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. Author manuscript; available in PMC: 2026 Aug 15.
Published in final edited form as: Environ Res. 2025 Apr 29;279(Pt 1):121709. doi: 10.1016/j.envres.2025.121709

Prenatal PFAS exposure and outcomes related to maternal gut microbiome composition in later pregnancy

Stephanie Morgan 1, Sayed Hassan Raza Shah 2, Sarah S Comstock 3, Jaclyn M Goodrich 4, Donghai Liang 5, Youran Tan 5, Kimberly McKee 6, Douglas Ruden 1, Alexandra R Sitarik 7,8, Andrea E Cassidy-Bushrow 7,9,10, Anne L Dunlop 11, Michael C Petriello 1,12, on behalf of program collaborators for Environmental influences on Child Health Outcomes
PMCID: PMC12136995  NIHMSID: NIHMS2080631  PMID: 40311903

Abstract

The composition of the gut microbiome is dependent on factors including diet, lifestyle, and exposure to environmental chemicals, and has implications for human health. Per- and polyfluoroalkyl substances (PFAS), a class of man-made chemicals that have nonstick and flame-retardant properties may impact on gut microbiome composition. Our objective was to elucidate links between PFAS and maternal gut microbiome composition in two geographically diverse sites of the Environmental Influences on Child Health Outcomes program. The present analysis includes participants in the Atlanta African American Maternal Child Cohort;ATL AA and a predominately non-Hispanic White subsample of the Michigan Archive for Research on Child Health Cohort;MARCH with serum or plasma PFAS concentrations measured in early or late pregnancy and 16s rRNA sequencing from maternal gut microbiome samples available primarily in later pregnancy (2nd-3rd trimester). Linear regression models tested associations between prenatal PFAS levels (separately for the 1st/3rd trimesters) and measures of alpha diversity, bacterial composition differences, and differential taxonomic abundance. Bayesian Kernel Machine Regression and Elastic net regression mixture modeling were also incorporated. In both cohorts, multiple PFAS were significantly associated with the relative abundance of specific microbiome taxa even after adjustment for covariates including maternal diet, age, race, BMI, and smoking; A total of 16 significant family-level associations were identified for ATL AA (e.g., PFOA with Clostridiaceae; natural log fold change=0.94) and 13 significant family-level associations identified for MARCH e.g., PFOS with Desulfovibrionaceae; natural log fold change=−1.53 (pFDR<0.05), but similarities between cohorts were lacking. Mixture analyses did not identify interactive or combined effects but did provide modest evidence of inclusion of individual PFAS in beta diversity models in both cohorts. In 2 distinct cohorts, there were significant associations between prenatal PFAS and the relative abundance of several bacterial taxa, but these differences were cohort-specific. This work suggests that PFAS may modulate the gut microbiome during pregnancy.

Keywords: PFAS, Microbiome, Maternal Exposures, Pregnancy, Environmental Health

Introduction

The gut microbiota, a diverse and extensive collection of commensal bacteria within the digestive tract, is a well-characterized site of metabolism in which the products have a sizable impact on overall host health. It functions to gather nutrients, detoxify xenobiotics, renew and maintain the intestinal barrier, and protect against pathogens through competitive inhibition of colonization.1–5 The symbiotic relationship between gut microbiota and the host is mediated through neural, endocrinologic, immunological, and metabolic pathways. 6–9 The gut microbiota shifts in composition throughout the lifespan, and in particular, during pregnancy.1 As a result of physiological changes in pregnancy, the rate of metabolism increases, hormones directly and indirectly alter gut microbiome composition, and the immune system produces a state of low-grade inflammation, leading to increased gut permeability1, 3, 10, 11 in order to support energy storage in fat to provide for fetal growth and lactation and to educate the fetal immune system.1, 3, 12 A diverse gut microbiota during pregnancy indicates a balanced microbial community that can support optimal fetal development and maternal well-being.13 Dysbiosis (i.e., any change in composition of resident commensal communities relative to that found in healthy individuals, including loss of diversity) during pregnancy has been associated with several complications, including gestational diabetes mellitus (GDM), preterm labor, and fetal growth restriction. 3, 14, 15 Dysbiosis can be identified by examining changes in specific taxa of bacteria or by looking at broader diversity metrics (e.g., alpha diversity measures summarize the structure of a microbiome with respect to the number of taxonomic groups and/or distribution of abundances of the groups, and beta diversity measures summarize which samples differ with consideration of sequence abundances or the presence–absence of sequences).16 A diverse gut microbiota has been associated with a more robust immune system and more efficient digestion, while reduced diversity has been associated with impaired ability to metabolize nutrients and xenobiotics, which can lead to increased systemic inflammation and oxidative stress.17 Thus, understanding factors that can perturb microbiome form and function may be especially important during times of microbiome flux including pregnancy.

The health of the gut microbiome is dependent on a variety of factors including diet, lifestyle, infections, medication use, and environmental factors. 3, 18–22 Recently, animal studies have shown that environmental chemicals such as persistent organic pollutants (POPs) can alter microbiome composition. 21, 23 Many studies have focused on legacy pollutants including polychlorinated biphenyls (PCBs), 23–27 but emerging contaminants with similarly long biological half-lives such as per- and polyfluoroalkyl substances (PFAS) may also directly or indirectly impact microbiome composition. PFAS are a class of thousands of man-made chemicals that have nonstick, surfactant, and flame-retardant properties; they are used in a variety of industrial processes and consumer products, including cookware, paints, cosmetics, and food packaging. Although the manufacturing of long chain legacy PFAS including PFOA and PFOS has been phased out in the United States beginning around 2002, short chain replacements such as GenX have been readily produced since 28–32 and many have long biological and environmental half-lives that bioaccumulate in biological tissues, including the gut lining. 33, 34 PFAS exposure has been previously related to diseases of the cardiovascular, immune, endocrine, reproductive, and metabolic systems, and recent literature has shown the role PFAS play in modulating the gut microbiome. 35–40 PFAS exposures have been shown to be associated with reduced gut microbiome diversity and increased ratio of pathogenic to commensal bacteria, as well as a decrease in production of microbiota-derived short-chain fatty acids (SCFAs). 37, 41–43 Animal, and some human studies, have also demonstrated that exposure to PFAS during critical developmental periods can lead to permanent changes in gut microbiome composition. 43–46 Epidemiological studies focusing on associations between PFAS concentrations during pregnancy and maternal microbiome composition are lacking. As prenatal PFAS exposures have also been associated with adverse pregnancy outcomes such as preterm labor and fetal growth restriction, 40, 47, 48 it is important to elucidate links between PFAS exposures and maternal microbiome composition in diverse pregnancy cohorts. We hypothesize that higher maternal blood PFAS levels during pregnancy will be associated with differential gut microbiome composition and decreased diversity measures. Here, we leveraged the Environmental Influences on Child Health Outcomes (ECHO) platform and present results from subsamples of the Atlanta African American Maternal Child Cohort and Michigan Archive for Research on Child Health Cohort where maternal gut microbiome sequencing and PFAS concentrations were available. Significant associations between PFAS and specific gut microbiota taxa were identified, but these were cohort-specific. This analysis can provide further insight into the microbiome as a target of PFAS toxicity and may implicate a possible mechanism linking vertical exposures to offspring health.

Methods:

Cohort Descriptions:

This work leverages extant samples from two sites of the Environmental Influences on Child Health Outcomes (ECHO) program.49, 50 Associations between maternal PFAS exposure and maternal microbiome composition are reported for each cohort separately and datasets were not combined due to differences in sample collection, microbiome sequencing, and ASV vs. OTU-specific bioinformatics workflows. Cohort descriptions and pertinent methods are described below and summarized in Table 1.

Table 1.

Characteristics and comparisons of study cohorts

Variable ATL AA
N=101
MARCH
N=61
p-valuea
Age <0.001
 Median [Q1; Q3] 25.0 [21.0; 28.0] 36.0 [33.0; 39.0]
 N (%) Missing 0 (0%) 0 (0%)
Race <0.001
 White, N (Column %) 0 (0.00%) 55 (90.2%)
 Black and African American, N (Column %) 101 (100%) 5 (8.20%)
 Asian Indian, N (Column %) 0 (0.00%) <5 (1.64%)c
 N (%) Missing 0 (0%) 0 (0%)
BMI 0.12
 Median [Q1; Q3] 25.5 [22.8; 32.3] 23.9 [21.8; 28.9]
 N (%) Missing 0 (0%) 0 (0%)
Smoked prior to pregnancy 0.083
 No, N (Column %) 79 (78.2%) 55 (90.2%)
 Yes, N (Column %) 22 (21.8%) 6 (9.84%)
 N (%) Missing 0 (0%) 0 (0%)
Dairy (servings) 0.27
 Median [Q1; Q3] 1.13 [0.51; 1.57] 1.24 [0.83; 1.50]
 N (%) Missing 28 (27.7%) 6 (9.8%)
Fruits and Vegetables (cups) <0.001
 Median [Q1; Q3] 7.09 [5.96; 9.02] 2.77 [2.15; 3.88]
 N (%) Missing 25 (24.8%) 5 (8.2%)
Added Sugar (teaspoons) <0.001
 Median [Q1; Q3] 7.92 [4.28; 11.1] 11.3 [9.10; 13.3]
 N (%) Missing 28 (27.7%) 7 (11.5%)
Fiber (grams) 0.40
 Median [Q1; Q3] 16.2 [10.6; 24.6] 15.0 [11.7; 18.9]
 N (%) Missing 27 (26.7%) 5 (8.2%)
Meat, fish, poultry, beans, eggs (servings) N/A
 Median [Q1; Q3] 2.01 [1.10; 3.43] N/Ab
 N (%) Missing 28 (27.7%) 61 (100%)
a

calculated using the wilcoxon rank sum test, the chi-square test, or fisher’s exact test.

b

not measured in cohort.

c

<5 is used due to privacy concerns.

ATL AA, Atlanta African American cohort; MARCH, Michigan Archive for Research on Child Health Cohort

Atlanta African American Maternal Child Cohort.

The present analysis included participants in the Atlanta African American Maternal Child Cohort (ATL AA cohort hereafter) which is an ongoing prospective birth cohort that began enrollment in 2014; samples for the analysis described herein were collected pregnant participants during 2014-2019.51, 52 Participants were recruited from two prenatal clinics in Atlanta, Georgia, spanning a socioeconomically diverse array of patients. Inclusion criteria included: 1) self-identifying as African American or Black; 2) being born in the US; 3) presenting with a singleton pregnancy between 8-14 weeks gestation; 4) ability to communicate in English; 5) between 18-40 years; 6) absence of chronic medical conditions. ATL AA excluded (from enrollment), women who were taking medications chronically for a condition but retained women in the cohort who were given a prescription medication once enrolled. The research protocol was reviewed and approved by the Emory University Institutional Review Board; all participants provided written informed consent. The ATL AA cohort and the collection of the relevant covariates has been well described in48, 51, 53–55 and the sub-cohort used for these analyses is summarized below. Participants with either a 1st or 3rd trimester PFAS measurement as well as a 3rd trimester gut microbiota sample were included in the current analysis. Rectal swabs were self-collected as part of a clinic visit between 28- and 39-weeks gestation (median [Q1, Q3] = 30.1 [28.7, 32.3]). At the time of statistical analysis, a total of 108 women had a 3rd trimester rectal swab sequenced and 101 of those had PFAS quantified during the 1st and/or 3rd trimesters (N=76 with 1st trimester PFAS data; N=77 with 3rd trimester PFAS data).

The Michigan Archive for Research on Child Health Cohort.

The Michigan Archive for Research on Child Health (MARCH) cohort began recruitment of pregnant women in 2016 and closed recruitment in 202356. The MARCH study enrolled pregnant women from 21 prenatal clinics serving 11 birthing hospitals in the lower peninsula of the state of Michigan. The analysis described herein included a subset of pregnant women who gave written informed consent for providing fecal samples and health data. This study was approved by the human subjects’ research protection program at Michigan State University (IRB numbers:16-1429, 17-1352, 00005020). Inclusion criteria for these analyses were limited to pregnant women recruited at their first prenatal appointment from ten sites in the lower peninsula, (more than 50% of the women included in the current sample were primarily recruited at the Ann Arbor, Michigan sites), 18 years of age or older, as well as English speaking. A total of 61 women were included in analyses. These participants had a pregnancy plasma sample available for PFAS analysis (N=52 from 2nd trimester, N=9 from 3rd trimester) as well as a pregnancy stool sample available for 16S analysis (N=2 from 2nd trimester, N=56 from 3rd trimester, N=3 with gestational age unknown). Gestational ages of PFAS samples ranged from 16 to 34 weeks (median [Q1, Q3] = 26.3 [25.1, 27.1]), while gestational age at stool sample collection ranged from 25 to 41 weeks (median [Q1, Q3] = 34.2 [31.9, 36.5]). Note that in covariate adjusted models, Asian Indian women were excluded due to small sample size and ECHO restrictions related to anonymity. Relevant covariates were derived from birth certificates or questionnaire. Additionally, unlike in ATL AA, we were unable to stratify results by trimester of PFAS measurement due to insufficient sample sizes.

