Proximity of residence to trichloroethylene-emitting sites and increased risk of offspring congenital heart defects among older women

Maternal exposure to housing renovation during the periconceptional period and the risk of offspring with isolated congenital heart disease: a case-control study

BACKGROUND

Congenital heart disease (CHD) is the most prevalent birth defect in recent decades. The aim of this research was to examine the association between maternal housing renovation exposure during the periconceptional period and isolated congenital heart disease (CHD) in their offspring.

METHODS

A multi-hospitals case-control study was conducted from six tertiary A hospitals in Xi'an, Shaanxi, Northwest China based on questionnaires and interviews to address this question. The cases included fetuses or newborns diagnosed with CHD. Controls consisted of healthy newborns without birth defects. In total, 587 cases and 1180 controls were enrolled in this study. The association between maternal periconceptional housing renovation exposure and isolated CHD for offspring was assessed by estimating odds ratios (OR) with multivariate logistic regression models.

RESULTS

After adjusting for potential confounding variables, it was found that maternal exposure to home improvement projects was associated with a higher probability of isolated CHD in offspring (adjusted OR: 1.77, 95% CI: 1.34, 2.33). Additionally, the risk of the ventricular septal defect (VSD) and patent ductus arteriosus (PDA) for CHD types was significantly associated with maternal exposure to housing renovations (VSD: adjusted OR = 1.56, 95% CI: 1.01, 2.41; PDA: adjusted OR = 2.50, 95% CI: 1.41, 4.45).

CONCLUSIONS

Our study suggests that maternal exposure to housing renovation during the periconceptional period was associated with an increased risk of isolated CHD in offspring. Consequently, it would be beneficial to avoid living in a renovated home from 12 months before pregnancy through the first trimester to lower isolated CHD in infants.

Association between maternal exposure to indoor air pollution and offspring congenital heart disease: a case–control study in East China

Background

Previous research suggested an association between maternal exposure to ambient air pollutants and the risk of congenital heart disease (CHD). However, the effect of individual prenatal exposure to indoor air pollutants on CHD occurrence was not reported.

Methods

We performed a hospital-based case–control study to investigate the association between personal air pollution exposure during pregnancy and the risk of CHD in offspring. A total of 44 cases and 75 controls were included from two hospitals in East China. We investigated maternal and residential environmental characteristics using a questionnaire and obtained personal indoor air samples to assess particulate matter (PM) and volatile organic compounds (VOCs) from 22–30 gestational weeks. Formaldehyde, benzene, toluene, xylene, total volatile organic compounds (TVOCs), PM_2.5, and PM₁₀ were assessed. Logistic regression was performed to assess associations and interactions between individual indoor air pollutants and CHD after adjusting for confounders. The potential residential environmental factors affecting the risks of indoor air pollutants on CHD were also assessed.

Results

Median TVOC (0.400 vs. 0.005 mg/m³, P < 0.001) exposure levels in cases were significantly higher than controls. A logistic regression model adjusted for confounders revealed that exposure to high levels of indoor TVOCs (AOR 7.09, 95% CI 2.10–23.88) during pregnancy was associated with risks for CHD and the occurrence of some major CHD subtype in offspring. These risk effects were enhanced in pregnant women living in a newly renovated house but were mitigated by household use of smoke ventilators when cooking. We observed a positive interaction of maternal exposure to TVOCs and PM_2.5 and the risk for CHD.

Conclusions

Maternal exposure to indoor VOCs and PMs may increase the risk of giving birth to foetuses with CHD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-13174-0.

Cx43 overexpression is involved in the hyper-proliferation effect of trichloroethylene on human embryonic stem cells

Trichloroethylene (TCE) is a major environmental contaminant. Maternal exposure of TCE is linked to developmental defects, but the mechanisms remain to be elucidated. Along with a strategy of 3Rs principle, human embryonic stem cells (hESCs) are regarded as most promising in vitro models for developmental toxicity studies. TCE interfered with hESCs differentiation, but no report was available for TCE effects on hESCs proliferation. Here, we aimed to explore the toxic effects and mechanisms of TCE on hESCs proliferation. Treatment with TCE, did not affect the pluripotency genes expression. However, TCE enhanced hESCs proliferation, manifested by increased cell number, PCNA expression and EdU incorporation. Moreover, TCE exposure upregulated the protein expression levels of Cx43 and cyclin-dependent kinases. Knockdown of Cx43 attenuated the TCE-induced cell hyper-proliferation and CDK2 upregulation. Furthermore, TCE increased Akt phosphorylation, and the inhibition of Akt blocked the TCE-induced Cx43 overexpression and cell proliferation. In conclusion, TCE exposure resulted in upregulation of Cx43 via Akt phosphorylation, consequently stimulated CDK2 expression, contributing to hyper-proliferation in hESCs. Our study brings to light that TCE stimulated the proliferation of hESCs via Cx43, providing a new research avenue for the causes of TCE-induced developmental toxicity.

Levels of urinary metabolites of benzene compounds, trichloroethylene, and polycyclic aromatic hydrocarbons and their correlations with socioeconomic, demographic, dietary factors among pregnant women in six cities of China

Maternal exposure to benzene and related compounds, trichloroethylene, and polycyclic aromatic hydrocarbons has been suggested as risk factors for reproductive and developmental problem. In different countries and groups, there are differences in socioeconomic circumstances, consumer products, dietary habits, lifestyles, and so on, resulting in different exposure risks from these chemicals. This study investigated the correlation between their metabolite concentrations and socioeconomic, demographic, and dietary factors to explore the possible exposure source of the concerned pollutants in pregnant women. We conducted biological monitoring to assess the exposure of these chemicals using urine samples from 590 to 639 pregnant women during 2nd or 3rd trimester of pregnancy in six cities of China. Socioeconomic and demographic characteristics and dietary habits were collected from questionnaires. The detection rate was over 74% of the urine samples for all metabolites. Compared with the Fourth National Report on Human Exposure to Environmental Chemical concentrations for females (FNRHEEC, the US Centers for Disease Control and Prevention), the metabolite concentrations of benzene compounds and trichloroethylene, excluding MA reported here, were higher. Principal component analysis results showed that SBMA and MHA could be proxy of the principal sources of metabolites for benzene compounds. The concentrations of SBMA and MA were higher in Fuzhou and Wuhan, respectively. The concentration of DCVMA was higher in Shenzhen, Xi'an, and Nanning, and the concentration of PGA was higher in Fuzhou, Wuhan, and Xi'an. Also, the 1-OHPG concentration in Wuhan is higher than that in Fuzhou and Shenzhen. Unhealthy dietary habits, using cosmetics and indoor exposure, contacting chemical solvent during pregnancy were associated with increased benzene compounds, trichloroethylene, and PAH exposure. There were significant positive associations between 1-OHPG level and maternal BMI, low education status, and cooking without a range hood. Pregnant women in China may be at a greater risk of exposure to most of the target compounds than US females, and their exposure levels varied in different regions. Some adverse environmental and behavioral factors may increase the exposure of environmental toxins, which can urge people to take measures to reduce the health risk to pregnant women during pregnancy.

Maternal trichloroethylene exposure and metabolic gene polymorphisms may interact during fetal cardiovascular malformation

This study aimed to analyze the potential association between trichloroethylene (TCE) exposure and congenital heart disease (CHD) and to explore the effect of metabolic enzyme gene polymorphisms on heart development. A multicenter case-control study was conducted. The trichloroethylene concentrations were measured by UPLC-MSMS in urine. Fourteen SNPs in the GSTA1, GSTP1, MPO, NAT1, NAT2, CYP1A1, CYP1A2, CYP2E1 and EPHX1 genes were genotyped using an improved multiplex ligation detection reaction (iMLDR) technique. A total of 283 cases and 331 controls with maternal urine and/or venous blood were included in the present study. The median NAcDCVC was 7.65 ng/mL in the case group and 7.43 ng/mL in the control group. There was no significant difference in the NAcDCVC concentration between the CHD subtypes and controls (P > 0.05). The GA/AA of GSTA1 rs3957357 could increase the risk of CHDs under the dominant model (aOR = 2.26, 95 % CI: 1.31, 3.90), but other SNPs were not associated with CHDs (P > 0.05). GA or AA genotypes of GSTA1 rs3957357 with lower levels of TCE exposure were 3.53 times at risk relative to mothers carrying the wild type genotype. In conclusion, maternal exposure to trichloroethylene alone is not associated with the occurrence of fetal CHD and CHD subtypes. Maternal GSTA1 rs3957357 may increase the risk of CHD in offspring. TCE exposure and metabolic gene polymorphisms probably interact with each other to induce fetal cardiovascular malformation, but larger sample size studies are needed to confirm this hypothesis.

