Perinatal dioxin exposure and the neurodevelopment of Vietnamese toddlers at 1 year of age

Effects of exposure to 3,6-DBCZ on neurotoxicity and AhR pathway during early life stages of zebrafish (Danio rerio)

Polyhalogenated carbazoles (PHCZs) are emerging environmental pollutants, yet limited information is available on their embryotoxicity and neurotoxicity. Therefore, the current work was performed to investigate the adverse effects of 3,6-dibromocarbazole (3,6-DBCZ), a typical PHCZs homolog, on the early life stages of zebrafish larvae. It revealed that the 96-hour post-fertilization (hpf) median lethal concentration (LC50) value of 3,6-DBCZ in zebrafish larvae was determined to be 0.7988 mg/L. Besides, 3,6-DBCZ reduced survival rates at concentrations ≥ 1 mg/L and decreased hatching rates at ≥ 0.25 mg/L at 48 hpf. In behavior tests, it inhibited locomotor activities and reduced the frequency of recorded acceleration states in response to optesthesia (a sudden bright light stimulus) at concentrations ≥ 160 μg/L. Meanwhile, 3,6-DBCZ exposure decreased the frequency of recorded acceleration states in the startle response (tapping mode) at concentrations ≥ 6.4 μg/L. Pathologically, with the transgenic zebrafish model (hb9-eGFP), we observed a strikingly decreased axon length and number in motor neurons after 3,6-DBCZ treatment, which may be ascribed to the activation of the AhR signaling pathway, as evidenced by the molecular docking analysis and Microscale thermophoresis (MST) assay suggested that 3,6-DBCZ binding to AhR-ARNT2 compound proteins. Through interaction with AhR-ARNT, a striking reduction of the anti-oxidative stress (sod1/2, nqo1, nrf2) and neurodevelopment-related genes (elavl3, gfap, mbp, syn2a) were observed after 3,6-DBCZ challenge, accompanied by a marked increased inflammatory genes (TNFβ, IL1β, IL6). Collectively, our findings reveal a previously unrecognized adverse effect of 3,6-DBCZ on zebrafish neurodevelopment and locomotor behaviors, potentially mediated through the activation of the AhR pathway. Furthermore, it provides direct evidence for the toxic concentrations of 3,6-DBCZ and the potential target signaling in zebrafish larvae, which may be beneficial for the risk assessment of the aquatic ecosystems.

Impacts of perinatal dioxin exposure on gaze behavior in 2-year-old children in the largest dioxin-contaminated area in Vietnam

Fifty-five children aged 2 years from a birth cohort in the largest dioxin-contaminated area in Bien Hoa city, Vietnam participated in this survey to examine gaze behavior. Exposure levels were indicated by 2,3,7,8-tetrachlorodibenzo-p-dibenzodioxin (TCDD) and toxic equivalent of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (TEQ-PCDD/Fs) levels in maternal breast milk. The percentage of the total fixation duration on the face (% Face), mouth (% Mouth), and eye areas (% Eyes) when viewing silent and conversation scenes was used as gaze behavior indices. When they reached 3-year-old, autistic behavior was assessed using the Autism Spectrum Rating Scale (ASRS). A general linear model adjusted for confounding factors was used to compare gaze indices and ASRS scores between high and low dioxin exposure groups. Effects of perinatal dioxin exposure on gaze behavior were found only when viewing conversation scenes indicated by lower % Face for boys in high TCDD exposure group and lower % Eyes for girls in high TEQ-PCDD/Fs group. Increased autistic traits showed by higher ASRS scores at 3-year-old were found in both gender in the high TCDD exposure group. These findings indicate that perinatal TCDD and TEQ-PCDD/Fs exposure may reduce gaze behavior in 2-year-old children, predicting increased autistic traits at 3-year-old.

Neurodevelopmental Effects of Perinatal TCDD Exposure Differ from Those of Other PCDD/Fs in Vietnamese Children Living near the Former US Air Base in Da Nang, Vietnam

This study reports that children exposed to 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD), the major toxin in Agent Orange, from the breast milk of mothers residing near the former Da Nang US air base in Vietnam may have specific alterations in higher brain functions, resulting in social and communication deficits, including autism spectrum disorder (ASD). After the age of 8 years, girls with high TCDD showed increased attention deficit hyperactivity disorder (ADHD)-like behaviors and altered mirror neuron activity, which is often observed in children with ASD. However, no significant relationship between autistic traits and toxic equivalency values of polychlorinated dibenzodioxins and polychlorinated dibenzofurans (TEQ-PCDD/Fs) was found in these children. Notably, boys with high levels of TEQ-PCDD/Fs showed poor language and motor development in the first 3 years of life, although boys with high TCDD levels did not. However, at 8 years of age, boys with high TCDD showed reading learning difficulties, a neurodevelopmental disorder. These findings suggest that perinatal TCDD exposure impacts social-emotional cognitive functions, leading to sex-specific neurodevelopmental disorders-learning difficulty in boys and ADHD in girls. Future studies with a greater number of children exposed to high levels of TCDD are necessary to estimate the threshold values for neurodevelopmental effects.