Microbiome Datasets:

ATL AA cohort.

Maternal rectal swab samples were collected (rather than voided stool) at prenatal visits at 28 weeks and beyond (third trimester; late pregnancy) (with most collected between 28-36 weeks due to timing the research visits with a standard prenatal blood collection in that window). The initial dataset included a total of 108 women with 3rd trimester stool community composition characterized using 16S sequencing. Of these 108, 101 had prenatal PFAS data (described in detail below). DNA was extracted from participant swab samples using the DNeasy PowerSoil Kit (cat# 12888-100, Qiagen). Amplification of the V3-V4 regions of the 16S rRNA gene was performed using a two-step-PCR previously described.57 Amplicons were visualized on a 2% agarose gel, quantified, pooled in equimolar concentration, and purified prior to sequencing on an Illumina HiSeq 2500 (University of Maryland Genome Institute) modified to generate 300 bp paired-end reads.58 Bioinformatic processing of the sequence data has been described previously,59 with reads assembled and chimeras removed per dada2 protocol and sequences clustered into amplicon sequence variants (ASVs). Taxonomy was assigned to each amplicon sequence variant (ASV) generated using PECAN (version 1.0). The sequencing depths of the 101 samples remaining for analysis ranged from 1,184 to 109,109 (Q1=18,785, median=24,205, Q3=33,934).

MARCH cohort.

Stool samples were collected in plastic stool hats at home by participants during the third trimester of pregnancy similar to previously described methods.60 Resulting samples were returned to the lab via US mail allowing the sample to remain at non-ideal temperatures for an average of 4 days before storage at −80°C (Omnigene tubes are manufactured to preserve the sample for up to 2 weeks at room temperature). Genomic DNA was extracted from the stool samples using MoBio Powersoil DNA Isolation kit (Qiagen MoBio, Carlsbad, CA) and 16S amplicon libraries assembled as described previously.61 MARCH used a 250bp region of the V4 region of the 16S gene for amplification. Operational taxonomic unit (OTU) taxonomies were assigned by phylotype using the SILVA reference taxonomy (release 128). The dataset included a total of 101 MARCH women with 3rd trimester stool community composition characterized using 16S sequencing. The majority of stool samples were packed in Omnigene tubes; however, one sample used a ParaPak tube, while another sample had an unknown tube type. These two samples were dropped prior to analysis. Also, one sample had a sequencing depth of 1 and was dropped prior to analysis. A threshold of 97% sequencing similarity was used for operational taxonomic units (OTU) clustering. The dataset included a total of 98 MARCH women with later pregnancy (2nd and 3rd trimester) stool community composition characterized using 16S sequencing; of these, 61 had prenatal PFAS data (described in detail below). The sequencing depths of these 61 samples ranged from 19,191 to 120,778 (Q1=59,716, median=70,726, Q3=86,212). None of the 61 women had recent antibiotic exposure prior to stool sample collection. (Harmonization of ATL AA datasets which utilize ASV pipelines and MARCH 16S datasets which use OTU pipelines was not attempted here due to many differences between cohorts including sample collection and sequencing primer choice. Some studies have shown community compositions can differ up to 10% depending on which pipeline is chosen.62)

PFAS Datasets:

ATL AA cohort.

A total of 15 PFAS compounds were quantified in 1st and 3rd trimester serum; only 7 of the 15 compounds had a detection rate >50% averaged between the two time points; we focused statistical analyses on PFAS available at both collections for ATL AA. PFAS compounds and detection rates are listed in Table S1 with PFAS compounds included in analyses indicated with a superscript. PFAS compounds were reported in ng/mL, and values <LOD imputed as LOD/2 This was selected rather than quantile regression imputation of left-censored data (QRILC), because LODs of some PFAS differed between analytical runs for this dataset. Serum PFAS were analyzed at two laboratories for ATL AA. These two laboratories were part of the Children’s Health Exposure Analysis Resource (CHEAR) and the Human Health Exposure Analysis Resource (HHEAR) laboratories, including Wadsworth Center/New York University Laboratory Hub (Wadsworth/NYU) and the Laboratory of Exposure Assessment and Development for Environmental Research (LEADER) at Emory University. For both sites, LODs were defined as the lowest concentrations in the calibration curve, where the signal to noise ratio of the observed signal was ≥3 with an accuracy within 100 ± 20%. 67 CHEAR and HHEAR are exposure assessment consortia of the National Institute of Environmental Health Studies and the core laboratories of CHEAR/HHEAR implemented harmonized quality control procedures for delivering comparable data.63, 64 Briefly, serum PFAS were extracted and measured using hybrid-solid-phase extraction (SPE) and ultra-performance liquid chromatography (LC) coupled to tandem mass spectrometry (MS) (Wadsworth) and online SPE coupled with high-performance LC-MS/MS (Emory). Quantification was completed using isotope dilution with appropriate mass labeled PFAS standards and calibration curves. Further details of the solid phase extraction techniques and analytical methods for PFAS quantification have been described previously.47, 65

MARCH cohort.

PFAS in the plasma of MARCH women during the 2nd and 3rd trimester was quantified by the Wadsworth HHEAR Targeted Analysis Laboratory using solid phase extraction techniques as described previously and above 66, 67 and included 13 PFAS (Table S1),Of these 13 compounds, 5 had a detection rate ~50% and were retained for analysis (PFHxS: 100%, PFOS: 100%, PFNA: 100%, PFOA: 96.9%, and PFDA: 47.7%). Quantile regression imputation of left-censored data (QRILC) was performed using the R Package imputeLCMD for values less than the limit of detection. This is our preferred method for handling mass spectrometry-based data below LODs based off past reports comparing upwards of 8 different imputation methods (QRILC had the best performance for left-censored missing not at random data).68 All PFAS data were log-transformed, resulting in data on the log(ng/mL) scale. PFAS included in statistical analyses for both cohorts are summarized in Figure 1 and Table S1.

Figure 1:

Figure 1:

Log concentration of PFHxS, PFOS, PFOA, PFNA, PFDA, PFUNDA, and NMFOSAA compared between ATL AA and Michigan MARCH cohorts. Trimester differences within ATL AA women were tested using generalized estimating equations, while cohort differences in late pregnancy were tested using Analysis of Variance. p<0.05 was considered significant. N includes both detectable and non-detectable (after imputing <LOD values). Bar represents median, the top of the box is Q1, and the bottom of the box is Q3. PFAS were measured in serum for ATL AA and plasma for MARCH. PFUNDA and NMFOSAA were not included in Michigan analyses due to low detection rates and are therefore not shown in the plot. Values <LOD have been imputed (see methods for further detail). PFAS, per- and polyfluoroalkyl substances; ATL AA, Atlanta African American cohort; NMFOSAA, N-methyl Perfluorooctane sulfonamido acetic acid; PFDA, perfluorodecanoic acid; PFHxS, perfluorohexane sulfonic acid; PFNA, perfluorononanoic acid; PFOA, perfluorooctanoic acid; PFOS, perfluorooctanesulfonic acid; PFUnDA, Perfluoroundecanoic acid.

Statistical Analyses

Analyses were performed in R version 4.4.0; statistical significance was pre-specified at level 0.05. Basic cohort characteristics were compared using the Wilcoxon rank sum test, the chi-square test, or fisher’s exact test, as appropriate. Trimester differences in PFAS levels within ATL AA women were tested using generalized estimating equations (GEE), while cohort differences in PFAS levels were tested using Analysis of variance (ANOVA). Bacterial relative abundances at the phylum level were compared between cohorts using Wilcoxon rank sum tests. For PFAS/microbiota associations, statistical analyses for both cohorts were generally similar, taking into account differences in data availability, and were completed separately with no data harmonization between cohorts. For the ATL AA cohort, linear regression was used to test associations between prenatal PFAS levels (separately for the 1st and 3rd trimesters) and measures of gut alpha diversity (richness,69 Pielou’s evenness,70 Shannon’s diversity71) adjusting the technical variable sequencing depth (i.e., “minimally adjusted model”) which is common for studies of the microbiome. Full covariate selection was completed using a directed acyclic graph methodology taking into account what covariates were available for both cohorts, covariates known to impact the exposure, outcome, or both, and the total number of variables in the model (Figure S1). Fully adjusted models were fitted, and included sequencing depth, maternal age, maternal BMI at first prenatal visit, maternal diet (described in further detail below), and tobacco use since the month prior to pregnancy (per medical record or self-report). For MARCH, fully adjusted models were similar and also included sequencing depth, maternal age at birth, maternal race, maternal pre-pregnancy BMI, maternal diet, and smoking prior to pregnancy. Note that, Asian Indian women were excluded in adjusted models due to ECHO restrictions on small sample sizes (n<5). Complete-case analysis was used for adjusted models. Stool beta diversity was calculated using the R vegan package72 and was defined using both Canberra73 and Bray-Curtis dissimilarity74 indices to capture different types of abundance shifts (Bray-Curtis gives more weight to abundant species while Canberra treats all species pairs equally). Although beta-diversity associations are directionless, it is possible to examine which taxa load onto each Principle Component (PCO). In ATL AA, Canberra PCO1 was positively correlated with Ruminococcaceae, while PCO2 was positively correlated with Streptococcaceae. Bray-Curtis PCO1 was positively correlated with Lachnospiraceae, while PCO2 was positively correlated with Lactobacillaceae (Figures S2–5). In MARCH, Canberra PCO1 was positively correlated with Firmicutes_unclassified, while PCO2 was positively correlated with Bacillales_Incertae_Sedis_XI. Bray-Curtis PCO1 was positively correlated with Bacteroidaceae, while PCO2 was positively correlated with Firmicutes_unclassified (Figures S-9). The adonis2 function of vegan72 was used to perform PERMANOVA tests for differential stool bacterial composition by PFAS levels using 1,000 permutations, fitting using both minimally and fully adjusted models. To test for differential taxonomic abundance between exposure to different PFAS, taxa tests were performed using two different methods: Analysis of Compositions of Microbiomes with Bias Correction 2 (ANCOM-BC2), with the R package ANCOMBC, as well as DESeq, using the R package DESeq2.75, 76 ANCOM-BC2 was considered the primary testing method (used for both ASV/OTU and family-level testing), as this has been shown to produce consistent results across studies and testing methods,77 while DESeq was used for across and within cohort comparisons at the family level. Sequencing depth adjustment was not necessary for taxa testing, as this is inherently accounted for in both methods. A prevalence cutoff (i.e., the percentage of samples that had the taxa present at any abundance; non-zero) of 1% was used to avoid testing overly sparse taxa; Benjamini & Hochberg (1995) false discovery rate (FDR) correction was performed, with pFDR<0.05 considered significant. We considered each PFAS (and within trimester for ATL AA) as one set of exposure and FDR corrected within that exposure set. Taxa testing was performed at both the family level to summarize potentially large shifts in composition due to PFAS exposure as well as the individual ASV/OTU level to capture more subtle and specific variations.