Linking metal (Pb, Hg, Cd) industrial air pollution risk to blood metal levels and cardiovascular functioning and structure among children in Syracuse, NY

BACKGROUND

Exposure to air pollution has been linked to individual health effects in occupational environments and communities proximate to air pollution sources. Use of estimated chemical concentrations from the Risk Screening Environmental Indicators (RSEI) model, derived from the Toxics Release Inventory, can help approximate some contributions to individual lifetime exposure to risk from air pollution and holds potential for linkages with specific health outcome data.

OBJECTIVES

Our objectives were: (1) use regression modeling to test for associations between observed blood metal concentrations in children and RSEI total air concentrations of the same metals released from proximate manufacturing facilities; (2) determine the relative contribution of RSEI air pollution to blood metal concentrations; and (3) examine associations between chronic metal exposure and cardiovascular functioning and structure in study participants.

METHODS

Using data synthesis methods and regression modeling we linked individual blood-based levels of lead, mercury, and cadmium(Pb, Hg, Cd) and cardiovascular functioning and structure to proximate industrial releases of the same metals captured by the Environmental Protection Agency's (EPA) RSEI geographic microdata.

RESULTS

We found that RSEI-derived ground-level ambient air concentrations of Hg and Cd were a significant predictor of blood metal levels, when controlling for covariates and other exposure variables. In addition to associations with blood metal findings, RSEI concentrations also predicted cardiovascular dysfunction and risk including changes in left-ventricular mass, blood pressure, and heart rate.

DISCUSSION

Right-to-know data, such as EPA's RSEI, can be linked to objective health outcomes, rather than simply serving as a non-specific risk estimate. These data can serve as a proxy for hazard exposure and should be used more widely to understand the dynamics of environmental exposure. Furthermore, since these data are both a product of and contribute to regulatory decision making, they could serve as an important link between disease risk and translation-orientated national environmental health policy.

Evaluation of interactive effects between paternal alcohol consumption and paternal socioeconomic status and environmental exposures on congenital heart defects

BACKGROUND

While the maternal risk factors on congenital heart defects (CHDs) have often been assessed, paternal contribution to CHDs, especially the joint effects of paternal risk factors on CHDs remain unknown. This study examined the major impacts of paternal alcohol consumption and its interaction (on multiplicative and additive scales) with paternal socioeconomic status (SES) and environmental exposures on CHDs in China.

METHODS

A population-based case-control study involving 4,726 singleton CHDs cases and 4,726 controls (without any malformation and matched on hospital, gender, and gestational age) was conducted in Guangdong, China, 2004-2014. Information on parental demographics, behavioral patterns, disease/medication, and environmental exposures (3 months before pregnancy) was collected through face-to-face interviews. Conditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) while controlling for all parental factors.

RESULTS

Paternal alcohol consumption was associated with an increased OR of CHDs (adjusted OR = 2.87, 95% CI: 2.25-3.65). Additionally, paternal smoking, industry occupation, organic solvent contact, virus infection and antibiotic use, living in rural areas, low household income, and migrant status were significantly associated with CHDs (ORs ranged: 1.42-4.44). Significant additive or multiplicative interactions were observed between paternal alcohol consumption and paternal smoking, industrial occupation, and low income on any CHDs (interaction contrast ratio [ICR] = 4.72, 95% CI: 0.96-8.47] and septal defects (ICRs ranged from 2.04 to 2.79, p < .05).

CONCLUSIONS

Paternal alcohol consumption and multiple paternal factors were significantly associated with CHDs in China. Paternal smoking and low SES factors modified paternal alcohol consumption-CHDs relationships. Further studies are needed to confirm these findings.

Environmental and Socioeconomic Factors Influence the Live-Born Incidence of Congenital Heart Disease: A Population-Based Study in California

BACKGROUND

The development of congenital heart disease (CHD) is multifactorial with genetic and environmental influences. We sought to determine the relationship between socioeconomic and environmental factors with the incidence of CHD among live‐born infants in California and to determine whether maternal comorbidities are in the causal pathway.

METHODS AND RESULTS

This was a population‐based cohort study in California (2007–2012). The primary outcome was having significant CHD. Predictors included socioeconomic status and environmental exposure to pollutants determined by U.S. Census data. A social deprivation index and environmental exposure index was assigned based on neighborhood socioeconomic variables, categorized into 4 quartiles. Quartile 1 was the best with the least exposure to pollutants and social deprivation, and quartile 4 was the worst. Multivariate logistic regression and mediation analyses were performed. Among 2 419 651 live‐born infants, the incidence of CHD was 3.2 per 1000 live births. The incidence of CHD was significantly higher among those in quartile 4 compared with quartile 1 (social deprivation index: 0.35% versus 0.29%; odds ratio [OR], 1.31; 95% CI, 1.21–1.41; environmental exposure index: 0.35% versus 0.29%; OR, 1.23; 95% CI, 1.15–1.31) after adjusting for maternal race/ethnicity and age and accounting for the relationship between the 2 primary predictors. Maternal comorbidities explained 13% (95% CI, 10%–20%) of the relationship between social deprivation index and environmental exposure index with the incidence of CHD.

CONCLUSIONS

Increased social deprivation and exposure to environmental pollutants are associated with the incidence of live‐born CHD in California. Maternal comorbidities explain some, but not all, of this relationship. These findings identify targets for social policy initiatives to minimize health disparities.

Developmental toxicity of trichloroethylene in zebrafish (Danio rerio)

Trichloroethylene (TCE), an industrial solvent and degreaser, is an environmental toxicant that contaminates over half of Superfund sites, is a known carcinogen, and is linked to congenital defects and neurodegenerative disease. The developmental toxicity of TCE near ecologically relevant levels needs further characterization in order to better assess health risks of exposure. In this study, the toxicodynamics of TCE in the zebrafish (Danio rerio) model was investigated through the establishment of a LC50 concentration and by monitoring the acute developmental toxicity of ecologically relevant concentrations (0, 5, 50, and 500 parts per billion; ppb) of TCE during two different exposure lengths (1-72 hours post fertilization (hpf) and 1-120 hpf). Acute developmental toxicity was assessed by monitoring survival and hatching, larval morphology, larval heart rate, and behavioral responses during an embryonic photomotor response test and a larval visual motor response test. Embryonic exposure to TCE was associated with decreased percent hatch at 48 hpf, altered larval morphology, increased heart rate, and altered behavioral responses during the photomotor response test and visual motor response test. Larval morphology and behavioral alterations were more pronounced in the 1-120 hpf exposure length trials. The observed alterations suggest developmental TCE toxicity is still a concern at regulatory concentrations and that timing of exposure influences developmental toxicity.

HNF4a transcription is a target of trichloroethylene toxicity in the embryonic mouse heart

In exploration of congenital heart defects produced by TCE, Hepatocyte Nuclear Factor 4 alpha (HNF4a) transcriptional activity was identified as a central component. TCE exposure altered gene transcription in the chick heart in a non-monotonic pattern where only low dose exposure inhibited transcription by HNF4a. As the chick embryo is non-placental, we examine here HNF4a as a target of TCE in developing mouse embryos. Benfluorex and Bi6015, published agonist and antagonist, respectively, of HNF4a were compared to low dose TCE exposure. Pregnant mice were exposed to 10 ppb (76 nM) TCE, 5 μM Benfluorex, 5 μM Bi6015, or a combination of Bi6015 and TCE in drinking water. Litters (E12) were collected during a sensitive window in heart development. Embryonic hearts were collected, pooled for extraction of RNA and marker expression was examined by quantitative PCR. Multiple markers, previously identified as sensitive to TCE exposure in chicks or as published targets of HNF4a transcription were significantly affected by Benfluorex, Bi6015 and TCE. Activity of TCE and both HNF4a-specific reagents on transcription argues that HNF4a is a component of TCE cardiotoxicity and likely a proximal target of low dose exposure during development. The effectiveness of these reagents after delivery in maternal drinking water suggests that neither maternal metabolism, nor placental transport is protective of exposure.

