Mercury in fish and adverse reproductive outcomes: results from South Carolina

Preterm Birth and Metal Mixture Exposure among Pregnant Women from the Navajo Birth Cohort Study

BACKGROUND

Preterm birth (PTB), defined as birth before 37 wk gestation, is associated with hypertension, diabetes, inadequate prenatal care, unemployment or poverty, and metal exposure. Indigenous individuals are more likely to have maternal risk factors associated with PTB compared with other populations in the United States; however, the role of environmental metals on PTB among pregnant Indigenous women remains uncertain. Previous research identified associations between PTB and individual metals, but there is limited investigation on metal mixtures and this birth outcome.

OBJECTIVES

We used a mixtures analysis framework to investigate the association between metal mixtures and PTB among pregnant Indigenous women from the Navajo Birth Cohort Study (NBCS).

METHODS

Maternal urine and blood samples were collected at the time of study enrollment and analyzed for metals by inductively coupled plasma dynamic reaction cell mass spectrometry. Bayesian Profile Regression was used to identify subgroups (clusters) of individuals with similar patterns of coexposure and to model association with PTB.

RESULTS

Results indicated six subgroups of maternal participants with distinct exposure profiles, including one group with low exposure to all metals and one group with total arsenic, cadmium, lead, and uranium concentrations exceeding representative concentrations calculated from the National Health and Nutrition Examination Survey (NHANES). Compared with the reference group (i.e., the lowest exposure subgroup), the subgroup with the highest overall exposure had a relative risk of PTB of 2.9 times (95% credible interval: 1.1, 6.1). Exposures in this subgroup were also higher overall than NHANES median values for women 14-45 years of age.

DISCUSSION

Given the wide range of exposures and elevated PTB risk for the most exposed subgroups in a relatively small study, follow-up investigation is recommended to evaluate associations between metal mixture profiles and other birth outcomes and to test hypothesized mechanisms of action for PTB and oxidative stress caused by environmental metals. https://doi.org/10.1289/EHP10361.

Association between maternal fish consumption during pregnancy and preterm births: the Japan Environment and Children's Study

BACKGROUND

Fish are a rich source of essential nutrients that protect against preterm birth. However, as fish can absorb environmental pollutants, their consumption can also increase the risk of preterm birth. This study aimed to assess whether maternal fish consumption during pregnancy is associated with preterm birth in a nationwide large Japanese cohort that consumed relatively high amounts and many types of fish.

METHODS

This study included 81,428 mother-child pairs enrolled in a nationwide prospective Japanese birth cohort study. Fish consumption was assessed using a validated food frequency questionnaire. Multivariate logistic regression was used to investigate the association of total consumption of fish, fatty fish and lean fish, fish paste, and seafood and clams with preterm birth, adjusted for potential confounders.

RESULTS

There was no association between overall fish consumption and preterm births. However, the highest quintile of fish paste consumption was significantly associated with an increased risk of preterm birth (odds ratio [OR]: 1.11; 95% confidence interval [CI: 1.04, 1.17]). The consumption of baked fish paste at least three times per week was significantly associated with preterm birth (OR: 1.20; 95% CI: 1.03, 1.40). Consumption of other types of fish, except fish paste, was not significantly associated with preterm birth risk.

CONCLUSIONS

Fish paste consumption may increase the risk of preterm birth. Further studies are required to confirm this association.

Nannochloropsis oculata feed additive alleviates mercuric chloride-induced toxicity in Nile tilapia (Oreochromis niloticus)