To examine the extent to which later pregnancy PFAS mixtures associate with microbiota composition, Bayesian Kernel Machine Regression (BKMR) modeling was implemented using the R package bkmr.78 PFAS measurements were normalized prior to BKMR (mean=0, SD=1) for interpretation purposes. Each alpha diversity metric was fit as BKMR outcomes, as well as the first two PCOs of both beta diversity metrics. All default parameters were used, except that 10,000 iterations were performed (instead of 1,000), and variable selection was performed. Sequencing depth was used as an adjustment covariate. Trace plots were used to investigate model convergence. Elastic net regression (ENR) was also utilized as an alternative approach to BKMR also focusing on each alpha diversity metric as well as the first two principal coordinates of both beta diversity metrics as outcomes. The R glmnet package 79 was used to fit elastic net models, while the caret package80 was used to perform parameter tuning (with best values selected based on minimum Root Mean Square Error). Models were trained using a simple random sample of 80% of the data and tested using the remaining 20% to calculate R2 values. Sequencing depth was forced into all models (i.e., no shrinkage applied). BKMR can identify the largest contributing variables and their interactions as well as their combined association with outcomes, while ENR is useful for large datasets by reducing model overfitting. ENR handles datasets with large numbers of parameters of unclear significance and creates a model by using principles from Lasso and Ridge regression.81, 82

Maternal Diet;

As maternal diet is a known modulator of gut microbiome diversity and abundance83 as well as a possible source of PFAS,84 efforts were made to incorporate extant maternal dietary information in to fully adjusted models. In ATL AA, a semi-quantitative food frequency questionnaire was administered at prenatal visits 1 and 2.85 If more than one dietary survey was completed by a participant, the one closest to the time of stool sample collection was retained for analysis. Estimated daily intake of fiber (grams), added sugar (teaspoons), fruits and vegetables (cups), dairy (servings), as well as meat, fish, poultry, beans, eggs (servings) was used for analysis purposes. In MARCH, prenatal survey data was available which included a dietary questionnaire administered using National Cancer Institute’s Five-Factor Screener, available from PhenX Nutrition and Dietary Supplement protocols.86 Estimated daily intake of fiber (grams), added sugar (teaspoons), fruits and vegetables (cups), and dairy (servings) was used for analysis purposes. In both cohorts, any observations >2 SDs above or below the mean were set to missing. To reduce the number of dietary variables needed for adjustment, principal component analysis (PCA) was performed in both cohorts. The first two principal components explained 81% of the variance in diet variables in ATL AA and 76% of the variance in MARCH; these were therefore used in adjusted models (referred to simply as “maternal diet” throughout manuscript). For both cohorts, we also report Pearson correlations between each PFAS and each individual dietary variable (Figures S10–S11).

Results:

Cohort demographics, PFAS concentrations, and microbiome composition.

Demographics for both cohorts are summarized in Table 1. For ATL AA, gestational age at PFAS measurement during the early pregnancy sample (1st trimester) ranged from 6.9 to 12.9 weeks (median [Q1, Q3] = 10.9 [9.0, 12.0]), while gestational age at PFAS measurement during the later time point (3rd trimester) ranged from 28.0 to 36.4 weeks (median [Q1, Q3] = 29.4 [28.4, 30.4]. Michigan mothers were typically older than ATL AA mothers (p<0.001); all ATL AA mothers were Black/African American (by study design), while 90% were White in the Michigan sub-cohort (p<0.001). Further, fruit and vegetable intake was lower, while added sugar was higher in Michigan mothers (both p<0.001). In ATL AA mothers, PFHxS, PFOS, PFNA, and PFUNDA significantly increased from early to later pregnancy (Figure 1). Between ECHO sites, ATL AA mothers had higher PFHxS, PFNA, and PFDA than MARCH mothers during later pregnancy (Figure 1). In ATL AA, fiber significantly inversely correlated with PFOA, but there were no other significant correlations between PFAS and maternal dietary variables in ATL AA or any observed in MARCH. Finally, we compared microbiome composition between the two cohorts (Figure 2). At the phylum level, relative abundances of seven of eight phyla tested (all but Firmicutes, pFDR =0.46) were significantly different by cohort at pFDR <0.05. Bacteroidetes (pFDR =0.001), Proteobacteria (pFDR <0.001), and Verrucomicrobia (pFDR <0.001) had significantly higher abundances in the Michigan cohort, while Actinobacteria (pFDR =0.001), Synergistetes (pFDR <0.001), Fusobacteria (pFDR <0.001), and Campilobacterota (pFDR <0.001) had significantly higher abundances in the ATL AA cohort.

Figure 2:

Figure 2:

Differences in later pregnancy maternal gut microbiome of ATL AA (N=101) and MARCH (N=61) women. Phyla relative abundances by cohort were compared using Wilcoxon rank sum tests for the top 8 phyla plotted above. Seven of the eight phyla tested (all but Firmicutes, pFDR=0.46) were significantly different by cohort at pFDR<0.05. Bacteroidetes (pFDR=0.001), Proteobacteria (pFDR<0.001), and Verrucomicrobia (pFDR<0.001) had significantly higher abundances in the Michigan cohort, while Actinobacteria (pFDR=0.001), Synergistetes (pFDR<0.001), Fusobacteria (pFDR<0.001), and Campilobacterota (pFDR<0.001) had significantly higher abundances in the ATL AA cohort. * Denotes statistical significance by Wilcoxon rank sum tests.

ATL AA, Atlanta African American cohort

Differences in stool diversity metrics by PFAS levels in Atlanta (ATL AA) mothers.

When we examined various PFAS for association with 3rd trimester gut alpha diversity metrics, only 1st trimester NMFOSAA was significantly positively associated with 3rd trimester richness of gut microbiome in minimally adjusted models (β [95% CI] = 15.23 [0.22, 30.23]; p=0.047; Table 2). However, this association was no longer statistically significant in fully adjusted models (β [95% CI] = 17.23 [−1.49, 35.95]; p=0.070; Table 2), and no other associations reached significance in fully adjusted models. When compositional differences in gut (i.e., beta-diversity) by PFAS levels were assessed using minimally adjusted models, PFAS levels explained roughly 1.1% to 1.7% of the variance in microbiota composition (based on estimated R2 values), which were non-significant (Table 3; all p≥0.12). Results were similar after full covariate adjustment (Table 3; roughly 1.6% to 2.1% of variance explained by various PFAS, all p≥0.18).

Table 2.

Association between 1st or 3rd trimester PFAS and 3rd trimester gut alpha diversity in ATL AA.

Alpha Diversity Metric PFAS Measurement Minimally Adjusteda Fully Adjustedb
N β [95% CI]c p-value N β [95% CI]c p-value
1st Trimester PFAS
Richness NMFOSAA 66 15.23 [0.22, 30.23] 0.047 47 17.23 [−1.49, 35.95] 0.070
PFDA 66 −1.41 [−19.84, 17.02] 0.88 47 5.47 [−17.17, 28.10] 0.63
PFHxS 76 −4.65 [−31.74, 22.45] 0.73 53 3.87 [−34.98, 42.72] 0.84
PFNA 76 −4.44 [−22.47, 13.59] 0.63 53 −5.40 [−28.01, 17.20] 0.63
PFOA 76 −0.19 [−18.15, 17.76] 0.98 53 4.48 [−22.98, 31.94] 0.74
PFOS 76 −0.53 [−23.59, 22.52] 0.96 53 3.16 [−34.21, 40.53] 0.87
PFuNDA 66 −6.99 [−27.22, 13.23] 0.49 47 −4.69 [−29.93, 20.56] 0.71
Evenness NMFOSAA 66 0.015 [−0.007, 0.037] 0.18 47 0.017 [−0.009, 0.043] 0.20
PFDA 66 0.002 [−0.025, 0.029] 0.88 47 0.007 [−0.024, 0.038] 0.67
PFHxS 76 −0.008 [−0.047, 0.031] 0.67 53 0.002 [−0.051, 0.055] 0.94
PFNA 76 −0.008 [−0.034, 0.018] 0.55 53 −0.016 [−0.046, 0.015] 0.30
PFOA 76 −0.010 [−0.036, 0.015] 0.42 53 −0.009 [−0.047, 0.028] 0.62
PFOS 76 −0.010 [−0.043, 0.024] 0.57 53 −0.003 [−0.054, 0.048] 0.91
PFuNDA 66 −0.010 [−0.040, 0.019] 0.49 47 −0.023 [−0.056, 0.011] 0.18
Diversity NMFOSAA 66 0.14 [−0.01, 0.29] 0.068 47 0.15 [−0.03, 0.34] 0.097
PFDA 66 −0.01 [−0.19, 0.18] 0.93 47 0.04 [−0.18, 0.26] 0.70
PFHxS 76 −0.05 [−0.32, 0.22] 0.70 53 0.01 [−0.36, 0.39] 0.94
PFNA 76 −0.05 [−0.23, 0.13] 0.61 53 −0.09 [−0.31, 0.13] 0.41
PFOA 76 −0.04 [−0.22, 0.13] 0.62 53 −0.04 [−0.30, 0.23] 0.78
PFOS 76 −0.04 [−0.27, 0.19] 0.75 53 −0.01 [−0.37, 0.35] 0.96
PFuNDA 66 −0.08 [−0.29, 0.12] 0.42 47 −0.12 [−0.37, 0.12] 0.31
3rd Trimester PFAS
Richness NMFOSAA 77 1.66 [−9.96, 13.28] 0.78 50 2.10 [−13.02, 17.23] 0.78
PFDA 77 −4.72 [−15.19, 5.75] 0.37 50 −9.04 [−22.67, 4.60] 0.19
PFHxS 77 −4.98 [−45.04, 35.09] 0.81 50 3.51 [−50.20, 57.22] 0.90
PFNA 77 −10.71 [−36.78, 15.36] 0.42 50 −24.60 [−59.65, 10.45] 0.16
PFOA 77 −4.37 [−17.49, 8.75] 0.51 50 −6.72 [−25.73, 12.29] 0.48
PFOS 77 −14.60 [−31.27, 2.07] 0.085 50 −16.43 [−49.66, 16.81] 0.32
PFuNDA 77 −2.85 [−13.89, 8.19] 0.61 50 −5.76 [−19.37, 7.84] 0.40
Evenness NMFOSAA 77 0.005 [−0.012, 0.022] 0.57 50 0.013 [−0.008, 0.033] 0.21
PFDA 77 0.002 [−0.013, 0.018] 0.75 50 −0.003 [−0.022, 0.016] 0.77
PFHxS 77 −0.006 [−0.064, 0.052] 0.84 50 −0.024 [−0.098, 0.049] 0.51
PFNA 77 −0.005 [−0.042, 0.033] 0.81 50 −0.031 [−0.079, 0.017] 0.20
PFOA 77 −0.005 [−0.024, 0.014] 0.57 50 −0.003 [−0.029, 0.024] 0.83
PFOS 77 −0.010 [−0.035, 0.014] 0.40 50 0.001 [−0.045, 0.048] 0.95
PFuNDA 77 0.006 [−0.010, 0.022] 0.43 50 0.005 [−0.014, 0.024] 0.58
Diversity NMFOSAA 77 0.03 [−0.08, 0.15] 0.57 50 0.07 [−0.08, 0.22] 0.35
PFDA 77 0.00 [−0.10, 0.11] 0.98 50 −0.04 [−0.18, 0.09] 0.52
PFHxS 77 −0.01 [−0.42, 0.39] 0.96 50 −0.07 [−0.60, 0.46] 0.79
PFNA 77 −0.03 [−0.29, 0.24] 0.85 50 −0.23 [−0.58, 0.12] 0.19
PFOA 77 −0.03 [−0.16, 0.10] 0.64 50 −0.04 [−0.23, 0.15] 0.65
PFOS 77 −0.09 [−0.26, 0.08] 0.28 50 −0.04 [−0.37, 0.29] 0.81
PFuNDA 77 0.03 [−0.08, 0.14] 0.63 50 0.01 [−0.13, 0.14] 0.92
a

Adjusted for sequencing depth.

b

Adjusted for sequencing depth, maternal age, maternal BMI at first prenatal visit, tobacco use since month prior to pregnancy, and maternal diet.

c

Change in specified alpha diversity metric, per log(ng/mL) increase in PFAS measurement with 95% confidence intervals. PFAS values <LOD were imputed as LOD/2. Pielou’s evenness, Shannon’s diversity

PFAS, per- and polyfluoroalkyl substances; ATL AA, Atlanta African American cohort; NMFOSAA, N-methyl Perfluorooctane sulfonamido acetic acid; PFDA, perfluorodecanoic acid; PFHxS, perfluorohexane sulfonic acid; PFNA, perfluorononanoic acid; PFOA, perfluorooctanoic acid; PFOS, perfluorooctanesulfonic acid; PFUnDA, Perfluoroundecanoic acid.

Table 3.