Risk of congenital heart defects in offspring exposed to maternal diabetes mellitus: an updated systematic review and meta-analysis

PURPOSE

A systematic review and meta-analysis was performed to assess the risk of congenital heart defects (CHDs) and its specific phenotypes associated with maternal diabetes mellitus (DM) including pregestational diabetes mellitus (PGDM) and gestational diabetes mellitus (GDM).

METHODS

PubMed, Embase, Medline, Google Scholar, Cochrane Libraries, China National Knowledge Infrastructure, Wanfang Database, Chinese Scientific Journals Fulltext Database and China Biology Medicine disc were searched from the inception dates to 15 December 2018, to identify case-control or cohort studies assessing the association between maternal DM and risk of CHDs. The exposure of interest was maternal DM; the outcomes of interest were CHDs and its specific phenotypes. Either a fixed- or a random-effects model was used to calculate the overall combined risk estimates. Subgroup analyses were performed to explore potential heterogeneity moderators.

RESULTS

Total 52 studies, which involved 259,917 patients with CHDs among 16,929,835 participants, were included for analysis. Overall, mothers with DM compared with those without DM had a significantly higher risk of CHDs in offspring [odds ratios (OR) = 2.71, 95% confidence intervals (CI) 2.28-3.23]. When data were restricted to different types of DM, a significantly increased risk of CHDs was observed among mothers with PGDM (OR = 3.18, 95% CI 2.77-3.65) and GDM (OR = 1.98, 95% CI 1.66-2.36). Our study suggested the risk of CHDs was significantly higher among mothers with PGDM than those with GDM. Additionally, this study suggested maternal DM was significantly associated with most phenotypes of CHDs; of these, double outlet of the right ventricle (OR = 10.89; 95% CI 8.77-13.53), atrioventricular septal defect (OR = 5.74; 95% CI 3.20-10.27) and truncus arteriosus (OR = 5.06; 95% CI 2.65-9.65) were identified as the first three of the most common phenotypes of CHDs associated with maternal DM.

CONCLUSIONS

The maternal DM including PGDM and GDM are significantly associated with risk of CHDs and its most phenotypes. The PGDM seems to be more likely to cause CHDs in offspring than GDM. Further studies are needed to clarify the underlying mechanisms.

Urinary trichloroacetic acid and high blood pressure: A cross-sectional study of general adults in Shijiazhuang, China

Exposure to trichloroacetic acid (TCAA) and its parent chemicals potentially linked to cardiovascular disease. However, the association between TCAA and blood pressure (BP) has not been studied to date. The purpose of this study was to examine the potential association between urinary TCAA levels and BP in a Chinese population. We measured BP parameters (including systolic BP, diastolic BP and pulse pressure) and TCAA concentrations in the urine of 569 adults from a primary health care clinic in Shijiazhuang, China. Logistic and linear regressions were used to investigate the relationships between the urinary TCAA levels and BP parameters. To evaluate the robustness of the results, we conducted sensitivity analyses by re-analysing data after excluding urine samples with extreme specific creatinine values. We found that urine TCAA levels were positively associated with systolic BP and pulse pressure based on trend tests after adjusting for potential confounders (both p for trend < 0.05). Finally, only the association of TCAA with systolic BP remained significant in the sensitivity analyses (p < 0.05). Our results suggested that TCAA exposure was associated with increased BP in adults. Because urinary TCAA has been proposed as a valid biomarker of disinfection by-product (DBP) ingestion through disinfected drinking water, our results further suggest that exposure to drinking water DBPs may contribute to high BP in humans. Additional research is needed to confirm these findings and to evaluate opportunities for intervention.

Role of Risk of Bias in Systematic Review for Chemical Risk Assessment: A Case Study in Understanding the Relationship Between Congenital Heart Defects and Exposures to Trichloroethylene

The National Academy of Science has recommended that a risk of bias (RoB; credibility of the link between exposure and outcome) assessment be conducted on studies that are used as primary data sources for hazard identification and dose-response assessment. Few applications of such have been conducted. Using trichloroethylene and congenital heart defects (CHDs) as a case study, we explore the role of RoB in chemical risk assessment using the National Toxicology Program's Office of Health Assessment and Translation RoB tool. Selected questions were tailored to evaluation of CHD and then applied to 12 experimental animal studies and 9 epidemiological studies. Results demonstrated that the inconsistent findings of a single animal study were likely explained by the limitations in study design assessed via RoB (eg, lack of concurrent controls, unvalidated method for assessing outcome, unreliable statistical methods, etc). Such limitations considered in the context of the body of evidence render the study not sufficiently reliable for the development of toxicity reference values. The case study highlights the utility of RoB as part of a robust risk assessment process and specifically demonstrates the role RoB can play in objectively selecting candidate data sets to develop toxicity values.

Trichloroethylene perturbs HNF4a expression and activity in the developing chick heart

Exposure to trichloroethylene (TCE) is linked to formation of congenital heart defects in humans and animals. Prior interactome analysis identified the transcription factor, Hepatocyte Nuclear Factor 4 alpha (HNF4a), as a potential target of TCE exposure. As a role for HNF4a is unknown in the heart, we examined developing avian hearts for HNF4a expression and for sensitivity to TCE and the HNF4a agonist, Benfluorex. In vitro analysis using a HNF4a reporter construct showed both TCE and HFN4a to be antagonists of HNF4a-mediated transcription at the concentrations tested. HNF4a mRNA is expressed transiently in the embryonic heart during valve formation and cardiac development. Embryos were examined for altered gene expression in the presence of TCE or Benfluorex. TCE altered expression of selected mRNAs including HNF4a, TRAF6 and CYP2C45. There was a transition between inhibition and induction of marker gene expression in embryos as TCE concentration increased. Benfluorex was largely inhibitory to selected markers. Echocardiography of exposed embryos showed reduced cardiac function with both TCE and Benfluorex. Cardiac contraction was reduced by 29% and 23%, respectively at 10 ppb. The effects of TCE and Benfluorex on autocrine regulation of HNF4a, selected markers and cardiac function argue for a functional interaction of TCE and HNF4a. Further, the dose-sensitive shift between inhibition and induction of marker expression may explain the nonmonotonic-like dose response observed with TCE exposure in the heart.

Systematic literature review of reproductive outcome associated with residential proximity to polluted sites

This study aims to assess the evidence on adverse pregnancy outcome associated with living close to polluted industrial sites, and identify the strengths and weaknesses of published epidemiological studies. A systematic literature search has been performed on all epidemiological studies published in developed countries since 1990, on the association between residential proximity to industrial sites (hazardous waste sites, industrial facilities and landfill sites) and adverse pregnancy outcome (low birth weight, preterm birth, small for gestational age, intrauterine growth retardation, infant mortality, congenital malformation). Based on 41 papers, our review reveals an excess risk of reproductive morbidity. However, no studies show significant excess risk of mortality including fetal death, neonatal or infant mortality and stillbirth. All published studies tend to show an increased risk of congenital abnormalities, yet not all are statistically significant. All but two of these studies revealed an excess risk of low birth weight. Results for preterm birth, small for gestational age and intrauterine growth retardation show the same pattern. There is suggestive evidence from the post-1990 literature that residential proximity to polluted sites (including landfills, hazardous waste sites and industrial facilities) might contribute to adverse reproductive outcomes, especially congenital malformations and low birth weight-though not mortality. This body of evidence has limitations that impede the formulation of firm conclusions, and new, well-focused studies are called for. The review findings suggest that continued strengthening of rules governing industrial emissions as well as industrial waste management and improved land use planning are needed.

