Children's environmental chemical exposures in the USA, NHANES 2003-2012

Environmental phenol exposures in 6- to 12-week-old infants: The Infant Feeding and Early Development (IFED) study

BACKGROUND

Exposure to phenols, endocrine-disrupting chemicals used in personal care and consumer products, is widespread. Data on infant exposures are limited despite heightened sensitivity to endocrine disruption during this developmental period. We aimed to describe distributions and predictors of urinary phenol concentrations among U.S. infants ages 6-12 weeks.

METHODS

The Infant Feeding and Early Development (IFED) study is a prospective cohort study of healthy term infants enrolled during 2010-2013 in the Philadelphia region. We measured concentrations of seven phenols in 352 urine samples collected during the 6- or 8- and/or 12-week study visits from 199 infants. We used linear mixed models to estimate associations of maternal, sociodemographic, infant, and sample characteristics with natural-log transformed, creatinine-standardized phenol concentrations and present results as mean percent change from the reference level.

RESULTS

Median concentrations (μg/L) were 311 for methylparaben, 10.3 for propylparaben, 3.6 for benzophenone-3, 2.1 for triclosan, 1.0 for 2,5-dichlorophenol, 0.7 for BPA, and 0.3 for 2,4-dichlorophenol. Geometric mean methylparaben concentrations were approximately 10 times higher than published estimates for U.S. children ages 3-5 and 6-11 years, while propylparaben concentrations were 3-4 times higher. Infants of Black mothers had higher concentrations of BPA (83%), methylparaben (121%), propylparaben (218%), and 2,5-dichorophenol (287%) and lower concentrations of benzophenone-3 (-77%) and triclosan (-53%) than infants of White mothers. Triclosan concentrations were higher in breastfed infants (176%) and lower in infants whose mothers had a high school education or less (-62%). Phenol concentrations were generally higher in summer samples.

CONCLUSIONS

Widespread exposure to select environmental phenols among this cohort of healthy U.S. infants, including much higher paraben concentrations compared to those reported for U.S. children, supports the importance of expanding population-based biomonitoring programs to infants and toddlers. Future investigation of exposure sources is warranted to identify opportunities to minimize exposures during these sensitive periods of development.

Chemical mixture that targets the epidermal growth factor pathway impairs human trophoblast cell functions

Pregnant women are exposed to complex chemical mixtures, many of which reach the placenta. Some of these chemicals interfere with epidermal growth factor receptor (EGFR) activation, a receptor tyrosine kinase that modulates several placenta cell functions. We hypothesized that a mixture of chemicals (Chem-Mix) known to reduce EGFR activation (polychlorinated biphenyl (PCB)-126, PCB-153, atrazine, trans-nonachlor, niclosamide, and bisphenol S) would interfere with EGFR-mediated trophoblast cell functions. To test this, we determined the chemicals' EGFR binding ability, EGFR and downstream effectors activation, and trophoblast functions (proliferation, invasion, and endovascular differentiation) known to be regulated by EGFR in extravillous trophoblasts (EVTs). The Chem-Mix competed with EGF for EGFR binding, however only PCB-153, niclosamide, trans-nonachlor, and BPS competed for binding as single chemicals. The effects of the Chem-Mix on EGFR phosphorylation were tested by exposing the placental EVT cell line, HTR-8/SVneo to control (0.1% DMSO), Chem-Mix (1, 10, or 100 ng/ml), EGF (30 ng/ml), or Chem-Mix + EGF. The Chem-Mix - but not the individual chemicals - reduced EGF-mediated EGFR phosphorylation in a dose dependent manner, while no effect was observed in its downstream effectors (AKT and STAT3). None of the individual chemicals affected EVT cell invasion, but the Chem-Mix reduced EVT cell invasion independent of EGF. In support of previous studies that have explored chemicals targeting a specific pathway (estrogen/androgen receptor), current findings indicate that exposure to a chemical mixture that targets the EGFR pathway can result in a greater impact compared to individual chemicals in the context of placental cell functions.

Adolescent endocrine disrupting chemical exposure and academic achievement

BACKGROUND

Epidemiologic studies support associations of exposure to endocrine disrupting chemicals (EDCs), such as some phthalates, phenols, and parabens with a wide range of cognitive and behavioral traits. While many of these traits are associated with academic achievement, the relationship of EDC exposure specifically with academic achievement in adolescence has not yet been studied.

OBJECTIVE

We assessed the association of urinary biomarker concentrations of EDCs with academic achievement in adolescents as well as the potential for psychosocial factors to modify associations.

METHODS

We quantified urinary concentrations of select EDCs in 205 adolescent participants from the New Bedford Cohort (NBC), a prospective birth cohort of children born to mothers residing near the New Bedford Harbor Superfund site in Massachusetts, and estimated associations between EDCs and adolescent academic achievement assessed with the Wide Range Achievement Test (WRAT). Measures of socioeconomic status and the home environment were used to estimate psychosocial stress.

RESULTS

Urinary concentrations of antiandrogenic phthalates were inversely associated with Math Computation scores. For example, each doubling of the concentration of antiandrogenic phthalate metabolites in urine was associated with a 1.94 point decrease (95% CI: 3.84, -0.05) in Math Computation scores, indicating poorer performance. For the most part, associations were stronger in adolescents with more, as compared to less, social disadvantage, but most of these differences did not achieve statistical significance.

CONCLUSION

Our findings support the potential for adolescents' exposure to antiandrogenic phthalates to correlate with poorer academic achievement in math, particularly among participants with greater psychosocial stress.