Proper modulation of AHR signaling is necessary for establishing neural connectivity and oligodendrocyte precursor cell development in the embryonic zebrafish brain

2,3,7,8-tetrachlorodibenzo-[p]-dioxin (TCDD) is a persistent global pollutant that exhibits a high affinity for the aryl hydrocarbon receptor (AHR), a ligand activated transcription factor. Epidemiological studies have associated AHR agonist exposure with multiple human neuropathologies. Consistent with the human data, research studies using laboratory models have linked pollutant-induced AHR activation to disruptions in learning and memory as well as motor impairments. Our understanding of endogenous AHR functions in brain development is limited and, correspondingly, scientists are still determining which cell types and brain regions are sensitive to AHR modulation. To identify novel phenotypes resulting from pollutant-induced AHR activation and ahr2 loss of function, we utilized the optically transparent zebrafish model. Early embryonic TCDD exposure impaired embryonic brain morphogenesis, resulted in ventriculomegaly, and disrupted neural connectivity in the optic tectum, habenula, cerebellum, and olfactory bulb. Altered neural network formation was accompanied by reduced expression of synaptic vesicle 2. Loss of ahr2 function also impaired nascent network development, but did not affect gross brain or ventricular morphology. To determine whether neural AHR activation was sufficient to disrupt connectivity, we used the Gal4/UAS system to express a constitutively active AHR specifically in differentiated neurons and observed disruptions only in the cerebellum; thus, suggesting that the phenotypes resulting from global AHR activation likely involve multiple cell types. Consistent with this hypothesis, we found that TCDD exposure reduced the number of oligodendrocyte precursor cells and their derivatives. Together, our findings indicate that proper modulation of AHR signaling is necessary for the growth and maturation of the embryonic zebrafish brain.

Adverse effects of dioxins on cognitive ability and motor performance of 5-year-old children residing in a hotspot of dioxin contamination originating from Agent Orange in Vietnam: A prospective cohort study

Bien Hoa airbase is the most dioxin-polluted hotspot in Vietnam. In 2012, a birth cohort living around Bien Hoa airbase was recruited for assessment of physical and neurological development. In the present study, neurodevelopment scores at 5 years of age were assessed by the Kaufman Assessment Battery for Children, Second Edition and the Movement Assessment Battery for Children, Second Edition for 185 children in Bien Hoa and 104 children in Ha Dong (unexposed control group) to clarify the effects of dioxin. 2,3,7,8-tetrachlorodibenzo-p-dioxin concentrations in breast milk of women in Bien Hoa were approximately three times higher than those of women in Ha Dong (2.33 vs. 0.69 pg/g fat, p < 0.001). In general, neurodevelopment scores were lower in Bien Hoa children than in Ha Dong children. In boys, scores differed for number recall (12.6 vs. 14.0, p = 0.036), triangles (10.7 vs. 12.4, p = 0.005), manual dexterity (8.3 vs. 9.7, p = 0.037), balance (7.4 vs. 10.3, p < 0.001), and total movement scores (8.0 vs. 10.1, p = 0.003). After adjusting for covariates, linear regression analysis indicated that the scores of the triangles, balance, and total movement tests were inversely associated with levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin and of toxic equivalency of polychlorinated dibenzodioxins and polychlorinated dibenzofurans. In girls, scores differed for the triangles test (11.0 vs. 12.6, p = 0.005), hand movement test (9.6 vs. 11.3, p = 0.003), and balance test (9.1 vs. 10.7, p = 0.050); toxic equivalency of polychlorinated dibenzofurans was inversely associated with hand movement and balance scores. Overall, perinatal dioxin exposure appears to have a long-term impact on neurodevelopment.

The associations of prenatal exposure to dioxins and polychlorinated biphenyls with neurodevelopment at 6 Months of age: Multi-pollutant approaches

BACKGROUND

Prenatal exposure to persistent organic pollutants, including polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), dioxin-like polychlorinated biphenyls (DL-PCBs), and nondioxin-like PCBs (NDL-PCBs), has been hypothesized to have a detrimental impact on neurodevelopment. However, the association of prenatal exposure to a dioxin and PCB mixture with neurodevelopment remains largely inconclusive partly because these chemical levels are correlated.

OBJECTIVES

We aimed to elucidate the association of in utero exposure to a mixture of dioxins and PCBs with neurodevelopment measured at 6 months of age by applying multipollutant methods.

METHODS

A total of 514 pregnant women were recruited between July 2002 and October 2005 in the Sapporo cohort, Hokkaido Study on Environment and Children's Health. The concentrations of individual dioxin and PCB isomers were assessed in maternal peripheral blood during pregnancy. The mental and psychomotor development of the study participants' infants was evaluated using the Bayley Scales of Infant Development-2nd Edition (n = 259). To determine both the joint and individual associations of prenatal exposure to a dioxin and PCB mixture with infant neurodevelopment, Bayesian kernel machine regression (BKMR) and quantile-based g-computation were employed.

RESULTS

Suggestive inverse associations were observed between in utero exposure to a dioxin and PCB mixture and infant psychomotor development in both the BKMR and quantile g-computation models. In contrast, we found no association of a dioxin and PCB mixture with mental development. When group-specific posterior inclusion probabilities were estimated, BKMR suggested prenatal exposure to mono-ortho PCBs as the more important contributing factors to early psychomotor development compared with the other dioxin or PCB groups. No evidence of nonlinear exposure-outcome relationships or interactions among the chemical mixtures was detected.

