Prenatal exposure to legacy PFAS and neurodevelopment in preschool-aged Canadian children: The MIREC cohort

Prenatal exposure to per- and polyfluoroalkyl substances, fetal thyroid function, and intelligence quotient at 7 years of age: Findings from the Sheyang Mini Birth Cohort Study

BACKGROUND

Prenatal exposure to per- and polyfluoroalkyl substances (PFASs) influences neurodevelopment. Thyroid homeostasis disruption is thought to be a possible underlying mechanism. However, current epidemiological evidence remains inconclusive.

OBJECTIVES

This study aimed to explore the effects of prenatal PFAS exposure on the intelligence quotient (IQ) of school-aged children and assess the potential mediating role of fetal thyroid function.

METHODS

The study included 327 7-year-old children from the Sheyang Mini Birth Cohort Study (SMBCS). Cord serum samples were analyzed for 12 PFAS concentrations and 5 thyroid hormone (TH) levels. IQ was assessed using the Wechsler Intelligence Scale for Children-Chinese Revised (WISC-CR). Generalized linear models (GLM) and Bayesian Kernel Machine Regression (BKMR) were used to evaluate the individual and combined effects of prenatal PFAS exposure on IQ. Additionally, the impact on fetal thyroid function was examined using a GLM, and a mediation analysis was conducted to explore the potential mediating roles of this function.

RESULTS

The molar sum concentration of perfluorinated carboxylic acids (ΣPFCA) in cord serum was significantly negatively associated with the performance IQ (PIQ) of 7-year-old children (β = -6.21, 95 % confidence interval [CI]: -12.21, -0.21), with more pronounced associations observed among girls (β = -9.57, 95 % CI: -18.33, -0.81) than in boys. Negative, albeit non-significant, cumulative effects were noted when considering PFAS mixture exposure. Prenatal exposure to perfluorooctanoic acid, perfluorononanoic acid, and perfluorooctanesulfonic acid was positively associated with the total thyroxine/triiodothyronine ratio. However, no evidence supported the mediating role of thyroid function in the link between PFAS exposure and IQ.

CONCLUSIONS

Increased prenatal exposure to PFASs negatively affected the IQ of school-aged children, whereas fetal thyroid function did not serve as a mediator in this relationship.

Prenatal exposure to mixtures of per- and polyfluoroalkyl substances and organochlorines affects cognition in adolescence independent of postnatal exposure

BACKGROUND

Studies on cognitive and neurodevelopmental outcomes have shown inconsistent results regarding the association with prenatal exposure to perfluoroalkyl substance (PFAS) and organochlorines. Assessment of mixture effects of correlated chemical exposures that persist in later life may contribute to the unbiased evaluation and understanding of dose-response associations in real-life exposures.

METHODS

For a subset of the 4th Flemish Environment and Health Study (FLEHS), concentrations of four PFAS and six organochlorines were measured in respectively 99 and 153-160 cord plasma samples and 15 years later in adolescents' peripheral serum by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS). Sustained and selective attention were measured at 14-15 years with the Continuous Performance Test (CPT) and Stroop Test as indicators of potential neurodevelopmental deficits. Quantile g-computation was applied to assess the joint associations between prenatal exposure to separate and combined groups of PFAS and organochlorines and performance in the CPT and Stroop Test at adolescence. Subsequently, individual effects of each chemical compound were analyzed in mixed effects models with two sets of covariates. Analytical data at birth and at the time of cognitive assessment allowed for off-setting postnatal exposure.