Exposure to phthalates and DiNCH among preschool children in Sweden: Urinary metabolite concentrations and predictors of exposure

Several plasticizing chemicals induce endocrine disrupting effects in humans, and the indoor environment is suggested to be a source of exposure. As children are particularly vulnerable to the effects from exposure to endocrine disrupting chemicals (EDCs), it is essential to monitor exposure to EDCs such as phthalates and non-phthalate plasticizers in indoor environments intended for use by children. The aim of this study was to assess everyday plasticizer exposure among preschool-aged children in Sweden by measuring urinary plasticizer metabolite concentrations. In addition, it was investigated whether the concentrations would be altered as a result of the children spending part of the day at preschool, in comparison with weekend exposure, when they may spend more time in home environments or engage in various weekend and leisure activities. For this purpose, fourteen metabolites from eight phthalates (di-ethylhexyl phthalate, DEHP; di-n-butyl phthalate, DnBP; di-isobutyl phthalate, DiBP; butyl-benzyl phthalate, BBzP; di-iso-nonyl phthalate, DiNP; di-propylheptyl phthalate, DPHP; di-iso-decyl phthalate, DiDP; and di-ethyl phthalate, DEP) and one non-phthalate plasticizer (di-isononyl cyclohexane 1,2-dicarboxylate, DiNCH) were measured in 206 urine samples collected at four occasions, i.e. twice during the winter and twice during the spring from 54 children (mean 5.1 years, SD 0.94) enrolled at eight preschools in Sweden. A detection frequency (DF) of 99.9% for the 14 metabolites indicates a widespread exposure to plasticizers among children in Sweden. Compared to previous Swedish and international studies performed during approximately the same time period, high urinary concentrations of monobenzyl phthalate (MBzP), a metabolite from the strictly regulated BBzP, were measured in this study (median 17 ng/mL). Overall, high urinary phthalate metabolite concentrations were observed in this study compared to the US CDC-NHANES from the same time period and similar age-group. Compared to European studies, however, similar concentrations were observed for most metabolites and the urinary concentrations from few participating children exceeded the human biomonitoring guidance values (HBM-GV) for children. After days with preschool attendance, lower urinary concentrations of metabolites originating from DEP and phthalates that are strictly regulated within the EU REACH legislation (DEHP, DnBP, and DiBP) and higher concentrations of metabolites originating from DiNP, DPHP, and DiDP, i.e. less or non-regulated phthalates were found compared the urinary concentrations of these metabolites in weekends. This may indicate that factors in the indoor environment itself are important for the extent of the plasticizer exposure. All the analyzed metabolites were measured in lower concentrations in urine collected from children attending preschools built or renovated after the year 2000, while no seasonal differences were observed in this study.

Environmental Toxicants and the Developing Brain

Early life represents the most rapid and foundational period of brain development and a time of vulnerability to environmental insults. Evidence indicates that greater exposure to ubiquitous toxicants like fine particulate matter (PM_2.5), manganese, and many phthalates is associated with altered developmental, physical health, and mental health trajectories across the lifespan. Whereas animal models offer evidence of their mechanistic effects on neurological development, there is little research that evaluates how these environmental toxicants are associated with human neurodevelopment using neuroimaging measures in infant and pediatric populations. This review provides an overview of 3 environmental toxicants of interest in neurodevelopment that are prevalent worldwide in the air, soil, food, water, and/or products of everyday life: fine particulate matter (PM_2.5), manganese, and phthalates. We summarize mechanistic evidence from animal models for their roles in neurodevelopment, highlight prior research that has examined these toxicants with pediatric developmental and psychiatric outcomes, and provide a narrative review of the limited number of studies that have examined these toxicants using neuroimaging with pediatric populations. We conclude with a discussion of suggested directions that will move this field forward, including the incorporation of environmental toxicant assessment in large, longitudinal, multimodal neuroimaging studies; the use of multidimensional data analysis strategies; and the importance of studying the combined effects of environmental and psychosocial stressors and buffers on neurodevelopment. Collectively, these strategies will improve ecological validity and our understanding of how environmental toxicants affect long-term sequelae via alterations to brain structure and function.

Toxicant exposure and the developing brain: A systematic review of the structural and functional MRI literature

Youth worldwide are regularly exposed to pollutants and chemicals (i.e., toxicants) that may interfere with healthy brain development, and a surge in MRI research has begun to characterize the neurobiological consequences of these exposures. Here, a systematic review following PRISMA guidelines was conducted on developmental MRI studies of toxicants with known or suspected neurobiological impact. Associations were reviewed for 9 toxicant classes, including metals, air pollution, and flame retardants. Of 1264 identified studies, 46 met inclusion criteria. Qualitative synthesis revealed that most studies: (1) investigated air pollutants or metals, (2) assessed exposures prenatally, (3) assessed the brain in late middle childhood, (4) took place in North America or Western Europe, (5) drew samples from existing cohort studies, and (6) have been published since 2017. Given substantial heterogeneity in MRI measures, toxicant measures, and age groups assessed, more research is needed on all toxicants reviewed here. Future studies should also include larger samples, employ personal exposure monitoring, study independent samples in diverse world regions, and assess toxicant mixtures.

Legacy Chemical Pollutants in House Dust of Homes of Pregnant African Americans in Atlanta

We developed and applied a method for measuring selected persistent organic pollutants (POPs) (i.e., polybrominated diphenyl ethers (PBDEs), organochlorine pesticides, and polychlorinated biphenyls (PCBs)) in dust collected from pregnant African Americans (AAs) in Atlanta using isotope dilution gas chromatography-tandem mass spectrometry. Limits of quantification were ranged from 0.10 to 2.50 ng/g dust. NIST standard reference material measurements demonstrated the robustness of our method. Our accuracies ranged from 82 to 108%, relative standard deviations ranged from 2 to 16%, and extraction recoveries ranged from 76 to 102%. We measured POPs in dust collected from 34 homes of pregnant AAs participating in the Atlanta AA birth cohort study who were enrolled from 2016 to 2019. Concentrations of POPs were detected in all samples with the frequencies of detection ranging from 8 to 100%. Concentrations of PBDE congeners 99 and 47, p,p'-DDT, and PCB153 were detected at some of the highest concentrations with geometric means of 1270, 730, 63.4 and 240 ng/g, respectively. The ratio of DDT/DDE was quite large (~2.7) indicating that p,p'-DDT remains intact in homes for long periods of time. These data demonstrate that care should be taken to remediate POPs in indoor dust, especially in vulnerable, disparate segments of the population.

Log-transformation of Independent Variables: Must We?

Epidemiologic studies often quantify exposure using biomarkers, which commonly have statistically skewed distributions. Although normality assumption is not required if the biomarker is used as an independent variable in linear regression, it has become common practice to log-transform the biomarker concentrations. This transformation can be motivated by concerns for nonlinear dose-response relationship or outliers; however, such transformation may not always reduce bias. In this study, we evaluated the validity of motivations underlying the decision to log-transform an independent variable using simulations, considering eight scenarios that can give rise to skewed X and normal Y. Our simulation study demonstrates that (1) if the skewness of exposure did not arise from a biasing factor (e.g., measurement error), the analytic approach with the best overall model fit best reflected the underlying outcome generating methods and was least biased, regardless of the skewness of X and (2) all estimates were biased if the skewness of exposure was a consequence of a biasing factor. We additionally illustrate a process to determine whether the transformation of an independent variable is needed using NHANES. Our study and suggestion to divorce the shape of the exposure distribution from the decision to log-transform it may aid researchers in planning for analysis using biomarkers or other skewed independent variables.