CONCLUSIONS

Applying the two complementary statistical methods for chemical mixture analysis, we demonstrated limited evidence of inverse associations of prenatal exposure to dioxins and PCBs with infant psychomotor development.

Perinatal Dioxin Exposure and Attention Deficit Hyperactivity Disorder (ADHD) Symptoms in Children Living in a Dioxin Contamination Hotspot in Vietnam

We examined children in Da Nang, a dioxin contamination hotspot in Vietnam, twice at 5 and 8 years of age, and investigated sex- and age-dependent differences in the effects of dioxin exposure on attention deficit hyperactivity disorder (ADHD) symptoms. We also studied autistic traits in children with ADHD symptoms. A total of 163 children participated in follow-up surveys at 5 and 8 years of age and were included in the present analysis. ADHD symptoms were assessed using an ADHD rating scale with inattention and hyperactivity-and-impulsivity (hyperactivity) subscales. Autistic behaviors were evaluated using the Autism Spectrum Rating Scale (ASRS). Perinatal dioxin exposure was indicated by dioxin levels in maternal breast milk. In boys, hyperactivity scores were significantly higher in the high 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) group only at 5 years of age. In girls, hyperactivity scores at 8 years of age were significantly higher in the high TCDD group, which was significantly associated with those at 5 years of age. In girls, ASRS unusual behavior scores were significantly higher with higher TCDD exposure and hyperactivity scores at 8 years of age. These results suggest that high perinatal TCDD exposure may increase ADHD likelihood and autistic traits, particularly in girls of 7–8 years of age.

Effects of perinatal dioxin exposure on mirror neuron activity in 9-year-old children living in a hot spot of dioxin contamination in Vietnam

BACKGROUND

For 8 years, we have followed up a birth cohort comprising 241 mother-and-infant pairs living around the Da Nang airbase, a hot spot of dioxin contamination in Vietnam, and have reported the impacts of perinatal dioxin exposure on the neurodevelopment of children at various ages. In the present study, 9 years after birth, we investigated the effects of perinatal dioxin exposure on mu and theta rhythms by analyzing EEG power during the execution and observation of hand movements, which indicate mirror neuron system activity.

METHODS

One hundred fifty-five 9-year-old children (86 boys and 69 girls) from the Da Nang birth cohort participated in the EEG examination with free viewing of hand movements. The dioxin levels in their mothers' breast milk, measured 1 month after birth, were used as perinatal dioxin exposure markers. A log transform of the ratio of EEG power during execution or observation of the hand movements relative to the power during observation of a bouncing ball for theta and mu rhythms was used to evaluate mirror neuron activity.

RESULTS

In both brain hemispheres, the log power ratio in the theta band was significantly higher (i.e., less reduction of power) during observation of hand movements in girls exposed to high levels of TCDD. In boys, however, dioxin congeners other than TCDD, including HxCDDs and several PCDF congeners, contributed to increased log power ratios in the theta band. Particularly for PCDF congeners, the log power ratios in the lowest group among 4 exposure groups were lowest and significantly increased (i.e., decreasing reduction of power) with increasing dose.

CONCLUSION

Perinatal TCDD exposure may influence the mirror neuron system of the brain, which plays an important role for social-emotional behavior in children, particularly in girls living in a hot spot of dioxin contamination in Vietnam.

Effects of Low-Dose Gestational TCDD Exposure on Behavior and on Hippocampal Neuron Morphology and Gene Expression in Mice

BACKGROUND

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a persistent and toxic environmental pollutant. Gestational exposure to TCDD has been linked to cognitive and motor deficits, and increased incidence of autism spectrum disorder (ASD) traits in children. Most animal studies of these neurodevelopmental effects involve acute TCDD exposure, which does not model typical exposure in humans.

OBJECTIVES

The aim of the study was to establish a dietary low-dose gestational TCDD exposure protocol and performed an initial characterization of the effects on offspring behavior, neurodevelopmental phenotypes, and gene expression.

METHODS

Throughout gestation, pregnant C57BL/6J mice were fed a diet containing a low dose of TCDD (9  ng TCDD/kg body weight per day) or a control diet. The offspring were tested in a battery of behavioral tests, and structural brain alterations were investigated by magnetic resonance imaging. The dendritic morphology of pyramidal neurons in the hippocampal Cornu Ammonis (CA)1 area was analyzed. RNA sequencing was performed on hippocampi of postnatal day 14 TCDD-exposed and control offspring.

RESULTS

TCDD-exposed females displayed subtle deficits in motor coordination and reversal learning. Volumetric difference between diet groups were observed in regions of the hippocampal formation, mammillary bodies, and cerebellum, alongside higher dendritic arborization of pyramidal neurons in the hippocampal CA1 region of TCDD-exposed females. RNA-seq analysis identified 405 differentially expressed genes in the hippocampus, enriched for genes with functions in regulation of microtubules, axon guidance, extracellular matrix, and genes regulated by SMAD3.

