Per- and polyfluoroalkyl substances (PFAS), perceived stress, and depressive symptoms in a prospective cohort study of black women

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are endocrine-disrupting chemicals with neurotoxic properties. PFAS have been associated with depressive symptoms among women in some studies, but little research has evaluated the effects of PFAS mixtures. Further, no study has investigated interactions of PFAS-depression associations by perceived stress, which has been shown to modify the effects of PFAS on other health outcomes.

OBJECTIVE

In a prospective cohort study of reproductive-aged Black women, we investigated associations between PFAS and depressive symptoms and the extent to which perceived stress modified these associations.

METHODS

We analyzed data from 1499 participants (23-35 years) in the Study of Environment, Lifestyle, and Fibroids. We quantified concentrations of nine PFAS in baseline plasma samples using online solid-phase extraction-liquid chromatography-isotope dilution tandem mass spectrometry. Participants reported perceived stress via the Perceived Stress Scale (PSS-4; range = 0-16) at baseline and depressive symptoms via the Center for Epidemiologic Studies Depression Scale (CESD; range = 0-44) at the 20-month follow-up visit. We used Bayesian Kernel Machine Regression to estimate associations between PFAS concentrations, individually and as a mixture, and depressive symptoms, and to assess effect modification by PSS-4 scores, adjusting for confounders.

RESULTS

Baseline perfluorodecanoic acid concentrations were associated with greater depressive symptoms at the 20-month follow-up, but associations for other PFAS were null. The PFAS were not associated with depressive symptoms when evaluated as a mixture. The association between the 90th percentile (vs. 50th percentile) of the PFAS mixture with CES-D scores was null at the 10th (β = 0.03; 95 % CrI = 0.20, 0.25), 50th (β = 0.02; 95 % CrI = -0.16, 0.19), and 90th (β = 0.01; 95 % CrI = 0.18, 0.20) percentiles of PSS-4 scores, suggesting perceived stress did not modify the PFAS mixture.

CONCLUSION

In this prospective cohort study, PFAS concentrations-assessed individually or as a mixture-were not appreciably associated with depressive symptoms, and there was no evidence of effect modification by perceived stress.

Non-persistent endocrine disrupting chemical mixtures and uterine leiomyomata in the study of environment, lifestyle and fibroids (SELF)

BACKGROUND

Results of studies investigating associations between individual endocrine-disrupting chemicals (EDCs) and incidence of uterine leiomyomata (UL), a hormone-dependent gynecological condition, have been inconsistent. However, few studies have evaluated simultaneous exposure to a mixture of EDCs with UL incidence.

METHODS

We conducted a case-cohort analysis (n = 708) of data from the Study of the Environment, Lifestyle and Fibroids (SELF), a prospective cohort study. Participants were aged 23-35 years at enrollment, had an intact uterus, and identified as Black or African American. We measured biomarker concentrations of 21 non-persistent EDCs, including phthalates, phenols, parabens, and triclocarban, in urine collected at baseline, 20-month, and 40-month clinic visits. We ascertained UL incidence and characteristics using ultrasounds at baseline and approximately every 20 months through 60 months. We used probit Bayesian Kernel Machine Regression (BKMR-P) to evaluate joint associations between EDC mixtures with cumulative UL incidence. We estimated the mean difference in the probit of UL incidence over the study period, adjusting for baseline age, education, years since last birth, parity, smoking status and body mass index. We converted probit estimates to odds ratios for ease of interpretation.

RESULTS

We observed that urinary concentrations of the overall EDC mixture were inversely associated with UL incidence in the overall mixtures model, with the strongest inverse associations at the 70th percentile of all biomarkers compared with their 50th percentile (odds ratio = 0.59; 95% confidence interval: 0.36, 0.96). Strongest contributors to the joint association for the mixture were bisphenol S (BPS), ethyl paraben (EPB), bisphenol F (BPF) and mono (2-ethyl-5-carboxypentyl) phthalate (MECPP), which each demonstrated inverse associations except for MECPP. There was suggestive evidence of an interaction between MECPP and EPB.