Using microalgae to alleviate the adverse effects of aquaculture pollutants, including metals, has recently gained much attention. In this context, bioaccumulation, hematological indices, oxidative and antioxidant responses, and histopathological alterations were investigated in Nile tilapia (Oreochromis niloticus) fed with either a control diet or diets containing Nannochloropsis oculata (N. oculata) after exposure to mercuric chloride in order to evaluate the role of this microalgae in protecting against mercury-induced toxicity. Fish exposed to HgCl2 at a dose of ¼ LC50 (0.3 mg/L) (Hg group) for 7-21 days exhibited a significant increase in total mercury concentration with a bioaccumulation pattern of liver>gills>muscle, and a significant decrease in all blood indices except mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), monocyte counts, and neutrophil counts. Malondialdehyde (MDA) levels were significantly increased in the Hg group at all time points relative to the control. Glutathione peroxidase (GPx) activity was significantly increased at days 14 and 21, while catalase (CAT) and GPx activities increased and decreased, respectively, at day 7 compared to the control. Additionally, lysozyme activity and immunoglobulin M (IgM) were significantly decreased in the Hg-exposed group. Severe histopathological alterations were evident in the liver, kidneys, and gills. However, supplementation with N. oculata at a low (5%, 50 g/kg feed) or high (10%, 100 g/kg feed) dose stabilized all parameters and reduced the severity of the histopathological alterations with the high N. oculata diet showing more prominent effects. These results suggest that feeding N. oculata protects Nile tilapia against mercuric chloride-induced toxicity.

Association of Mercury Exposure and Maternal Sociodemographics on Birth Outcomes of Indigenous and Tribal Women in Suriname

Information regarding adverse birth outcomes (ABO) of Indigenous and Tribal women living in the remote tropical rainforest of Suriname, where mercury (Hg) use is abundant in artisanal gold mining, is not available. In the context of a health system analysis, we examined the association between Hg exposure, maternal sociodemographics on the ABO of Indigenous and Tribal women living in Suriname’s interior and its capital, Paramaribo. ABO were determined in pregnant women enrolled from December 2016 to July 2019 in the Caribbean Consortium for Environmental and Occupational Health prospective environmental epidemiologic cohort study. Associations were explored using Pearson’s χ²-test and the Mann–Whitney U-test. Among 351 singleton participants, 32% were Indigenous, residing mainly in the interior (86.8%), and 23.1% had ABO. Indigenous participants had higher rates of ABO (29.8% vs. 19.8%) and preterm birth (PTB) (21.2% vs. 12.4%), higher Hg levels, delivered at a younger age, were less educated, and had lower household income compared to Tribal participants. Multivariate logistic regression models revealed that Indigenous participants had higher odds of ABO (OR = 3.60; 95% CI 1.70–7.63) and PTB (OR = 3.43; 95% CI 1.48–7.96) compared with Tribal participants, independent of Hg exposure and age at delivery. These results highlight the importance of effective risk reduction measures in support of Indigenous mothers, families, and communities.

Exposure to toxic metals and per- and polyfluoroalkyl substances and the risk of preeclampsia and preterm birth in the United States: a review

Preeclampsia and preterm birth are among the most common pregnancy complications and are the leading causes of maternal and fetal morbidity and mortality in the United States. Adverse pregnancy outcomes are multifactorial in nature and increasing evidence suggests that the pathophysiology behind preterm birth and preeclampsia may be similar-specifically, both of these disorders may involve abnormalities in placental vasculature. A growing body of literature supports that exposure to environmental contaminants in the air, water, soil, and consumer and household products serves as a key factor influencing the development of adverse pregnancy outcomes. In pregnant women, toxic metals have been detected in urine, peripheral blood, nail clippings, and amniotic fluid. The placenta serves as a "gatekeeper" between maternal and fetal exposures, because it can reduce or enhance fetal exposure to various toxicants. Proposed mechanisms underlying toxicant-mediated damage include disrupted placental vasculogenesis, an up-regulated proinflammatory state, oxidative stressors contributing to prostaglandin production and consequent cervical ripening, uterine contractions, and ruptured membranes and epigenetic changes that contribute to disrupted regulation of endocrine and immune system signaling. The objective of this review is to provide an overview of studies examining the relationships between environmental contaminants in the US setting, specifically inorganic (eg, cadmium, arsenic, lead, and mercury) and organic (eg, per- and polyfluoroalkyl substances) toxicants, and the development of preeclampsia and preterm birth among women in the United States.