DISCUSSION

Exposure to 9  ng TCDD/kg body weight per day throughout gestation was sufficient to cause specific behavioral and structural brain phenotypes in offspring. Our data suggest that alterations in SMAD3-regulated microtubule polymerization in the developing postnatal hippocampus may lead to an abnormal morphology of neuronal dendrites that persists into adulthood. These findings show that environmental low-dose gestational exposure to TCDD can have significant, long-term impacts on brain development and function. https://doi.org/10.1289/EHP7352.

Nutritional Intervention with Dried Bonito Broth for the Amelioration of Aggressive Behaviors in Children with Prenatal Exposure to Dioxins in Vietnam: A Pilot Study

Dioxins have been suggested to induce inflammation in the intestine and brain and to induce neurodevelopmental disorders such as autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD), partly due to deficits in parvalbumin-positive neurons in the brain that are sensitive to inflammatory stress. Previously, we reported ADHD traits with increased aggressiveness in children with prenatal exposure to dioxins in Vietnam, whereas dried bonito broth (DBB) has been reported to suppress inflammation and inhibit aggressive behavior in animal and human studies. In the present study, we investigated the association between dioxin exposure and the prevalence of children with highly aggressive behaviors (Study 1), as well as the effects of DBB on the prevalence of children with highly aggressive behaviors (Study 2). Methods: In Study 1, we investigated the effects of dioxin exposure on the prevalence of children with high aggression scores, which were assessed using the Children’s Scale of Hostility and Aggression: Reactive/Proactive (C-SHARP) in dioxin-contaminated areas. The data were analyzed using a logistic regression model after adjusting for confounding factors. In Study 2, we performed nutritional intervention by administering DBB for 60 days to ameliorate the aggressiveness of children with high scores on the C-SHARP aggression scale. The effects of DBB were assessed by comparing the prevalence of children with high C-SHARP scores between the pre- and post-intervention examinations. Results: In Study 1, only the prevalence of children with high covert aggression was significantly increased with an increase in dioxin exposure. In Study 2, in the full ingestion (>80% of goal ingestion volume) group, the prevalence of children with high covert aggression associated with dioxin exposure was significantly lower in the post-ingestion examination compared with in the pre-ingestion examination. However, in other ingestion (<20% and 20–79%) groups and a reference (no intervention) group, no difference in the prevalence of children with high covert aggression was found between the examinations before and after the same experimental period. Conclusions: The findings suggest that DBB ingestion may ameliorate children’s aggressive behavior, which is associated with perinatal dioxin exposure.

Gestational and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin in mice: Neurobehavioral effects on female offspring

Emerging evidence suggests that perinatal dioxin exposure affects neurodevelopment and impairs multiple brain functions, including cognitive, language, learning and emotion, in the offspring. However, the impacts of gestational and lactational exposure to dioxin on behavior and related molecular events are still not fully understood. In this study, female C57BL/6J mice were orally administered three doses of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) (0.1 or 10 μg/kg body weight (bw)) during the pregnancy and lactation periods. The locomotion, exploration and anxiety-related behaviors were examined by an open field test of the young adult female offspring at postnatal day 68. We found that the maternal TCDD exposure, particularly at a low dose, increased movement ability, novelty-exploration and certain anxiety-related behaviors in the offspring. Such hyperactivity-like behaviors were accompanied by the upregulation of certain genes associated with cholinergic neurotransmission or synaptogenesis in the offspring brain. In accordance with the potential enhancement of cholinergic neurotransmission due to the gene upregulations, the enzymatic activity of acetylcholinesterase was decreased, which might lead to excess acetylcholine and consequent hyper-excitation at the synapses. Thus, we found that gestational and lactational TCDD exposure at low dose caused hyperactivity-like behaviors in young adult female offspring and speculated the enhancement of cholinergic neurotransmission and synaptogenesis as potential molecular events underlying the neurobehavioral effects.

Dioxin exposure and sexual dimorphism of gaze behavior in prepubertal Vietnamese children living in Da Nang, a hot spot for dioxin contamination

Previous studies have reported that dioxin exposure alters sexual dimorphism of play behavior in pre-pubertal children. We aimed to investigate the effects of perinatal dioxin exposure, indicated by dioxins in breast milk, on sexual dimorphism of gaze behavior after adjusting for salivary testosterone (T). Participants were pre-pubertal children in a hot spot for dioxin contamination originating from herbicide spraying in Vietnam. We used eye tracking to assess gaze behavior in 172 children (100 boys and 72 girls) aged 8-9 years. Two sets of 15 pairs of pictures, one oriented towards boys and one oriented towards girls, containing 5 pairs of toy photos (non-biological stimuli) and 10 pairs of human line drawings (biological stimuli) were shown to all children. The total fixation duration for each picture was extracted using Tobii studio software and a feminine index of gaze behavior was defined as the ratio of the summed fixation duration for the girl- vs boy-oriented versions of each stimuli. When viewing non-biological stimuli, feminine index scores significantly increased with TCDD (β = 0.294) in girls only. For biological stimuli, however, feminine index scores significantly increased with TEQ-PCDD/Fs (β = 0.269) in boys and with TCDD in girls (β = 0.286). These associations were significant even after adjusting for salivary T levels, which were inversely associated with some dioxin congeners in girls. In addition, increased feminine index scores for biological stimuli were associated with lower cognitive scores for hand-movement and word-order tests in boys and for face-recognition tests in girls examined at 5 years of age. In conclusion, these results suggest that perinatal dioxin exposure may increase visual interest in girl-oriented objects through impairment of cognitive abilities in pre-pubertal Vietnamese children. PCDD congeners were associated with gaze behavior independently of T levels in boys, while this was only the case for TCDD levels in girls.

