not indicate any mixture effect of toxic metals or interactions between metals and iodine or selenium in relation to the hormones.

CONCLUSION

Our findings suggest that exposure to Cd and Hg, at levels globally prevalent through the diet, may affect thyroid function during pregnancy, independently of iodine and selenium levels. Further studies on potential implications for maternal and child health are warranted.

Children with Amalgam Dental Restorations Have Significantly Elevated Blood and Urine Mercury Levels

Human exposure to organic mercury (Hg) as methylmercury (MeHg) from seafood consumption is widely considered a health risk because pure methylmercury is extremely neurotoxic. In contrast, the clinical significance of Hg exposure from amalgam (AMG) dental restorations, the only other major nonoccupational source of Hg exposure, has long been debated. Here, we examined data from the two most recent National Health and Nutrition Examination Surveys (NHANES) on 14 181 subjects to assess the contributions of seafood consumption versus AMG to blood total mercury (THg), inorganic mercury (IHg), and methyl mercury (MeHg) and to urine creatinine corrected mercury (UTHg). All subjects were also classified as to their self-reported qualitative consumption of seafood (59% fish and 44% shellfish). Subjects with restorations were grouped into three groups (0) those without AMG (64.4%), (1) those with 1-5 dental AMG restorations (19.7%), (2) those with more than five AMG (16%). Seafood consumption increased total mercury in urine (UTHg) and total mercury (THg) and methyl mercury (MeHg) in blood, but unlike AMG, seafood did not increase blood inorganic mercury (IHg). Using stratified covariate (ANOVA) and multivariate (GLM) analyses revealed a strong correlation of blood (THg and IHg) and urine (UTHg) levels with the number of AMGs. In a subpopulation without fish consumption, having more than five AMG restorations raised blood THg (103%), IHg (221%), and urine UTHg (221%) over the group without AMG. The most striking difference was noted in classification by age: subjects under 6 years old with more than five AMG restorations had the highest blood IHg and urine UTHg among all age groups. Elevation of bivalent IHg on a large scale in children warrants urgent in-depth risk assessment with specific attention to genetic- and gender-associated vulnerabilities.

Prenatal methylmercury exposure is associated with decrease heart rate variability in children

BACKGROUND

Although several epidemiological studies have suggested mercury (Hg) might be associated with cardiotoxicity, the impact of Hg exposure on cardiac autonomic activity and blood pressure in children has not been investigated at Hg exposure levels equivalent to the Environmental Protection Agency (EPA) reference dose.

OBJECTIVE

To investigate the association between low dose prenatal and recent methylmercury (MeHg) exposures and cardiac autonomic function and blood pressure with adjustment for factors such as fish consumption among children from a high fish consumption coastal city.

METHODS

Children aged 7-8 years were recruited from the birth cohort of our previous study. Heart rate variability (HRV), resting heart rate (RHR) and blood pressure were measured as surrogate markers of cardiac autonomic function. Cord blood and current whole blood Hg concentration were used as biomarkers of prenatal and recent MeHg exposure, respectively. Recent fish consumption information was estimated with a food frequency questionnaire.

RESULTS

Among 604 children, median cord blood and whole blood Hg concentrations were 45.9 nmol/L (IQR: 32.8-65.03 nmol/L) and 13.57 nmol/L (IQR: 9.29-19.72 nmol/L), respectively. Our results demonstrated that prenatal MeHg exposure was associated with decreased HRV (i.e. low CVRR, SDRR, and RMSSD), reflecting reduced parasympathetic activity (i.e. low CCV_HF and HF), and a sympathovagal balance shift toward sympathetic predominance (i.e. high %LF and LF/HF ratio). Adjustment of recent fish consumption further increased the significance and magnitude of the adverse associations of MeHg.

CONCLUSION

The results of this study suggest that prenatal MeHg exposure is associated with decreased parasympathetic modulation of cardiac autonomic function in children.

Cellular and Molecular Mechanisms Mediating Methylmercury Neurotoxicity and Neuroinflammation

Methylmercury (MeHg) toxicity is a major environmental concern. In the aquatic reservoir, MeHg bioaccumulates along the food chain until it is consumed by riverine populations. There has been much interest in the neurotoxicity of MeHg due to recent environmental disasters. Studies have also addressed the implications of long-term MeHg exposure for humans. The central nervous system is particularly susceptible to the deleterious effects of MeHg, as evidenced by clinical symptoms and histopathological changes in poisoned humans. In vitro and in vivo studies have been crucial in deciphering the molecular mechanisms underlying MeHg-induced neurotoxicity. A collection of cellular and molecular alterations including cytokine release, oxidative stress, mitochondrial dysfunction, Ca²⁺ and glutamate dyshomeostasis, and cell death mechanisms are important consequences of brain cells exposure to MeHg. The purpose of this review is to organize an overview of the mercury cycle and MeHg poisoning events and to summarize data from cellular, animal, and human studies focusing on MeHg effects in neurons and glial cells. This review proposes an up-to-date compendium that will serve as a starting point for further studies and a consultation reference of published studies.

Temporal variation of total mercury levels in the hair of pregnant women from the Maternal-Infant Research on Environmental Chemicals (MIREC) study

Prenatal exposure to total mercury (T-Hg) comes from both natural and anthropogenic sources. T-Hg can cross the blood-brain and placental barriers, and may be associated with future neurological and physiological dysfunctions. Scalp hair is an optimal and non-invasive indicator of chronic T-Hg exposure. As part of the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, hair samples from 350 women were collected within weeks after giving birth, to determine temporal variations in T-Hg levels from preconception to delivery, and to compare these levels to corresponding levels measured in other matrices (maternal and umbilical cord blood, and infant's meconium). A maximum of 12 one-cm hair segments were cut starting at the scalp; segments closer to the scalp reflected recent exposure (within the last month). For proper comparison, the hair segments were matched with the collection dates for other matrices. GM hair T-Hg levels greatly decreased during pregnancy, from 0.26 μg g^-1 (preconception or full-length hair) to 0.18 μg g^-1 (at delivery or segments closer to the scalp). A similar decreasing trend was found for T-Hg in maternal blood: 1st trimester (0.60 μg L^-1) to 3rd trimester (0.47 μg L^-1). The median hair-to-blood ratios of T-Hg levels varied from 364 (1st trimester), to 408 (3rd trimester), to 229 (cord blood). Very low T-Hg levels were detected in meconium. Mercury levels in blood and hair correlated with consumption of large predatory fish.

Determination of Total Mercury in Solid Samples by Anodic Stripping Voltammetry

The anodic stripping voltammetry (ASV) was investigated to determine total mercury in solid samples using a gold electrode. The mercury was deposited on the gold electrode in a preconcentration step. The oxidation peak of mercury was irreversible. The optimal conditions of the procedure were found to be as follows: 0.05 mol L−1 HCl solution, deposition potential −0.5 V vs. Ag/AgCl/KCls, deposition time 40 s, and sweep rate 0.04 V s−1. Under the optimal conditions, the peak current showed a linear dependence on Hg2+ concentration in the range from 0.01 to 0.1 mg l−1. The detection limit and quantification limit were 4.28 µg L−1 and 12.98 µg L−1, respectively. The mean recovery and relative standard deviation were 91.2% and 2.4% (n = 9). The procedure was successfully applied for determining total mercury in samples collected from Hanoi light bulb warehouse—The Rang Dong Light Source and Vacuum Flask JSC. The results were compared with cold vapor atomic absorption spectrometry (CV-AAS).