Effects of low-level mercury exposure on brain-derived neurotrophic factor in preschool children

OBJECTIVES

Mercury (Hg), a ubiquitous heavy metal, could affect the neurodevelopment of the children, however, these associations are still equivocal. Brain derived neurotrophic factor (BDNF) plays an essential role in the central nervous system development in children. This study aimed to investigate the effects of low-level mercury exposure on serum BDNF levels and the influence of sex and dietary intake on these relationships in children.

METHODS

In this cross-sectional study, a total of 541 pre-school children were recruited, the blood mercury concentrations and serum BDNF levels were measured. The background information on demographic characteristics and dietary habits of the children was collected through questionnaires. Multivariable linear models after adjustment for potential confounders were used to evaluate the associations between mercury exposure and levels of BDNF in children.

RESULTS

The GMs of blood mercury concentrations and serum BDNF levels were 1.06 μg/L, 20.4 ng/mL, respectively. A significant positive association between blood mercury concentrations and serum BDNF levels was found. After stratification by sex, the blood mercury concentrations in children were positive associated with serum BDNF levels in girls but not in boys. However, these associations were attenuated when we further adjusted the children's dietary intake variables.

CONCLUSIONS

Our findings suggest that low-levels of mercury exposure may have sex-specific effects on BDNF levels in young children and that dietary intake may be potential confounders in these relationships. However, further studies are warranted to investigate the role of BDNF in the effects of mercury on neurodevelopment.

Prenatal Environmental Metal Exposure and Preterm Birth: A Scoping Review

Preterm birth (PTB) and its complications are the leading causes of under-five year old child deaths, accounting worldwide for an estimated one million deaths annually. The etiology of PTB is complex and multifactorial. Exposures to environmental metals or metalloids are pervasive and prenatal exposures to them are considered important in the etiology of PTB. We conducted a scoping review to determine the extent of prenatal exposures to four metals/metalloids (lead, mercury, cadmium and arsenic) and their association with PTB. We reviewed original research studies published in PubMed, Embase, the Cochrane Library, Scopus, POPLINE and the WHO regional indexes from 2000 to 2019; 36 articles were retained for full text review. We documented a higher incidence of PTB with lead and cadmium exposures. The findings for mercury and arsenic exposures were inconclusive. Metal-induced oxidative stress in the placenta, epigenetic modification, inflammation, and endocrine disruptions are the most common pathways through which heavy metals and metalloids affect placental functions leading to PTB. Most of the studies were from the high-income countries, reflecting the need for additional data from low-middle-income countries, where PTB rates are higher and prenatal exposure to metals are likely to be just as high, if not higher.

Recommended acceptable levels of maternal serum typical toxic metals from the perspective of spontaneous preterm birth in Shanxi Province, China

Preterm birth is an important issue of public reproductive health worldwide. The effects of the toxic metals on the likelihood of spontaneous preterm birth (SPB) are still under discussion. Our study aimed to investigate the association between maternal exposure to the five typical toxic metals or metalloid (i.e. arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), and lead (Pb)) and the SPB likelihood. The mothers delivering fetus with SPB (cases) and those with term healthy birth (controls) were chosen from a prospective birth cohort of 3201 women carried out in Shanxi Province, China. A total of 147 SPB cases and 381 controls were included in our nested case-control study. We collected maternal general information by questionnaire and collected their blood sample during recruitment. The serum concentrations of the five toxic metals were measured by inductively coupled-plasma mass spectrometry. We found that the demographic information between the cases and controls were well balanced. The participants in our study had relatively higher serum As concentration. For the other toxic metals (i.e. Cd, Cr, Hg, and Pb), their serum concentrations were overall in the middle range of those from general population. There were no significant associations of the serum concentrations of the five concerned toxic metals with the SPB likelihood. Our study results overall did not support that maternal exposure to As or Cd significantly contribute to the SPB risk in the current exposure level, as well as the other three toxic metals. We further proposed their upper concentration limits in maternal serum from the perspective of SPB likelihood during the early pregnant period, i.e. 18.2 ng/mL of As, 1.05 ng/mL of Cd, 0.96 ng/mL of Cr, 1.07 ng/mL of Hg, and 1.54 ng/mL of Pb.