RESULTS

In mixtures analysis, a simultaneous one-quantile increase in the natural log-transformed values of PFAS and organochlorines combined was associated with a decrease in the mean reaction time (RT) and the reaction time variability (RTV) in the CPT (β = -15.54, 95% CI:-29.64, -1.45, and β = -7.82, 95% CI: -14.97, -0.67 respectively) and for the mixture of PFAS alone with RT (β = -11.94, 95% CI: -23.29, -0.60). In the single pollutant models, these results were confirmed for the association between perfluorohexanesulfonate (PFHxS) with RT (β = -17.95, 95% CI = -33.35, -2.69) and hexachlorobenzene with RTV in the CPT (β = -5.78, 95% CI: -10.39, -0.76). Furthermore, the participants with prenatal exposure above the limit of quantification for perfluorononanoic acid (PFNA) had a significantly shorter RT and RTV in the CPT (β = -23.38, 95% CI: -41.55, -5.94, and β = -9.54, 95% CI: -19.75, -0.43, respectively).

CONCLUSION

Higher prenatal exposure to a PFAS mixture and a mixture of PFAS and organochlorines combined was associated with better sustained and selective attention during adolescence. The associations seemed to be driven by PFHxS and were not linked to exposure levels at the time of assessment.

Flawed MIREC fluoride and intelligence quotient publications: A failed attempt to undermine community water fluoridation

OBJECTIVE

To assess the evidence presented in a set of articles that use the Canadian Maternal-Infant Research on Environmental Chemicals (MIREC) study database to claim that community water fluoridation (CWF) is associated with harm to foetal and infant cognitive development.

METHODS

Critical appraisal of measurements and processes in the MIREC database, and articles derived therefrom. MIREC's cohort is approximately 2000 pregnant women recruited in 10 centres across Canada, 2008-2011, leading to measuring 512 children aged 3-6 years in six cities. Fluoride exposure was measured by city fluoridation status, self-reports and maternal spot urine samples. Intelligence Quotient (IQ) was measured using the Wechsler Preschool and Primary Scale of Intelligence (WPPSI-III) by different assessors in each city.

RESULTS

MIREC's fluoride and IQ measurements are invalid and therefore cannot support the claim that CWF is associated with IQ decline in children.

CONCLUSIONS

The MIREC fluoride-IQ articles' results should be considered unacceptable for legal and policy purposes; other water fluoridation studies and systematic reviews show no effect of fluoridation on cognition.

Lactational exposure to perfluorooctane sulfonate remains a potential risk in brain function of middle-aged male mice

Perfluorooctane sulfonate (PFOS) exerts adverse effects on neuronal development in young population. Limited evidences have shown that early-life PFOS exposure holds a potential risk for developing age-related neurodegenerative diseases such as Alzheimer's disease later in life. The present study investigated the effects of lactational PFOS exposure on cognitive function using one-year-old mice. Dams were exposed to PFOS (1 mg/kg body weight) through lactation by gavage. Male offspring were used for the behavior test battery to assess cognitive function. Western blot analysis was conducted to measure the levels of proteins related to the pathogenesis of Alzheimer's disease. PFOS-exposed mice displayed a mild deficiency in social recognition. In the hippocampus, the expression of tau protein was significantly increased. These results underline a mild effect of developing PFOS exposure on cognitive function and neurodegeneration. The present study presents the long-lasting effects of PFOS in middle-aged period and warrants a potential aftermath.

Association of prenatal exposure to perfluorinated and polyfluoroalkyl substances with childhood neurodevelopment: A systematic review and meta-analysis

BACKGROUND

Although previous studies have shown an association between prenatal exposure to perfluorinated and polyfluoroalkyl substances (PFAS) and neurodevelopmental disorders in children, the results have been inconsistent. We summarize studies on the association between prenatal PFAS exposure and neurodevelopment in children in order to better understand the relationship.

OBJECTIVE

We conducted a meta-analysis of prenatal PFAS exposure and developmental outcomes associated with intellectual, executive function and behavioral difficulty in children to explore the relationship between prenatal exposure to perfluorinated and polyfluoroalkyl substances (PFAS) and neurodevelopmental disorders in children.

METHODS

We searched for articles published up to August 3, 2023, included and quantified original studies on PFAS and child Intelligence Quotient (IQ), executive function and behavioral difficulty during pregnancy, and systematically summarized articles that could not be quantified.