Severe dioxin-like compound (DLC) contamination in e-waste recycling areas: An under-recognized threat to local health

Electrical and electronic waste (e-waste) burning and recycling activities have become one of the main emission sources of dioxin-like compounds (DLCs). Workers involved in e-waste recycling operations and residents living near e-waste recycling sites (EWRS) are exposed to high levels of DLCs. Epidemiological and experimental in vivo studies have reported a range of interconnected responses in multiple systems with DLC exposure. However, due to the compositional complexity of DLCs and difficulties in assessing mixture effects of the complex mixture of e-waste-related contaminants, there are few studies concerning human health outcomes related to DLC exposure at informal EWRS. In this paper, we have reviewed the environmental levels and body burdens of DLCs at EWRS and compared them with the levels reported to be associated with observable adverse effects to assess the health risks of DLC exposure at EWRS. In general, DLC concentrations at EWRS of many countries have been decreasing in recent years due to stricter regulations on e-waste recycling activities, but the contamination status is still severe. Comparison with available data from industrial sites and well-known highly DLC contaminated areas shows that high levels of DLCs derived from crude e-waste recycling processes lead to elevated body burdens. The DLC levels in human blood and breast milk at EWRS are higher than those reported in some epidemiological studies that are related to various health impacts. The estimated total daily intakes of DLCs for people in EWRS far exceed the WHO recommended total daily intake limit. It can be inferred that people living in EWRS with high DLC contamination have higher health risks. Therefore, more well-designed epidemiological studies are urgently needed to focus on the health effects of DLC pollution in EWRS. Continuous monitoring of the temporal trends of DLC levels in EWRS after actions is of highest importance.

Perinatal dioxin exposure and neurodevelopment of 2-year-old Vietnamese children in the most contaminated area from Agent Orange in Vietnam

Bien Hoa airbase is the most contaminated area of dioxin contamination from Agent Orange in Vietnam, but little is known about the neurodevelopmental effects of perinatal dioxin exposure on children living nearby. We recruited 210 mother-newborn resident pairs in 2012 and 78 pairs in 2015 and followed them for 2 years to assess the children's neurodevelopment. As a control group, we used 120 mother-child pairs recruited in 2014 in the Ha Dong district of Ha Noi City, an unexposed area. Perinatal dioxin exposure levels were indicated by levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and toxic equivalency values of polychlorodibenzodioxins, polychlorodibenzofurans, and nonortho-polychlorinated biphenyls (TEQ-PCDD/Fs/noPCBs) in maternal breast milk. The Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III) were used to assess neurodevelopment, and scores in each domain were compared between children with different exposure levels using general linear regression models and stratification by sex. Decreased expressive and composite language scores in boys and gross motor scores in girls were found in children exposed to TCDD ≥ 5.5 (pg/g lipid) compared with children with TCDD < 1.8. However, in matched pair analysis between children with TCDD ≥ 5.5 and <1.8 (pg/g lipid), lower expressive and composite language scores in boys exposed to TCDD ≥ 5.5 were significant, but lower gross motor scores in girls did not reach statistical significance. In addition, significant association was found between levels of PCDD congeners other than TCDD and gross motor scores in boys. These findings suggest that perinatal exposure of TCDD and other PCDD congeners affects development of language and gross motor skills, respectively, in boys at 2 years of age exposed to dioxins originating from Agent Orange in Vietnam.

Adverse effects of maternal dioxin exposure on fetal brain development before birth assessed by neonatal electroencephalography (EEG) leading to poor neurodevelopment; a 2-year follow-up study

We previously reported the adverse effects of perinatal dioxin exposure on child neurodevelopment around a former US military airbase in Vietnam. In the present study, we investigated the effects of maternal dioxin exposure on fetal brain development, which may predict neurodevelopmental outcomes in early childhood. A total of 55 newborns with mothers from dioxin-contaminated areas were recruited in the prefecture hospital in Bien Hoa, Vietnam. Dioxins in maternal breast milk collected 1 month after birth were used as a maternal exposure marker. Relative powers and coherence were computed from neonatal electroencephalogram (EEG) records during active sleep stages. Relationships between the EEG parameters and dioxin exposure markers were analyzed using linear regression and a general linear model after adjusting for gestational age, body length, and head circumference of infants at birth. Using data from 47 infants whose neurodevelopment was examined in a 2-year follow-up study, associations between EEG parameters and neurodevelopment were analyzed after adjusting for confounding factors. On the right frontal and parietal regions, relative delta powers were significantly decreased, and relative alpha and beta powers were significantly increased with increasing dioxin exposure. Increases in delta power and decreases in alpha power on the right frontal and parietal regions were associated with an increase in language scores at 2 years of age. Furthermore, intra- and inter-hemispheric coherence in theta and alpha bands were positively and inversely correlated with dioxin exposure, respectively, and increased intra-coherence in the right hemisphere was associated with lower language scores. These findings suggest that prenatal dioxin exposure affects neuronal activity and functional connectivity between brain regions, and may lead to poor language development.