Disruption of cardiogenesis in human embryonic stem cells exposed to trichloroethylene

Trichloroethylene (TCE) is ubiquitous in our living environment, and prenatal exposure to TCE is reported to cause congenital heart disease in humans. Although multiple studies have been performed using animal models, they have limited value in predicting effects on humans due to the unknown species-specific toxicological effects. To test whether exposure to low doses of TCE induces developmental toxicity in humans, we investigated the effect of TCE on human embryonic stem cells (hESCs) and cardiomyocytes (derived from the hESCs). In the current study, hESCs cardiac differentiation was achieved by using differentiation medium consisting of StemPro-34. We examined the effects of TCE on cell viability by cell growth assay and cardiac inhibition by analysis of spontaneously beating cluster. The expression levels of genes associated with cardiac differentiation and Ca²⁺ channel pathways were measured by immunofluorescence and qPCR. The overall data indicated the following: (1) significant cardiac inhibition, which was characterized by decreased beating clusters and beating rates, following treatment with low doses of TCE; (2) significant up-regulation of the Nkx2.5/Hand1 gene in cardiac progenitors and down regulation of the Mhc-7/cTnT gene in cardiac cells; and (3) significant interference with Ca²⁺ channel pathways in cardiomyocytes, which contributes to the adverse effect of TCE on cardiac differentiation during early embryo development. Our results confirmed the involvement of Ca²⁺ turnover network in TCE cardiotoxicity as reported in animal models, while the inhibition effect of TCE on the transition of cardiac progenitors to cardiomyocytes is unique to hESCs, indicating a species-specific effect of TCE on heart development. This study provides new insight into TCE biology in humans, which may help explain the development of congenital heart defects after TCE exposure. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1372-1380, 2016.

A systematic evaluation of the potential effects of trichloroethylene exposure on cardiac development

The 2011 EPA trichloroethylene (TCE) IRIS assessment, used developmental cardiac defects from a controversial drinking water study in rats (Johnson et al. [51]), along with several other studies/endpoints to derive reference values. An updated literature search of TCE-related developmental cardiac defects was conducted. Study quality, strengths, and limitations were assessed. A putative adverse outcome pathway (AOP) construct was developed to explore key events for the most commonly observed cardiac dysmorphologies, particularly those involved with epithelial-mesenchymal transition (EMT) of endothelial origin (EndMT); several candidate pathways were identified. A hypothesis-driven weight-of-evidence analysis of epidemiological, toxicological, in vitro, in ovo, and mechanistic/AOP data concluded that TCE has the potential to cause cardiac defects in humans when exposure occurs at sufficient doses during a sensitive window of fetal development. The study by Johnson et al. [51] was reaffirmed as suitable for hazard characterization and reference value derivation, though acknowledging study limitations and uncertainties.

Association between alcohol consumption during pregnancy and risks of congenital heart defects in offspring: meta-analysis of epidemiological observational studies

Background

To explore the association between maternal alcohol consumption and/or binge drinking and congenital heart defects (CHDs), we conducted a meta-analysis for more sufficient evidence on this issue.

Methods

We searched Medline, EMBASE, and the Cochrane Library from their inceptions to December 2014 for case-control and cohort studies that assessed the association between maternal alcohol consumption and CHD risk. Study-specific relative risk estimates were calculated using random-effect or fixed-effect models.

Results

A total of 19 case-control studies and 4 cohort studies were included in the meta-analysis. We observed a null association between maternal alcohol consumption during pregnancy and the risk of CHDs. Even in the analysis of different trimesters of pregnancy, we found little association between the two.

Conclusions

This meta-analysis suggests that maternal alcohol consumption is modestly not associated with the risk of CHDs. However, further investigation is needed to confirm this conclusion.

Mitochondrial Dysfunction, Disruption of F-Actin Polymerization, and Transcriptomic Alterations in Zebrafish Larvae Exposed to Trichloroethylene

Trichloroethylene (TCE) is primarily used as an industrial degreasing agent and has been in use since the 1940s. TCE is released into the soil, surface, and groundwater. From an environmental and regulatory standpoint, more than half of Superfund hazardous waste sites on the National Priority List are contaminated with TCE. Occupational exposure to TCE occurs primarily via inhalation, while environmental TCE exposure also occurs through ingestion of contaminated drinking water. Current literature links TCE exposure to various adverse health effects including cardiovascular toxicity. Current studies aiming to address developmental cardiovascular toxicity utilized rodent and avian models, with the majority of studies using relatively higher parts per million (mg/L) doses. In this study, to further investigate developmental cardiotoxicity of TCE, zebrafish embryos were treated with 0, 10, 100, or 500 parts per billion (ppb; μg/L) TCE during embryogenesis and/or through early larval stages. After the appropriate exposure period, angiogenesis, F-actin, and mitochondrial function were assessed. A significant dose-response decrease in angiogenesis, F-actin, and mitochondrial function was observed. To further complement this data, a transcriptomic profile of zebrafish larvae was completed to identify gene alterations associated with the 10 ppb TCE exposure. Results from the transcriptomic data revealed that embryonic TCE exposure caused significant changes in genes associated with cardiovascular disease, cancer, and organismal injury and abnormalities with a number of targets in the FAK signaling pathway. Overall, results from our study support TCE as a developmental cardiovascular toxicant, provide molecular targets and pathways for investigation in future studies, and indicate a need for continued priority for environmental regulation.

Maternal Alcohol Consumption before and during Pregnancy and the Risks of Congenital Heart Defects in Offspring: A Systematic Review and Meta-analysis

OBJECTIVE

Epidemiologic studies have reported conflicting results regarding maternal alcohol consumption before and during pregnancy, and the risk of congenital heart defects (CHDs). However, a systematic review and meta-analysis of the association between maternal alcohol consumption and CHDs in offspring has not been conducted.

DESIGN

We searched MEDLINE and EMBASE for articles catalogued between their inception and February 16, 2015; we identified relevant published studies that assessed the association between maternal alcohol consumption and CHD risk. Two authors independently assessed the eligibility of the retrieved articles and extracted data from them. Study-specific relative risk estimates were pooled by random-effects or fixed-effects models.

RESULTS

From the 1527 references, a total of 19 case-control studies and four cohort studies were enrolled in this meta-analysis. The summary of 23 studies related to CHDs indicated an overall pooled relative risk of 1.13 (95% confidence interval: 0.96, 1.29) among mothers drinking before or during pregnancy. Statistically significant heterogeneity was detected (Q = 196.61, P < .001, I(2) = 88.8%) with no publication bias (Egger's test: P = .157). We conducted stratified and meta-regression analyses to identify the origin of the heterogeneity among studies.

CONCLUSION

In summary, this meta-analysis provided no positive association between maternal alcohol consumption and risk of CHDs.

Air toxics and birth defects: a Bayesian hierarchical approach to evaluate multiple pollutants and spina bifida

BACKGROUND

While there is evidence that maternal exposure to benzene is associated with spina bifida in offspring, to our knowledge there have been no assessments to evaluate the role of multiple hazardous air pollutants (HAPs) simultaneously on the risk of this relatively common birth defect. In the current study, we evaluated the association between maternal exposure to HAPs identified by the United States Environmental Protection Agency (U.S. EPA) and spina bifida in offspring using hierarchical Bayesian modeling that includes Stochastic Search Variable Selection (SSVS).

METHODS

The Texas Birth Defects Registry provided data on spina bifida cases delivered between 1999 and 2004. The control group was a random sample of unaffected live births, frequency matched to cases on year of birth. Census tract-level estimates of annual HAP levels were obtained from the U.S. EPA's 1999 Assessment System for Population Exposure Nationwide. Using the distribution among controls, exposure was categorized as high exposure (>95(th) percentile), medium exposure (5(th)-95(th) percentile), and low exposure (<5(th) percentile, reference). We used hierarchical Bayesian logistic regression models with SSVS to evaluate the association between HAPs and spina bifida by computing an odds ratio (OR) for each HAP using the posterior mean, and a 95% credible interval (CI) using the 2.5(th) and 97.5(th) quantiles of the posterior samples. Based on previous assessments, any pollutant with a Bayes factor greater than 1 was selected for inclusion in a final model.