Association between 1st or 3rd trimester PFAS and 3rd trimester gut beta diversity in ATL AA

Beta Diversity Metric PFAS Measurement Minimally Adjusteda Fully Adjustedb
N R2 p-valuec N R2 p-valuec
1st Trimester PFAS
Canberra NMFOSAA 66 0.016 0.22 47 0.021 0.61
PFDA 66 0.015 0.65 47 0.021 0.67
PFHxS 76 0.013 0.35 53 0.019 0.68
PFNA 76 0.013 0.57 53 0.018 0.88
PFOA 76 0.013 0.43 53 0.019 0.59
PFOS 76 0.013 0.60 53 0.019 0.49
PFUNDA 66 0.015 0.70 47 0.020 0.89
Bray-Curtis NMFOSAA 66 0.017 0.24 47 0.023 0.25
PFDA 66 0.015 0.46 47 0.018 0.78
PFHxS 76 0.012 0.54 53 0.017 0.66
PFNA 76 0.013 0.48 53 0.018 0.62
PFOA 76 0.012 0.64 53 0.018 0.64
PFOS 76 0.012 0.62 53 0.020 0.34
PFUNDA 66 0.015 0.52 47 0.020 0.66
3rd Trimester PFAS
Canberra NMFOSAA 77 0.012 0.78 50 0.019 0.92
PFDA 77 0.013 0.58 50 0.021 0.35
PFHxS 77 0.012 0.81 50 0.019 0.83
PFNA 77 0.013 0.44 50 0.020 0.45
PFOA 77 0.013 0.38 50 0.021 0.34
PFOS 77 0.013 0.40 50 0.020 0.74
PFUNDA 77 0.014 0.12 50 0.021 0.18
Bray-Curtis NMFOSAA 77 0.012 0.66 50 0.016 0.89
PFDA 77 0.011 0.86 50 0.019 0.63
PFHxS 77 0.011 0.86 50 0.019 0.54
PFNA 77 0.012 0.58 50 0.020 0.44
PFOA 77 0.012 0.54 50 0.019 0.53
PFOS 77 0.011 0.74 50 0.018 0.66
PFUNDA 77 0.013 0.36 50 0.021 0.35
a

Adjusted for sequencing depth.

b

Adjusted for sequencing depth, maternal age, maternal BMI at first prenatal visit, tobacco use since month prior to pregnancy, and maternal diet.

c

PERMANOVA proportion of variance explained by PFAS measurement (R2) and corresponding p-value.

PFAS values <LOD were imputed as LOD/2.

PFAS, per- and polyfluoroalkyl substances; ATL AA, Atlanta African American cohort; NMFOSAA, N-methyl Perfluorooctane sulfonamido acetic acid; PFDA, perfluorodecanoic acid; PFHxS, perfluorohexane sulfonic acid; PFNA, perfluorononanoic acid; PFOA, perfluorooctanoic acid; PFOS, perfluorooctanesulfonic acid; PFUnDA, Perfluoroundecanoic acid; n, sample size; R2, coefficient of determination.

Difference in stool family and ASV- level abundances by PFAS levels in ATL AA.

When ANCOM-BC2 was used to test for family-level differences in 3rd trimester gut microbiome by specific PFAS levels, a total of 60 tests representing 26 of 82 unique families were found to be significant at the pFDR<0.05 level in unadjusted models (45 families were positively associated with PFAS measures and 15 were negatively associated with PFAS measures; Table 4). After full covariate adjustment, one family remained significant. Specifically, 3rd trimester PFOA was positively associated with the relative abundance of Clostridiaceae (pFDR=0.024). Clostridiales_vadinBB60_group was nearly negatively associated with 1st trimester PFHxS (pFDR=0.073). When ANCOM-BC2 was used to test for differences at the highest resolution available (i.e., individual ASV abundances) in 3rd trimester gut by PFAS levels, 2026 associations were significant prior to covariate adjustment (pFDR<0.05, supplemental data download). After covariate adjustment, a total of 13 significant associations were identified (across all ASV/PFAS compound combinations; Supplemental data download). Interestingly, all 13 significant associations were with PFOA and 12 of 13 were with 3rd trimester PFOA. Specifically, 3rd trimester PFOA was significantly inversely associated with ASVs of the genera Streptococcus, Bacteroides, Anaerostipes, Intestinibacter, Christensenellaceae_R-7_group, Bifidobacterium, and Coprococcus_1 and was significantly positively associated with ASVs of the taxonomy Prevotella buccalis, Porphyromonas, Lachnospiraceae_NK4A136_group, Ruminiclostridium_6, and Lachnospiraceae_UCG-010. Of these, Bifidobacterium exhibited the largest negative effect size (natural log fold change (LFC)= −8.41), while Lachnospiraceae_UCG-010 exhibited the largest positive effect size (LFC= 3.77). Finally, first trimester PFOA was significantly positively associated with a Sutterella ASV (LFC=1.52; pFDR=0.012).

Table 4.

Association between 1st and 3rd trimester PFAS compounds and family level abundance among ATL AA women.

Family PFAS Trimester Unadjusted Adjusted

N LFCa pFDR N LFCb pFDR
f_Aerococcaceae PFHxS 1st Trimester 76 0.57 1.20E-02 53 1.1 6.46E-01
f_Aerococcaceae PFOA 1st Trimester 76 0.4 2.51E-02 53 1.01 1.00E+00
f_Aerococcaceae PFOA 3rd Trimester 77 0.45 4.11E-04 50 0.21 1.00E+00
f_Aerococcaceae PFOS 1st Trimester 76 0.81 9.11E-05 53 1.14 1.00E+00
f_Akkermansiaceae PFHxS 1st Trimester 76 −0.64 4.35E-02 53 −0.59 1.00E+00
f_Akkermansiaceae PFNA 1st Trimester 76 −0.73 4.32E-02 53 −0.61 1.00E+00
f_Akkermansiaceae PFOA 1st Trimester 76 −0.52 3.95E-02 53 −0.63 1.00E+00
f_Alcaligenaceae PFHxS 1st Trimester 76 5.8 5.11E-03 53 −16.34 1.00E+00
f_Alcaligenaceae PFHxS 3rd Trimester 77 −2.65 1.28E-02 50 −0.04 1.00E+00
f_Alcaligenaceae PFOA 1st Trimester 76 4.08 9.11E-03 53 2.96 1.00E+00
f_Alcaligenaceae PFOS 1st Trimester 76 3.02 2.02E-03 53 3.5 1.00E+00
f_Anaerolineaceae PFOS 1st Trimester 76 0.54 2.55E-06 53 −0.07 1.00E+00
f_Anaerovoracaceae PFHxS 1st Trimester 76 −0.57 8.70E-03 53 −0.53 1.00E+00
f_Bacillaceae PFOS 1st Trimester 76 −0.13 2.80E-02 53 4.55 1.00E+00
f_Brevibacteriaceae PFOA 1st Trimester 76 1.82 5.45E-06 53 11.67 5.07E-01
f_Brevibacteriaceae PFOA 3rd Trimester 77 1.13 5.19E-04 50 7.09 1.00E+00
f_Burkholderiaceae PFOS 1st Trimester 76 1.67 3.19E-02 53 2.41 1.00E+00
f_Butyricicoccaceae PFHxS 1st Trimester 76 0.68 1.09E-03 53 0.85 6.46E-01
f_Butyricicoccaceae PFOS 1st Trimester 76 0.37 1.61E-04 53 −0.13 1.00E+00
f_Clostridiaceae PFOA 3rd Trimester 77 0.42 7.40E-03 50 0.94 2.42E-02
f_Clostridiales_vadinBB60_group PFHxS 1st Trimester 76 −1.18 3.31E-05 53 5.6 7.27E-02
f_Clostridiales_vadinBB60_group PFOA 1st Trimester 76 −0.41 2.51E-02 53 −0.71 7.22E-01
f_Dermabacteraceae PFHxS 1st Trimester 76 5.59 6.65E-04 53 0.56 1.00E+00
f_Dermabacteraceae PFOA 1st Trimester 76 1.06 2.51E-02 53 0.36 1.00E+00
f_Dermabacteraceae PFOS 1st Trimester 76 0.75 3.20E-03 53 0.16 1.00E+00
f_Enterococcaceae PFHxS 1st Trimester 76 1.18 5.22E-04 53 1.43 6.46E-01
f_Enterococcaceae PFHxS 3rd Trimester 77 1.45 4.97E-04 50 −0.28 1.00E+00
f_Enterococcaceae PFOS0 1st Trimester 76 0.7 1.19E-05 53 1.08 1.00E+00
f_Flavobacteriaceae PFOA 1st Trimester 76 1.27 4.37E-02 53 9.76 1.00E+00
f_Flavobacteriaceae PFOS 1st Trimester 76 −1.6 2.02E-03 53 −6.54 1.00E+00
f_Listeriaceae PFOS 1st Trimester 76 1.75 3.19E-02 53 NA NA
f_Microbacteriaceae PFOS 1st Trimester 76 2.35 2.75E-02 53 4.16 1.00E+00
f_Moraxellaceae PFHxS 1st Trimester 76 2.4 2.18E-02 53 NA NA
f_Moraxellaceae PFOS 1st Trimester 76 1.5 5.35E-03 53 NA NA
f_Peptostreptococcaceae PFOS 1st Trimester 76 0.58 3.54E-02 53 0.33 1.00E+00
f_Propionibacteriaceae PFHxS 1st Trimester 76 0.91 5.13E-03 53 −3.18 1.00E+00
f_Propionibacteriaceae PFOA 1st Trimester 76 0.65 8.72E-03 53 −11.91 1.00E+00
f_Propionibacteriaceae PFOS 1st Trimester 76 1.08 1.30E-06 53 10.32 1.00E+00
f_Pseudomonadaceae PFHxS 1st Trimester 76 12.38 1.27E-03 53 14.13 1.00E+00
f_Pseudomonadaceae PFNA 1st Trimester 76 3.68 4.32E-02 53 3.5 1.00E+00
f_Pseudomonadaceae PFOA 1st Trimester 76 4.69 8.72E-03 53 4.38 1.00E+00
f_Pseudomonadaceae PFOS 1st Trimester 76 3.84 4.53E-04 53 4.73 1.00E+00
f_Rhodospirillaceae PFHxS 1st Trimester 76 −2.9 3.58E-05 53 NA NA
f_Rhodospirillaceae PFHxS 3rd Trimester 77 13.55 2.38E-04 50 NA NA
f_Rhodospirillaceae PFNA 1st Trimester 76 −0.89 4.32E-02 53 NA NA
f_Rhodospirillaceae PFOA 3rd Trimester 77 0.52 1.99E-02 50 NA NA
f_Rhodospirillaceae PFOS 1st Trimester 76 0.42 2.02E-03 53 NA NA
f_Selenomonadaceae PFDA 3rd Trimester 77 0.54 3.13E-02 50 1.78 1.00E+00
f_Selenomonadaceae PFHxS 1st Trimester 76 −1.9 3.31E-05 53 0.42 1.00E+00
f_Selenomonadaceae PFNA 1st Trimester 76 1.12 1.31E-02 53 −1.53 1.00E+00
f_Selenomonadaceae PFOA 1st Trimester 76 0.74 1.67E-03 53 −1.06 6.40E-01
f_Selenomonadaceae PFOA 3rd Trimester 77 1.4 1.48E-05 50 10.95 1.00E+00
f_Spirochaetaceae PFHxS 1st Trimester 76 −1.01 6.65E-04 53 −1.31 6.75E-01
f_Staphylococcaceae PFHxS 1st Trimester 76 0.74 7.64E-04 53 1.51 4.42E-01
f_Staphylococcaceae PFOA 3rd Trimester 77 0.32 2.02E-02 50 0.38 1.00E+00
f_Staphylococcaceae PFOS 1st Trimester 76 0.93 2.12E-06 53 1.28 1.00E+00
f_Victivallaceae PFOA 3rd Trimester 77 0.67 2.02E-02 50 NA NA
f_Victivallaceae PFOS 1st Trimester 76 0.35 4.68E-02 53 NA NA
f_Weeksellaceae PFOA 1st Trimester 76 −1.33 4.21E-02 53 −12.93 1.00E+00
f_Weeksellaceae PFOS 1st Trimester 76 −1.34 2.30E-03 53 −2.01 1.00E+00
a

Natural log fold change (LFC) in family abundance, per log(ng/mL) increase in PFAS measurement, prior to covariate adjustment.

b

Natural log fold change (LFC) in family abundance, per log(ng/mL) increase in PFAS measurement, after adjusting for maternal age, maternal BMI at first prenatal visit, tobacco use since month prior to pregnancy, and maternal diet. All tests where either the unadjusted or adjusted model was significant is shown.