Low-level maternal exposure to cadmium, lead, and mercury and birth outcomes in a Swedish prospective birth-cohort

Observational studies have indicated that low-to-moderate exposure to cadmium (Cd), lead (Pb), and mercury (Hg) adversely affects birth anthropometry, but results are inconclusive. The aim of this study was to elucidate potential impact on birth anthropometry of exposure to Cd, Pb, and Hg in pregnant women, and to identify the main dietary sources. In the NICE (Nutritional impact on Immunological maturation during Childhood in relation to the Environment) birth-cohort in northern Sweden, blood and urine were collected from pregnant women in early third trimester. Cd, Pb and Hg were measured in erythrocytes (n = 584), and Cd also in urine (n = 581), by inductively coupled plasma mass spectrometry. Dietary data were collected through a semi-quantitative food frequency questionnaire administered in mid-third trimester. Birth anthropometry data were extracted from hospital records. In multivariable-adjusted spline regression models, a doubling of maternal erythrocyte Cd (median: 0.29 μg/kg) above the spline knot of 0.50 μg/kg was associated with reduced birth weight (B: -191 g; 95% CI: -315, -68) and length (-0.67 cm; -1.2, -0.14). The association with birth weight remained when the analysis was restricted to never-smokers. Likewise, a doubling of erythrocyte Hg (median 1.5 μg/kg, mainly MeHg) above 1.0 μg/kg, was associated with decreased birth weight (-59 g; -115, -3.0), and length (-0.29 cm; -0.54, -0.047). Maternal Pb (median 11 μg/kg) was unrelated to birth weight and length. Erythrocyte Cd was primarily associated with intake of plant derived foods, Pb with game meat, tea and coffee, and Hg with fish. The results indicated that low-level maternal Cd and Hg exposure were associated with poorer birth anthropometry. Further prospective studies in low-level exposed populations are warranted.

Fish as bioindicators: coal and mercury pollution in Colombia's ecosystems

Mining in Colombia affects 488,672 ha (298,391 in coal mining and 190,281 in gold mining). However, Colombia has insufficient studies on mining and its repercussions, which limits estimates of mining impacts on ecosystems and the human population. Due to the rise of mining activities in Colombia, the negative impacts generated by coal and Hg will also continue to increase. This review analyzes national information levels on coal and Hg in island/coastal/marine as well as freshwater ecosystems and human groups using fishery resources as a framework. This is because fish are the main source of animal protein in marine coastal-island and mainland communities. Here, 15 of 32 Colombian departments have records on total mercury (THg) in water, sediments, fish, and human communities. Around 205 ton/year of mercury is discharged into the ecosystem. In human hair for example (15.3 to 50.15 μg/g), mercury exceeds the international maximum levels allowed (ILA) and the national standard (5.0 μg/g). Mercury levels in freshwater fish show 3.3 μg/g of THg and levels in marine and coastal-island fish are 1.2 μg/g THg exceeding the ILA (0.5 μg/g) standard for fish that will be consumed. Carnivorous species have a THg between 0.04 and 2.55 μg/g suggesting bioaccumulation and magnification of heavy metals. These findings were then compared with available international information.

The Relationship between Mercury Exposure Indices and Dietary Intake of Fish and Shellfish in Women of Childbearing Age

Women of childbearing age who are susceptible to mercury exposure were studied to understand the relation between mercury intake through fish and shellfish consumption and mercury exposure indices from blood, hair, and urine samples. A total of 711 women of childbearing age from coastal areas with a high concentration of mercury exposure in Korea were studied. Data were collected on demographic characteristics, dietary intake of fish and shellfish using the simple Food Frequency Questionnaire. Mercury concentration was estimated from the collected samples of blood, hair, and urine. The geometric mean of blood methyl mercury concentration of mercury exposure through seafood was 3.06 μg/L for the low tertile, 3.12 μg/L for the middle tertile, and 3.60 μg/L for the high tertile, indicating a clear tendency of blood methyl mercury to increase as the mercury exposure by fish and shellfish intake ascended. For total blood mercury and hair mercury, the middle and high tertiles had higher values than the low. Mercury exposure through fish and shellfish intake is a main factor for an increase of blood methyl mercury concentration in women of childbearing age. More attention needs to be paid to mercury exposure through seafood intake, considering the serious effect mercury concentration has on women of childbearing age.

Toxic metal (Cd, Hg, Mn, Pb) partition in the maternal/foetal unit: A systematic mini - review of recent epidemiological studies

The aim of this study was to summarise the available information regarding the partition of toxic metal (Cd, Hg, Mn, Pb) levels in the maternal/foetal unit from large epidemiological studies. We performed a systematic search of PubMed/MedLine, EMBASE, and ISI Web of Science for papers on Cd, total Hg, Mn or Pb levels in the maternal/cord blood that were published in English (n > = 200; 2010-2017). Data on year of publication, sample size, location, year of survey, and main results were extracted. We found a total of 35 papers. Most studies included large convenience samples of healthy pregnant women. The maternal/cord blood was properly used as a biomarker of prenatal exposure to toxic metals. The partition of these toxic metal levels in the maternal/foetal unit was metal-specific. Cd median levels (IQR) in cord blood reported worldwide were much lower [∼ 70 % < LOD = ± 0.11 μg/L] than those found in maternal blood [0.23 μg/L (0.15-0.35), ∼ 65 % > LOD]. Considering that Cd was under LOD in 70 % of the cord blood, Cd cord:maternal ratio as well as Cd cord proportion were not provided. Total Hg median levels (IQR) in cord blood [0.75 μg/L (0.40-1.19), ∼30 % < LOD = ±0.35 μg/L] were usually higher than in maternal blood [0.55 μg/L (0.40-0.85), ∼ 10 % < LOD = ±0.15 μg/L]. Hg cord:maternal ratio was 1.34 (1.00-1.91), and infants born would have Hg cord:(cord + maternal) proportion ranged from 0.50 to 0.63. Mn was the only metal that was detected in 100 % in both maternal (LOD : ±0.50 μg/L) and cord (LOD = ±0.2 μg/L) blood. Mn median levels (IQR) in cord blood [32.96 μg/L (26.90-40.10)] were 2 times higher than in maternal blood [14.01 μg/L (11.50-17.58)]. Mn cord:maternal ratio was 2.35 (1.09-3.80), and infants born would have Mn proportion ranged from 0.52 to 0.79. Pb median levels (IQR) in cord blood [5.79 μg/L (4.34-8.38), ∼ 5% < LOD : ±2.07 μg/L] were usually equal to or lower than those reported in maternal blood [8.07 μg/L (5.79-10.76), ∼ 1% < LOD = ±1.03 μg/L]. Pb cord:maternal ratio was 0.71 (0.59-0.96), and infants born would have Pb proportion ranged from 0.37 to 0.49. Globally, the results indicate that total Hg and Mn levels were lower in maternal blood but higher in cord blood. However, much greater variability was seen with Cd and Pb. At delivery, total Hg and Pb levels in maternal blood were strong predictors of cord blood levels. Our findings empty that understanding the partition, levels and correlations of toxic metals in the maternal/cord blood may help to elucidate the adverse effects of these metals on foetuses and neonates.