RESULTS

Twenty-five HAPs were selected in the final analysis to represent "bins" of highly correlated HAPs (ρ > 0.80). We identified two out of 25 HAPs with a Bayes factor greater than 1: quinoline (ORhigh = 2.06, 95% CI: 1.11-3.87, Bayes factor = 1.01) and trichloroethylene (ORmedium = 2.00, 95% CI: 1.14-3.61, Bayes factor = 3.79).

CONCLUSIONS

Overall there is evidence that quinoline and trichloroethylene may be significant contributors to the risk of spina bifida. Additionally, the use of Bayesian hierarchical models with SSVS is an alternative approach in the evaluation of multiple environmental pollutants on disease risk. This approach can be easily extended to environmental exposures, where novel approaches are needed in the context of multi-pollutant modeling.

Maternal residential proximity to chlorinated solvent emissions and birth defects in offspring: a case-control study

BACKGROUND

Some studies have noted an association between maternal occupational exposures to chlorinated solvents and birth defects in offspring, but data are lacking on the potential impact of industrial air emissions of these solvents on birth defects.

METHODS

With data from the Texas Birth Defects Registry for births occurring in 1996-2008, we examined the relation between maternal residential proximity to industrial air releases of chlorinated solvents and birth defects in offspring of 60,613 case-mothers and 244,927 control-mothers. Maternal residential exposures to solvent emissions were estimated with metrics that took into account residential distances to industrial sources and annual amounts of chemicals released. Logistic regression was used to generate odds ratios and 95% confidence intervals for the associations between residential proximity to emissions of 14 chlorinated solvents and selected birth defects, including neural tube, oral cleft, limb deficiency, and congenital heart defects. All risk estimates were adjusted for year of delivery and maternal age, education, race/ethnicity, and public health region of residence.

RESULTS

Relative to exposure risk values of 0, neural tube defects were associated with maternal residential exposures (exposure risk values >0) to several types of chlorinated solvents, most notably carbon tetrachloride (adjusted odds ratio [aOR] 1.42, 95% confidence interval [CI] 1.09, 1.86); chloroform (aOR 1.40, 95% CI 1.04, 1.87); ethyl chloride (aOR 1.39, 95% CI 1.08, 1.79); 1,1,2-trichloroethane (aOR 1.56, 95% CI 1.11, 2.18); and 1,2,3-trichloropropane (aOR 1.49, 95% CI 1.08, 2.06). Significant associations were also noted between a few chlorinated solvents and oral cleft, limb deficiency, and congenital heart defects. We observed stronger associations between some emissions and neural tube, oral cleft, and heart defects in offspring of mothers 35 years or older, such as spina bifida with carbon tetrachloride (aOR 2.49, 95% CI 1.09, 5.72), cleft palate with 1,2-dichloroethane (aOR 1.93, 95% 1.05, 3.54), cleft lip with or without cleft palate with ethyl chloride (aOR 1.81, 95% CI 1.06, 3.07), and obstructive heart defects with trichloroethylene (aOR 1.43, 95% CI 1.08, 1.88).

CONCLUSIONS

These findings suggest that maternal residential proximity to industrial emissions of chlorinated solvents might be associated with selected birth defects in offspring, especially among older mothers.

Critical review of the epidemiologic literature regarding the association between congenital heart defects and exposure to trichloroethylene

The most recent Integrated Risk Information System review of trichloroethylene (TCE; CAS# 79-01-6) has suggested that congenital heart defects (CHD) are a critical endpoint associated with exposure to this solvent. This conclusion was drawn, at least partly, from epidemiologic data, including several relatively recent studies. The current article critically reviews this epidemiologic literature, focusing on study quality and consistency. Literature searches uncovered approximately a dozen studies that specifically addressed associations between TCE and congenital malformations in eight populations. Four of these reported positive associations between TCE and heart defects, with significant relative risks as high as 5-6 in some subgroups. However, each of the positive studies had substantial design or analytical flaws that could easily explain the results, thereby limiting the conclusions that can be drawn. Five studies found no positive association with TCE, and several of these reported substantially fewer cases than expected despite similar/higher exposures compared to positive studies, further detracting from causal conclusions. Overall, this epidemiologic literature provides no substantive or consistent evidence linking TCE to CHD.

Potential effects of environmental chemical contamination in congenital heart disease

There is compelling evidence that prenatal exposures to environmental xenobiotics adversely affect human development and childhood. Among all birth defects, congenital heart disease (CHD) is the most prevalent of all congenital malformations and remains the leading cause of death. It has been estimated that in most cases the causes of heart defects remain unknown, while a growing number of studies have indicated the potential role of environmental agents as risk factors in CHD occurrence. In particular, maternal exposure to chemicals during the first trimester of pregnancy represents the most critical window of exposure for CHD. Specific classes of xenobiotics (e.g. organochlorine pesticides, organic solvents, air pollutants) have been identified as potential risk factors for CHD. Nonetheless, the knowledge gained is currently still incomplete as a consequence of the frequent heterogeneity of the methods applied and the difficulty in estimating the net effect of environmental pollution on the pregnant mother. The presence of multiple sources of pollution, both indoor and outdoor, together with individual lifestyle factors, may represent a further confounding element for association with the disease. A future new approach for research should probably focus on individual measurements of professional, domestic, and urban exposure to physical and chemical pollutants in order to accurately retrace the environmental exposure of parents of affected offspring during the pre-conceptional and pregnancy periods.

Low-dose trichloroethylene alters cytochrome P450-2C subfamily expression in the developing chick heart

Trichloroethylene (TCE) is an organic solvent and common environmental contaminant. TCE exposure is associated with heart defects in humans and animal models. Primary metabolism of TCE in adult rodent models is by specific hepatic cytochrome P450 enzymes (Lash et al. in Environ Health Perspect 108:177-200, 2000). As association of TCE exposure with cardiac defects is in exposed embryos prior to normal liver development, we investigated metabolism of TCE in the early embryo. Developing chick embryos were dosed in ovo with environmentally relevant doses of TCE (8 and 800 ppb) and RNA was extracted from cardiac and extra-cardiac tissue (whole embryo without heart). Real-time PCR showed upregulation of CYP2H1 transcripts in response to TCE exposure in the heart. No detectable cytochrome expression was found in extra-cardiac tissue. As seen previously, the dose response was non-monotonic and 8 ppb elicited stronger upregulation than 800 ppb. Immunostaining for CYP2C subfamily expression confirmed protein expression and showed localization in both myocardium and endothelium. TCE exposure increased protein expression in both tissues. These data demonstrate that the earliest embryonic expression of phase I detoxification enzymes is in the developing heart. Expression of these CYPs is likely to be relevant to the susceptibility of the developing heart to environmental teratogens.

Nongenetic risk factors and congenital heart defects

Advances have been made in identifying genetic etiologies of congenital heart defects. Through this knowledge, preventive strategies have been designed and instituted, and prospective parents are counseled regarding their risk of having an affected child. Great strides have been made in genetic variant identification, and genetic susceptibility to environmental exposures has been hypothesized as an etiology for congenital heart defects. Unfortunately, similar advances in understanding have not been made regarding strategies to prevent nongenetic risk factors. Less information is available regarding the potential adverse effect of modifiable risk factors on the fetal heart. This review summarizes the available literature on these modifiable exposures that may alter the risk for congenital heart disease. Information regarding paternal characteristics and conditions, maternal therapeutic drug exposures, parental nontherapeutic drug exposures, and parental environmental exposures are presented. Factors are presented in terms of risk for congenital heart defects as a group. These factors also are broken down by specific defect type. Although additional investigations are needed in this area, many of the discussed risk factors present an opportunity for prevention of potential disease.

Association between maternal exposure to housing renovation and offspring with congenital heart disease: a multi-hospital case-control study

BACKGROUND

Congenital heart disease (CHD) is one of the most prevalent birth defects. Housing renovations are a newly recognized source of indoor environmental pollution that is detrimental to health. A growing body of research suggests that maternal occupational exposure to renovation materials may be associated with an increased risk of giving birth to fetuses with CHD. However, the effect of indoor housing renovation exposure on CHD occurrence has not been reported.