Developing human biomonitoring as a 21st century toolbox within the European exposure science strategy 2020-2030

Human biomonitoring (HBM) is a crucial approach for exposure assessment, as emphasised in the European Commission's Chemicals Strategy for Sustainability (CSS). HBM can help to improve chemical policies in five major key areas: (1) assessing internal and aggregate exposure in different target populations; 2) assessing exposure to chemicals across life stages; (3) assessing combined exposure to multiple chemicals (mixtures); (4) bridging regulatory silos on aggregate exposure; and (5) enhancing the effectiveness of risk management measures. In this strategy paper we propose a vision and a strategy for the use of HBM in chemical regulations and public health policy in Europe and beyond. We outline six strategic objectives and a roadmap to further strengthen HBM approaches and increase their implementation in the regulatory risk assessment of chemicals to enhance our understanding of exposure and health impacts, enabling timely and targeted policy interventions and risk management. These strategic objectives are: 1) further development of sampling strategies and sample preparation; 2) further development of chemical-analytical HBM methods; 3) improving harmonisation throughout the HBM research life cycle; 4) further development of quality control / quality assurance throughout the HBM research life cycle; 5) obtain sustained funding and reinforcement by legislation; and 6) extend target-specific communication with scientists, policymakers, citizens and other stakeholders. HBM approaches are essential in risk assessment to address scientific, regulatory and societal challenges. HBM requires full and strong support from the scientific and regulatory domain to reach its full potential in public and occupational health assessment and in regulatory decision-making.

Children Environmentally Exposed to Agrochemicals in Rural Areas Present Changes in Oxidative Status and DNA Damage

Rural children are exposed to several chemicals. This study evaluated the environmental co-exposure of rural children to cholinesterase inhibitor insecticides and metals/metalloids, and the resulting oxidative stress and DNA damage. Seventy-two children (5 to 16 years old) were studied at two different moments: period 1, when agrochemicals were less used, and period 2, when agrochemicals were extensively used in agriculture. Biomonitoring was performed by evaluating butyrylcholinesterase (BuChE) activity in serum; arsenic (As), chromium (Cr), lead (Pb), and nickel (Ni) levels in blood; malondialdehyde (MDA) in plasma; glutathione peroxidase (GSH-Px) and glutathione S-transferase (GST) activities in whole blood; non-protein thiol levels in erythrocytes; and micronuclei (MN) assay in exfoliated buccal cells. Cr and As levels were higher than the reference values in both periods, and Ni levels were higher than the reference values in period 2 alone. BuChE activity was inhibited in period 2 compared with period 1. In period 2, there was an increase in endogenous antioxidants and a decrease in MDA, probably demonstrating a compensatory mechanism as a response to increasing xenobiotics. Also in period 2, the MN frequency increased and BuChE and As were positively associated, suggesting co-exposure. On the other hand, in period 1, it was observed that Cr, Ni, and Pb blood levels were negatively associated with GSH-Px and GST, while MDA was positively associated with As levels. Our findings demonstrated an imbalance in endogenous antioxidants, contributing to genotoxicity and lipoperoxidation, probably in response to exposure to xenobiotics, especially carcinogenic elements (Cr, As, and Ni).

A review on advances in removal of endocrine disrupting compounds from aquatic matrices: Future perspectives on utilization of agri-waste based adsorbents

In the recent past, a class of emerging contaminants particularly endocrine disrupting compounds (EDCs) in the aquatic environment have gained a lot of attention. This is due to their toxic behaviour, affecting endocrine activities in humans as well as among aquatic animals. Presently, there are no regulations and discharge limits for EDCs to preclude their negative impact. Furthermore, the conventional treatment processes fail to remove EDCs efficiently. This necessitates the need for more research aimed at development of advanced alternative treatment methods which are economical, efficient, and sustainable. This paper focusses on the occurrence, fate, toxicity, and various treatment processes for removal of EDCs. The treatment processes (physical, chemical, biological and hybrid) have been comprehensively studied highlighting their advantages and disadvantages. Additionally, the use of agri-waste based adsorption technologies has been reviewed. The aim of this review article is to understand the prospect of application of agri-waste based adsorbents for efficient removal of EDCs. Interestingly, research findings have indicated that the use of these low-cost and abundantly available agri-waste based adsorbents can efficiently remove the EDCs. Furthermore, the challenges and future perspectives on the use of agri-waste based adsorbents have been discussed.

Developmental Exposure to Endocrine Disrupting Chemicals and Its Impact on Cardio-Metabolic-Renal Health

Developmental origin of health and disease postulates that the footprints of early life exposure are followed as an endowment of risk for adult diseases. Epidemiological and experimental evidence suggest that an adverse fetal environment can affect the health of offspring throughout their lifetime. Exposure to endocrine disrupting chemicals (EDCs) during fetal development can affect the hormone system homeostasis, resulting in a broad spectrum of adverse health outcomes. In the present review, we have described the effect of prenatal EDCs exposure on cardio-metabolic-renal health, using the available epidemiological and experimental evidence. We also discuss the potential mechanisms of their action, which include epigenetic changes, hormonal imprinting, loss of energy homeostasis, and metabolic perturbations. The effect of prenatal EDCs exposure on cardio-metabolic-renal health, which is a complex condition of an altered biological landscape, can be further examined in the case of other environmental stressors with a similar mode of action.