Prenatal dioxin exposure and neuropsychological functioning in the Seveso Second Generation Health Study

BACKGROUND

Prenatal 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure has been shown to alter sexual differentiation of the brain in animal models, impacting pubertal development, behavior, cortical dominance, and cognition. The effects of early life exposure to dioxin-like compounds on human neurodevelopment, however, are less clear and warrant further investigation.

METHODS

The Seveso Women's Health Study (SWHS), initiated in 1996, is a well-characterized cohort of 981 Italian women who lived in proximity to an industrial accident in July 1976 that resulted in one of the highest residential TCDD exposures on record. In 2014-2016, we enrolled offspring born after the accident into the Seveso Second Generation Health Study. Children aged 7-17 years old (n = 161) completed a neuropsychological assessment spanning executive function and reverse learning (Wisconsin Card Sort), non-verbal intelligence (Raven's Progressive Matrices), attention and hyperactivity (Connor's Continuous Performance (CPT), and memory (Rey's Auditory Verbal Learning). We used multivariate regression with robust standard error estimates accounting for clustering of siblings to model the associations between these outcomes and prenatal exposure defined as TCDD measured in maternal serum collected soon after the explosion and estimated to pregnancy.

RESULTS

The children (82 male, 79 female) averaged 13.1 (±2.9) years of age. Adjusting for covariates, a 10-fold increase in maternal serum TCDD was not adversely associated with reverse learning/set-shifting, memory, attention/impulsivity, or non-verbal intelligence. In sex-stratified models, prenatal TCDD was associated with more non-perseverative errors in boys but not in girls (p_int = 0.04). TCDD was also associated with attention deficits on the CPT but only among children with the shortest breastfeeding histories.

CONCLUSIONS

While overall, there were no significant associations, the observed differential neurotoxic sensitivities to TCDD by sex and lactation history may warrant confirmation in future studies.

Dioxins as potential risk factors for autism spectrum disorder

Autism spectrum disorder (ASD) has emerged as a major public health concern due to its fast-growing prevalence in recent decades. Environmental factors are thought to contribute substantially to the variance in ASD. Interest in environmental toxins as causes of ASD has arisen due to the high sensitivity of the developing human brain to toxic chemicals, particularly to dioxin and certain dioxin-like compounds (dioxins). As a group of typical persistent organic pollutants, dioxins have been found to exert adverse effects on human brain development. In this paper, we review the evidence for association of exposure to dioxins with neurodevelopmental abnormalities related to ASD based on both human epidemiological and animal studies. It has been documented that exposure to dioxins during critical developmental periods increased risk for ASD. This notion has been demonstrated in different populations exposed to high or background level of dioxins. Furthermore, the effects and mechanisms of action of dioxins relevant to the pathophysiology and pathogenesis of ASD are summarized, describing potential underlying mechanisms linking dioxin exposure with ASD onset. Further studies focusing on effects of prenatal/perinatal exposure to individual dioxin congeners or to mixtures of dioxins on ASD-associated behavioral and neurobiological consequences in animal models, and on the mechanisms of actions of dioxins, are needed in order to better understand how dioxin exposure might contribute to increased risk for ASD.

Infant Dietary Exposures to Environmental Chemicals and Infant/Child Health: A Critical Assessment of the Literature

BACKGROUND

The benefits of breastfeeding to the infant and mother have been well documented. It is also well known that breast milk contains environmental chemicals, and numerous epidemiological studies have explored relationships between background levels of chemicals in breast milk and health outcomes in infants and children.

OBJECTIVES

In this paper, we examine epidemiological literature to address the following question: Are infant exposures to background levels of environmental chemicals in breast milk and formula associated with adverse health effects? We critically review this literature a) to explore whether exposure-outcome associations are observed across studies, and b) to assess the literature quality.

METHODS

We reviewed literature identified from electronic literature searches. We explored whether exposure-outcome associations are observed across studies by assessing the quality (using a modified version of a previously published quality assessment tool), consistency, and strengths and weaknesses in the literature. The epidemiological literature included cohorts from several countries and examined infants/children either once or multiple times over weeks to years. Health outcomes included four broad categories: growth and maturation, morbidity, biomarkers, and neurodevelopment.

RESULTS

The available literature does not provide conclusive evidence of consistent or clinically relevant health consequences to infants exposed to environmental chemicals in breast milk at background levels.

CONCLUSIONS

It is clear that more research would better inform our understanding of the potential for health impacts from infant dietary exposures to environmental chemicals. A critical data gap is a lack of research on environmental chemicals in formula and infant/child health outcomes. https://doi.org/10.1289/EHP1954.

Sex-specific effects of perinatal dioxin exposure on eating behavior in 3-year-old Vietnamese children

Background

We previously reported that perinatal dioxin exposure increased autistic traits in children living in dioxin-contaminated areas of Vietnam. In the present study, we investigated the impact of dioxin exposure on children’s eating behavior, which is often altered in those with developmental disorders.