CONCLUSION

There is evidence of sex-specific relationship between PFAS exposure and children's PIQ. We found that PFOS [β = -1.56, 95% CI = -2.96, - 0.07; exposure = per 1 ln (ng/ml) increase], PFOA [β = -1.87, 95% CI = -3.29, - 0.46; exposure = per 1 ln (ng/ml) increase], PFHxS [β = -2.02, 95% CI = -3.23, - 0.81; exposure = per 1 ln (ng/ml) increase] decreased performance IQ in boys, but PFOS [β = 1.56, 95% CI = 0.06, 3.06; exposure = per 1 ln (ng/ml) increase] increased performance IQ in girls. PFAS are associated with executive function impairments in children, but not related to behavioral difficulty in children.

Occurrence of Major Perfluorinated Alkylate Substances in Human Blood and Target Organs

Human exposure to perfluorinated alkylate substances (PFASs) is usually assessed from the concentrations in serum or plasma, assuming one-compartment toxicokinetics. To characterize body distributions of major PFASs, we obtained and extracted tissue samples from 19 forensic autopsies of healthy adult subjects who had died suddenly and were not known to have elevated levels of PFAS exposure. As target organs of toxicological importance, we selected the liver, kidneys, lungs, spleen, and brain, as well as whole blood. Samples weighing about 0.1 g were analyzed by liquid chromatography coupled to triple mass spectrometers. Minor variations in PFAS concentrations were found between the kidney cortex and medulla and between lung lobes. Organ concentrations of perfluorooctanoic sulfonate (PFOS) and perfluorononanoate (PFNA) correlated well with blood concentrations, while perfluorooctanoate (PFOA) and perfluorohexanoic sulfonate (PFHxS) showed more variable associations. Likewise, the liver concentrations correlated well with those of other organs. Calculations of relative distributions were carried out to assess the interdependence of organ retentions. Equilibrium model predictions largely explained the observed PFAS distributions, except for the brain. Although the samples were small and affected by a possible lack of homogeneity, these findings support the use of blood-PFAS concentrations as a measure of PFAS exposure, with the liver possibly acting as the main organ of retention.

Prenatal exposure to per-and polyfluoroalkyl substances and child executive function: Evidence from the Shanghai birth cohort study

BACKGROUND

Per-and polyfluoroalkyl substances (PFAS) are ubiquitous in the environment and accumulate in humans. Toxicological studies have indicated the potential neurotoxicity of PFAS during the fetal development. However, in epidemiological studies, the association between prenatal exposure to PFAS and executive function in offspring remains unclear.

OBJECTIVES

To investigate the association between prenatal exposure to PFAS and executive function in offspring.

METHOD

This study included 1765 mother-child pairs in the Shanghai Birth Cohort, a prospective birth cohort enrolled during 2013-2016. The levels of 10 PFAS were measured in maternal plasma samples collected during early gestation. Child executive function was assessed at 4 years of age using the parent-reported Behavior Rating Inventory of Executive Function-Preschool version (BRIEF-P), which provided 4 composite measures: Inhibitory Self-Control Index, Flexibility Index, Emergent Metacognition Index, and Global Executive Composite. We used multivariable linear regression to examine the associations between individual PFAS and BRIEF-P scores. Bayesian kernel machine regression (BKMR) was employed to evaluate the joint effects. We also investigated whether these associations were modified by sex.

RESULT

We found no significant associations between prenatal PFAS exposure and BRIEF-P scores when the child was 4 years old. BKMR analysis showed no joint effect of the PFAS mixture on child executive function. RCS analysis indicated that the majority of relationships between PFAS and BRIEF-P did not deviate from the linear relationship, even though there was a nonlinear association between PFUA and EMI. Additionally, the associations were not modified by sex.

CONCLUSION

Overall, our findings showed that there were no associations between prenatal exposure to PFAS and child executive function at 4 years of age.