In vitro impact of genistein and mono(2-ethylhexyl) phthalate (MEHP) on the eicosanoid pathway in spermatogonial stem cells

Perinatal exposures to endocrine disrupting chemicals (EDCs) alter the male reproductive system. Infants are exposed to genistein (GEN) through soy-based formula, and to Mono(2-ethylhexyl) Phthalate (MEHP), metabolite of the plasticizer DEHP. Spermatogonial stem cells (SSCs) are formed in infancy and their integrity is essential for spermatogenesis. Thus, understanding the impact of EDCs on SSCs is critical. Prostaglandins (PGs) are inflammatory mediators synthesized via the eicosanoid pathway starting with cyclooxygenases (Coxs), that regulate physiological and pathological processes. Our goal was to study the eicosanoid pathway in SSCs and examine whether it was disrupted by GEN and MEHP, potentially contributing to their adverse effects. The mouse C18-4 cell line used as SSC model expressed high levels of Cox1 and Cox2 genes and proteins, and eicosanoid pathway genes similarly to levels measured in primary rat spermatogonia. Treatments with GEN and MEHP at 10 and 100 μM decreased Cox1 gene and protein expression, whereas Cox2, phospholipase A2, prostaglandin synthases transcripts, PGE2, PGF2a and PGD2 were upregulated. Simultaneously, the transcript levels of spermatogonia progenitor markers Foxo1 and Mcam and differentiated spermatogonial markers cKit and Stra8 were increased. Foxo1 was also increased by EDCs in primary rat spermatogonia. This study shows that the eicosanoid pathway is altered during SSC differentiation and that exposure to GEN and MEHP disrupts this process, mainly driven by GEN effects on Cox2 pathway, while MEHP acts through an alternative mechanism. Thus, understanding the role of Cox enzymes in SSCs and how GEN and MEHP exposures alter their differentiation warrants further studies.

Children and Parents' Awareness Regarding Potential Hazards Derived from the Use of Chemical Products in Greece

Over the last decades, human activities prompted the high production and widespread use of household chemical products, leading to daily exposure of humans to several chemicals. The objective of this study was to investigate the frequency of chemicals' use by children and parents in Greece and estimate the level of risk awareness and understanding among them. A total of 575 parents and children were asked to answer an anonymous, closed-ended, validated, and self-administered questionnaire. One-third of the children and almost half of the parents participating in the study believed that commonly used chemical products do not pose any risk to human health or to the environment, despite the product labelling. The majority of both children (61.8%) and parents (70.6%) were informed about product safety via the product labelling. Around 20% in both groups could not differentiate between systemic toxicity and acute lethal effects depicted by pictograms on the label and milder hazards, such as skin irritation. Moreover, the information on hazard and precautionary statements appearing on the label was very poorly perceived. Therefore, as both children and parents seem not to clearly identify the hazards and risks arising from the use of everyday chemical products, targeted awareness policies should be implemented to support the safe use of household products.

Trends in environmental chemical concentrations in the Canadian population: Biomonitoring data from the Canadian Health Measures Survey 2007-2017

Ten years of nationally representative biomonitoring data collected between 2007 and 2017 are available from the Canadian Health Measures Survey (CHMS). These data establish baseline environmental chemical concentrations in the general population. Here we sought to evaluate temporal trends in environmental chemical exposures in the Canadian population by quantifying changes in biomarker concentrations measured in the first five two-year cycles of the CHMS. We identified 39 chemicals that were measured in blood or urine in at least three cycles and had detection rates over 50% in the Canadian population. We calculated geometric mean concentrations for each cycle using the survey weights provided. We then conducted analyses of variance to test for linear trends over all cycles. We also calculated the percent difference in geometric means between the first and most recent cycle measured. Of the 39 chemicals examined, we found statistically significant trends across cycles for 21 chemicals. Trends were decreasing for 19 chemicals from diverse chemical groups, including metals and trace elements, phenols and parabens, organophosphate pesticides, per- and polyfluoroalkyl substances, and plasticizers. Significant reductions in chemical concentrations included di-2-ethylhexyl phthalate (DEHP; 75% decrease), perfluorooctane sulfate (PFOS; 61% decrease), perfluorooctanoic acid (PFOA; 58% decrease), dimethylphosphate (DMP; 40% decrease), lead (33% decrease), and bisphenol A (BPA; 32% decrease). Trends were increasing for two pyrethroid pesticide metabolites, including a 110% increase between 2007 and 2017 for 3-phenoxybenzoic acid (3-PBA). No significant trends were observed for the remaining 18 chemicals that included arsenic, mercury, fluoride, acrylamide, volatile organic compounds, and polycyclic aromatic hydrocarbons. National biomonitoring data indicate that concentrations, and therefore exposures, have decreased for many priority chemicals in the Canadian population. Concentrations for other chemical groups have not changed or have increased, although average concentrations remain below thresholds of concern derived from human exposure guidance values. Continued collection of national biomonitoring data is necessary to monitor trends in exposures over time.

Trends in urinary metabolites of polycyclic aromatic hydrocarbons (PAHs) in the non-smoking U.S. population, NHANES 2001-2014

BACKGROUND

Recent studies indicate airborne PAH levels have decreased in the U.S., but it is unclear if this has resulted in PAH exposure changes in the U.S.

POPULATION

OBJECTIVE

Examine temporal trends in urinary metabolites of Naphthalene, Fluorene, Phenanthrene, and Pyrene in U.S. non-smokers, 6+ years old.

METHODS

We used biomonitoring data from the National Health and Nutrition Examination Survey (NHANES) program, 2001-2014, (N = 11,053) using survey weighted linear regression. Models were adjusted for age, sex, race/ethnicity, creatinine, BMI, income, diet, and seasonality. Stratified models evaluated the effect of age, sex, and race/ethnicity on trends.

RESULTS

Between 2001 and 2014, Naphthalene exposure increased 36% (p < 0.01); Pyrene exposure increased 106% (p < 0.01); Fluorene and Phenanthrene exposure decreased 55% (p < 0.01), and 37% (p < 0.01), respectively. Naphthalene was the most abundant urinary PAH, 20-fold higher than Fluorene and Phenanthrene, and over 50-fold higher than Pyrene compared to reference groups, effect modification was observed by age (Naphthalene, Pyrene), sex (Fluorene, Pyrene), and race/ethnicity (Naphthalene, Fluorene, Phenanthrene, Pyrene).

SIGNIFICANCE

This study shows exposure to Naphthalene and Pyrene increased, while exposure to Fluorene and Phenanthrene decreased among the non-smoking U.S. general population between 2001 and 2014, suggesting environmental sources of PAHs have changed over the time period.