METHODS

A multi-hospital case-control study was designed to investigate the association between maternal periconceptional housing renovation exposure and the risk of CHD for offspring. In total, 346 cases and 408 controls were enrolled in this study from four hospitals in China. Exposure information was based on a questionnaire given to women during pregnancy. The association between housing renovation exposure and CHD occurrence was assessed by estimating odds ratios (OR) with logistic regression models adjusted for potential confounders.

RESULTS

The risk for CHD in offspring was significantly associated with maternal exposure to housing renovations (AOR: 1.89, 95% CI: 1.29-2.77). There were similar risks for cardiac defects with or without extra-cardiac malformation (AOR of 2.65 and 1.76, respectively). Maternal housing renovation exposure may increase the fetus' risk of suffering from conotruncal defect or anomalous venous return. There were significant risks for cardiac defects if the pregnant woman moved into a new house within one month after decoration at either 3 months before pregnancy (AOR: 2.38, 95% CI: 1.03 to 5.48) or during first trimester (AOR: 4.00, 95% CI: 1.62 to 9.86).

CONCLUSIONS

Maternal exposure to housing renovations may have an increased risk of giving birth to fetuses with some selected types of CHD. This relationship was stronger for women who moved into a newly decorated house. However, considering the limited number of subjects and the problem of multiple exposures, more research is needed to clarify the effects seen here.

Human health effects of trichloroethylene: key findings and scientific issues

BACKGROUND

In support of the Integrated Risk Information System (IRIS), the U.S. Environmental Protection Agency (EPA) completed a toxicological review of trichloroethylene (TCE) in September 2011, which was the result of an effort spanning > 20 years.

OBJECTIVES

We summarized the key findings and scientific issues regarding the human health effects of TCE in the U.S. EPA's toxicological review.

METHODS

In this assessment we synthesized and characterized thousands of epidemiologic, experimental animal, and mechanistic studies, and addressed several key scientific issues through modeling of TCE toxicokinetics, meta-analyses of epidemiologic studies, and analyses of mechanistic data.

DISCUSSION

Toxicokinetic modeling aided in characterizing the toxicological role of the complex metabolism and multiple metabolites of TCE. Meta-analyses of the epidemiologic data strongly supported the conclusions that TCE causes kidney cancer in humans and that TCE may also cause liver cancer and non-Hodgkin lymphoma. Mechanistic analyses support a key role for mutagenicity in TCE-induced kidney carcinogenicity. Recent evidence from studies in both humans and experimental animals point to the involvement of TCE exposure in autoimmune disease and hypersensitivity. Recent avian and in vitro mechanistic studies provided biological plausibility that TCE plays a role in developmental cardiac toxicity, the subject of substantial debate due to mixed results from epidemiologic and rodent studies.

CONCLUSIONS

TCE is carcinogenic to humans by all routes of exposure and poses a potential human health hazard for noncancer toxicity to the central nervous system, kidney, liver, immune system, male reproductive system, and the developing embryo/fetus.

Adverse birth outcomes and maternal exposure to trichloroethylene and tetrachloroethylene through soil vapor intrusion in New York State

BACKGROUND

Industrial spills of volatile organic compounds (VOCs) in Endicott, New York (USA), have led to contamination of groundwater, soil, and soil gas. Previous studies have reported an increase in adverse birth outcomes among women exposed to VOCs in drinking water.

OBJECTIVE

We investigated the prevalence of adverse birth outcomes among mothers exposed to trichloroethylene (TCE) and tetrachloroethylene [or perchloroethylene (PCE)] in indoor air contaminated through soil vapor intrusion.

METHODS

We examined low birth weight (LBW), preterm birth, fetal growth restriction, and birth defects among births to women in Endicott who were exposed to VOCs, compared with births statewide. We used Poisson regression to analyze births and malformations to estimate the association between maternal exposure to VOCs adjusting for sex, mother's age, race, education, parity, and prenatal care. Two exposure areas were identified based on environmental sampling data: one area was primarily contaminated with TCE, and the other with PCE.

RESULTS

In the TCE-contaminated area, adjusted rate ratios (RRs) were significantly elevated for LBW [RR = 1.36; 95% confidence interval (CI): 1.07, 1.73; n = 76], small for gestational age (RR = 1.23; 95% CI: 1.03, 1.48; n = 117), term LBW (RR = 1.68; 95% CI: 1.20, 2.34; n = 37), cardiac defects (RR = 2.15; 95% CI: 1.27, 3.62; n = 15), and conotruncal defects (RR = 4.91; 95% CI: 1.58, 15.24; n = 3). In the PCE-contaminated area, RRs for cardiac defects (five births) were elevated but not significantly. Residual socioeconomic confounding may have contributed to elevations of LBW outcomes.

CONCLUSIONS

Maternal residence in both areas was associated with cardiac defects. Residence in the TCE area, but not the PCE area, was associated with LBW and fetal growth restriction.

Residential proximity to environmental hazards and adverse health outcomes

How living near environmental hazards contributes to poorer health and disproportionate health outcomes is an ongoing concern. We conducted a substantive review and critique of the literature regarding residential proximity to environmental hazards and adverse pregnancy outcomes, childhood cancer, cardiovascular and respiratory illnesses, end-stage renal disease, and diabetes. Several studies have found that living near hazardous wastes sites, industrial sites, cropland with pesticide applications, highly trafficked roads, nuclear power plants, and gas stations or repair shops is related to an increased risk of adverse health outcomes. Government agencies should consider these findings in establishing rules and permitting and enforcement procedures to reduce pollution from environmentally burdensome facilities and land uses.

Modeling geographic risk of complex congenital heart defects in Eastern Wisconsin

BACKGROUND

Geographic variation may be an indicator of risk factors for birth defects. This study models the geographic distribution of three complex congenital heart defects (CHDs) in eastern Wisconsin, and evaluates effects of demographic census variables linked to geographic location.

METHODS

Cases of Hypoplastic Left Heart Syndrome (HLHS), Tetralogy of Fallot (TOF) and d-Transposition of the Great Arteries (d-TGAs) born between1995 and 2004 were identified from three medical centers serving eastern Wisconsin. Case diagnoses were assigned by a pediatric cardiologist using echocardiographic records. Births by ZIP code were obtained from the State of Wisconsin. ZIP Code demographic variables were derived from 2000 census data. Numbers of cardiac defects by ZIP code were modeled using cluster analysis and Poisson generalized additive models (GAMs) for spatial coordinates including all and white only cases (excluding trisomies). GAM analyses were repeated adjusting for census variables.

RESULTS

Four hundred forty-eight cases were ascertained. A significant south-to-north spatial gradient for HLHS, TOF, and combined CHDs, but not d-TGAs was identified. This gradient remained significant when census variables were included in the model for the full sample. In the analysis excluding non-white cases, findings were the same for TOF, combined CHDs, and d-TGAs. However, the geographic gradient for HLHS was not significant in the adjusted model.

CONCLUSIONS

A south-to-north gradient was apparent for two of three complex CHDs in eastern Wisconsin. For white cases, demographic variation seems to explain some of this spatial gradient in HLHS. Further studies are needed to confirm demographic and other risk factors underlying this geographic gradient.

Ambient air pollution and congenital heart disease: a register-based study

Maternal exposure to ambient air pollution has increasingly been linked to adverse pregnancy outcomes. The evidence linking this exposure to congenital anomalies is still limited and controversial. This case-control study investigated the association between maternal exposure to ambient particulate matter with aerodynamic diameter less than 10 μm (PM(10)), sulfur dioxide (SO(2)), nitrogen dioxide, nitric oxide (NO), ozone (O(3)), and carbon monoxide (CO) and the occurrence of congenital heart disease in the population of Northeast England (1993-2003). Each case and control was assigned weekly average (weeks 3-8 of pregnancy) of pollutant levels measured by the closest monitor to the mother's residential postcode. Using exposure as both continuous and categorical variables, logistic regression models were constructed to quantify the adjusted odds ratios of exposure to air pollutants and the occurrence of each outcome group. We found exposure to CO and NO to be associated with ventricular septal defect and cardiac septa malformations. CO was also associated with congenital pulmonary valve stenosis and NO with pooled cases of congenital heart disease and tetralogy of Fallot. Findings for SO(2), O(3) and PM(10) were less consistent.