The stage-specific toxicity of per- and polyfluoroalkyl substances (PFAS) in nematode Caenorhabditis elegans

Per- and Polyfluoroalkyl Substances (PFAS) are a diverse class of industrial chemicals that have been used for decades in industrial and commercial applications. Due to their widespread usages, persistence in the environment, and bioaccumulation in animals and humans, great public health concerns have been raised on adverse health risks of PFAS. In this study, ten PFAS were selected according to their occurrence in different water bodies. The wild-type worms were exposed to individual PFAS at 0, 0.1, 1,10, 100, and 200 μM, and the toxic effects of PFAS on growth, development, fecundity, and behavior at different life stages were investigated using a high-throughput screening (HTS) platform. Our results showed that perfluorooctanesulfonic acid (PFOS), 1H,1H, 2H, 2H-perfluorooctanesulfonamidoacetic acid (NEtFOSAA), perfluorobutanesulfonic (PFBS), and perfluorohexanesulfonic acid (PFHxS) exhibited significant inhibitive effects on the growth in the L4 larva and later stages of worms with concentrations ranging from 0.1 to 200 μmol/L. PFOS and PFBS significantly decreased the brood size of worms across all tested concentrations (p < 0.05), and the most potent PFAS is PFOS with BMC of 0.02013 μM (BMCL, 1.6e-06 μM). During adulthood, all PFAS induced a significant reduction in motility (p < 0.01), while only PFOS can significantly induce behavior alteration at the early larvae stage. Furthermore, the adverse effects occurred in larval stages were found to be the most susceptible to the PFAS exposure. These findings provide valuable insights into the potential adverse effects associated with PFAS exposure and show the importance of considering developmental stages in toxicity assessments.

Metabolic Perturbations Associated with an Exposure Mixture of Per- and Polyfluoroalkyl Substances in the Atlanta African American Maternal-Child Cohort

Prenatal exposure to single chemicals belonging to the per- and polyfluoroalkyl substances (PFAS) family is associated with biological perturbations in the mother, fetus, and placenta, plus adverse health outcomes. Despite our knowledge that humans are exposed to multiple PFAS, the potential joint effects of PFAS on the metabolome remain largely unknown. Here, we leveraged high-resolution metabolomics to identify metabolites and metabolic pathways perturbed by exposure to a PFAS mixture during pregnancy. Targeted assessment of perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorooctanesulfonic acid (PFOS), and perfluorohexanesulfonic acid (PFHxS), along with untargeted metabolomics profiling, were conducted on nonfasting serum samples collected from pregnant African Americans at 6-17 weeks gestation. We estimated the overall mixture effect and partial effects using quantile g-computation and single-chemical effects using linear regression. All models were adjusted for maternal age, education, parity, early pregnancy body mass index, substance use, and gestational weeks at sample collection. Our analytic sample included 268 participants and was socioeconomically diverse, with the majority receiving public health insurance (78%). We observed 13.3% of the detected metabolic features were associated with the PFAS mixture (n = 1705, p < 0.05), which was more than any of the single PFAS chemicals. There was a consistent association with metabolic pathways indicative of systemic inflammation and oxidative stress (e.g., glutathione, histidine, leukotriene, linoleic acid, prostaglandins, and vitamins A, C, D, and E metabolism) across all metabolome-wide association studies. Twenty-six metabolites were validated against authenticated compounds and associated with the PFAS mixture (p < 0.05). Based on quantile g-computation weights, PFNA contributed the most to the overall mixture effect for γ-aminobutyric acid (GABA), tyrosine, and uracil. In one of the first studies of its kind, we demonstrate the feasibility and utility of using methods designed for exposure mixtures in conjunction with metabolomics to assess the potential joint effects of multiple PFAS chemicals on the human metabolome. We identified more pronounced metabolic perturbations associated with the PFAS mixture than for single PFAS chemicals. Taken together, our findings illustrate the potential for integrating environmental mixture analyses and high-throughput metabolomics to elucidate the molecular mechanisms underlying human health.