The new kids on the block: Emerging obesogens

The current obesity epidemic is calling for action in the determination of contributing factors. Although social and life-style factors have been traditionally associated with metabolic disruption, a subset of endocrine-disrupting chemicals (EDCs), called obesogens are garnering increasing attention for their ability to promote adipose tissue differentiation and accumulation. For some chemicals, such as tributyltin, there is conclusive evidence regarding their ability to promote adipogenesis and their mechanism of action. In recent years, the list of chemicals that exert obesogenic potential is increasing. In this chapter, we review current knowledge of the most recent developments in the field of emerging obesogens with a specific focus on food additives, surfactants, and sunscreens, for which the mechanism of action remains unclear. We also review new evidence relative to the obesogenic potential of environmentally relevant chemical mixtures and point to potential therapeutic approaches to minimize the detrimental effects of obesogens. We conclude by discussing the available tools to investigate new obesogenic chemicals, strategies to maximize reproducibility in adipogenic studies, and future directions that will help propel the field forward.

Developmental origins of metabolic diseases

Almost 2 billion adults in the world are overweight, and more than half of them are classified as obese, while nearly one-third of children globally experience poor growth and development. Given the vast amount of knowledge that has been gleaned from decades of research on growth and development, a number of questions remain as to why the world is now in the midst of a global epidemic of obesity accompanied by the "double burden of malnutrition," where overweight coexists with underweight and micronutrient deficiencies. This challenge to the human condition can be attributed to nutritional and environmental exposures during pregnancy that may program a fetus to have a higher risk of chronic diseases in adulthood. To explore this concept, frequently called the developmental origins of health and disease (DOHaD), this review considers a host of factors and physiological mechanisms that drive a fetus or child toward a higher risk of obesity, fatty liver disease, hypertension, and/or type 2 diabetes (T2D). To that end, this review explores the epidemiology of DOHaD with discussions focused on adaptations to human energetics, placental development, dysmetabolism, and key environmental exposures that act to promote chronic diseases in adulthood. These areas are complementary and additive in understanding how providing the best conditions for optimal growth can create the best possible conditions for lifelong health. Moreover, understanding both physiological as well as epigenetic and molecular mechanisms for DOHaD is vital to most fully address the global issues of obesity and other chronic diseases.

Identifying environmental exposure profiles associated with timing of menarche: A two-step machine learning approach to examine multiple environmental exposures

BACKGROUND

Variation in the timing of menarche has been linked with adverse health outcomes in later life. There is evidence that exposure to hormonally active agents (or endocrine disrupting chemicals; EDCs) during childhood may play a role in accelerating or delaying menarche. The goal of this study was to generate hypotheses on the relationship between exposure to multiple EDCs and timing of menarche by applying a two-stage machine learning approach.

METHODS

We used data from the National Health and Nutrition Examination Survey (NHANES) for years 2005-2008. Data were analyzed for 229 female participants 12-16 years of age who had blood and urine biomarker measures of 41 environmental exposures, all with >70% above limit of detection, in seven classes of chemicals. We modeled risk for earlier menarche (<12 years of age vs older) with exposure biomarkers. We applied a two-stage approach consisting of a random forest (RF) to identify important exposure combinations associated with timing of menarche followed by multivariable modified Poisson regression to quantify associations between exposure profiles ("combinations") and timing of menarche.

RESULTS

RF identified urinary concentrations of monoethylhexyl phthalate (MEHP) as the most important feature in partitioning girls into homogenous subgroups followed by bisphenol A (BPA) and 2,4-dichlorophenol (2,4-DCP). In this first stage, we identified 11 distinct exposure biomarker profiles, containing five different classes of EDCs associated with earlier menarche. MEHP appeared in all 11 exposure biomarker profiles and phenols appeared in five. Using these profiles in the second-stage of analysis, we found a relationship between lower MEHP and earlier menarche (MEHP ≤ 2.36 ng/mL vs >2.36 ng/mL: adjusted PR = 1.36, 95% CI: 1.02, 1.80). Combinations of lower MEHP with benzophenone-3, 2,4-DCP, and BPA had similar associations with earlier menarche, though slightly weaker in those smaller subgroups. For girls not having lower MEHP, exposure profiles included other biomarkers (BPA, enterodiol, monobenzyl phthalate, triclosan, and 1-hydroxypyrene); these showed largely null associations in the second-stage analysis. Adjustment for covariates did not materially change the estimates or CIs of these models. We observed weak or null effect estimates for some exposure biomarker profiles and relevant profiles consisted of no more than two EDCs, possibly due to small sample sizes in subgroups.

CONCLUSION

A two-stage approach incorporating machine learning was able to identify interpretable combinations of biomarkers in relation to timing of menarche; these should be further explored in prospective studies. Machine learning methods can serve as a valuable tool to identify patterns within data and generate hypotheses that can be investigated within future, targeted analyses.

Exposure Load: Using biomonitoring data to quantify multi-chemical exposure burden in a population

People are often concurrently exposed to numerous chemicals. Here we sought to leverage existing large biomonitoring datasets to improve our understanding of multi-chemical exposures in a population. Using nationally-representative data from the 2012-2015 Canadian Health Measures Survey (CHMS), we developed Exposure Load, a metric that counts the number of chemicals measured in people above a defined concentration threshold. We calculated Exposure Loads based on five concentration thresholds: the analytical limit of detection (LOD) and the 50th, 75th, 90th and 95th percentiles. Our analysis considered 44 analyte biomarkers representing 26 chemicals from the 2012-2015 CHMS; complete biomarker data were available for 1858 participants aged 12-79 years following multiple imputation of results that were missing due to sample loss. Chemicals may have one or more biomarkers, and for the purposes of Exposure Load calculation, participants were considered to be exposed to a chemical if at least one biomarker was above the threshold. Distributions of Exposure Loads are reported for the total population, as well as by age group, sex and smoking status. Canadians had an Exposure Load between 9 and 21 (out of 26) when considering LOD as the threshold, with the majority between 13 and 18. At higher thresholds, such as the 95th percentile, the majority of Canadians had an Exposure Load between 0 and 3, although some people had an Exposure Load of up to 15, indicating high exposures to multiple chemicals. Adolescents aged 12-19 years had significantly lower Exposure Loads than adults aged 40-79 years at all thresholds and adults aged 20-39 years at the 50th and 75th percentiles. Smokers had significantly higher Exposure Loads than nonsmokers at all thresholds except the LOD, which was expected given that tobacco smoke is a known source of certain chemicals included in our analysis. No differences in Exposure Loads were observed between males and females at any threshold. These findings broadly suggest that Canadians are concurrently exposed to many chemicals at lower concentrations and to fewer chemicals at high concentrations. They should assist in identifying vulnerable subpopulations disproportionately exposed to numerous chemicals at high concentrations. Future work will use Exposure Loads to identify prevalent chemical combinations and their link with adverse health outcomes in the Canadian population. The Exposure Load concept can be applied to other large datasets, through collaborative efforts in human biomonitoring networks, in order to further improve our understanding of multiple chemical exposures in different populations.

