Levels of prenatal mercury exposure and their relationships to neonatal anthropometry in Wujiang City, China

Association of maternal metals exposure, metabolites and birth outcomes in newborns: A prospective cohort study

BACKGROUND

Maternal exposure to metals may pose a risk to the health of newborns, however, the underlying mechanisms remain ambiguous. Herein, we aimed to investigate the influence of metals exposure on birth outcomes and reveal the importance of metabolites in the exposure-outcomes association by using metabolomics methods.

METHODS

In our study, 292 mother-pairs were included who were recruited from the affiliated hospitals of Nanjing Medical University between 2006 and 2011. We measured fifteen metals (mercury, lead, vanadium, arsenic, zinc, cadmium, rubidium, copper, cobalt, iron, molybdenum, strontium, thallium, magnesium and calcium) and metabolites in maternal second trimester serums by using inductively coupled plasma mass spectrometry and ultra-high performance liquid chromatography high resolution accurate mass spectrometry, respectively. A multi-step statistical analysis strategy including exposome-wide association study (ExWAS) model, variable selection models and multiple-exposure models were performed to systematically appraise the associations of individual and mixed metals exposure with birth outcomes. Furthermore, differential metabolites that associated with metals exposure and birth outcomes were identified using linear regression models.

RESULTS

Metal's levels in maternal serums ranged from 0.05 μg/L to 1864.76 μg/L. In the ExWAS model, maternal exposure to arsenic was negatively associated with birth weight (β = 188.83; 95% CI: -368.27, -9.39), while maternal mercury exposure showed a positive association (β = 533.65; 95%CI: 179.40, 887.90) with birth weight. Moreover, each unit increase in mercury (1 ng/mL-log transformed) was associated with a 1.82 week-increase (95%CI: 0.85, 2.79) in gestational age. These findings were subsequently validated by variable selection models and multiple exposure models. Metabolomic analysis further revealed the significant role of 3-methyladenine in the relationship between arsenic exposure and birth weight.

CONCLUSION

This study provides new epidemiological evidence indicating the associations of metals exposure and neonatal birth outcomes, and emphasizes the potential role of metabolite biomarkers and their importance in monitoring adverse birth outcomes.

Maternal and fetal exposure to metal (loid)s, maternal nutrition status, and impact on prenatal growth in an energy rich zone and an urban area along the Persian Gulf

The main purposes of the study were to determine whether maternal and cord blood (MB and CB) levels of metal (loid)s (MLs) are different between industrial and urban areas. Subjects were derived from the petrochemical and gas area (PGA) of Asaluyeh County and the urban area (UA) of Bushehr County in Iran. Adjusted models revealed significant differences between the PGA and UA for maternal Fe, Cu, Mg, Cd, Zn, Ni, V and Pb levels, likewise cord Cu, V, Pb and Ni levels, which were higher in the PGA. Unadjusted models revealed there were decreases in neonatal weight and head circumference by 16.550 g and 0.059 cm, respectively for each Ln unit increase in maternal Cr levels. The mean blood levels of MLs significantly associated with food consumption frequency. The MLs were detected at higher levels in the body's fetuses and their mothers who resided in the PGA than those from the UA. So, the fetuses of mothers living in an industrial areas may be at higher risk from anthropometric measures. The impact of prenatal exposure to MLs on prenatal growth should be considered for better understanding in the further studies.

Gender differences in trace element exposures with cognitive abilities of school-aged children: a cohort study in Wujiang city, China

Trace elements persist in the environment, and their early exposure may adversely affect children's intellectual development. To clarify the influence of blood trace element levels in newborns and school-aged children, we used Wechsler Intelligence Scale for children (WISC-CR) to explore intellectual development level of 148 school-aged children based on a population cohort study. Lead (Pb), selenium (Se), arsenic (As), copper (Cu), manganese (Mn) and chromium (Cr) in cord blood and Pb, As, Cu in venous blood were determined by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometer (AAS). Our analysis of the correlation between children's mental development and trace element content found children's cognitive abilities negatively correlate with Pb (PIQ: β=-0.109, P=0.03737) and Cu (PIQ: β=-0.031, P=0.04431; FISQ: β=-0.031, P=0.02137) levels in cord blood. Prenatal low-level As exposure may negatively affect girls' performance intelligence quotient (PIQ) and verbal intelligence quotient (VIQ). There were differences in Se levels in cord blood and venous blood between boys and girls (P=0.010; P=0.073). High Se levels were associated with a lower VIQ in boys and a higher VIQ in girls. Prenatal exposure to Pb, As and Cu may weaken children's cognitive abilities at school age. Se exposure may have opposite effects on cognitive abilities affected by dose and gender.