PFAS, per- and polyfluoroalkyl substances; ATL AA, Atlanta African American cohort; NMFOSAA, N-methyl Perfluorooctane sulfonamido acetic acid; PFDA, perfluorodecanoic acid; PFHxS, perfluorohexane sulfonic acid; PFNA, perfluorononanoic acid; PFOA, perfluorooctanoic acid; PFOS, perfluorooctanesulfonic acid; n, sample size.

Differences in stool diversity metrics by PFAS levels in Michigan (MARCH) mothers.

In minimally adjusted models no significant associations were found between PFAS levels and stool bacterial richness, evenness, or diversity (Table 5; all p≥0.19). Results were similar in fully adjusted models (Table 5; all p≥0.16). When compositional differences (i.e., beta-diversity) in stool by PFAS levels were assessed in minimally adjusted models, both PFOA and PFNA were significantly associated with stool community composition when the Bray-Curtis metric was used. While there is no directionality to beta diversity associations, 2.9% to 4.3% of the variability in composition was explained (Table 6). PFOS explained 2.8% variability, but this was not significant (p=0.058). However, in fully adjusted models, associations were no longer significant for either PFOA (Bray-Curtis R2=0.018, p=0.37) or PFNA (Bray-Curtis R2=0.022, p=0.23), or PFOS (Bray-Curtis R2=0.031, p=0.06) with the percentage of variability described by the PFAS concentration being reduced compared to the minimally adjusted model

Table 5.

Association between PFAS and stool alpha diversity in later pregnancy in MARCH women.

Alpha Diversity Metric PFAS Measurement Minimally Adjusteda Fully Adjustedb

β [95% CI]c p-value β [95% CI]c p-value
Richness PFHxS −7.31 [−19.61, 5.00] 0.24 −5.91 [−18.37, 6.54] 0.34
PFOS −0.66 [−10.77, 9.45] 0.90 0.46 [−9.77, 10.69] 0.93
PFOA 0.96 [−5.02, 6.95] 0.75 0.88 [−6.03, 7.79] 0.80
PFNA −0.68 [−10.34, 8.97] 0.89 −1.62 [−11.75, 8.50] 0.75
PFDA −3.90 [−9.75, 1.95] 0.19 −1.37 [−7.90, 5.17] 0.68

Evenness PFHxS −0.008 [−0.046, 0.030] 0.69 −0.021 [−0.058, 0.016] 0.25
PFOS 0.007 [−0.024, 0.038] 0.67 −0.001 [−0.031, 0.029] 0.94
PFOA 0.008 [−0.010, 0.026] 0.38 −0.003 [−0.024, 0.017] 0.76
PFNA 0.014 [−0.015, 0.044] 0.33 −0.004 [−0.034, 0.026] 0.81
PFDA 0.009 [−0.009, 0.027] 0.33 −0.006 [−0.025, 0.013] 0.53

Diversity PFHxS −0.07 [−0.27, 0.12] 0.45 −0.13 [−0.32, 0.06] 0.16
PFOS 0.03 [−0.12, 0.19] 0.67 0.001 [−0.16, 0.16] 0.99
PFOA 0.04 [−0.05, 0.13] 0.37 −0.01 [−0.12, 0.09] 0.83
PFNA 0.06 [−0.09, 0.21] 0.39 −0.03 [−0.18, 0.13] 0.75
PFDA 0.03 [−0.06, 0.12] 0.55 −0.03 [−0.13, 0.07] 0.50
a

Adjusted for sequencing depth (N=61).

b

Adjusted for sequencing depth, maternal age at birth, maternal race, maternal pre-pregnancy BMI, maternal diet, and smoking prior to pregnancy (N=53).

c

Change in specified alpha diversity metric, per log(ng/mL) increase in PFAS measurement with 95% confidence intervals. Pielou’s evenness, Shannon’s diversity

Michigan Archive for Research on Child Health Cohort; MARCH, PFAS, per- and polyfluoroalkyl substances; PFHxS, perfluorohexane sulfonic acid; PFOS, perfluorooctanesulfonic acid; PFOA, perfluorooctanoic acid; PFNA, perfluorononanoic acid; PFDA, perfluorodecanoic acid

Table 6.

Association between PFAS and stool beta diversity in later pregnancy in MARCH women.

Beta Diversity Metric PFAS Measurement Minimally Adjusteda Fully Adjustedb

R2 p-valuec R2 p-valuec
Canberra PFHxS 0.017 0.29 0.021 0.20
PFOS 0.017 0.32 0.020 0.30
PFOA 0.019 0.15 0.018 0.48
PFNA 0.016 0.56 0.017 0.74
PFDA 0.015 0.75 0.018 0.50
Bray-Curtis PFHxS 0.015 0.43 0.020 0.25
PFOS 0.028 0.058 0.031 0.063
PFOA 0.043 0.009 0.018 0.37
PFNA 0.029 0.041 0.022 0.23
PFDA 0.011 0.69 0.024 0.16
a

Adjusted for sequencing depth (N=61).

b

Adjusted for sequencing depth, maternal age at birth, maternal race, maternal pre-pregnancy BMI, maternal diet, and smoking prior to pregnancy (N=53).

c

PERMANOVA proportion of variance explained by PFAS measurement (R2) and corresponding p-value.

Michigan Archive for Research on Child Health Cohort; MARCH, PFAS, per- and polyfluoroalkyl substances; PFHxS, perfluorohexane sulfonic acid; PFOS, perfluorooctanesulfonic acid; PFOA, perfluorooctanoic acid; PFNA, perfluorononanoic acid; PFDA, perfluorodecanoic acid; R2, coefficient of determination.

Difference in stool family and OTU-level abundances by PFAS levels in MARCH mothers and comparisons with ATL AA.

In unadjusted models, the relative abundance of 6 (of 171 tested) bacterial families were significantly associated (pFDR<0.05) with at least one PFAS measurement (Supplemental data download): Carnobacteriaceae, Desulfovibrionales, Fulvivirgaceae, Porphyromonadaceae, Selenomonadales, and Xanthomonadaceae. Carnobacteriaceae was the most replicable finding, being positively associated with 4 of the 5 PFAS measurements (all but PFHxS). Selenomonadales was positively associated with PFHxS only (LFC=1.56, pFDR=0.035), while Desulfovibrionales was negatively associated with PFOA only (LFC=−0.06, pFDR<0.001), Porphyromonadaceae was negatively associated with PFHxS only (LFC=−1.39, pFDR=0.035), and Xanthomonadaceae (LFC=−0.04, pFDR<0.001) and Fulvivirgaceae (LFC=−0.06, pFDR=0.034) were negatively associated with PFDA only. In fully adjusted models, a total of 8 significant tests across 6 bacterial families (of 171 tested, Table 7) reached statistical significance. PFHxS was inversely associated with 5 families including Bacteroidales_unclassified (LFC=−2.48, pFDR=0.0091), Bifidobacteriaceae (LFC=−1.27, pFDR=0.0096), Campylobacteraceae (LFC=−1.63, pFDR=0.0024), Desulfovibrionaceae (LFC=−1.84, pFDR=0.0024), and Enterobacterales_unclassified (LFC=−1.93, pFDR=0.0011). PFOS was also significantly inversely associated with Desulfovibrionaceae (LFC=−1.53, pFDR=0.012). Finally, Selenomonadales (unclassified) was positively associated with both PFHxS (LFC=2.1, pFDR=0.016) and PFOS (LFC=2.46, pFDR=0.012).

Table 7.

Gut microbiota families significantly associated with PFAS concentrations in fully adjusted models in MARCH women.

Family PFAS LFCa pFDR
Bacteroidales_unclassified PFHxS −2.48 9.09E-03
Bifidobacteriaceae PFHxS −1.27 9.65E-03
Campylobacteraceae PFHxS −1.63 2.38E-03
Desulfovibrionaceae PFHxS −1.84 2.38E-03
Desulfovibrionaceae PFOS −1.53 1.23E-02
Enterobacterales_unclassified PFHxS −1.93 1.15E-03
Selenomonadales_unclassified PFHxS 2.1 1.63E-02
Selenomonadales unclassified PFOS 2.46 1.23E-02
a

Natural log fold change (LFC) in family abundance, per log(ng/mL) increase in PFAS measurement, after adjusting for maternal age at birth, maternal race, maternal pre-pregnancy BMI, maternal diet, and smoking prior to pregnancy. Calculated using ANCOM-BC2.(N=53).

Michigan Archive for Research on Child Health Cohort; MARCH, PFAS, per- and polyfluoroalkyl substances; PFHxS, perfluorohexane sulfonic acid; PFOS, perfluorooctanesulfonic acid.

At higher taxonomic resolution, in unadjusted models, a total of 13 individual OTUs (of 393 tested) reached statistical significance (pFDR<0.05) for at least one PFAS measurement (Table S2). Consistent with family-level testing, OTU 197 of the family Carnobacteriaceae and the genus Granulicatella was positively associated with PFDA, PFNA, and PFOA. Additionally, OTU 284 of the family Flavobacteriaceae was negatively associated with PFDA and PFOS. The remaining 11 OTUs were significantly associated with one PFAS measurement. After full covariate adjustment, a total of 40 significant associations were identified (across all OTU/PFAS compound combinations; Table 8). Significant associations were evenly split between positive and inverse relationships and significant PFOS and PFHxS associations were most observed (21 and 12 respectively). Of these, Otu128 (Succiniclasticum) had the largest negative effect sizes with PFNA (LFC= −5.43) and PFOS (LFC= −3.3), followed by Otu133 (Senegalimassilia) and its association with PFHxS (LFC= −2.83). Conversely, Anaerococcus (LFC= 3.99) and Burkholderiales (LFC= 3.59) OTUs had the largest positive effect sizes with PFOS and PFNA, respectively. Also of note, certain taxa were significantly associated with more than one PFAS; Otu044 (Bilophila) was significantly negatively associated with PFHxS and PFOS, Otu124 (Burkholderiales) was significantly positively associated with PFDA, PFNA, PFOA, and PFOS, Otu128 (Succiniclasticum) was significantly negatively associated with PFNA, PFOA, and PFOS, and Otu145 (Selenomonadales) was significantly positively associated with PFHxS and PFOS.

Table 8.

Gut microbiota OTUs significantly associated with PFAS concentrations in fully adjusted models in MARCH women.