Association of biomarkers of exposure to metals and metalloids with maternal hormones in pregnant women from Puerto Rico

BACKGROUND

Metal(loid)s have been associated to adverse birth outcomes in experimental and epidemiological studies, but the underlying mechanism(s) are not well understood. Endocrine disruption may be a mechanism by which the metal(loid)s impact birth outcomes.

METHODS

Pregnant women were recruited through the Puerto Rico Testsite for Exploring Contamination Threats (PROTECT). Urine, blood, demographic and pregnancy-related data were collected at recruitment and subsequent visits. Sixteen metal(loid)s were analyzed in urine and blood samples, while nine maternal hormones (corticotropin-releasing hormone (CRH), sex-hormone binding globulin (SHBG), estriol (E3), progesterone, testosterone, thyroid-stimulating hormone (TSH), total triiodothyronine (T3), total thyroxine (T4), and free thyroxine (fT4)) were measured in serum samples from 815 singleton pregnancies. Linear mixed models with random intercepts were used to examine associations between metal(loid)s in blood and urine with hormone concentrations.

RESULTS

Arsenic blood concentrations were significantly associated with increased levels in CRH (%Δ: 23.0, 95%CI: 8.4-39.6) and decreased levels in testosterone (%Δ: ^-16.3, 95%CI: ^-26.2-^-5.1). Cobalt, manganese, and lead blood concentrations were associated with small increases in SHBG (%Δ range: 3.3-4.2), E3 (%Δ range: 3.9-8.7) and progesterone (%Δ range: 4.1-6.3) levels, respectively. Nickel blood concentration was inversely associated with testosterone levels (%Δ ^-13.3, 95%CI: ^-18.7-^-7.6). Significant interactions were detected for the association between nickel and study visit in relation to CRH (p < 0.02) and testosterone levels (p < 0.01).

CONCLUSION

Our analysis suggests that metal(loid)s may act as endocrine disruptors by altering prenatal hormone levels. This disruption may depend on specific windows of exposure during pregnancy. Additionally, some essential metal(loid)s such as managense and cobalt may be contributors to adverse maternal and fetal outcomes. The study of metal(loid)s as endocrine disruptors is in the early stages of epidemiological research and future studies are needed to further investigate these associations.

Assessment of chemical mixtures using biomarkers of combined biological activity: A screening study in human placentas

Humans are simultaneously exposed to complex mixtures of chemicals with limited knowledge on potential health effects, therefore improved tools for assessing these mixtures are needed. As part of the Human Biomonitoring for Europe (HBM4EU) Project, we aimed to examine the combined biological activity of chemical mixtures extracted from human placentas using one in vivo and four in vitro bioassays, also known as biomarkers of combined effect. Relevant endocrine activities (proliferative and/or reporter gene assays) and four endpoints were tested: the estrogen receptor (ER), androgen receptor (AR), and aryl hydrocarbon receptor (AhR) activities, as well as thyroid hormone (TH) signaling. Correlations among bioassays and their functional shapes were evaluated. Results showed that all placental extracts agonized or antagonized at least three of the abovementioned endpoints. Most placentas induced ER-mediated transactivation and ER-dependent cell proliferation, together with a strong inhibition of TH signaling and the AR transactivity; while the induction of the AhR was found in only one placental extract. The effects in the two estrogenic bioassays were positively and significantly correlated and the AR-antagonism activity showed a positive borderline-significant correlation with both estrogenic bioassay activities. However, the in vivo anti-thyroid activities of placental extracts were not correlated with any of the tested in vitro assays. Findings highlight the importance of comprehensively mapping the biological effects of "real-world" chemical mixtures present in human samples, through a battery of in vitro and in vivo bioassays. This approach should be a complementary tool for epidemiological studies to further elucidate the combined biological fingerprint triggered by chemical mixtures.

Thyroid disrupting chemicals and developmental neurotoxicity - New tools and approaches to evaluate hormone action

It is well documented that thyroid hormone (TH) action is critical for normal brain development and is mediated by both nuclear and extranuclear pathways. Given this dependence, the impact of environmental endocrine disrupting chemicals that interfere with thyroid signaling is a major concern with direct implications for children's health. However, identifying thyroid disrupting chemicals in vivo is primarily reliant on serum thyroxine (T4) measurements within greater developmental and reproductive toxicity assessments. These studies do not examine known TH-dependent phenotypes in parallel, which complicates chemical evaluation. Additionally, there exist no recommendations regarding what degree of serum T4 dysfunction is adverse, and little consideration is given to quantifying TH action within the developing brain. This review summarizes current testing strategies in rodent models and discusses new approaches for evaluating the developmental neurotoxicity of thyroid disrupting chemicals. This includes assays to identify adverse cellular effects of the brain by both immunohistochemistry and gene expression, which would compliment serum T4 measures. While additional experiments are needed to test the full utility of these approaches, incorporation of these cellular and molecular assays could enhance chemical evaluation in the regulatory arena.

Thresholds and Endocrine Disruptors: An Endocrine Society Policy Perspective

The concept of a threshold of adversity in toxicology is neither provable nor disprovable. As such, it is not a scientific question but a theoretical one. Yet, the belief in thresholds has led to traditional ways of interpreting data derived from regulatory guideline studies of the toxicity of chemicals. This includes, for example, the use of standard "uncertainty factors" when a "No Adverse Effect Level" (or similar "benchmark dose") is either observed, or not observed. In the context of endocrine-disrupting chemicals (EDCs), this approach is demonstrably inappropriate. First, the efficacy of a hormone on different endpoints can vary by several orders of magnitude. This feature of hormone action also applies to EDCs that can interfere with that hormone. For this reason, we argue that the choice of endpoint for use in regulation is critical, but note that guideline studies were not designed with this in mind. Second, the biological events controlled by hormones in development not only change as development proceeds but are different from events controlled by hormones in the adult. Again, guideline endpoints were also not designed with this in mind, especially since the events controlled by hormones can be both temporally and spatially specific. The Endocrine Society has laid out this logic over several years and in several publications. Rather than being extreme views, they represent what is known about hormones and the chemicals that can interfere with them.