Associations of maternal blood mercury with preeclampsia and birth outcomes

BACKGROUND

Mercury (Hg) is a highly toxic substance, and its harmful effects on maternal and infant health have been reported. Yet, the associations of Hg exposure with preeclampsia (PE) and adverse birth outcomes are not well understood.

OBJECTIVE

The aim of this study was to investigate the potential effects of maternal Hg exposure on PE and birth outcomes.

METHODS

We conducted a case-control study with 84 participants in China. Logistic models were used to estimate odds ratios for PE risk and birth outcomes according to maternal blood Hg levels, adjusting for potential confounding factors.

RESULTS

Elevated blood Hg levels were associated with increased risks of mild PE (aOR, 7.03; 95% CI, 1.61, 30.62; P < 0.01) and severe PE (aOR, 47.55; 95% CI, 5.27, 429.05; P < 0.05). We also found that increased blood Hg levels were associated with low birth weight (aOR, 1.12; 95% CI, 1.00, 1.25; P < 0.05) and preterm birth (PTB) (aOR, 1.22; 95% CI, 1.08, 1.38; P < 0.05).

CONCLUSIONS

Our study provided evidence that elevated blood Hg levels were significantly associated with an increased risk of PE. In addition, our findings support that increased blood Hg levels might be associated with low birth weight and PTB.

Mercury and Prenatal Growth: A Systematic Review

The intrauterine environment is critical for healthy prenatal growth and affects neonatal survival and later health. Mercury is a toxic metal which can freely cross the placenta and disrupt a wide range of cellular processes. Many observational studies have investigated mercury exposure and prenatal growth, but no prior review has synthesised this evidence. Four relevant publication databases (Embase, MEDLINE/PubMed, PsycINFO, and Scopus) were systematically searched to identify studies of prenatal mercury exposure and birth weight, birth length, or head circumference. Study quality was assessed using the NIH Quality Assessment Tool, and results synthesised in a narrative review. Twenty-seven studies met the review criteria, these were in 17 countries and used 8 types of mercury biomarker. Studies of birth weight (total = 27) involving populations with high levels of mercury exposure, non-linear methods, or identified as high quality were more likely to report an association with mercury, but overall results were inconsistent. Most studies reported no strong evidence of association between mercury and birth length (n = 14) or head circumference (n = 14). Overall, our review did not identify strong evidence that mercury exposure leads to impaired prenatal growth, although there was some evidence of a negative association of mercury with birth weight.

Urinary trace metals in association with fetal ultrasound measures during pregnancy

Toxic metals have been associated with lower birth weight while essential metals have been associated with higher birth weight. Evidence for other metals is either inconsistent or limited in terms of number of studies. This study analyzed 17 urinary metals, individually and as a mixture, and their association with measures of fetal growth in the LIFECODES birth cohort. Ultrasound was used to measure abdominal circumference, head circumference, and femur length and measures were used to calculate estimated fetal weight at ~26 and ~35 weeks. We calculated the z-score based on gestational age at scan, and estimated fetal weight (EFW) was combined with birth weight for longitudinal analyses. Metals were measured in samples collected at ~26 weeks. We used linear mixed effects models to examine associations between metals and repeated measures of each outcome, controlling for covariates. Principal components analysis reduced the biomarkers to predictors that may share some commonality. We found that an interquartile range increase in selenium was inversely associated with femur length z-score as well as other growth outcomes. Other essential metals, however, were associated with an increase in growth. Finally, the PCA component comprised of arsenic, mercury, and tin was associated with decreased head circumference z-score (-0.14 [95% CI: -0.23, -0.05]).

Human Biological Monitoring of Mercury Through Hair Samples in China

Mercury (Hg) is a global pollutant that affects environmental and human health. Considering the high toxicity of Hg, it is required to assess the exposure of Hg in human body for appropriate risk management. In this review paper, we summarized data obtained through regional and small-scaled human biomonitoring (HBM) program for Hg in hair samples in China, which can deliver scientific data to make decisions on environmental health policy. Besides, the major conclusions got from this study and perspectives for future works through these HBM program in China were presented. To better understand the current situation of hair Hg levels in China, a well-coordinated and designed national HBM program is urgently needed considering the requirements of the Minamata Convention on Mercury for effectiveness evaluation.