Uptake, efflux, and toxicity of inorganic and methyl mercury in the endothelial cells (EA.hy926)

Cardiovascular disease (CVD) is the major cause of morbidity, mortality, and health care costs in the United States, and possibly around the world. Among the various risk factors of CVD, environmental and dietary exposures to mercury (Hg), a highly toxic metal traditionally regarded as a neurotoxin, has been recently suggested as a potential contributor towards human atherosclerotic development. In this study, we investigated the toxicity, type of cell death, dose-dependent uptake, and efflux of inorganic HgII (as HgCl₂) and methylmercury or MeHg (as CH₃HgCl) in EA.hy926 endothelial cells, as these two forms of Hg are often reported to be present in human blood among the general populations (~20–30% as HgII and ~70–80% as MeHg). Our results showed that HgII is more toxic than MeHg to the endothelial cells, owing to the higher uptake into the cytoplasm and perhaps importantly lower efflux of HgII by the cells, thus the “net” accumulation by the endothelial cells is higher for HgII than MeHg when exposed to the same Hg levels in the media. Furthermore, both HgII and MeHg were found to induce apoptotic and necrotic cell death. This study has important implications for the contributions of these two common Hg species to the development of atherosclerosis, an important process leading to CVD.

Identifying a critical window of maternal metal exposure for maternal and neonatal thyroid function in China: A cohort study

BACKGROUND

China, a developing country, has a particularly serious problem with metal pollution. We evaluated the association of metal exposure during pregnancy with maternal and neonatal thyroid function, and identified the critical window for maternal metal exposure effects on maternal and neonatal thyroid functions.

METHODS

The maternal urinary concentrations of mercury (Hg), cadmium (Cd), arsenic (As) and cesium (Cs) were determined in pregnant women during their first (n = 389) or third (n = 257) trimesters in a prospective cohort from 2014 to 2015 in Nanjing, China, using an inductively coupled plasma mass spectrometry (ICP-MS) instrument. Maternal serum-free thyroxine (FT4) and thyroid-stimulating hormone (TSH) were measured by electrochemiluminescent microparticle immunoassays in the second and third trimesters. Neonatal TSH levels were detected 72 h after birth.

RESULTS

Hg (>0.162 µg/L), Cd (>0.084 µg/L), As (>0.348 µg/L) and Cs (>0.093 µg/L) were detectable in 76.9%, 90.1%, 100% and 100% of maternal urine samples from women in the first trimester of pregnancy. In the multiple adjusted linear regression models, maternal exposures to Hg and Cd in the first trimester were positively associated with maternal TSH levels in the second trimester (P < 0.01, P = 0.02). Moreover, maternal exposures to Cd and Cs in the first trimester were positively associated with neonatal TSH levels (P = 0.04, P = 0.02). In the Bayesian kernel machine regression (BKMR) model, the results were stable and consistent with the linear regression model.

CONCLUSIONS

Maternal exposure to Hg, Cd and Cs in the first trimester was related to TSH levels in mothers and newborns. Efforts to identify maternal and neonatal thyroid disruptors should carefully consider the effects of exposure to these metals.

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.

Dental amalgams and risk of gestational hypertension in the MIREC study

BACKGROUND

The potential association between the presence or replacement of dental amalgams and gestational hypertension (GH) is unclear.

OBJECTIVE

To assess the association between the presence or replacement of dental amalgams and the risk of GH in a prospective cohort study.

METHODS

We assessed dental amalgam status (presence or replacement), blood mercury concentrations, and measured blood pressure (BP) in 1817 pregnant women recruited in 10 Canadian cities. BP was assessed in each trimester of pregnancy and mercury concentrations in 1st and 3rd trimesters. Logistic regression analysis was performed to estimate the adjusted odds ratios (aOR) and 95% confidence intervals (CI) for the associations between dental amalgam status and GH. Concurrent measures with systolic BP (SBP) and diastolic BP (DBP) were assessing through linear generalized estimating equations.

RESULTS

Dental amalgam status was weakly statistically correlated with mercury concentrations but there was no evidence of an association with GH in women having 1-4 (aOR = 1.31 (0.92, 1.85)) or ≥ 5 dental amalgams (aOR = 1.32 (0.86, 2.04)), compared to women without amalgam reported at first trimester. Dental amalgam replacement reported in the first or third trimester was similarly not associated with GH (aOR = 0.75 (0.40, 1.42) and 0.73 (0.39, 1.34), respectively) but with SBP (beta = -1.58 (-2.95, -0.02)).

CONCLUSION

We found weak correlations between dental amalgams and blood mercury among pregnant women. However, the presence of dental amalgams or their replacement was not associated with GH but with decreased SBP for the replacement. Further studies are required.

Biomonitoring of maternal and fetal exposure to mercury in Sabzevar and its affecting risk factors

Fetuses and young children are sensitive to even low levels of exposure to Hg, which can damage their brain and adversely affect their central nervous system and cognitive development. This study was conducted to determine the maternal and fetal mercury burden levels in mothers presenting to Shahidan Mobini Hospital for delivery. Eighty-nine mothers were included in this study and 360 samples were taken from their placental tissue and blood (maternal blood) as well as their umbilical cord tissue blood (infant blood). Findings revealed a significant strong correlation (r = 0.890, p < 0.001) in blood mercury between mothers and their infants. According to multiple linear regression analysis, there was a significant positive association between living in rural areas and the level of mercury in the placental tissue (β = 11.09, p < 0.001). This positive association was also found in other samples. In addition, there was a significant association between maternal age and mercury level in the placental tissue (β = 5.56, p = 0.049), placental blood (β = 11.67, p = 0.003), umbilical cord tissue (β = 8.33, p = 0.004) and umbilical cord blood (β = 9.51, p < 0.001).