Exposure to New Emerging Bisphenols Among Young Children in Switzerland

Restrictions on the use of bisphenol A (BPA) in consumer products led to its replacement by various bisphenol (BP) analogues, yet young children's exposure to these analogues has been poorly characterized so far. This study aimed to characterize infants' and toddlers' exposure to BPA and 14 emerging BP analogues (i.e., bisphenol AF, bisphenol AP, bisphenol B, bisphenol BP, bisphenol C (BPC), bisphenol E, bisphenol F (BPF), bisphenol G, bisphenol M (BPM), bisphenol P, bisphenol PH, bisphenol S (BPS), bisphenol TMC, and bisphenol Z). We extracted infants' and toddlers' urine from diapers (n = 109) collected in Swiss daycare centers as a practical and noninvasive alternative approach to urinary biomonitoring. Bisphenols were present in 47% of the samples, with BPC and BPM being the most frequently detected (23% and 25% of all samples, respectively). The mean concentrations of urinary BPS and BPF were greater than that of BPA. This contrasts with data reported previously. Furthermore, statistical analysis revealed a significant and negative correlation between urinary BPM concentration and the population's age. Our results provide a first characterization of infants' and toddlers' exposure to bisphenols in Switzerland. This knowledge can be used to support ongoing biomonitoring studies and to prioritize exposure reduction and prevention strategies.

Concentrations and temporal trends in pesticide biomarkers in urine of Swedish adolescents, 2000-2017

Agricultural pesticides are extensively used for weed- and pest control, resulting in residues of these compounds in food. The general population is mainly exposed through dietary intake. Exposure to certain pesticides has been associated with adverse human health outcomes. Our aim was to assess urinary concentrations and temporal trends in the biomarkers of commonly used pesticides. Samples were collected from adolescents (n = 1060) in Scania, Sweden, from 2000 to 2017. Concentrations of 14 pesticide biomarkers were analyzed in urine using LC-MS/MS. Temporal trends in biomarker concentrations (ln-transformed) were evaluated using linear regression. Biomarkers of pyrethroids (3-PBA and DCCA), chlorpyrifos (TCPy), chlormequat (CCC), thiabendazole (OH-TBZ), and mancozeb (ETU) were detected in >90% of the population all sampling years. The biomarkers CCC and TCPy had the highest median concentrations (>0.8 µg/L), whereas the biomarkers of cyfluthrin (4F-3-PBA) and two pyrethroids (CFCA) had the lowest median concentrations (<0.02 µg/L). Increasing temporal trends were found for the biomarkers 3-PBA (3.7%/year), TCPy (1.7%/year) and biomarkers of pyrimethanil (11.9%/year) and tebuconazole (12.2%/year). Decreasing trends were found for CCC (-5.5%/year), OH-TBZ (-5.5%/year), and ETU (-3.9%/year). Our results suggest that Swedish adolescents are commonly exposed to pesticides in low concentrations (median concentrations <3.88 µg/L).

Synthetic Chemicals and Cardiometabolic Health Across the Life Course Among Vulnerable Populations: a Review of the Literature from 2018 to 2019

PURPOSE OF REVIEW

Although vulnerable populations are disproportionately exposed to synthetic chemicals with endocrine disrupting properties, few recent reviews have summarized the impact of synthetic chemicals on cardiometabolic health among these groups.

RECENT FINDINGS

Of 37 eligible epidemiological studies among vulnerable populations published between January 2018 and April 2019 in which over half were prospective, the most investigated populations were pregnant women and children. Racial/ethnic minorities, individuals of low socioeconomic status (SES), and those occupationally exposed were studied the least. The most studied persistent organic pollutants (POPs) were per-/poly-fluoroalkyl substances (PFAS), and the most studied non-POPs were phenols. Across chemical classes, studies found certain POPs (e.g., PFAS) and non-POPs (i.e., phenols, phthalates, and parabens) to be associated with gestational diabetes and dysregulated glucose metabolism. Results for other cardiometabolic health outcomes were inconsistent but suggested certain chemicals may negatively affect cardiometabolic health. Synthetic chemicals likely adversely affect cardiometabolic health, but current findings were inconclusive. Few recent studies focused on racial/ethnic minorities, low SES, and occupationally exposed populations. To address poor cardiometabolic health and related disparities, more studies across vulnerable populations are warranted.

Heightened susceptibility: A review of how pregnancy and chemical exposures influence maternal health

Pregnancy is a unique period when biological changes can increase sensitivity to chemical exposures. Pregnant women are exposed to multiple environmental chemicals via air, food, water, and consumer products, including flame retardants, plasticizers, and pesticides. Lead exposure increases risk of pregnancy-induced hypertensive disorders, although women's health risks are poorly characterized for most chemicals. Research on prenatal exposures has focused on fetal outcomes and less on maternal outcomes. We reviewed epidemiologic literature on chemical exposures during pregnancy and three maternal outcomes: preeclampsia, gestational diabetes, and breast cancer. We found that pregnancy can heighten susceptibility to environmental chemicals and women's health risks, although variations in study design and exposure assessment limited study comparability. Future research should include pregnancy as a critical period for women's health. Incorporating biomarkers of exposure and effect, deliberate timing and method of measurement, and consistent adjustment of potential confounders would strengthen research on the exposome and women's health.

Maternal Exposure to Environmental Disruptors and Sexually Dimorphic Changes in Maternal and Neonatal Oxidative Stress

CONTEXT

Early pregnancy exposure to endocrine disrupting chemicals (EDCs) may contribute to poor birth outcomes through oxidative stress (OS)-mediated disruption of the maternal and fetal milieu. Most studies have investigated the effect of single EDC exposures on OS.

OBJECTIVE

Assess the association of uniquely weighted mixtures of early pregnancy exposures with the maternal and neonatal OS markers.

DESIGN

Prospective analysis of mother-infant dyads.

SETTING

University hospital.

PARTICIPANTS

56 mother-infant dyads.