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.

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.

Exposure to endocrine disruptors during adulthood: consequences for female fertility

Endocrine disrupting chemicals are ubiquitous chemicals that exhibit endocrine disrupting properties in both humans and animals. Female reproduction is an important process, which is regulated by hormones and is susceptible to the effects of exposure to endocrine disrupting chemicals. Disruptions in female reproductive functions by endocrine disrupting chemicals may result in subfertility, infertility, improper hormone production, estrous and menstrual cycle abnormalities, anovulation, and early reproductive senescence. This review summarizes the effects of a variety of synthetic endocrine disrupting chemicals on fertility during adult life. The chemicals covered in this review are pesticides (organochlorines, organophosphates, carbamates, pyrethroids, and triazines), heavy metals (arsenic, lead, and mercury), diethylstilbesterol, plasticizer alternatives (di-(2-ethylhexyl) phthalate and bisphenol A alternatives), 2,3,7,8-tetrachlorodibenzo-p-dioxin, nonylphenol, polychlorinated biphenyls, triclosan, and parabens. This review focuses on the hypothalamus, pituitary, ovary, and uterus because together they regulate normal female fertility and the onset of reproductive senescence. The literature shows that several endocrine disrupting chemicals have endocrine disrupting abilities in females during adult life, causing fertility abnormalities in both humans and animals.

Oral exposure of pregnant rats to toxic doses of methylmercury alters fetal accumulation

Methylmercury (CH₃Hg⁺) is an environmental toxicant that may lead to significant pathologies in exposed individuals. The current study assessed the disposition and toxicological effects of 2.5 or 7.5mgkg^-1 CH₃Hg⁺, conjugated to cysteine (Cys; Cys-S-CH₃Hg) and administered orally to pregnant and non-pregnant Wistar and TR^- rats. Rats were euthanized on gestational day 20 and the content of mercury in each fetus, amniotic sac, and placenta was determined. The brain, liver, and kidneys were removed from each fetus for estimation of mercury content. From the dams, a sample of blood, kidneys, liver, and brain were removed at the time of euthanasia. The findings from this study indicate that pregnancy leads to significant changes in the handling of mercuric ions, particularly in the liver. Furthermore, there are significant differences in the handling of non-nephrotoxic and nephrotoxic doses of Cys-S-CH₃Hg by maternal and fetal organs.

Seafood consumption habits of South Carolina shrimp baiters

Shrimp baiting is a fishing technique used by many South Carolinians and has been regulated in the state since the late 1980s. A postcard survey was developed and included with 400 South Carolina Department of Natural Resources (SCDNR) annual surveys of registered shrimp baiters over a two-year period. The survey contained questions concerning frequency, portion size, baiting locations, and preparation techniques for shrimp as well as other species consumed and demographic information. An overall response rate of 37% was received. The majority of respondents were men over the age of 55 years. Charleston and Beaufort counties were the most common locations for shrimp baiting. Almost half (45.9%) of respondents reported eating locally caught shrimp at least 2-3 times per month. The most common portion size was ½ pound (8 oz. or 277 g), with 44.8% of respondents reporting this as their typical amount of shrimp ingested at one meal. Only 3.7% of respondents reported typically eating the whole shrimp, while all other respondents ingested shrimp with the head removed. The most commonly consumed species besides shrimp were blue crab, oysters, and flounder. According to the US Food and Drug Administration mercury (Hg) guidelines, the majority (97%) of our respondents were not at risk for consuming unsafe levels of Hg from locally caught shrimp. However, this does not take into account other local seafood eaten or other contaminants of concern. These consumption results may be used in conjunction with data on contaminant levels in shrimp to determine potential adverse health risks associated with consumption of locally caught shrimp.

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.

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.