Toxicity of mercury: Molecular evidence

Minamata disease in Japan and the large-scale poisoning by methylmercury (MeHg) in Iraq caused wide public concerns about the risk emanating from mercury for human health. Nowadays, it is widely known that all forms of mercury induce toxic effects in mammals, and increasing evidence supports the concern that environmentally relevant levels of MeHg could impact normal biological functions in wildlife. The information of mechanism involved in mercurial toxicity is growing but knowledge gaps still exist between the adverse effects and mechanisms of action, especially at the molecular level. A body of data obtained from experimental studies on mechanisms of mercurial toxicity in vivo and in vitro points to that disruption of the antioxidant system may play an important role in the mercurial toxic effects. Moreover, the accumulating evidence indicates that signaling transduction, protein or/and enzyme activity, and gene regulation are involving in mediating toxic and adaptive response to mercury exposure. We conducted here a comprehensive review of mercurial toxic effects on wildlife and human, in particular synthesized key findings of molecular pathways involved in mercurial toxicity from the cells to human. We discuss the molecular evidence related mercurial toxicity to the adverse effects, with particular emphasis on the gene regulation. The further studies relying on Omic analysis connected to adverse effects and modes of action of mercury will aid in the evaluation and validation of causative relationship between health outcomes and gene expression.

Mercury speciation in prenatal exposure in Slovenian and Croatian population - PHIME study

In recent years, several studies have addressed the issue of prenatal exposure to methylmercury (MeHg); however, few have actually analysed MeHg blood concentrations. Our study population included mothers and their new-borns from Slovenia (central region; N = 584) and Croatia (coastal region; N = 234). We have measurements of total Hg (THg) and MeHg in maternal hair, maternal peripheral blood, and cord blood. Cord blood Hg concentrations were low to moderate (median THg = 1.84 ng/g and MeHg = 1.69 ng/g). The proportion of THg as MeHg (%MeHg) in maternal and cord blood varied between 4% and 100% (coefficient of variation, CV = 32%) and between 8% and 100% (CV = 20%), respectively. Our data shows that variability of %MeHg was higher at lower blood THg levels. Concentrations of MeHg in maternal blood and cord blood were highly correlated (R_s = 0.943), in the case of inorganic Hg correlation was significant but weaker (R_s = 0.198). MeHg levels in maternal blood and cord blood were positively associated with seafood intake, maternal age, and negatively associated with pre-pregnancy BMI. Additionally, MeHg in maternal blood was positively associated with plasma selenium levels, and cord blood MeHg was negatively associated with parity. The results of multiple linear regression models showed that speciation analysis provides more defined estimation of prenatal exposure in association modelling. Associations between Hg exposure and cognitive performance of children (assessed using Bayley Scales of Infant and Toddler development) adjusted for maternal or child Apolipoprotein E genotypes showed higher model R² and lower p-values when adjusted for MeHg compared to THg. This study demonstrates that Hg speciation improves the association between exposure and possible negative health effects.

Prenatal and Early Postnatal Exposure to Total Mercury and Methylmercury from Low Maternal Fish Consumption

The aim of this study was to investigate the influence of low fish consumption on prenatal and early postnatal exposure to mercury species. The samples of umbilical cord blood and maternal milk as well as interviewer-administered questionnaires were collected from 142 Slovak mother-child pairs. The mean total mercury (THg) concentrations in cord blood and milk were 0.949 μg/L and 0.376 μg/kg, respectively. The mean methylmercury (MeHg) concentration in cord blood was 0.504 μg/L. Fish eaters had significantly higher cord blood MeHg concentrations than non-fish eaters (p = 0.030); no difference was found in milk or cord blood THg concentrations. The bivariate analysis showed a positive correlation between cord blood MeHg and consumption of sea fish and shellfish (r_s = 0.320, p < 0.001); after adjustment for the potential confounders, the association was weakened (β = 0.173, p = 0.059). Nevertheless, the decision tree method showed sea fish and shellfish consumption to be the best predictor of cord blood MeHg. Furthermore, a negative association was found between THg concentrations in maternal milk and freshwater fish consumption (β = - 0.193, p = 0.017), which might indicate a beneficial effect of freshwater fish consumption. The results suggest there is a need for future research to investigate the benefits versus the adverse effects of low maternal fish consumption on child development.

Concentration of mercury species in hair, blood and urine of individuals occupationally exposed to gaseous elemental mercury in Asturias (Spain) and its comparison with individuals from a control group formed by close relatives

Between November 19th, 2012 and December 3rd, 2012, 50 workers were intoxicated with gaseous Hg in San Juan de Nieva (Asturias, Spain) during the maintenance of a heat exchanger of a zinc manufacturer. We have quantified the concentration of methylmercury (MeHg), ethylmercury (EtHg) and Hg(II) in blood, hair and urine samples of those individuals taken three years after the accident. Blood, hair and urine of their closest relatives were also analyzed to assess whether the mercury burden present in the intoxicated individuals was due to the occupational exposure or to environmental or lifestyle-related factors. The determination of the mercury species in the samples was carried out applying multiple spiking Isotope Dilution GC-ICP-MS. This procedure corrects for possible interconversion reactions between the Hg species during the sample preparation procedure. Linear correlations were observed for both groups when plotting MeHg in blood vs MeHg in hair, and MeHg in hair vs Hg (II) in urine. The concentrations of Hg species in the intoxicated individuals were not significantly different from those obtained in the control group except for MeHg in blood. Significantly higher levels of MeHg in blood were obtained in some of the intoxicated individuals who had not consumed fish or seafood since the accident. A different correlation between MeHg in hair and MeHg in blood was obtained for these individuals compared to the control group who showed a hair-to-blood ratio consistent with the reported value for people exposed to Hg via fish consumption. Our results suggest that ingested MeHg followed the same pathway of deposition in hair in exposed and non-exposed individuals. However, the exposed individuals with high MeHg levels in blood showed a significantly different extent of MeHg deposition in hair compared to the control group.

Rethinking the Dental Amalgam Dilemma: An Integrated Toxicological Approach

Mercury (Hg) has been identified as one of the most toxic nonradioactive materials known to man. Although mercury is a naturally occurring element, anthropogenic mercury is now a major worldwide concern and is an international priority toxic pollutant. It also comprises one of the primary constituents of dental amalgam fillings. Even though dental mercury amalgams have been used for almost two centuries, its safety has never been tested or proven in the United States by any regulatory agency. There has been an ongoing debate regarding the safety of its use since 1845, and many studies conclude that its use exposes patients to troublesome toxicity. In this review, we present in an objective way the danger of dental amalgam to human health based on current knowledge. This dilemma is addressed in terms of an integrated toxicological approach by focusing on four mayor issues to show how these interrelate to create the whole picture: (1) the irrefutable constant release of mercury vapor from dental amalgams which is responsible for individual chronic exposure, (2) the evidence of organic mercury formation from dental amalgam in the oral cavity, (3) the effect of mercury exposure on gene regulation in human cells which supports the intrinsic genetic susceptibility to toxicant and, finally, (4) the availability of recent epidemiological data supporting the link of dental amalgams to diseases such as Alzheimer’s and Parkinson.