MAIN OUTCOME MEASURES

The association of OS markers (nitrotyrosine, dityrosine, chlorotyrosine) in maternal first trimester and term, and cord blood plasma with maternal first trimester exposure levels of each of 41 toxicants (trace elements, metals, phenols, and phthalates) from 56 subjects was analyzed using Spearman correlations and linear regression. The association of OS markers with inflammatory cytokines and birth outcomes were analyzed by Spearman correlation and linear regression analysis, respectively. Weighted mixtures of early pregnancy exposures were created by principal component analysis and offspring sex-dependent and independent associations with oxidative stress markers were assessed.

RESULTS

(1) An inverse relationship between levels of maternal/cord OS markers and individual EDCs was evident. In contrast, when assessed as EDC mixtures, both direct and inverse associations were evident in a sex-specific manner; (2) the maternal term OS marker, nitrotyrosine, was inversely associated with gestational age, and (3) both direct and inverse associations were evident between the 3 OS markers and individual cytokines.

CONCLUSIONS

Provides proof of concept that effects of exposures on OS varies when assessed as EDC mixtures versus individually.

Endocrine Disruption and Reproductive Pathology

During the past 20 years, investigations involving endocrine active substances (EAS) and reproductive toxicity have dominated the landscape of ecotoxicological research. This has occurred in concert with heightened awareness in the scientific community, general public, and governmental entities of the potential consequences of chemical perturbation in humans and wildlife. The exponential growth of experimentation in this field is fueled by our expanding knowledge into the complex nature of endocrine systems and the intricacy of their interactions with xenobiotic agents. Complicating factors include the ever-increasing number of novel receptors and alternate mechanistic pathways that have come to light, effects of chemical mixtures in the environment versus those of single EAS laboratory exposures, the challenge of differentiating endocrine disruption from direct cytotoxicity, and the potential for transgenerational effects. Although initially concerned with EAS effects chiefly in the thyroid glands and reproductive organs, it is now recognized that anthropomorphic substances may also adversely affect the nervous and immune systems via hormonal mechanisms and play substantial roles in metabolic diseases, such as type 2 diabetes and obesity.

Racial/ethnic disparities in disease burden and costs related to exposure to endocrine-disrupting chemicals in the United States: an exploratory analysis

OBJECTIVE

Studies have documented disparities in exposure to endocrine-disrupting chemicals (EDC), but no studies have investigated potential implications for racial/ethnic disparities in chronic disease and associated costs. Our objective was to examine EDC levels in the US population according to race/ethnicity and to quantify disease burden and associated costs.

STUDY DESIGN AND SETTING

EDC exposure levels in 2007-2010 were obtained from the National Health and Nutrition Examination Surveys. The associated disease burden and costs for 12 exposure-response relationships were determined for non-Hispanic Whites, non-Hispanic Blacks, Mexican Americans, Other Hispanics, and Other/Multicultural.

RESULTS

EDC exposure levels and associated burden of disease and costs were higher in non-Hispanic Blacks ($56.8 billion; 16.5% of total costs) and Mexican Americans ($50.1 billion; 14.6%) compared with their proportion of the total population (12.6% and 13.5%, respectively). Associated costs among non-Hispanic whites comprised 52.3% of total costs ($179.8 billion) although they comprise 66.1% of the US population. These disparities are driven by generally higher exposure to persistent pesticides and flame retardants among non-Hispanic blacks and Mexican Americans.

CONCLUSION

Our estimates suggest that racial/ethnic disparities in chronic diseases in the US may be because of chemical exposures and are an important tool to inform policies that address such disparities.

Early pregnancy exposure to endocrine disrupting chemical mixtures are associated with inflammatory changes in maternal and neonatal circulation

Endocrine disrupting chemicals (EDCs) are ubiquitous, and pregnancy is a sensitive window for toxicant exposure. EDCs may disrupt the maternal immune system, which may lead to poor pregnancy outcomes. Most studies investigate single EDCs, even though "real life" exposures do not occur in isolation. We tested the hypothesis that uniquely weighted mixtures of early pregnancy exposures are associated with distinct changes in the maternal and neonatal inflammasome. First trimester urine samples were tested for 12 phthalates, 12 phenols, and 17 metals in 56 women. Twelve cytokines were measured in first trimester and term maternal plasma, and in cord blood after delivery. Spearman correlations and linear regression were used to relate individual exposures with inflammatory cytokines. Linear regression was used to relate cytokine levels with gestational age and birth weight. Principal component analysis was used to assess the effect of weighted EDC mixtures on maternal and neonatal inflammation. Our results demonstrated that maternal and cord blood cytokines were differentially associated with (1) individual EDCs and (2) EDC mixtures. Several individual cytokines were positively associated with gestational age and birth weight. These observed associations between EDC mixtures and the pregnancy inflammasome may have clinical and public health implications for women of childbearing age.

Disruption in Thyroid Signaling Pathway: A Mechanism for the Effect of Endocrine-Disrupting Chemicals on Child Neurodevelopment

Thyroid hormones are crucial in normal brain development. Transient and mild thyroid hormone insufficiency in pregnancy is also associated with impaired neurodevelopment in the offspring (e.g., 3-4 IQ score loss in association with maternal free thyroxine in the lowest fifth percentile). While inadequate iodine intake remains the most common underlying cause of mild thyroid hormone insufficiency in vulnerable populations including pregnant women, other factors such as exposure to environmental contaminants have recently attracted increasing attention, in particular in interaction with iodine deficiency. Endocrine-disrupting chemicals (EDCs) are natural and synthetic substances with ubiquitous exposure in children and adults including pregnant women. EDCs interfere, temporarily or permanently, with hormonal signaling pathways in the endocrine system by binding to hormone receptors and modifying gene expression. Other mechanisms involve alterations in production, metabolism, and transfer of hormones. Experimental studies have shown that exposures to EDCs affect various brain processes such as neurogenesis, neural differentiation and migration, as well as neural connectivity. Neuroimaging studies confirm brain morphological abnormalities (e.g., cortical thinning) consistent with neurodevelopmental impairments as a result of EDC exposures at standard use levels. In this review, we provide an overview of present findings from toxicological and human studies on the anti-thyroid effect of EDCs with a specific attention to fetal and early childhood exposure. This brief overview highlights the need for additional multidisciplinary studies with a focus on thyroid disruption as an underlying mechanism for developmental neurotoxicity of EDC, which can provide insight into modifiable risk factors of developmental delays in children.