Association between maternal exposure to ambient air pollution and congenital heart disease: A register-based spatiotemporal analysis

Recent studies have linked maternal exposure to air pollution with a range of adverse pregnancy outcomes. However, the available evidence linking this exposure to congenital anomalies is still limited and controversial. The present case-control study tested the hypothesis that maternal exposure to ambient black smoke and sulfur dioxide is a risk factor for the occurrence of congenital heart disease. The authors used registry-based data on congenital heart disease for the population of the northeast of England in 1985-1996. A 2-stage spatiotemporal model was developed to predict weekly black smoke and sulfur dioxide levels at each maternal place of residence. Controls were frequency-matched to cases by year of birth (control-to-case ratio of 4:1). Two sets of analyses were performed, using predicted mean values of exposure and 1,000 simulated scenarios of exposure. The analyses were adjusted for birth year, socioeconomic status, infant sex, season of conception, and degree of urbanity. The authors found a weak association between maternal exposure to black smoke and congenital malformations of cardiac chambers and connections only when using exposure as a continuous variable. When the authors used quartiles of exposure, odds ratios did not show a dose-response relation for consecutive quartiles. For sulfur dioxide, the results were not indicative of any association.

Exposure to low-dose trichloroethylene alters shear stress gene expression and function in the developing chick heart

Trichloroethylene is an organic solvent used as an industrial degreasing agent. Due to its widespread use and volatile nature, TCE is a common environmental contaminant. Trichloroethylene exposure has been implicated in the etiology of heart defects in human populations and animal models. Recent data suggest misregulation of Ca2+ homeostasis in H9c2 cardiomyocyte cell line after TCE exposure. We hypothesized that misregulation of Ca2+ homeostasis alters myocyte function and leads to changes in embryonic blood flow. In turn, changes in cardiac flow are known to cause cardiac malformations. To investigate this hypothesis, we dosed developing chick embryos in ovo with environmentally relevant doses of TCE (8 and 800 ppb). RNA was isolated from control and treated embryos at specific times in development for real-time PCR analysis of blood flow markers. Effects were observed on Endothelin-1 (ET-1), Nitric Oxide Synthase-3 (NOS-3) and Krüppel-like Factor 2 (KLF2) expression relative to TCE exposure and consistent with reduced flow. Further, we measured function in the developing heart after TCE exposure by isolating cardiomyocytes and measuring half-width of contraction and sarcomere lengths. These functional data showed a significant increase in half-width of contraction after TCE exposure. These data suggest that perturbation of cardiac function contributes to the etiology of congenital heart defects in TCE-exposed embryos.

Altered cardiac function and ventricular septal defect in avian embryos exposed to low-dose trichloroethylene

Trichloroethylene (TCE) is the most frequently reported organic groundwater contaminant in the United States. It is controversial whether gestational TCE exposure causes congenital heart defects. The basis for TCE's proposed cardiac teratogenicity is not well understood. We previously showed that chick embryos exposed to 8 ppb TCE during cardiac morphogenesis have reduced cardiac output and increased mortality. To further investigate TCE's cardioteratogenic potential, we exposed in ovo chick embryos to TCE and evaluated the heart thereafter. Significant mortality was observed following TCE exposures of 8-400 ppb during a narrow developmental period (Hamburger-Hamilton [HH] stages 15-20, embryo day ED2.3-3.5) that is characterized by myocardial expansion, secondary heart looping, and endocardial cushion formation. Of the embryos that died, most did so between ED5.5 and ED6.5. Echocardiography of embryos at ED5.5 found that TCE-exposed hearts displayed significant functional and morphological heterogeneity affecting heart rate, left ventricular mass, and wall thickness. Individual embryos were identified with cardiac hypertrophy as well as with hypoplasia. Chick embryos exposed to 8 ppb TCE at HH17 that survived to hatch exhibited a high incidence (38%, p < 0.01, n = 16) of muscular ventricular septal defects (VSDs) as detected by echocardiography and confirmed by gross dissection; no VSDs were found in controls (n = 14). The TCE-induced VSDs may be secondary to functional impairments that alter cardiac hemodynamics and subsequent ventricular foramen closure, an interpretation consistent with recent demonstrations that TCE impairs calcium handling in cardiomyocytes. These data demonstrate that TCE is a cardiac teratogen for chick.

Maternal residential proximity to waste sites and industrial facilities and conotruncal heart defects in offspring

Most studies of the relationship between maternal residential proximity to sources of environmental pollution and congenital cardiovascular malformations have combined heart defects into one group or broad subgroups. The current case-control study examined whether risk of conotruncal heart defects, including subsets of specific defects, was associated with maternal residential proximity to hazardous waste sites and industrial facilities with recorded air emissions. Texas Birth Defects Registry cases were linked to their birth or fetal death certificate. Controls without birth defects were randomly selected from birth certificates. Distances from maternal addresses at delivery to National Priority List (NPL) waste sites, state superfund waste sites, and Toxic Release Inventory (TRI) facilities were determined for 1244 cases (89.5% of those eligible) and 4368 controls (88.0%). Living within 1 mile of a hazardous waste site was not associated with risk of conotruncal heart defects [adjusted odds ratio (aOR) = 0.83, 95% confidence interval (CI) = 0.54, 1.27]. This was true whether looking at most types of defects or waste sites. Only truncus arteriosus showed statistically elevated ORs with any waste site (crude OR: 2.80, 95% CI 1.19, 6.54) and with NPL sites (crude OR: 4.63, 95% CI 1.18, 13.15; aOR 4.99, 95% CI 1.26, 14.51), but the latter was based on only four exposed cases. There was minimal association between conotruncal heart defects and proximity to TRI facilities (aOR = 1.10, 95% CI = 0.91, 1.33). Stratification by maternal age or race/ethnic group made little difference in effect estimates for waste sites or industrial facilities. In this study population, maternal residential proximity to waste sites or industries with reported air emissions was not associated with conotruncal heart defects or its subtypes in offspring, with the exception of truncus arteriosus.

Getting to the heart of the matter: epidemiology of cyanotic heart defects

Congenital heart defects (CHDs) are the most common type of birth defect, making significant contributions to infant morbidity and mortality, but not all CHDs contribute equally to such outcomes. Although cyanotic CHDs constitute some of the most serious CHDs, its epidemiology is poorly understood. We present a comprehensive systematic review of the literature on the epidemiology of cyanotic CHD, with emphasis on the most current knowledge on identified risk/etiologic factors. Literature for this review was identified by searching the PubMed database from the National Center for Biotechnology Information at the US National Library of Medicine as well as bibliographies of identified papers. The 100 reports that contributed to this review describe risk factors such as infant sex, race, and ethnicity, environmental exposures, and maternal and paternal age. Several studies reported differences in prevalence rates by race and ethnicity and elevated sex ratios, and they identified some risk factors, including advanced maternal age. Investigators have made significant progress in the effort to describe the etiology of cyanotic CHDs, but discrepancies, such as the variation in prevalence rates by race and ethnicity and the impact of environmental exposures, still need to be addressed.