Extenuation of in utero toxic effects of MeHg in the developing neurons by Fisetin via modulating the expression of synaptic transmission and plasticity regulators in hippocampus of the rat offspring

The neurotoxic environmental contaminant, methylmercury (MeHg), has shown to have detrimental effects on the developing brain when exposed during gestation. We have shown in our earlier studies that gestational administration of 3,3',4',7-Tetrahydroxyflavone or Fisetin reduces the toxic effects of MeHg in the developing rat brain. The current study has pivoted to study the mechanism behind the mitigating action of Fisetin against prenatal MeHg exposure induced neurotoxicity. Negligible data is available about the toxicity targets of MeHg in the developing brain. Studies have exhibited that MeHg exposure cause toxic effects on synaptic transmission and plasticity in the offspring brain. Hence, we aimed to study the effect of Fisetin on MeHg induced alterations in the expressions of regulatory genes and proteins involved in synaptic plasticity and transmission. Pregnant rats were grouped according to the type of oral administration as, (i) Control, (ii) MeHg (1.5 mg/kg b. w.), (iii) MeHg + Fisetin (30 mg/kg b. w.) and (iv) Fisetin (30 mg/kg b. w). Maternal administration of Fisetin prevented MeHg exposure induced downregulation of neurogranin (Nrgn), dendrin (Ddn), Syntaxin 1 A (Stx1a), Lin-7 homolog A (Lin7a), Complexin-2 (Cplx2) and Exocyst complex component 8 (Exoc8) genes in the offspring rat. Fisetin also prevented MeHg exposure induced downregulation of brain derived neurotrophic factor (BDNF), Glial-cell derived neurotrophic factor (GDNF) protein expressions and hampered reactive astrogliosis in the hippocampus of F₁ generation rats. Hence, through this study, we conclude that Fisetin modulates the expression of regulatory genes and proteins involved in synaptic transmission and plasticity and extenuates MeHg neurotoxicity in the developing rat brain.

Hospital centered surveillance of births in Gaza, Palestine, 2011-2017 and heavy metal contamination of the mothers reveals long-term impact of wars

Prevalence of preterm, low birth weight and birth defects increased significantly since 2011 in Gaza, Palestine. No change in known co-factors of reproductive health justified this rise. Two military attacks in 2012 and 2014 introduced novel risk factors for outcomes at birth: contamination by teratogenic and carcinogenic heavy metals weapon-remnants, ongoing impoverishment, and impaired rehabilitation of waste management. It was previously shown that mothers exposed to military attacks had higher metal load than those unexposed and mother's heavy metals trans-pass placenta. We investigated association in time of heavy metal contamination and reproductive health using hospital-based surveillance (2011-2016-2017) of births, accompanied by assessment in 2016 of metal load in mother and newborn hair. Mother's housing proximal to unmanaged waste predicted preterm birth and birth defects, and these women had highest load of heavy metals. Poor diet predicted low birth weight. Circumstances prevent investigation of heavy metals molecular impact(s) during fetal development.

Blood total mercury and methylmercury among pregnant mothers in Charleston, South Carolina, USA

BACKGROUND

Maternal blood total mercury (THg) is a biomarker for prenatal methylmercury (MeHg) exposure. Few studies have quantified both blood THg and MeHg during pregnancy, and few studies have reported longitudinal trends.

OBJECTIVES

We analyzed blood THg and MeHg in a cohort of pregnant mothers in Charleston, South Carolina (n = 83), and investigated whether blood THg or MeHg changed between early and late gestation.

METHODS

THg and MeHg were analyzed in blood samples from early (12 ± 1.7 weeks) and late (35 ± 2.2 weeks) gestation.

RESULTS

Blood %MeHg (of THg) averaged 63% (range: 10-114%) and 61% (range: 12-117%) during early and late gestation, respectively. In unadjusted analyses, blood MeHg decreased from early to late pregnancy (paired t-test, p = 0.04), while THg did not change (paired t-test, p = 0.34). When blood MeHg was normalized by the hematocrit, this decrease was no longer statistically significant (paired t-test, p = 0.09).

CONCLUSIONS

In unadjusted analyses, blood MeHg, but not THg, decreased significantly between early and late gestation; this decrease was due in part to hemodilution. Percent MeHg (of THg) varied by up to one order of magnitude. Results highlight the importance of Hg speciation in maternal blood samples to assess prenatal MeHg exposure.

Chemokine CCL4 Induced in Mouse Brain Has a Protective Role against Methylmercury Toxicity

Methylmercury (MeHg) is selectively toxic to the central nervous system, but mechanisms related to its toxicity are poorly understood. In the present study, we identified the chemokine, C-C motif Chemokine Ligand 4 (CCL4), to be selectively upregulated in the brain of MeHg-administered mice. We then investigated the relationship between CCL4 expression and MeHg toxicity using in vivo and in vitro approaches. We confirmed that in C17.2 cells (a mouse neural stem cell line) and the mouse brain, induction of CCL4 expression occurs prior to cytotoxicity caused by MeHg. We also show that the addition of recombinant CCL4 to the culture medium of mouse primary neurons attenuated MeHg toxicity, while knockdown of CCL4 in C17.2 cells resulted in higher MeHg sensitivity compared with control cells. These results suggest that CCL4 is a protective factor against MeHg toxicity and that induction of CCL4 expression is not a result of cytotoxicity by MeHg but is a protective response against MeHg exposure.

Prenatal exposure to mercury and longitudinally assessed fetal growth: Relation and effect modifiers

BACKGROUND

Prenatal mercury exposure has been related to reductions in anthropometry at birth. Levels of mercury have been reported as being relatively elevated in the Spanish population.

OBJECTIVE

To investigate the relation between prenatal exposure to mercury and fetal growth.

METHODS

Study subjects were pregnant women and their newborns (n:1867) participating in a population-based birth cohort study set up in four Spanish regions from the INMA Project. Biparietal diameter (BPD), femur length (FL), abdominal circumference (AC), and estimated fetal weight (EFW) were measured by ultrasounds at 12, 20, and 34 weeks of gestation. Size at and growth between these points were assessed by standard deviation (SD) scores adjusted for constitutional characteristics. Total mercury (T-Hg) was determined in cord blood. Associations were investigated by linear regression models, adjusted by sociodemographic, environmental, nutritional - including four seafood groups - and lifestyle-related variables in each sub-cohort. Final estimates were obtained using meta-analysis. Effect modification by sex, seafood intake and polychlorinated biphenyl (PCB) congener 153 concentration was assessed.

RESULTS

Geometric mean of cord blood T-Hg was 8.2μg/L. All the estimates of the association between prenatal Hg and growth from 0 to 12 weeks showed reductions in SD-scores, which were only statistically significant for BPD. A doubling of cord blood T-Hg was associated with a 0.58% reduction in size of BPD at week 12 (95% confidence interval -CI-: - 1.10, - 0.07). Size at week 34 showed estimates suggestive of a small reduction in EFW, i.e., a doubling of T-Hg levels was associated with a reduction of 0.38% (95% CI: - 0.91, 0.15). An interaction between PCB153 and T-Hg was found, with statistically significant negative associations of T-Hg with AC and EFW in late pregnancy among participants with PCB153 below the median.