OTU PFAS Phylum Class Order Family Genus LFCa pFDR
Otu006 PFOS Firmicutes Negativicutes Veillonellales Veillonellaceae Megasphaera −1.56 0.0076
Otu009 PFHxS Actinobacteria Actinobacteria Bifidobacteriales Bifidobacteriaceae Bifidobacterium −1.27 0.0132
Otu023 PFHxS Bacteroidetes Bacteroidia Bacteroidales Bacteroidales_unclassified Bacteroidales_unclassified −2.48 0.0123
Otu024 PFOS Firmicutes Negativicutes Acidaminococcales Acidaminococcaceae Acidaminococcus −2.1 0.0004
Otu038 PFOS Actinobacteria Actinobacteria Bifidobacteriales Bifidobacteriaceae Bifidobacteriaceae_unclassified 2.36 0.0085
Otu044 PFHxS Proteobacteria Deltaproteobacteria Desulfovibrionales Desulfovibrionaceae Bilophila −1.82 0.0042
Otu044 PFOS Proteobacteria Deltaproteobacteria Desulfovibrionales Desulfovibrionaceae Bilophila −1.4 0.0120
Otu069 PFDA Bacteroidetes Bacteroidia Bacteroidales Prevotellaceae Prevotellamassilia −2.14 0.0022
Otu071 PFOS Actinobacteria Coriobacteriia Coriobacteriia_unclassified Coriobacteriia_unclassified Coriobacteriia_unclassified 2.46 0.0017
Otu080 PFHxS Proteobacteria Gammaproteobacteria Enterobacterales Enterobacterales_unclassified Enterobacterales_unclassified −1.93 0.0027
Otu081 PFOS Bacteroidetes Bacteroidia Bacteroidales Prevotellaceae Prevotellaceae_unclassified 2.2 0.0002
Otu104 PFOS Firmicutes Negativicutes Acidaminococcales Acidaminococcaceae Acidaminococcaceae_unclassified 3.34 0.0002
Otu112 PFHxS Firmicutes Bacilli Lactobacillales Lactobacillaceae Lactobacillus 1.12 0.0132
Otu114 PFHxS Firmicutes Clostridia Clostridiales Ruminococcaceae Massiliimalia −1.4 0.0046
Otu116 PFOS Firmicutes Erysipelotrichia Erysipelotrichales Erysipelotrichaceae Holdemanella 1.22 0.0011
Otu117 PFHxS Actinobacteria Coriobacteriia Eggerthellales Eggerthellaceae Gordonibacter −1.4 0.0027
Otu120 PFOS Actinobacteria Actinobacteria Actinomycetales Actinomycetaceae Actinomyces 1.16 0.0020
Otu122 PFHxS Firmicutes Bacilli Lactobacillales Lactobacillaceae Lacticaseibacillus 1.14 0.0146
Otu123 PFHxS Firmicutes Clostridia Clostridiales Ruminococcaceae Pseudoflavonifractor −1.21 0.0341
Otu124 PFDA Proteobacteria Betaproteobacteria Burkholderiales Burkholderiales_unclassified Burkholderiales_unclassified 2.5 0.0022
Otu124 PFNA Proteobacteria Betaproteobacteria Burkholderiales Burkholderiales_unclassified Burkholderiales_unclassified 3.59 0.0367
Otu124 PFOA Proteobacteria Betaproteobacteria Burkholderiales Burkholderiales_unclassified Burkholderiales_unclassified 2.2 0.0093
Otu124 PFOS Proteobacteria Betaproteobacteria Burkholderiales Burkholderiales_unclassified Burkholderiales_unclassified 3.22 0.0002
Otu128 PFNA Firmicutes Negativicutes Acidaminococcales Acidaminococcaceae Succiniclasticum −5.43 0.0030
Otu128 PFOA Firmicutes Negativicutes Acidaminococcales Acidaminococcaceae Succiniclasticum −2.38 0.0058
Otu128 PFOS Firmicutes Negativicutes Acidaminococcales Acidaminococcaceae Succiniclasticum −3.3 0.0002
Otu133 PFHXS Actinobacteria Coriobacteriia Coriobacteriales Coriobacteriaceae Senegalimassilia −2.83 0.0042
Otu134 PFOS Firmicutes Bacilli Lactobacillales Streptococcaceae Lactococcus 0.78 0.0071
Otu137 PFOS Firmicutes Clostridia Clostridiales Ruminococcaceae Harryflintia −0.62 0.0120
Otu145 PFHXS Firmicutes Negativicutes Selenomonadales Selenomonadales_unclassified Selenomonadales_unclassified 2.1 0.0213
Otu145 PFOS Firmicutes Negativicutes Selenomonadales Selenomonadales_unclassified Selenomonadales_unclassified 1.95 0.0023
Otu147 PFHXS Campilobacterota Campylobacteria Campylobacterales Campylobacteraceae Campylobacter −1.63 0.0042
Otu150 PFOS Firmicutes Clostridia Clostridiales Lachnospiraceae Faecalicatena 0.57 0.0120
Otu155 PFOA Actinobacteria Coriobacteriia Eggerthellales Eggerthellaceae Slackia −1.88 0.0172
Otu165 PFOS Firmicutes Clostridia Clostridiales Peptoniphilaceae Peptoniphilus 1.24 0.0076
Otu175 PFOS Actinobacteria Coriobacteriia Eggerthellales Eggerthellaceae Raoultibacter −0.93 0.0120
Otu179 PFOS Proteobacteria Gammaproteobacteria Pseudomonadales Moraxellaceae Acinetobacter −0.79 0.0085
Otu209 PFOS Firmicutes Clostridia Clostridiales Lachnospiraceae Oribacterium 1.08 0.0026
Otu215 PFOS Firmicutes Clostridia Clostridiales Peptoniphilaceae Anaerococcus 3.99 0.0026
Otu234 PFOS Firmicutes Clostridia Clostridiales Peptostreptococcaceae Peptostreptococcus −0.86 0.0085
a

Natural log fold change (LFC) in OTU abundance, per log(ng/mL) increase in PFAS measurement, after adjusting for maternal age at birth, maternal race, maternal pre-pregnancy BMI, maternal diet, and smoking prior to pregnancy. Calculated using ANCOM-BC2. (N=53).

Michigan Archive for Research on Child Health Cohort; MARCH, PFAS, per- and polyfluoroalkyl substances; PFHxS, perfluorohexane sulfonic acid; PFOS, perfluorooctanesulfonic acid; PFOA, perfluorooctanoic acid; PFNA, perfluorononanoic acid; PFDA, perfluorodecanoic acid; OTU, Operational Taxonomic Unit

Finally, the association between PFAS compounds and family-level abundances were next visualized between cohorts (ATL AA vs. MARCH) incorporating results from an additional, less conservative testing method (DESeq), as shown in Figure 3 (numeric data available in Supplemental data download). A total of 18 families were significantly associated with at least one PFAS compound across cohorts and testing methods, but none of these were shared across cohorts. LFC effect sizes were generally consistent across testing methods, (spearman correlation = 0.46, p<0.001), but which specific families were declared statistically significant were discrepant, with more significant results being identified by DESeq than ANCOM-BC2.

Figure 3:

Figure 3:

Association between PFAS compounds and family level abundances in both cohorts, using two different testing methods (ANCOM-BC2 vs. DESeq). 3rd trimester PFAS was used in ATL AA, while 2nd and 3rd trimester PFAS was used in the Michigan cohort. Models are adjusted for maternal age, maternal race (MARCH only), maternal BMI, smoking prior to pregnancy, and maternal diet. N=50 for adjusted ATL AA, while N=53 for adjusted MARCH cohort models. A 1% prevalence threshold is used for all tests. Grey areas indicate either 1.) family not found in cohort, 2.) family did not reach prevalence threshold in cohort, or 3.) model did not converge. PFUNDA and NMFOSAA are only included in the ATL AA analysis. Natural log fold change (LFC) values are plotted, with an asterisk provided if pFDR<0.05. PFAS, per- and polyfluoroalkyl substances; ATL AA, Atlanta African American cohort; NMFOSAA, N-methyl Perfluorooctane sulfonamido acetic acid; PFDA, perfluorodecanoic acid; PFHxS, perfluorohexane sulfonic acid; PFNA, perfluorononanoic acid; PFOA, perfluorooctanoic acid; PFOS, perfluorooctanesulfonic acid; PFUnDA, Perfluoroundecanoic acid; ANCOM-BC2, Analysis of Compositions of Microbiomes with Bias Correction; DESeq, Differential gene expression analysis based on the negative binomial distribution

Examining associations with PFAS and microbiome diversity using mixture methods in ATL AA and MARCH mothers.

With our statistically significant observations linking individual PFAS to specific microbial taxa, we next utilized two distinct mixture methods, BKMR, which can determine overall effect estimation as well as interactions between toxicants as well as ENR, which has been shown useful under multicollinearity conditions87 to identify associations between PFAS mixtures and overall microbial composition and diversity. The association between PFAS mixtures and stool richness, evenness, and diversity (i.e., alpha-diversity measures) was first examined using BKMR in both ATL AA and MARCH. In both ATL AA and MARCH, overall mixture effects were non-significant (i.e., 95% credible intervals include zero) for all alpha-diversity measures (Table 9A). Similarly, posterior inclusion probabilities (PIPs) were generally low (Table 9B) with only PFOA in MARCH nearing what can be interpreted as a weak effect (Evenness; PIP=0.33, Diversity; PIP=0.38); (for reference, between 0.5 and 0.75-weak, 0.75 and 0.95-positive, 0.95 and 0.99-strong, and values > 0.99 as decisive evidence.88)

Table 9A.

BKMR overall mixture effects for ATL AA and MARCH mothers.

Outcome β [95% CI]a
ATL AA
Richness −5.42 [−29.84, 19.00]
Evenness 0.00 [−0.02, 0.02]
Diversity 0.01 [−0.16, 0.17]
Canberra PCO1 −0.02 [−0.10, 0.05]
Canberra PCO2 −0.02 [−0.07, 0.04]
Bray-Curtis PCO1 −0.05 [−0.17, 0.06]
Bray-Curtis PCO2 −0.01 [−0.08, 0.07]

MARCH
Richness −0.51 [−6.96, 5.93]
Evenness 0.00 [−0.02, 0.02]
Diversity 0.01 [−0.08, 0.11]
Canberra PCO1 −0.00 [−0.06, 0.05]
Canberra PCO2 0.00 [−0.04, 0.04]
Bray-Curtis PCO1 0.05 [−0.03, 0.13]
Bray-Curtis PCO2 0.00 [−0.04, 0.05]
a

The overall mixture effect, defined as the mean value of the outcome when all PFAS concentrations are at the 75th percentile minus the mean value of the outcome when all PFAS concentrations are at the 25th percentile. N=77 for ATL AA (N with 3rd trimester PFAS); N=61 for MARCH. Adjusted for sequencing depth.

PFAS, per- and polyfluoroalkyl substances; ATL AA, Atlanta African American cohort; MARCH, Michigan Archive for Research on Child Health Cohort; NMFOSAA, N-methyl Perfluorooctane sulfonamido acetic acid; PFDA, perfluorodecanoic acid; PFHxS, perfluorohexane sulfonic acid; PFNA, perfluorononanoic acid; PFOA, perfluorooctanoic acid; PFOS, perfluorooctanesulfonic acid; PFUnDA, Perfluoroundecanoic acid. BKMR, Bayesian kernel machine regression; PCO, Principle Component.

Table 9B.

BKMR Posterior Inclusion Probabilities (PIPs).

PFAS Richness Evenness Diversity Canberra PCO1 Canberra PCO2 Bray-Curtis PCO1 Bray-Curtis PCO2
ATL AA
NMFOSAA 0.08 0.02 0.02 0.44 0.29 0.46 0.36
PFUNDA 0.14 0.08 0.09 0.62 0.40 0.62 0.39
PFDA 0.15 0.02 0.03 0.43 0.33 0.42 0.38
PFOA 0.11 0.02 0.04 0.50 0.32 0.53 0.37
PFNA 0.12 0.01 0.02 0.46 0.28 0.37 0.49
PFHxS 0.05 0.02 0.02 0.36 0.31 0.33 0.29
PFOS 0.16 0.00 0.03 0.47 0.31 0.44 0.39

MARCH
PFHxS 0.11 0.08 0.08 0.32 0.21 0.38 0.34
PFOS 0.12 0.10 0.11 0.32 0.28 0.39 0.38
PFOA 0.17 0.33 0.38 0.47 0.25 0.69 0.37
PFNA 0.13 0.08 0.05 0.29 0.28 0.40 0.34
PFDA 0.21 0.08 0.03 0.27 0.31 0.38 0.35

Model output is summarized and visualized in 3 different ways, as shown in Figure 4, with Fig 4C–D examining mixing effects (i.e. interactions). Similarly, no significant associations were found, and effect sizes were consistent regardless of the quantile used for fixed PFAS measurements. For beta diversity, similar null results for the overall mixture effect were found for the first and second principal coordinates (PCO1 and PCO2) of both Canberra and Bray-Curtis dissimilarity in both ATL AA and MARCH. However, compared to alpha-diversity measures, PIPs were generally higher. For example, in ATL AA, PFUNDA received a PIP of 0.62 for PCO1 of Canberra and Bray Curtis dissimilarity as well as PFOA receiving PIP values of 0.50 and 0.53 for the two diversity measures respectively. In MARCH, PFOA received a PIP of 0.69 for PCO1 of Bray Curtis dissimilarity, meaning a 69% probability of inclusion of PFOA. When Elastic Net Regressions were run, results were consistent with linear regression results, with no associations identified between PFAS compounds and alpha diversity (i.e., all coefficients were shrunk to zero and not retained in models; Table 10). For beta-diversity measures, in ATL AA, R2 values were generally low (ranging from 0.016 to 0.329), indicating PFAS compounds did not explain a large amount of variability in microbiota measurements (Table 10). In fact, the largest observed R2 value was for Bray-Curtis PCO2 (32.9% of variability explained), which was solely due to sequencing depth rather than PFAS compounds, as shrinkage was applied to all models, and PFAS were not retained in the model. Multiple PFAS compounds were only retained for Canberra PCO1, where PFUNDA exhibited a negative association and PFNA exhibited a positive one. In MARCH however, PFOS and PFOA were retained in the Canberra PCO1 and Bray-Curtis PCO2 models, while PFHxS and PFOA were retained in the Bray-Curtis PCO1 model. PFOA was retained in 3 of the 4 beta diversity models, consistent with previous PERMANOVA testing. However, the percentage of variability explained by sequencing depth and retained PFAS compounds was again low, with 0.1% of the variability explained for Canberra PCO1, 3.6% of the variability explained for Bray-Curtis PCO2, and 5.9% of the variability explained for Bray-Curtis PCO1.