Effects of lead, mercury, aluminium and manganese co-exposure on the serum BDNF concentration of pre-school children in Taizhou, China

Previous studies have shown that toxic metal exposure can have adverse effects on the nervous system of children, but the toxicology of metal co-exposure on neurodevelopment remains to be clarified. Brain derived neurotrophic factor (BDNF) plays an important role in nervous system development, but the possible effects of metal co-exposure on the serum BDNF concentrations of children remain unknown. A total of 561 children living in Taizhou City, China were recruited to participate in our cross-sectional multicenter survey. We measured their blood Pb, Hg, Al and Mn levels and serum BDNF concentrations as well as determined their associations in the total and within sex subgroups. The geometric means of the blood Pb, Hg, Al and Mn levels in all the participants were 67.18 μg/L, 1.01 μg/L, 52.03 μg/L and 18.26 μg/L, respectively. The serum BDNF concentration in children was 19.45 ng/mL. After adjusting for confounders, the blood Pb levels were significantly negatively associated with the serum BDNF concentrations in all the subjects and boys but not in girls. In addition, a significantly negative interaction between blood Pb and blood Hg and a positive interaction between blood Pb and blood Al on serum BDNF concentrations were also observed in boys but not in girls. Our findings highlight the toxic effects of metal co-exposure on serum BDNF levels in pre-school children and indicate that these effects might differ by gender, which suggest that special attention should be paid to the sex-specific effects of metal exposure.

Placental metal concentrations and birth outcomes: The Environment and Childhood (INMA) project

OBJECTIVE

To examine the association of placental levels of arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb), manganese (Mn), and chromium (Cr) with birth outcomes (birth weight, length, and head circumference, low birth weight [LBW], gestational age, preterm delivery, and small for gestational age [SGA]) in mother-child pairs from the Environment and Childhood (INMA) Project in Spain.

METHODS

Metal concentrations were measured in placenta tissue samples randomly selected from five INMA cohorts. Data on birth outcomes were obtained from medical records. Associations were assessed in a sub-sample of 327 mother-infant pairs by regression models adjusted for confounding factors and for all metals simultaneously. Effect modification by sex was also evaluated.

RESULTS

Elevated placental Cd levels (>5.79 vs. <3.30 ng/g) were associated with reduced birth weight (-111.8 g, 95%CI = -215.6; -8.06, p-trend = 0.01) and length (-0.62 cm, 95%CI = -1.20; -0.04, p-trend = 0.02), while a 10% increase in Cd was associated with 1.21-fold increased odds (95%CI = 1.01; 1.43) of LBW in the global sample but with 14% lower odds (95%CI = 0.78; 0.96) of preterm delivery in males (P_interaction = 0.10). Detected (vs. undetected) Hg was associated with reduced head circumference (-0.49 cm, 95%CI = -1.00; 0.03) in females (P_interaction = 0.03). A 10% increase in placental Mn was associated with slight increases in gestational age (0.04 weeks, 95%CI = 0.01; 0.07) in the global sample and in head circumference (0.05 cm, 95%CI = -0.01; 0.10) in females (P_interaction = 0.03). Elevated Cr levels (>99.6 vs. <56.1 ng/g) were associated with reduced birth length (-0.68 cm, 95%CI = -1.33; -0.04, p-trend = 0.02) and slightly increased gestational age (0.35 weeks, 95%CI = -0.07; 0.77, p-trend = 0.08) in the global sample. As and Pb were detected in few placentas (27% and 13%, respectively) and were not associated with any studied birth outcome.

CONCLUSIONS

Data suggest that in utero exposure to Cd, Hg, and Cr could adversely affect fetal growth, whereas Mn and Cr appear to have a positive effect on gestational age. Given the relatively small number of subjects, sex-specific associations should be interpreted with caution.

Blood mercury concentration, fish consumption and anthropometry in Chinese children: A national study

OBJECTIVE

This study sought to obtain national cross-sectional data for blood mercury levels and risk factors for mercury exposure in Chinese children aged 0 to 6years to provide evidence to support preventive measures for reducing childhood blood mercury levels.