CONCLUSIONS

Exposure to mercury during pregnancy was associated with early reductions in BPD. Moreover, an antagonism with PCB 153 was observed with noteworthy reductions late in pregnancy in AC and EFW in the group with lower PCB153.

Blood heavy metal concentrations in pregnant Korean women and their children up to age 5years: Mothers' and Children's Environmental Health (MOCEH) birth cohort study

The present study assessed the associations of heavy metal concentrations in pregnant women with the concentrations in their children during early childhood. This study is a part of the Mothers' and Children's Environmental Health (MOCEH) study, a Korean multi-center prospective birth cohort study of 1751 pregnant women who were recruited from 2006 to 2010. We completed the follow-up of children who were 5years-old in 2016. Lead, total mercury, and cadmium were measured in women during early and late pregnancy, in cord blood, and in children who were 2, 3, and 5years-old. Lead concentration was lowest in cord blood, highest in 24month-old children, and then decreased with child age. Total mercury concentration was highest in cord blood, and gradually decreased with child age. Cadmium concentration was lowest in cord blood, and increased with child age. After adjusting for child sex, maternal age, and maternal education level, we found strong correlations between the levels of lead and total mercury in women during late pregnancy with the levels in cord blood; however, there were weak correlations between the levels of these metals in women during late pregnancy and cord blood with the levels in their children. In conclusion, maternal lead and mercury concentrations correlated with the levels in cord blood and in children up to age 60months. This correlation may be due to high trans-placental transmission of these metals and shared living environment such as environmental exposure, food consumption, and lifestyle.

Mercury in Children: Current State on Exposure through Human Biomonitoring Studies

Mercury (Hg) in children has multiple exposure sources and the toxicity of Hg compounds depends on exposure routes, dose, timing of exposure, and developmental stage (be it prenatal or postnatal). Over the last decades, Hg was widely recognized as a threat to the children’s health and there have been acknowledgements at the international level of the need of a global policy intervention—like the Minamata treaty—aimed at reducing or preventing Hg exposure and protecting the child health. National human biomonitoring (HBM) data has demonstrated that low levels of exposure of Hg are still an important health concern for children, which no one country can solve alone. Although independent HBM surveys have provided the basis for the achievements of exposure mitigation in specific contexts, a new paradigm for a coordinated global monitoring of children’s exposure, aimed at a reliable decision-making tool at global level is yet a great challenge for the next future. The objective of the present review is to describe current HBM studies on Hg exposure in children, taking into account the potential pathways of Hg exposure and the actual Hg exposure levels assessed by different biomarkers.

Inorganic mercury prevents the differentiation of SH-SY5Y cells: Amyloid precursor protein, microtubule associated proteins and ROS as potential targets

Exposure to mercury (Hg) occurs through different pathways and forms including methylmecury (MeHg) from seafood and rice, ethylmercury (EtHg), and elemental Hg (Hg⁰) from dental amalgams and artisanal gold mining. Once in the brain all these forms are transformed to inorganic Hg (I-Hg), where it bioaccumulates and remains for long periods. Hg is a well-known neurotoxicant, with its most damaging effects reported during brain development, when cellular key events, such as cell differentiation take place. A considerable number of studies report an impairment of neuronal differentiation due to MeHg exposure, however the effects of I-Hg, an important form of Hg found in brain, have received less attention. In this study, we decided to examine the effects of I-Hg exposure (5, 10 and 20μM) on the differentiation of SH-SY5Y cells induced by retinoic acid (RA, 10μM). We observed extension of neuritic processes and increased expression of neuronal markers (MAP2, tubulin-βIII, and Tau) after RA stimulation, all these effects were decreased by the co-exposure to I-Hg. Interestingly, I-Hg increased the levels of reactive oxygen species (ROS) and nitric oxide (NO) accompanied with increased levels of inducible nitric oxide synthase (iNOS) and, dimethylarginine dimethylaminohydrolase 1 (DDHA1). Remarkably I-Hg decreased levels of nitric oxide synthase neuronal (nNOS). Moreover I-Hg reduced the levels of tyrosine hydroxylase (TH) and amyloid precursor protein (APP) a protein recently involved in neuronal differentiation. These data suggest that the exposure to I-Hg impairs cell differentiation, and point to new potential targets of Hg toxicity such as APP and NO signaling.

Contaminación por mercurio de leche materna de madres lactantes de municipios de Antioquia con explotación minera de oro

Introducción. La leche materna es esencial para el desarrollo del ser humano, pero puede contener sustancias tóxicas provenientes de la contaminación ambiental, especialmente en las áreas mineras.Objetivo. Determinar la prevalencia de la contaminación con mercurio de la leche materna de mujeres lactantes residentes en los municipios con explotación minera de oro.Materiales y métodos. Se hizo un estudio transversal de 150 madres lactantes de cuatro municipios mineros de Antioquia (El Bagre, Segovia, Remedios y Zaragoza), a quienes se les hizo una encuesta sobre factores sociodemográficos, ocupacionales y ambientales relacionados con el mercurio, y se les tomaron muestras de leche materna, de orina y de cabello. Se calculó el promedio de la concentración de mercurio y las prevalencias municipales de contaminación.Resultados. El promedio de la concentración de mercurio en la leche materna fue de 2,5 (± desviación estándar 9,2) μg/L. La prevalencia de muestras de leche materna con niveles altos de mercurio fue de 11,7 %.Conclusión. En este estudio se evidencia un grave problema en las regiones mineras auríferas de Antioquia por el efecto de la contaminación con mercurio en sectores de la población más vulnerable.

Associations of blood mercury, inorganic mercury, methyl mercury and bisphenol A with dental surface restorations in the U.S. population, NHANES 2003-2004 and 2010-2012

The potential adverse health effects of mercury from amalgam and bisphenol A (BPA) from composite resin have been significant concerns. It is unclear whether dental restorative materials significantly contribute to mercury or BPA levels. The purpose of this study is to use NHANES data including 14,703 subjects (2003-2004: n=7514; 2011-2012: n=7189) to examine the association between Dental Surface Restorations (DSR) and blood total mercury (THg), inorganic mercury (IHg), methyl mercury (MeHg) and urinary BPA through the stratification of covariates and multivariate analysis. Subjects were divided into three groups based on the number of dental surface restorations (DSRs, 0, 1-8, >8). Blood THg and IHg in 2003-2004 were significantly higher in the subjects with DSR (geometric mean of 0.48, 0.69 and 1.17μg/l for THg; 0.32, 0.33 and 0.39μg/l for IHg with DSR 0, 1-8 and >8). Similarly, increases of THg, IHg and MeHg were also observed in 2013-2014 (geometric mean of 0.51, 0.69 and 0.99μg/l for THg; 0.40, 0.49 and 0.66μg/l for MeHg; 0.20, 0.22 and 0.29μg/l for IHg with DSR 0, 1-8 and >8). Linear regression model analysis revealed blood THg and IHg in 2003-2004 and THg, IHg and MeHg in 2011-2012 were quantitatively associated with the number of DSRs. A dramatic decrease in urinary BPA from 2003 to 2004-2011-2012 was observed, but no significant increase with DSRs in either period of study. In conclusion, significant increases in blood THg, IHg, and MeHg in the subjects with DSRs are confirmed in a nationally representative population, a critical step in assessing the potential risk of adverse effects from dental restorative materials, but no association between dental fillings and urinary BPA was found.