Figure 4:

Figure 4:

The association between PFAS mixture and the first principal coordinate (PCO1) of Bray-Curtis using BKMR in ATL AA and MARCH women. A-B: univariate relationship between each PFAS measurement and Bray-Curtis PCO1 (with 95% credible intervals), where all other PFAS measurements are fixed to the median for A) ATL AA and B) MARCH. C-D: the overall effect of the PFAS measurements, by comparing the value of Bray-Curtis PCO1 when all of predictors are at a particular percentile (x-axis) as compared to when all of them are at their 50th percentile for C) ATL AA and D) MARCH. E-F: the effect of a single PFAS measurement (y-axis) being at the 75th vs. 25th percentile, when all remaining PFAS measurements are fixed to a particular percentile (indicated by color) for E) ATL AA and F) MARCH. Numerical data available in Table 9; N=77 for all ATL AA (N with 3rd trimester PFAS); N=61 for MARCH; adjusted for sequencing depth..PFAS, per- and polyfluoroalkyl substances; ATL AA, Atlanta African American cohort; NMFOSAA, N-methyl Perfluorooctane sulfonamido acetic acid; PFDA, perfluorodecanoic acid; PFHxS, perfluorohexane sulfonic acid; PFNA, perfluorononanoic acid; PFOA, perfluorooctanoic acid; PFOS, perfluorooctanesulfonic acid; PFUnDA, Perfluoroundecanoic acid; est, estimate; q_fixed, quartile fixed.

Table 10:

Elastic Net model results for associating PFAS measurements with late pregnancy microbiota outcomes in ATL AA and MARCH women.

Outcome R2* β†
NMFOSAA PFUNDA PFDA PFOA PFNA PFHxS PFOS
ATL AA
Richness 0.085 . . . . . . .
Evenness 0.210 . . . . . . .
Diversity 0.050 . . . . . . .
Canberra PCO1 0.032 . −0.008 . . 0.003 . .
Canberra PCO2 0.093 −0.002 . . . . . .
Bray-Curtis PCO1 0.016 . −0.001 . . . . .
Bray-Curtis PCO2 0.329 . . . . . . .

MARCH
Richness 0.398 . . . . . . .
Evenness 0.003 . . . . . . .
Diversity 0.053 . . . . . . .
Canberra PCO1 0.001 . . . −0.042 . . 0.016
Canberra PCO2 0.485 . . . . . . .
Bray-Curtis PCO1 0.059 . . . 0.055 . 0.004 .
Bray-Curtis PCO2 0.036 . . . −0.038 . . 0.067
*

Amount of variability in outcome explained by retained PFAS measurements and sequencing depth

†

Change in outcome, per log(ng/mL) increase in PFAS measurement. 3rd trimester PFAS only used for ATL AA, while 2nd and 3rd trimester PFAS used for Michigan cohort. N=77 for ATL AA (N with 3rd trimester PFAS); N=61 for MARCH. Adjusted for sequencing depth.

PFAS, per- and polyfluoroalkyl substances; ATL AA, Atlanta African American cohort; MARCH, Michigan Archive for Research on Child Health Cohort; NMFOSAA, N-methyl Perfluorooctane sulfonamido acetic acid; PFDA, perfluorodecanoic acid; PFHxS, perfluorohexane sulfonic acid; PFNA, perfluorononanoic acid; PFOA, perfluorooctanoic acid; PFOS, perfluorooctanesulfonic acid; PFUnDA, Perfluoroundecanoic acid. BKMR, Bayesian kernel machine regression; PCO, Principle Component; R2, coefficient of determination.

Discussion

This study aimed to describe associations of prenatal PFAS exposure with maternal gut microbiome diversity and composition using data from two distinct ECHO sites collected during early and later pregnancy. In both the Michigan and Atlanta cohorts, individual PFAS were not associated with statistically significant differences in stool bacterial richness, evenness, or diversity, and associations with overall compositional differences were diminished after covariate adjustment. Mixtures analysis focusing on beta-diversity measures did not result in strong evidence of interaction or mixture effects, although multiple PFAS were retained in ENR and BKMR models for both cohorts (although the amount of variability explained was low). However, in both cohorts, there were significant associations between prenatal PFAS and the relative abundance of several bacterial families and individual taxa, indicating that PFAS may impact the abundance of specific taxa of the gut microbiome. In this study, we observed significant associations between bacterial families and specific taxa in the gut microbiome of pregnant women primarily with PFOA and PFHxS, but these associations were not shared between cohorts (associations with PFOS, PFNA, PFDA, PFUNDA, and NMFOSAA were also observed when DESeq analysis was completed).

In our study we observed multiple family and ASV/OTU level associations with at least one of 7 PFAS measured in unadjusted or adjusted models, and these associations were predominately cohort-specific. In the ATL AA cohort, where both early and late pregnancy PFAS levels were available, using our most conservative and specialized analysis method, ANCOM-BC2, even after full adjustment we observed a significant positive association between the family Clostridiaceae and 3rd trimester PFOA. At the higher taxonomic resolution, a total of 13 significant associations were identified with all 13 significant associations being with PFOA (12 of 13 were with 3rd trimester PFOA). These included ASVs of the genera Streptococcus, Bacteroides, Anaerostipes, Intestinibacter, Christensenellaceae_R-7_group, Bifidobacterium, and Coprococcus_1, Prevotella buccalis, Porphyromonas, Lachnospiraceae_NK4A136_group, Ruminiclostridium_6, and Lachnospiraceae_UCG-010. Of these, Bifidobacterium exhibited the largest negative effect size (LFC= −8.41), while Lachnospiraceae_UCG-010 exhibited the largest positive effect size (LFC= 3.77). Bifidobacterium normally increases throughout pregnancy and has been implicated as a positive mediator of feto-placental development.89 Our observation linking PFOA exposure to strong decreases in this beneficial bacterium is intriguing and implicate the importance of possible future mechanistic intervention studies focused on this genera. Similarly, the observation that PFOA was significantly negatively associated with Anaerostipes, is potentially clinically relevant as this genus is known to be the main butyrate producer and multiple studies have linked decreased SCFA production to pregnancy outcomes.90 In the Michigan cohort, 6 families reached statistical significance for at least one PFAS measurement after full adjustment using ANCOM-BC2 analyses (i.e., Bacteroidales_unclassified, Bifidobacteriaceae, Campylobacteraceae, Selenomonadales, Enterobacterales_unclassified, Desulfovibrionales, and Selenomonadales_unclassified), but none of these significant associations were seen in ATL AA. In MARCH, most of these family-level associations were with PFHxS and in the negative direction. Interestingly, Bifidobacterium (within the family Bifidobacteriaceae), has been linked to pregnancy complications such as preeclampsia and is known as the primary microbial member in the gut of healthy infants.91 Bifidobacteriaceae species are important for the primary colonization and immune system education during early life, thus any environmental maternal stressors that may modulate levels of these microbes may impact the vertical transmission to offspring.91 At the higher resolution, most bacteria were significantly associated with a single PFAS, however Burkholderiales_unclassified was significantly positively associated with PFDA, PFNA, PFOA, and PFOS while Succiniclasticum was negatively associated with PFNA, PFOA, and PFOS. Information related to these genera and relationships to pregnancy are limited. Similarities between the two cohorts at the genus level were also null. The lack of overlap in observed associations between the two cohorts may be due to differences in sample collection (rectal swab versus whole stool), due to the distinct 16S rRNA primers used to amplify distinct regions of the 16S gene (V3-V4 versus V4), inherent differences in cohort demographics, or the approach to not harmonize datasets prior to analysis. As 7 of 8 major phyla were different in ATL AA compared to MARCH, there was a high likelihood that any significant associations with PFAS would be cohort specific. Although information linking the above-mentioned bacterial families/genera to adverse pregnancy outcomes or offspring health are limited, some evidence points to possible links to metabolism and growth. For example, in unadjusted models, we observed a robust positive association between multiple PFAS and the bacterial family, Carnobacteriaceae, in the Michigan cohort. Carnobacteriaceae are lactic acid-producing bacilli involved in carbohydrate metabolism, and increased levels have been associated with relapsing cholelithiasis.92, 93 Additionally, PFAS were associated with multiple members of the Firmicutes phyla in ATL AA and in MARCH; members of this phylum have been linked to metabolic disorders including obesity during pregnancy.94 Finally, multiple PFAS:Proteobacteria phyla associations were observed in ATL AA (e.g., positive associations between Sutterella and PFOA) and MARCH (e.g., Burkholderiales_unclassified positively associated with PFDA, PFNA, PFOA, and PFOS). Proteobacteria are gram negative bacteria with lipopolysaccharide (LPS) on the microbial membrane which can lead to low-grade inflammation implicated in maternal and child health.95, 96

Our study is one of a few epidemiological studies that have examined associations between PFAS and the maternal gut microbiome. Other human studies have identified associations between PFAS exposures and offspring microbiome composition but have primarily focused on breast milk PFAS concentrations. For example, breastmilk PFOS concentrations were associated with increased diversity at 6 weeks and the sum of breastmilk PFAS associated with Bacteroides vulgatus at 1 year of age.46 In a Norwegian cohort, 1-month postpartum breast milk PFOS levels were significantly associated with 5% less microbiome alpha-diversity while children exposed to high breastmilk PFOA levels lacked a sub-OTU of Lactobacillus zeae and displayed a 1.1-fold increase of a sub-OTU within the genus Enterococcus.42 To our knowledge only one other study has investigated maternal PFAS concentrations and maternal gut microbiome during pregnancy. In a study of 30 pregnant mothers from Finland, six species differed during pregnancy by PFAS quartiles. Methanobrevibacter smithii, unclassified Methanobrevibacter sequences, and Subdoligranulum variabile abundances were increased in highly exposed mothers, while Erysipelotrichaceae bacterium 6145, Bacteroides nordii and Ruminococcus lactaris were decreased with higher exposures. This important work used metagenomic sequencing techniques which limits direct comparisons with our observations but provides additional insights into how PFAS may impact on maternal and offspring microbiome form and function.45

Since PFAS exposures do not occur in isolation, we used ENR and BKMR to correlate a mixture of PFAS with alpha and beta diversity metrics and found that PFAS mixtures also had a minor effect on variability of gut bacteria. Over the past several years, mixture modeling, such as weight quantile sum (WQS) regression, Lasso, ENR, and BKMR, has been adapted for use in the environmental health sciences to estimate the health effects of multi-pollutant mixtures. 78, 82, 97–99 We utilized ENR and BKMR for their flexibility and robustness. Other pregnancy studies have utilized BKMR to investigate how mixtures of PFAS are associated with a variety of outcomes including gestational diabetes, thyroid hormones and preterm birth. PIPs for specific PFAS reported in these studies were similar to what we report here for beta diversity measures.100–102 Here, no strong mixing effects of PFAS (i.e., statistical interactions) were demonstrated between PFAS and diversity metrics. The null results observed may be influenced by our relatively small number of detectable PFAS used in these models and relatively small number of subjects. As exposomics and untargeted-based approaches become more common in large pregnancy cohort studies such as ECHO, these types of mixture methodologies may become more useful in elucidating links between body burden of exposure and health outcomes.