METHODS

A multi-stage, stratified, clustered random sampling survey was conducted May 2013-Mar 2015. Shanghai, Jilin, Shanxi, Guangdong, Qinghai, Yunnan and Hubei, which are located in seven different geographical regions in China, were selected as the study field. A total of 14,202 children aged 0-6years participated in the study. Whole-blood venous samples (3ml) were collected from the subjects for mercury exposure assessment. The DMA-80 was applied for mercury detection, and a health questionnaire gathering information on related confounders was completed by the subjects' parents of the subjects after they received guidance from the investigators. A general linear model was used for the primary descriptive statistical analysis. Odds ratios (ORs) and 95%CIs for the risk factors were estimated using unconditional logistic regression.

RESULTS

A total of 14,202 eligible samples were collected. The mean mercury level was 1.39μg/L. Other results were as follows: median 1.23μg/L, p25 0.86μg/L, p75 1.73μg/L, and GM 1.10μg/L. Of the seven geographical regions, Qinghai, in northwestern China, had a median mercury level of 0.37μg/L, which was significantly lower than the mercury level in Guangdong, in southeastern China (2.01μg/L). The median blood mercury level of children in suburban areas was 1.34μg/L, which was remarkably higher than that of children in rural areas (1.09μg/L). Dichotomous subgroups were generated using the median mercury concentration. Unconditional logistic regression analysis revealed that fish consumption may contribute to increased blood mercury levels (p<0.05). Additionally, we observed significantly positive associations between mercury concentrations and the children's anthropometric characteristics (BMI; p<0.05).

CONCLUSIONS

Blood mercury concentrations among Chinese children aged 0-6years were considered low, and children who consumed more marine fish, freshwater fish and shellfish tended to have higher mercury concentrations. Our study suggests that children's growth is likely affected by the positive effects of mercury, which may have implications concerning the positive effects of fish consumption.

Children's environmental health based on birth cohort studies of Asia

Numerous studies have explored the associations between environmental pollutants and pediatric health. Recent studies have investigated the issue in Asia, but no systematic review has been published to date. This study aims to elucidate the issue by summarizing relevant epidemiologic evidence for cohorts in Asia, using information from the Birth Cohort Consortium of Asia (BiCCA). Environmental pollutants include mercury, environmental tobacco smoke (ETS), polychlorinated biphenyls (PCB), perfluoroalkyl substances (PFAS) and phthalates. This study sought to classify the effects of such compounds on fetal growth and pregnancy outcomes, neurodevelopment and behavioral problems, allergic disease and immune function and the endocrine system and puberty. These evidences showed ETS has been associated with infant birth weight, children's neurodevelopment and allergy disease; mercury and PCB have been shown to affect children's neurodevelopment; phthalate has effects on endocrine function; PFAS alters children's neurodevelopment, the endocrine system, and the allergic response. However, more consistent and coordinated research is necessary to understand the whole picture of single environmental and/or co-exposure and children's health. Therefore, harmonization and international collaboration are also needed in Asia.

Factors associated with mercury levels in human placenta and the relationship to neonatal anthropometry in Jamaica and Trinidad & Tobago

The aim of this study was to investigate the mercury levels in human placenta and its relationship to neonatal anthropometry for a group of selected pregnant women in Kingston and Manchester in Jamaica and St. Joseph in Trinidad & Tobago. The participants were interviewed on their fish intake. Neonatal anthropometric data were also recorded. The placental mercury concentrations ranged from 0.64±0.5μg/kg to 1.4±0.6μg/kg. The most significant associated factor for prenatal mercury exposure was maternal fish intake. Those pregnant women who regularly ate shark recorded the highest placenta mercury concentrations. Their neonates also had slightly smaller mean head circumference and lower birth weight. The mean placental mercury concentrations in this study were found to be lower than the literature values. Therefore it was difficult to detect any significant changes in neonatal anthropometry. This type of study can contribute to the extent of mercury exposure in the region.

Prenatal mercury exposure and birth outcomes

BACKGROUND

Results regarding the association between mercury exposure and anthropometry at birth, gestational length and placental weight are inconsistent, as is the role of seafood intake in these associations.

OBJECTIVE

We assessed whether prenatal mercury exposure is associated with anthropometry at birth, placental weight and gestational length in a population with a relatively high exposure to mercury from seafood consumption.