Methods

A total of 185 mother-and-child pairs previously enrolled in a birth cohort in dioxin-contaminated areas participated in this survey, conducted when the children reached 3 years of age. Perinatal dioxin exposure levels in the children were estimated using dioxin levels in maternal breast milk after birth. Mothers were interviewed using the Children’s Eating Behaviour Questionnaire (CEBQ). A multiple linear regression model was used to analyze the association between dioxin exposure and CEBQ scores, after controlling for covariates such as location, parity, maternal age, maternal education, maternal body mass index, family income, children’s gestational age at delivery, and children’s age at the time of the survey. A general linear model was used to analyze the effects of sex and dioxin exposure on CEBQ scores.

Results

There was no significant association between most dioxin congeners or toxic equivalencies of polychlorinated dibenzo-p-dioxins/furans (TEQ-PCDDs/Fs) and CEBQ scores in boys, although significant associations between some eating behavior sub-scores and 1,2,3,4,6,7,8,9-octachlorodibenzofuran were observed. In girls, there was a significant inverse association between levels of TEQ-PCDFs and enjoyment of food scores and between levels of TEQ-PCDFs and TEQ-PCDDs/Fs and desire to drink scores. Two pentachlorodibenzofuran congeners and 1,2,3,6,7,8-hexachlorodibenzofuran were associated with a decreased enjoyment of food score, and seven PCDF congeners were associated with a decreased desire to drink score. The adjusted mean enjoyment of food score was significantly lower in children of both sexes exposed to high levels of TEQ-PCDFs. There was, however, a significant interaction between sex and TEQ-PCDF exposure in their effect on desire to drink scores, especially in girls.

Conclusions

Perinatal exposure to dioxin can influence eating behavior in children and particularly in girls. A longer follow-up study would be required to assess whether emotional development that affects eating styles and behaviors is related to dioxin exposure.

Electronic supplementary material

The online version of this article (10.1186/s12887-018-1171-2) contains supplementary material, which is available to authorized users.

Association of dioxin exposure and reproductive hormone levels in men living near the Bien Hoa airbase, Vietnam

Dioxins are endocrine-disrupting chemicals, and their effects on reproductive functions are well-documented. The aim of the present study was to measure the levels of reproductive hormones in 42 men residing near a dioxin-contaminated area in Vietnam. We measured levels of 17 2,3,7,8-substituted congeners of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) and four non-ortho polychlorinated biphenyls (PCBs) in blood. Levels of follicle-stimulating hormone, luteinizing hormone, progesterone, prolactin, estradiol, and total testosterone were measured in serum. Blood dioxin levels were elevated; the levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin was 7.3pg/g fat. Seven of the men had testosterone levels below 250ng/dL, and nine men had prolactin levels above 9.7ng/mL. Four PCDD congeners, two PCDF congeners, one PCB congener, and the sum TEQ of PCDDs, PCDDs/Fs, and PCDDs/Fs/PCBs were positively and significantly correlated with prolactin levels. Two PCDD congeners, six PCDF congeners, two PCB congeners, and the TEQs of PCDFs and PCBs were negatively and significantly correlated with testosterone levels. There were no significant correlations between dioxin congeners and follicle-stimulating hormone, luteinizing hormone, or progesterone levels.

Prenatal dioxin exposure estimated from dioxins in breast milk and sex hormone levels in umbilical cord blood in Vietnamese newborn infants

Dioxin concentrations remain elevated in the environment and humans residing near the former US Air Force base in Bien Hoa city, South Vietnam. We recruited 210 mother-infant pairs for whom breast milk dioxin levels were reported in our previous study. Cord blood samples were collected from 162 mother-infant pairs. We selected 16 cord blood samples with a volume over 20mL and fat content of ≥0.03g. Toxic equivalent levels of polychlorinated dibenzodioxins and polychlorinated dibenzofurans (TEQ-PCDD/Fs) and concentrations of 17 congeners, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), in cord blood were measured and compared with levels in breast milk (Study 1). Levels of 2,3,7,8-TCDD and TEQ-PCDD/Fs in cord blood samples were highly and significantly correlated with those in breast milk samples in the same pairs. This suggests dioxins in breast milk reflect prenatal dioxin exposure. Estradiol (E2) and testosterone (TS) were measured in cord blood serum from 162 samples. Associations between dioxins in breast milk and cord blood sex hormones were analyzed by infant sex, after adjusting for confounding factors (Study 2). Increased levels of TEQ-PCDD/Fs in breast milk were associated with decreased cord blood TS in girls. In boys, a significant reduction of cord blood TS was observed in those exposed to 2,3,7,8-TCDD at high levels (≥5.5pg/g lipid). There was no significant association between E2 and dioxins in breast milk in either sex. These results suggest increased prenatal dioxin exposure is associated with decreased cord TS, but in boys, only high level of 2,3,7,8-TCDD influence cord blood TS.