The mechanism for how PFAS alter the microbiome is still unclear, but multiple direct and indirect effects have been hypothesized. Previous studies in mice suggest PFAS accumulate in the liver and greatly impact hepatic metabolic pathways, such as lipid and glucose metabolism, and increase oxidative stress and inflammation.103 Alterations in lipid and glucose metabolism can impact what is absorbed from the digestive system and therefore could alter the substrates available for the microbiome to utilize, leading to a change in relative microbiota populations. Additionally, we and others have shown that PFAS can impact on primary and secondary bile acid levels through multiple mechanisms including effects at the site of liver and intestine.104, 105 Bile acids have been shown to have inherent antimicrobial properties, bile acid levels shift throughout pregnancy, and extremely high levels can lead to intrahepatic cholestasis of pregnancy and subsequently adverse pregnancy outcomes.106–108 Also, PFAS have been shown to increase oxidative stress and impact inflammation which could contribute to a leaky-gut membrane and decreased production of SCFAs, and perhaps lead to alterations in gut microbiome substrates and populations.109, 110 In addition to these indirect effects on the host, there is some evidence of direct cytotoxicity of PFAS on bacteria, although most of this work has focused on environmentally-relevant bacteria.111 Researchers have shown that PFAS, especially long-chain PFAS, can cause oxidative stress or DNA damage, growth inhibition, and impacts on bacterial cell walls.112 More work needs to be done using mammalian relevant bacteria to elucidate if these surfactant chemicals can directly modulate microbiome form and function.

One strength of this study is the utilization of two distinct ECHO sites of pregnant women, with each cohort representing distinct populations of mothers. Although sample sizes were relatively similar for each cohort, we did observe more significant taxa associations between later pregnancy PFAS and later maternal microbiome in MARCH than in ATL AA when ANCOM-BC2 analysis was utilized. The majority of the MARCH cohort participants were from Ann Arbor, Michigan, and predominately white, older than ATL AA and with lower BMI. Studying associations between PFAS and microbiome composition in diverse cohorts is important as exposures to environmental chemicals as well as toxicological effects can vary due to geographical, structural racism, or lifestyle differences. Increased age has been associated with higher body burdens of PFAS.113, 114 In our study however, some concentrations of PFAS were higher in ATL AA mothers compared to MARCH mothers, particularly PFHxS, PFNA, and PFDA during later pregnancy, but we hesitate to make strong comparisons due to serum versus plasma differences (although concentrations within the two blood matrices appear similar for many PFAS).115 Additionally, there were differences in when later pregnancy plasma or serum was collected which could impact on PFAS concentrations.116 Multiple large studies including the National Health and Nutrition Examination Survey have shown that race is a significant predictor of PFAS concentrations, but the direction of association is not always reproducible. In comparison to other pregnancy cohorts of similar timeframe and national averages, concentrations of the abundant PFAS here were for the most part similar except for PFHxS which seems to be higher in both ATL AA and MARCH and PFOA which is lower.40, 117 An interesting finding in our study is PFAS levels increased over the progression of pregnancy. This finding was recently reported for the full Atlanta African American Maternal-Child Cohort and authors implicate continued exposures via drinking water and increased exposures via dietary changes, personal care, or cosmetics perhaps unique to the African American cohort.64 This interesting observation is different compared to other cohorts which report decreased circulating PFAS throughout pregnancy.116 Hypotheses of this decrease include physiological changes during pregnancy in renal function, hepatic metabolism, and blood volume, as well as placental transfer to the fetus.116, 118, 119 More work to elucidate underlying biobehavioral sources of PFAS variability, especially during pregnancy, is critical, as concentrations of these pollutants are likely socially patterned and impacted by dietary and other behavior-related choices.114, 120, 121 Fish and meat associated with increased PFAS levels in some studies113, 122 as well as processed or packaged foods32 in other reports. Here, we did not observe strong associations between maternal diet variables and circulating PFAS levels except for an inverse relationship with fiber intake. Other studies have shown inverse fiber associations with PFOA, PFNA, and PFOS, but it is not well established if these observations are due to increased excretion of PFAS or by possible cholesterol confounding.123 Lastly, geographical location can impact PFAS levels through ground water sources, with residents living close to wastewater treatment facilities, manufacturing plants, and military bases seen to have higher levels of PFAS.124, 125

Our study has limitations that may have impacted observed associations between PFAS exposures and the pregnancy gut microbiome. The primary limitation is an analysis strategy that did not attempt to harmonize the 16S results between the two cohorts. Due to the multiple reasons described above, especially differences in microbiome sampling strategies, we instead focused on separate analyses and a “posthoc” examination of similar trends between cohorts. With the initiation of the second phase of the ECHO program, harmonization of microbiome datasets will be more feasible and will better allow for comparisons between cohorts. The authors here had no control of cohort-specific sampling conditions, timing, sequencing strategies, and PFAS quantitation. A limitation of the ECHO cycle 1 research platform is that it represents a collection of independent cohorts and investigators with unique study protocols, data collection, and biological sampling across numerous sites. For example, although both cohorts collected biological specimens during later pregnancy, analyses for MARCH included data from 2nd and 3rd trimester whereas ATL AA was solely from 3rd trimester, which also limits direct comparisons between the cohorts. Additionally, PFAS as a class represents over 4000 individual chemicals found in the environment, but the analytical approaches used for this study focused on a small subset of primarily well characterized long-chain legacy compounds. Although emerging short-chain and fluorotelomer replacements (e.g., 6:2 FTS/GenX) likely have considerably shorter biological half-lives than legacy long-chain (e.g., PFOS/PFOA), these newer compounds have been recently found at high concentrations throughout the world and are detectable in the blood of humans. While focusing on a subset of abundantly identified PFAS, as done here (i.e. 50% detectable here), is common in environmental epidemiology. Mixture studies incorporating the lower abundant PFAS may increase the chance of observing significant interactions. A third limitation is a lack of an additional more complex regression model that includes additional covariates known to relate to the variability of the microbiome or exposure. Although we have added covariates including maternal diet, additional unexplored variables including maternal exercise, sleep patterns, and socioeconomic status126–128 may have also impacted on the significance of observed associations and may be useful to investigate in future studies. Similarly, a brief dietary screener (in the MARCH cohort) and a FFQ (in the Atlanta cohort) were chosen as the diet assessment tools for their brevity and their previous validation against gold-standard diet assessment methods (i.e., multiple 24-hour dietary recalls). Comprehensive diet assessment, including probiotics/prebiotics was not feasible at the time due to the many competing data elements that were collected. An additional limitation is a lack of examining the impact of first trimester PFAS on how the maternal microbiome shifts from early to late pregnancy. As PFAS have been shown to be modulators of the immune system, act as endocrine disrupting chemicals, and perturb metabolism, it is plausible to hypothesize that PFAS could impact on microbiome flux during pregnancy. Finally, this study is focusing solely on 16S rRNA results to identify microbiome composition/form, and each site included here used distinct 16S primers and unique sequencing processing pipelines. Future research should include metagenomics-based approaches as well as metabolomics to allow for the measurement of microbiota-derived metabolites and identification of specific biological pathways associated with perturbations in the function of the microbiome.

The clinical significance of the observed microbiome alterations is difficult to estimate and likely premature, however, several species/strains within bacterial families significantly associated with PFAS have been associated with human pathophysiology. For example, Bacteroidales, negatively associated with PFAS here, function to produce SCFAs to maintain gut barrier stability and metabolize bile acids.129 Decreased levels could lead to leaky-gut barrier, inability to re-use bile acid products, and could predispose colonization of the gut by pathogenic bacteria. Additionally, the family Clostridiaceae, seen to be positively associated with PFOA in third trimester women in ATL AA, contains the pathogen Clostridium difficile, which causes pseudomembranous colitis and toxic megacolon as well as Clostridium botulinum and tetani, responsible for botulism and tetanus illnesses, respectively.130, 131. With these observations, it would be interesting to examine associations between circulating PFAS and toxic metabolites created by pathogens as well as disease severity and recalcitrance to therapeutics. As the gut microbiome has a systemic impact on overall human health including critical periods of development such as pregnancy, it is extremely relevant to further investigate this mechanism and human health outcomes. Future studies that leverage metagenomics-based approaches in well characterized pregnancy cohorts are critical to identify microbiota-focused biomarkers of environmental perturbation or possible therapeutic targets to decrease disease risk associated with environmental chemicals.

In summary, maternal PFAS were significantly associated with changes in cohort-specific taxa of the gut microbiome during pregnancy, but not overall diversity measures. Future studies will examine if these microbiome associations mediate PFAS-induced maternal and offspring health outcomes.

Supplementary Material

1
2

Highlights.

  • ATL AA mothers had different microbiome composition than MARCH as well as higher circulating PFHxS, PFNA and PFDA.

  • 16 significant family-level associations were identified for ATL AA and 13 significant family-level associations identified for MARCH.

  • In both cohorts, alpha and beta diversity measures were not significantly associated with any PFAS.

  • Chemical mixture analyses provided modest evidence of inclusion of individual PFAS in beta diversity models in both cohorts.

Acknowledgements:

We acknowledge Wadsworth HHEAR collaborators for measuring maternal PFAS concentrations for this study. The authors wish to thank our ECHO Colleagues; the medical, nursing, and program staff; and the children and families participating in the ECHO cohorts. We also acknowledge the contribution of the following ECHO Program collaborators: ECHO Components—Coordinating Center: Duke Clinical Research Institute, Durham, North Carolina: Smith PB, Newby LK; Data Analysis Center: Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland: Jacobson LP; Research Triangle Institute, Durham, North Carolina: Catellier DJ; Person-Reported Outcomes Core: Northwestern University, Evanston, Illinois: Gershon R, Cella D; • Human Health Exposure Analysis Resource: Wadsworth Center, Menands, New York: Parsons P, Kurunthachalam K; RTI International, Research Triangle Park, North Carolina: Fennell TR, Sumner SJ, Du X. ECHO Awardees and Cohorts— Michigan State University, East Lansing, MI: Kerver JM; Henry Ford Health, Detroit, MI: Barone C; Michigan Department of Health and Human Services, Lansing, MI: Fussman C; Michigan State University, East Lansing, MI: Paneth N; University of Michigan, Ann Arbor, MI: Elliott M; Wayne State University, Detroit, MI: Ruden D.

Funding Source:

Research reported in this publication was supported by the Office of the Director at the National Institutes of Health under award numbers U2COD023375 (Coordinating Center and Petriello’s Opportunities and Infrastructure Fund Award), U24OD023382 (Data Analysis Center), U24OD023319 with co-funding from the Office of Behavioral and Social Science Research (PRO Core), U2CES026542 (HHEAR Parsons, Kannan), U2CES030857 (HHEAR Fennell, Sumner, Du), UG3/UH3OD023318 (Dunlop), UG3/OD023285 and UH3OD023285 (Kerver), the Michigan Health Endowment Fund under award numbers G-1608-140432 and R-1605-140007 and from Michigan State University Center for Research in Autism, Intellectual and Neurodevelopmental Disabilities (C-RAIND). This research could not have been done without the collaboration of Hurley Medical Center and Hurley Residency Clinic in Flint, MI, Hutzel Medical Center, DMC Center for Obstetrics and Gynecology, and University Health Center in Detroit, MI Munson Hospital and Grand Traverse Women’s Clinic in Traverse City, MI, University of Michigan Hospital, Von Voigtlander Women’s Center, West Ann Arbor Health Center, and Obstetrics and Gynecology at Briarwood Center in Ann Arbor, MI, St. John’s Providence Park, Metro Partners in Women’s Health, and Women’s Health Consultants in Novi, MI, St. Joseph Mercy Hospital, IHA Canton Obstetrics and Gynecology, and IHA Domino Farms in Ann Arbor, MI, Sinai Grace Hospital, Sinai Grace OB-GYN Women’s Health Centers, Northwest Women’s Care, and DMC Northwest Women’s Care in Detroit, MI, Beaumont Dearborn Hospital and Oakwood OB-GYN Associates in Dearborn, MI, Covenant Hospital, Central Michigan University Health in Saginaw, MI, SHMG OB/GYN, Grand Rapids Women’s Health, and Spectrum Health in Grand Rapids, MI, Blue Water OB/GYN, NorthPointe OB/GYN, McLaren Port Huron Hospital in Port Huron, MI. This work was supported by the Environmental Influences on Child Health Outcomes (ECHO) program, Office of the Director, National Institutes of Health, under Award Numbers 5U2COD023375-05/A03-3824, the National Institute of Health (NIH) research grants [R21ES032117, R01NR014800, R01MD009064, R24ES029490, R01MD009746], NIH Center Grants [P50ES02607, P30ES019776, UH3OD023318, U2CES026560, U2CES026542], and Environmental Protection Agency (USEPA) center grant [83615301]. Associated faculty were supported in part by the National Institute of Environmental Health Sciences [P30ES036084, P42ES030991, R01ES034407-01A1, R01ES035692-01A1] at the National Institutes of Health. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

Footnotes

Conflicts of Interest: No conflicts financial or otherwise to report.

Declaration of Interest Statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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