Maternal prenatal fish consumption and cognition in mid childhood: Mercury, fatty acids, and selenium

BACKGROUND

Few studies of maternal prenatal fish intake have included biomarkers of exposure to mercury, long-chain n-3 fatty acids, and selenium, which are hypothesized to mediate associations with child neurodevelopment.

OBJECTIVES

Examine associations of maternal prenatal fish intake with child neurodevelopment accounting for biomarkers.

METHODS

In 1999-2002 we enrolled pregnant women into the Project Viva cohort. At median 27.9weeks gestation, we estimated maternal fish intake using food frequency questionnaires, and collected blood. We assayed erythrocytes for total mercury and selenium, and plasma for fatty acids including n-3 docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). In mid-childhood (median 7.7years), we administered cognitive tests including the Kauffman Brief Intelligence Test (KBIT). We performed multivariable linear regression analyses adjusting for maternal and child characteristics including home environment and maternal intelligence.

RESULTS

Among 1068 pairs (872 with blood), mean (SD) exposures were: maternal fish intake 1.7 (1.5)servings/week, mercury 4.0 (3.6)ng/g, DHA+EPA 98.4 (41.8)mcg/ml, selenium 205.6 (34.6)ng/ml. Child KBIT verbal scores (mean 112.2, SD 15.0) were not related to any exposures: maternal fish intake (0.15; 95% CI: -0.50, 0.79), mercury (0.08; -0.18, 0.35), DHA+EPA (0.01; -0.22, 0.24), and selenium (0.20; -0.09, 0.50). Associations with KBIT nonverbal scores and tests of memory and visual motor abilities were similarly null. Mutual adjustment for each of the exposure measures did not substantially change estimates.

CONCLUSIONS

In this population with an average fish consumption of about 1 1/2 weekly servings, we did not see any evidence for an association of maternal prenatal fish intake, or of mercury, DHA+EPA, or selenium status, with verbal or non-verbal intelligence, visual motor function, or visual memory at median 7.7years of age.

Dental associations with blood mercury in pregnant women

Objectives

There is curiosity concerning the source of mercury that is absorbed into the mother's blood and which may affect the developing fetus. This study therefore sets out to determine the extent to which dental amalgam (DA) may contribute to total blood mercury (TBHg) levels of pregnant women in the UK.

Methods

Whole blood samples and information on diet and socio‐demographic factors were collected from pregnant women (n = 4484) enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC). The whole blood samples were assayed for total mercury levels using inductively coupled plasma dynamic reaction cell mass spectrometry (ICP‐DRC‐MS), and the women were retrospectively asked about features of their dental care during the pregnancy. Linear regression was used to estimate the relative contributions of DA to TBHg levels (log‐transformed) based on R² values, compared to the results from dietary and socio‐demographic variables.

Results

The contribution to the variance of the mothers' TBHg levels by dental variables was 6.47%, a figure comparable to the 8.75% shown for seafood consumption in this population. Dietary and dental variables explained 20.16% of the variance, with socio‐demographic variables contributing only a further 3.40%. The number of amalgams in the mouth at the start of pregnancy accounted for most of the variance in dental variables.

Conclusions

Dental amalgam contributes a comparable amount of variance in TBHg to seafood consumption in this population. However, because the measures of DA exposure were imprecise, these findings are likely to be an underestimate. There is no evidence to date in the literature that fetal exposures to mercury from maternal DAs have adverse effects on the developing child, but long‐term studies are warranted.

The extent of mercury (Hg) exposure among Saudi mothers and their respective infants

A total of 1016 healthy Saudi mothers and their respective infants (aged 3-12 months) were recruited from 57 Primary Health Care Centers (PHCCs) in Riyadh, Saudi Arabia, to evaluate the extent of mercury (Hg) exposure and predict its sources in the healthy Saudi population. Total Hg levels were measured in maternal urine, breast milk, blood, and hair and in the infants' urine and hair. Only 1.9% of the mothers had urinary Hg (UHg)>10 μg/l, the limit for asymptomatic adults recommended by the World Health Organization, but the median (0.99 μg/l) was higher than in other countries. Also, 49.3% of the mothers had UHg>1 μg/l, the German reference value for adults. Median infant UHg was 0.729 μg/l, and 77 and 93 % of the infants had levels higher than 0.4 and 0.1 μg/l, the reference values of the Centers for Disease Control and Prevention and for Germany, respectively. The median Hg level in breast milk was 0.884 μg/l. Even though 43.2% of the milk samples were above the background level for Hg in human milk (1 μg/l), our results were lower than those reported from other countries. Median maternal total Hg in blood was 0.637 μg/l, and only 0.4 and 6.9% of samples were higher than the Hg reference levels of 5.8 μg/l of the Environmental Protection Agency (EPA) and of 2 μg/l for Germany, respectively. Total Hg levels in hair (HHg) varied widely among mothers and infants, but only 3.9% of the mothers and 2.8% of the infants had HHg>1 μg/g (the EPA reference level). Median HHg values were 0.117 μg/g dry weight in mothers and 0.1 μg/g dry weight in infants; both were lower than in other countries. The Hg levels in mothers and their respective infants were relatively low, but our results were consistent with other studies indicating that dental amalgam fillings and fish consumption were the main predictors of maternal Hg exposure. Among the several biomarkers of Hg exposure, Hg levels in maternal hair and urine were the strongest predictors of infant exposure. The lack of an association between Hg in breast milk and Hg in infant urine and hair suggested that the infants were exposed to Hg predominately during pregnancy rather than during breastfeeding. We expect that our data can serve as a baseline for further biomonitoring and follow-up studies, particularly of the long-term impact of Hg on childhood neurodevelopment.

Mercury health effects among the workers extracting gold from carpets and dusted clays through amalgamation and roasting processes

Mercury (Hg) is a highly toxic metal which can cause serious health effects. The aim of this research was to determine the concentrations of total Hg (T-Hg), methyl Hg (Me-Hg), and inorganic Hg (I-Hg) in the biological samples (plasma, red blood cells (RBCs), urine, hair, and nails) of the exposed goldsmith workers. This is the first study that determines the detailed Hg concentrations in the biological samples (plasma, RBCs, urine, hair, and nails) of the exposed goldsmith workers and correlates them with the diseases noted among the workers in a single paper. Biological samples were collected from goldsmith workers (n = 40) and analyzed for T-Hg, Me-Hg, and I-Hg using atomic absorption spectrometer equipped with mercury hydride system. The mean T-Hg concentration in RBCs (33 μg L(-1)), plasma (11.8 μg L(-1)), urine (167 μg L(-1)), hair (4.21 μg g(-1)), and nails (5.91 μg g(-1)) were higher than the control RBCs (1.64 μg L(-1)), plasma (0.55 μg L(-1)), urine (2.72 μg L(-1)), hair (0.35 μg g(-1)), and nails (0.51 μg g(-1)). All workers participated in this study were suffering from physical and mental diseases. The concentration of Hg was found higher among the workers suffering from mental diseases as compared to those suffering from physical diseases. Among the physical diseases, the most serious diseases were sexual dysfunction, skin diseases, and fatigue because the workers suffering from these diseases had higher concentration of Hg than the workers with other diseases. The occurrence of physical diseases (88%) was greater than the mental diseases (53%) among the workers. The correlations of physical and mental diseases with experience (years of work) and exposure time were significant (p < 0.05), while nonsignificant (p > 0.05) correlation was observed between demographic parameters and Hg concentrations in the biological samples of the workers. The burning process of amalgamated gold is a significant source of Hg exposure to goldsmith workers; therefore, awareness and precautionary measures are needed to provide protection to them.