METHODS

Total mercury (T-Hg) was determined in cord blood from 1869 newborns with birth outcome measures, within the Spanish multicenter INMA cohort from 2004 to 2008. We adjusted cohort specific linear and Cox regression models to evaluate the association between T-Hg and birth anthropometry (weight, length, and head circumference), placental weight and gestational length. Non-spontaneous labor was taken to be censoring in the survival analysis. Final estimates were obtained using meta-analysis.

RESULTS

Geometric mean T-Hg was 8.2μg/L. A doubling of T-Hg was associated with a 7.7g decrease in placental weight (95% CI: -13.6, -1.8) and marginally with head circumference (beta: -0.052cm, 95% CI: -0.109, 0.005). T-Hg was also inversely related to weight and length, although with weaker estimates. Mercury exposure was not associated with the length of gestation. The inverse relation between T-Hg and growth was enhanced when the intake of different seafood groups was adjusted for in the models.

CONCLUSIONS

Prenatal mercury exposure may be associated with reduced placental and fetal growth. Confounding by fish intake should be considered when assessing these relationships.

Environmental influences on reproductive health: the importance of chemical exposures

Chemical exposures during pregnancy can have a profound and life-long impact on human health. Because of the omnipresence of chemicals in our daily life, there is continuous contact with chemicals in food, water, air, and consumer products. Consequently, human biomonitoring studies show that pregnant women around the globe are exposed to a variety of chemicals. In this review we provide a summary of current data on maternal and fetal exposure, as well as health consequences from these exposures. We review several chemical classes, including polychlorinated biphenyls, perfluoroalkyl substances, polybrominated diphenyl ethers, phenols, phthalates, pesticides, and metals. Additionally, we discuss environmental disparities and vulnerable populations, and future research directions. We conclude by providing some recommendations for prevention of chemical exposure and its adverse reproductive health consequences.

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.

Effects of Environmental Exposures on Fetal and Childhood Growth Trajectories

Delayed fetal growth and adverse birth outcomes are some of the greatest public health threats to this generation of children worldwide because these conditions are major determinants of mortality, morbidity, and disability in infancy and childhood and are also associated with diseases in adult life. A number of studies have investigated the impacts of a range of environmental conditions during pregnancy (including air pollution, endocrine disruptors, persistent organic pollutants, heavy metals) on fetal and child development. The results, while provocative, have been largely inconsistent. This review summarizes up to date epidemiologic studies linking major environmental pollutants to fetal and child development and suggested future directions for further investigation.

Mercury Exposure in Healthy Korean Weaning-Age Infants: Association with Growth, Feeding and Fish Intake

Low-level mercury (Hg) exposure in infancy might be harmful to the physical growth as well as neurodevelopment of children. The aim of this study was to investigate postnatal Hg exposure and its relationship with anthropometry and dietary factors in late infancy. We recruited 252 healthy Korean infants between six and 24 months of age from an outpatient clinic during the 2009/2010 and 2013/2014 seasons. We measured the weight and height of the infants and collected dietary information using questionnaires. The Hg content of the hair and blood was assessed using inductively coupled plasma mass spectroscopy. The geometric mean Hg concentration in the hair and blood was 0.22 (95% confidence interval: 0.20–0.24) µg/g and 0.94 (n = 109, 95% confidence interval: 0.89–0.99) µg/L, respectively. The hair Hg concentration showed a good correlation with the blood Hg concentration (median hair-to-blood Hg ratio: 202.7, r = 0.462, p < 0.001) and was >1 µg/g in five infants. The hair Hg concentration showed significant correlations with weight gain after birth (Z-score of the weight for age—Z-score of the birthweight; r = −0.156, p = 0.015), the duration (months) of breastfeeding as the dominant method of feeding (r = 0.274, p < 0.001), and the duration of fish intake more than once per week (r = 0.138, p = 0.033). In an ordinal logistic regression analysis with categorical hair Hg content (quartiles), dietary factors, including breastfeeding as the dominant method of feeding in late infancy (cumulative odds ratio: 6.235, 95% confidence interval: 3.086–12.597, p < 0.001) and the monthly duration of fish intake more than once per week (cumulative odds ratio: 1.203, 95% confidence interval: 1.034–1.401; p = 0.017), were significantly associated with higher hair Hg content. Weight gain after birth was not, however, significantly associated with hair Hg content after adjustment for the duration of breastfeeding as the dominant method of feeding. Low-level Hg exposure through breastfeeding and fish intake as a complementary food did not directly affect anthropometry in this population. If prolonged breastfeeding is expected, however, the Hg exposure through fish intake may need to be monitored for both mothers and infants.