A relationship in adrenal androgen levels between mothers and their children from a dioxin-exposed region in Vietnam

Over the past decades, southern Vietnam has been burdened by dioxins from contaminated herbicides sprayed during the Vietnam War. In a previous study, we found that dioxin exposure decreased levels of salivary dehydroepiandrosterone (DHEA), an adrenal androgen, in 3-year-old children. In present study, to assess the relationship between adrenal hormones disruption in lactating mothers and in children, we compared mother-child pairs from dioxin- and nondioxin-contaminated regions. In 2010 and 2011, mother-child pairs from a dioxin hotspot region (n=37) and a non-contaminated region (n=47) were recruited and donated breast milk and serum samples for dioxin and steroid hormones determination. Mothers were 20-30years old and had given birth to their first child between 4 and 16weeks previously. One year later, saliva samples were collected from the children. Dioxin levels in breast milk were determined by gas chromatography/high-resolution mass spectrometry. Salivary DHEA, cortisol in children and androstenedione (A-dione), estradiol, cortisol, and DHEA in maternal serum were analyzed by liquid chromatography/tandem mass spectrometry. Concentrations of dioxin congeners in the hotspot region were 2- to 5-fold higher than in samples from the non-contaminated region. Salivary DHEA levels in children and serum A-dione levels in mothers were significantly higher in the hotspot region; no difference was found in the levels of other hormones. Moreover, there was a significant positive correlation between the elevated hormone levels in mothers and children (r=0.62, p<0.001). Several dioxin congeners exhibited strong significant dose-response relationships with salivary DHEA and serum A-dione levels. Our findings suggest that dioxin disrupts adrenal androgens in mothers and breastfeeding children through the same mechanism.

Effects of Perinatal Dioxin Exposure on Development of Children during the First 3 Years of Life

OBJECTIVE

To investigate the longitudinal effects of perinatal exposure to dioxin on neurodevelopment and physical growth of a birth cohort during the first 3 years of life.

STUDY DESIGN

A total of 217 mother-infant pairs living in a dioxin-contaminated area in Vietnam were followed up. Perinatal dioxin exposure of infants was estimated by the measurement of dioxin levels in breast milk of nursing mothers. Neurodevelopment of infants and children, including cognitive, language, and motor development, was determined at 4 months, 1 year, and 3 years of age. Physical growth, including weight, height, and head and abdominal circumferences, was measured at birth, 1 and 4 months, and 1 and 3 years of age. Multivariate mixed models were applied for analyzing repeated measures.

RESULTS

In boys, composite motor and gross motor scores were decreased with increasing exposure of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TetraCDD). The high toxic equivalent of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/PCDFs-TEQ) group showed a significant decrease in expressive communication score. In girls, there was no decreased score in any neurodevelopment aspects in high-exposure groups. All body size measures in boys were decreased in the high-exposure groups of 2,3,7,8-TetraCDD and PCDDs/PCDFs-TEQ. In girls, high 2,3,7,8-TetraCDD and PCDDs/PCDFs-TEQ exposure was associated with increased head and abdominal circumferences.

CONCLUSIONS

Perinatal dioxin exposure affects physical growth and neurodevelopment of infants and children in the first 3 years of life in a sex-specific manner.

Impacts of Perinatal Dioxin Exposure on Motor Coordination and Higher Cognitive Development in Vietnamese Preschool Children: A Five-Year Follow-Up

Dioxin concentrations remain elevated in the environment and in humans residing near former US Air Force bases in South Vietnam. Our previous epidemiological studies showed adverse effects of dioxin exposure on neurodevelopment for the first 3 years of life. Subsequently, we extended the follow-up period and investigated the influence of perinatal dioxin exposure on neurodevelopment, including motor coordination and higher cognitive ability, in preschool children. Presently, we investigated 176 children in a hot spot of dioxin contamination who were followed up from birth until 5 years old. Perinatal dioxin exposure levels were estimated by measuring dioxin levels in maternal breast milk. Dioxin toxicity was evaluated using two indices; toxic equivalent (TEQ)-polychlorinated dibenzo-p-dioxins/furans (PCDDs/Fs) and concentration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Coordinated movements, including manual dexterity, aiming and catching, and balance, were assessed using the Movement Assessment Battery for Children, Second Edition (Movement ABC-2). Cognitive ability was assessed using the nonverbal index (NVI) of the Kaufman Assessment Battery for Children, Second Edition (KABC-II). In boys, total test and balance scores of Movement ABC-2 were significantly lower in the high TEQ- PCDDs/Fs group compared with the moderate and low exposure groups. NVI scores and the pattern reasoning subscale of the KABC-II indicating planning ability were also significantly lower in the high TCDD exposure group compared with the low exposure group of boys. However, in girls, no significant differences in Movement ABC-2 and KABC-II scores were found among the different TEQ-PCDDs/Fs and TCDD exposure groups. Furthermore, in high risk cases, five boys and one girl highly exposed to TEQ-PCDDs/Fs and TCDD had double the risk for difficulties in both neurodevelopmental skills. These results suggest differential impacts of TEQ-PCDDs/Fs and TCDD exposure on motor coordination and higher cognitive ability, respectively. Moreover, high TEQ-PCDDs/Fs exposure combined with high TCDD exposure may increase autistic traits combined with developmental coordination disorder.