Sources of Mercury Exposure to Children in Low- and Middle-Income Countries

BACKGROUND

Many children in low- and middle-income countries face enhanced risks of exposure to contaminants via the environment, parental occupation, and other routes. While mercury (Hg) is a global pollutant whose transport properties allow it to have an impact even in pristine areas, the presence of significant Hg sources in the developing world can cause localized effects that are more severe than those observed in other areas.

OBJECTIVES

This paper provides a narrative review of sources of Hg exposure to people in the developing world with a particular focus on children, and presents an overview of key aspects to this important issue.

METHODS

We searched Web of Knowledge and Google Scholar using keywords including combinations of "mercury" and one or more of the following: "children," "exposure," "breast milk," "artisanal mining," "prenatal," "religion," "medicine," "dental amalgam," "chlor-alkali," "VCM," "vaccine," "e-waste," "industry," "beauty," "cosmetics," "strategies," "child labor," "costs," and "developing countries" to find peer-reviewed articles pertaining to Hg exposure in the developing world.

RESULTS

Sources of Hg exposure include mining, consumption, industrial operations, religious practices, traditional medicines, beauty products, vaccines, dental amalgams, and waste scavenging and recycling.

CONCLUSION

Children in the developing world are often subject to higher levels of Hg exposure than those living in developed countries due to the higher prevalence of Hg-intensive industrial processes and consumer products, lack of environmental regulation, and limits in mobility and food choices, among other factors. This issue can be addressed through additional research to fill in data gaps on exposure sources, establish sound and enforceable policies, and increase education and participation in affected communities. Challenges to addressing this problem include limited resources for needed equipment, training, and manpower to implement solutions.

Methylmercury in the breast milk of Japanese mothers and lactational exposure of their infants

The human fetus is known to be exposed to methylmercury (MeHg), but little is known about the risk of infant exposure via breast milk. To evaluate the lactational exposure to MeHg via breast milk in Japanese infants, the levels of total mercury (THg) and MeHg were determined in breast milk and maternal blood using samples from a birth cohort study at the Tohoku Study of Child Development. Maternal blood and breast milk were collected one day postpartum and one month after delivery, respectively. The median THg (and MeHg) concentrations in maternal RBCs, plasma and breast milk were 17.8 ng g(-1) (17.8 ng g(-1)), 1.51 ng g(-1) (1.33 ng g(-1)) and 0.81 ng g(-1) (0.45 ng g(-1)), respectively (n=27). The median percentage of MeHg in THg was 54% in breast milk. Breast milk contained substantial amounts of MeHg, which was strongly associated with the internal accumulation of MeHg and the lipid content of the milk (r=0.684). The range of lipid contents in milk varied widely from 0.50 to 6.60 g/100 g of milk, with a median of 3.60 g/100 g. The median (range) weekly average intake of MeHg via breast milk was estimated to be 0.63 μg kg(-1) (0.08-1.68 μg kg(-1)) BW/week. Because the MeHg and lipid contents in milk substantially fluctuate, an investigation of the variations of MeHg and lipid content in breast milk may be required for a more precise risk assessment.

Differential DNA methylation in umbilical cord blood of infants exposed to mercury and arsenic in utero

Mercury and arsenic are known developmental toxicants. Prenatal exposures are associated with adverse childhood health outcomes that could be in part mediated by epigenetic alterations that may also contribute to altered immune profiles. In this study, we examined the association between prenatal mercury exposure on both DNA methylation and white blood cell composition of cord blood, and evaluated the interaction with prenatal arsenic exposure. A total of 138 mother-infant pairs with postpartum maternal toenail mercury, prenatal urinary arsenic concentrations, and newborn cord blood were assessed using the Illumina Infinium Methylation450 array. White blood cell composition was inferred from DNA methylation measurements. A doubling in toenail mercury concentration was associated with a 2.5% decrease (95% CI: 5.0%, 1.0%) in the estimated monocyte proportion. An increase of 3.5% (95% CI: 1.0, 7.0) in B-cell proportion was observed for females only. Among the top 100 CpGs associated with toenail mercury levels (ranked on P-value), there was a significant enrichment of loci located in North shore regions of CpG islands (P = 0.049), and the majority of these loci were hypermethylated (85%). Among the top 100 CpGs for the interaction between arsenic and mercury, there was a greater than expected proportion of loci located in CpG islands (P = 0.045) and in South shore regions (P = 0.009) and all of these loci were hypermethylated. This work supports the hypothesis that mercury may be contributing to epigenetic variability and immune cell proportion changes, and suggests that in utero exposure to mercury and arsenic, even at low levels, may interact to impact the epigenome.

Synergism between exposure to mercury and use of iodine supplements on thyroid hormones in pregnant women

OBJECTIVE

To evaluate the association between mercury exposure and thyroid-stimulating hormone (TSH), total triiodothyronine (TT3) and free thyroxine (FT4) levels during pregnancy as well as to explore if there is any synergic action between mercury and intake of iodine from different sources.

METHODS

The study population was 1407 pregnant women participating in the Spanish INMA birth cohort study. Total mercury concentrations were analyzed in cord blood. Thyroid hormones (THs) were measured in serum samples collected at 13.2±1.5 weeks of gestation. The association between mercury and TH levels was evaluated with multivariate linear regression models. Effect modification caused by iodine intake from supplements and diet was also evaluated.

RESULTS

The geometric means of TSH, TT3, FT4 and mercury were 1.1μU/L, 2.4nmol/L, 10.5pmol/L and 7.7μg/L, respectively. Mercury levels were marginally significantly associated with TT3 (β: -0.05; 95%CI: -0.10, 0.01), but were neither associated with TSH nor FT4. The inverse association between mercury and TT3 levels was stronger among the iodine supplement consumers (-0.08; 95%CI: -0.15, -0.02, interaction p-value=0.07). The association with FT4 followed the same pattern, albeit not significant.

CONCLUSION

Prenatal mercury exposure was inversely associated with TT3 levels among women who took iodine supplements during pregnancy. These results could be of public health concern, although further research is needed.