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.

Metals exposure and risk of small-for-gestational age birth in a Canadian birth cohort: The MIREC study

BACKGROUND

Lead, mercury, cadmium and arsenic are some of the most common toxic metals to which Canadians are exposed. The effect of exposure to current low levels of toxic metals on fetal growth restriction is unknown.

OBJECTIVE

The aim of this study was to examine relationships between exposure to lead, mercury, cadmium and arsenic during pregnancy, and risk of small for gestational age (SGA) birth.

METHODS

Lead, mercury, cadmium and arsenic levels were measured in blood samples from the first and third trimesters in 1835 pregnant women from across Canada. Arsenic species in first trimester urine were also assessed. Relative risks and 95% confidence intervals were estimated using log binomial multivariate regression. Important covariates including maternal age, parity, pre-pregnancy BMI, and smoking, were considered in the analysis. An exploratory analysis was performed to examine potential effect modification of these relationships by single nucleotide polymorphisms (SNPs) in GSTP1 and GSTO1 genes.

RESULTS

No association was found between blood lead, cadmium or arsenic and risk for SGA. We observed an increased risk for SGA for the highest compared to the lowest tertile of exposure for mercury (>1.6 µg/L, RR=1.56.; 95% CI=1.04-2.58) and arsenobetaine (>2.25 µg/L, RR=1.65; 95% CI=1.10-2.47) after adjustment for the effects of parity and smoking. A statistically significant interaction was observed in the relationship between dimethylarsinic acid (DMA) levels in urinary arsenic and SGA between strata of GSTO1 A104A (p for interaction=0.02). A marginally significant interaction was observed in the relationship between blood lead and SGA between strata of GSTP1 A114V (p for interaction=0.06).

CONCLUSIONS

These results suggest a small increase in risk for SGA in infants born to women exposed to mercury and arsenic. Given the conflicting evidence in the literature this warrants further investigation in other pregnant populations.

Low-level prenatal mercury exposure in north China: an exploratory study of anthropometric effects

In order to investigate anthropometric effects of mercury (Hg) exposure, we examined the status of human prenatal exposure to Hg species, including total mercury (THg), methylmercury (MeHg) and inorganic mercury (IHg), in North China, as well as their potential effects on fetal and infant growth. Hg concentrations in various bioindicators were measured from 50 Chinese women and newborns in 2011. The participants were followed for 12 months to collect anthropometric information. Linear and two-level regression analyses were performed to determine the associations between Hg levels and body growth. The geometric mean levels of THg in the placenta, cord blood, fetal hair, and maternal blood, hair, and urine were 25.88 μg/kg dry wt, 2.73 μg/L, 572.98 μg/kg, 2.29 μg/L, 576.54 μg/kg, and 0.58 μg/g creatinine, respectively. Nearly 100% of Hg presented as IHg in urine, and the percentage of IHg in other bioindicators was 14.86-48.73%. We observed significantly negative associations between Hg levels in some matrixes and anthropometry of neonates (weight and height) and infants (height) (p < 0.05). THg levels in maternal hair were also negatively associated with infant growth rate of weight during 12 months after delivery (p = 0.017). This study suggests that low-level prenatal Hg exposure could play a role in attenuating fetal and infant growth, and the effects of MeHg and IHg are different.

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

Considering the different ability of placental transfer, an assessment of the cord:maternal blood ratio for both methylmercury (MeHg) and inorganic mercury (IHg) is needed especially for interpreting the low-level prenatal exposure. In this study, we conducted a Monte Carlo-based meta-analysis to comprehensively estimate that ratio for MeHg (RMeHg) and IHg (RIHg). The obtained values followed log-normal distributions, with a mean (standard deviation) of 1.89 (0.98) and 1.01 (0.55) for RMeHg and RIHg, respectively. We also estimated the percentage of MeHg in the blood by means of THg in cord and maternal blood using the RMeHg and RIHg, and obtained a value very close to the measured one (relative deviation, -0.4%). In conclusion, the fetus is exposed to approximately twice as much MeHg and to the same level of IHg as in maternal blood; the introduced model provides a rough but reasonable estimate of the percentage of MeHg in the blood.