Residential proximity to waste sites and industrial facilities and chromosomal anomalies in offspring

A few studies have found chromosomal anomalies in offspring associated with a maternal residence near waste sites, but did not examine the effect of living near industrial facilities, and most combined specific anomalies into heterogeneous groups. With a case-control study design, we investigated whether maternal residential proximity to hazardous waste sites or industrial facilities with chemical air emissions was associated with chromosomal anomalies in births. Maternal residences of 2099 Texas births with chromosomal anomalies and 4368 control births without documented malformations were related to boundaries of hazardous waste sites and street addresses of industrial facilities through geographic information systems. With adjustment for maternal age, race/ethnicity, and education, maternal residence within 1mile of a hazardous waste site (relative to farther away) was not associated with chromosomal anomalies in offspring except for Klinefelter variants among Hispanic births (odds ratios (OR) 7.9, 95% confidence interval (CI) 1.1-42.4). Women 35 years or older who lived within 1mile of industries with emissions of heavy metals were two times more likely (95% CI 1.1-4.1) than women living farther away to have offspring with chromosomal anomalies including trisomies 13, 18, or 21 or sex chromosome abnormalities. Among women 40 years or older, maternal residence within a mile of industries with solvent emissions was associated with chromosomal anomalies in births (OR 4.8, 95% CI 1.2-42.8). Study findings suggest some relation between residential proximity to industries with emissions of solvents or heavy metals and chromosomal anomalies in births to older mothers.

Linking environmental hazards and birth defects data

The authors describe methods for linking birth certificate and birth defect registry data to potential environmental hazards and assess potential confounding factors. Cases of selected birth defects from the Texas Birth Defects Registry were linked to their respective birth/ fetal death records. Comparison births were randomly selected from the 1996-2000 Texas birth records. Maternal addresses were related through a geographic information system to boundaries of hazardous waste sites and point locations of industries. Approximately 89% of maternal addresses of case births and 88% of comparison births were successfully related in distance to these sites and industries. Maternal characteristics associated with living within one mile of these sites included belonging to any group besides non-Hispanic white and having lower education attainment (< 16 years) or a residence within the city limits. In linking environmental and health outcome databases, researchers should be aware of factors that may confound associations between exposure and outcomes.

Maternal residential proximity to waste sites and industrial facilities and oral clefts in offspring

OBJECTIVE

This study examined the association between oral clefts and maternal residential proximity to waste sites or industries.

METHODS

In a case-control study, maternal residences at birth of 1781 births with oral clefts and 4368 comparison births were related to locations of waste sites and industrial facilities in Texas through geographic information systems.

RESULTS

Compared with women who lived farther, women who lived within a mile of these sites or facilities were not more likely to have offspring with oral clefts. Among women > or =35 years, oral clefts in offspring were associated with living within a mile of industrial facilities (odds ratio [OR] = 2.4, 95% confidence interval [CI] = 1.3-4.2), especially smelters (OR = 15.0, 95% CI = 2.8-151).

CONCLUSION

These findings suggest that maternal residential proximity to industries might be associated with oral clefts in births to older mothers.

Trichloroethylene exposure during cardiac valvuloseptal morphogenesis alters cushion formation and cardiac hemodynamics in the avian embryo

It is controversial whether trichloroethylene (TCE) is a cardiac teratogen. We exposed chick embryos to 0, 0.4, 8, or 400 ppb TCE/egg during the period of cardiac valvuloseptal morphogenesis (2-3.3 days' incubation) . Embryo survival, valvuloseptal cellularity, and cardiac hemodynamics were evaluated at times thereafter. TCE at 8 and 400 ppb/egg reduced embryo survival to day 6.25 incubation by 40-50%. At day 4.25, increased proliferation and hypercellularity were observed within the atrioventricular and outflow tract primordia after 8 and 400 ppb TCE. Doppler ultrasound revealed that the dorsal aortic and atrioventricular blood flows were reduced by 23% and 30%, respectively, after exposure to 8 ppb TCE. Equimolar trichloroacetic acid (TCA) was more potent than TCE with respect to increasing mortality and causing valvuloseptal hypercellularity. These results independently confirm that TCE disrupts cardiac development of the chick embryo and identifies valvuloseptal development as a period of sensitivity. The hypercellular valvuloseptal profile is consistent with valvuloseptal heart defects associated with TCE exposure. This is the first report that TCA is a cardioteratogen for the chick and the first report that TCE exposure depresses cardiac function. Valvuloseptal hypercellularity may narrow the cardiac orifices, which reduces blood flow through the heart, thereby compromising cardiac output and contributing to increased mortality. The altered valvuloseptal formation and reduced hemodynamics seen here are consistent with such an outcome. Notably, these effects were observed at a TCE exposure (8 ppb) that is only slightly higher than the U.S. Environmental Protection Agency maximum containment level for drinking water (5 ppb) .

Trichloroethylene and dichloroethylene: a critical review of teratogenicity

Trichloroethylene (TCE) and dichloroethylene (DCE) are high-volume industrial chemicals frequently found as contaminants in public drinking water supplies. The developmental toxicity of both chemicals has been evaluated in laboratory and epidemiologic studies. It has been suggested that TCE and DCE are specific cardiac teratogens and that drinking water contaminated with them increases the risk of congenital heart defects in exposed human populations. In contrast, other laboratory and epidemiologic studies do not find an increase in developmental effects, either in general or specifically affecting the heart. This laboratory and epidemiologic base was reviewed to evaluate the strengths and weaknesses of the conflicting published reports. We conclude that the weight of experimental and epidemiologic evidence does not support the hypothesis that TCE or DCE is a selective developmental toxicant in general or a cardiac teratogen specifically.

Toward the etiologies of congenital heart diseases

Congenital heart disease remains a significant cause of morbidity and mortality. In recent years, significant advances in molecular genetics, improved understanding of morphogenesis, recognition of specific patterning of abnormalities within and between species, and the impact of the Human Genome Project have accounted for these advances. Continued rapid developments in genomics and proteomics are anticipated. Epidemiologic investigations continue to be necessary to assess the influence of the environment on genetics. We are on the threshold of influencing the occurrence of congenital heart diseases.

Trichloroethylene-contaminated drinking water and congenital heart defects: a critical analysis of the literature

The organic solvent trichloroethylene (TCE) is a metal degreasing agent and an intermediate in the production of fluorochemicals and polyvinyl chloride. TCE is also a common, persistent drinking water contaminant. Several epidemiological studies have alleged links between TCE exposure during pregnancy and offspring health problems including congenital heart defects (CHDs); however, the results of these studies are inconsistent, difficult to interpret, and involve several confounding factors. Similarly, the results of animal studies examining the potential of TCE to elicit cardiac anomalies have been inconsistent, and they have often been performed at doses far exceeding the highest levels ever reported in the drinking water. To determine what is known about the relationship between TCE and the incidence of CHDs, a comprehensive analysis of all available epidemiological data and animal studies was performed. Additionally, in vivo and in vitro studies examining possible mechanisms of action for TCE were evaluated. The specific types of heart defects alleged to have been caused by TCE in animal and human epidemiology studies were categorized by the morphogenetic process responsible for the defect in order to determine whether TCE might disrupt any specific developmental process. This analysis revealed that no single process was clearly affected by TCE, providing support that gestational TCE exposure does not increase the prevalence of CHDs. As a final evaluation, application of Hill's causality guidelines to the collective body of data revealed no indication of a causal link between gestational TCE exposure at environmentally relevant concentrations and CHDs.

Effects of trichloroethylene and its metabolite trichloroacetic acid on the expression of vimentin in the rat H9c2 cell line

Trichloroethylene (TCE) and its metabolite trichloroacetic acid (TCAA) are environmental contaminants with specific toxicity for the embryonic heart. In an effort to identify the cellular pathways disrupted by TCE and TCAA during heart development, we investigated their effects on expression of vimentin, a marker of cardiac differentiation. Previous studies had shown that the level of vimentin transcript was inhibited in rat embryonic heart after maternal exposure to TCE via drinking water. In the same study, maternal exposure to TCAA produced the opposite effect, inducing an increased level of vimentin mRNA. In this study, we selected an in vitro system, the rat cardiac myoblast cell line H9c2, to further characterize the molecular mechanisms used by TCE and TCAA to disrupt normal heart development. In particular, we investigated the effects of both toxicants on vimentin, at both the RNA and protein levels, using dose-response and time course curves. Our experimental findings indicate that vimentin expression is affected by TCE and TCAA in H9c2 cells similarly as in vivo. The work is significant because it provides a suitable in vitro model for studies looking at toxicant effects on myocardiac cells, and it suggests that vimentin is a good marker of TCE exposure in the embryonic heart.