CONCLUSION

In this prospective ultrasound study, we observed evidence of an inverse association between the overall mixture of urinary biomarker concentrations of non-persistent EDCs with UL incidence.

Personal Care Products, Socioeconomic Status, and Endocrine-Disrupting Chemical Mixtures in Black Women

Personal care products (PCPs) are sources of exposure to endocrine-disrupting chemicals (EDCs) among women, and socioeconomic status (SES) may influence these exposures. Black women have inequitable exposure to EDCs from PCP use, but no study has investigated how exposure to EDCs through PCPs may vary by SES, independent of race. Using data from the Study of Environment, Lifestyle, and Fibroids, a cohort of reproductive-aged Black women (n = 751), we quantified associations between PCPs and urinary biomarker concentrations of EDC mixtures (i.e., phthalates, phenols, parabens) within SES groups, defined using k-modes clustering based on education, income, marital status, and employment. Information about PCP use and SES was collected through questionnaires and interviews. We used principal component analysis to characterize the EDC mixture profiles. Stratified linear regression models were fit to assess associations between PCP use and EDC mixture profiles, quantified as mean differences in PC scores, by SES group. Associations between PCP use and EDC mixture profiles varied by SES group; e.g., vaginal powder use was associated with a mixture of phenols among lower SES women, whereas this association was null for higher SES women. Findings suggest that SES influences PCP EDC exposure in Black women, which has implications for public health interventions.

An Industry-Relevant Metal Mixture, Iron Status, and Reported Attention-Related Behaviors in Italian Adolescents

BACKGROUND

Exposure to environmental metals has been consistently associated with attention and behavioral deficits in children, and these associations may be modified by coexposure to other metals or iron (Fe) status. However, few studies have investigated Fe status as a modifier of a metal mixture, particularly with respect to attention-related behaviors.

METHODS

We used cross-sectional data from the Public Health Impact of Metals Exposure study, which included 707 adolescents (10-14 years of age) from Brescia, Italy. Manganese, chromium, and copper were quantified in hair samples, and lead was quantified in whole blood, using inductively coupled plasma mass spectrometry. Concentrations of Fe status markers (ferritin, hemoglobin, transferrin) were measured using immunoassays or luminescence assays. Attention-related behaviors were assessed using the Conners Rating Scales Self-Report Scale-Long Form, Parent Rating Scales Revised-Short Form, and Teacher Rating Scales Revised-Short Form. We employed Bayesian kernel machine regression to examine associations of the metal mixture with these outcomes and evaluate Fe status as a modifier.

RESULTS

Higher concentrations of the metals and ferritin were jointly associated with worse self-reported attention-related behaviors: metals and ferritin set to their 90th percentiles were associated with 3.0% [β = 0.03 ; 95% credible interval (CrI): - 0.01 , 0.06], 4.1% (β = 0.04 ; 95% CrI: 0.00, 0.08), and 4.1% (β = 0.04 ; 95% CrI: 0.00, 0.08) higher T -scores for self-reported attention deficit/hyperactivity disorder (ADHD) index, inattention, and hyperactivity, respectively, compared with when metals and ferritin were set to their 50th percentiles. These associations were driven by hair manganese, which exhibited nonlinear associations with all self-reported scales. There was no evidence that Fe status modified the neurotoxicity of the metal mixture. The metal mixture was not materially associated with any parent-reported or teacher-reported scale.

CONCLUSIONS

The overall metal mixture, driven by manganese, was adversely associated with self-reported attention-related behavior. These findings suggest that exposure to multiple environmental metals impacts adolescent neurodevelopment, which has significant public health implications. https://doi.org/10.1289/EHP12988.

Assessing the mediating role of iron status on associations between an industry-relevant metal mixture and verbal learning and memory in Italian adolescents

BACKGROUND

Metals, including lead (Pb), manganese (Mn), chromium (Cr) and copper (Cu), have been associated with neurodevelopment; iron (Fe) plays a role in the metabolism and neurotoxicity of metals, suggesting Fe may mediate metal-neurodevelopment associations. However, no study to date has examined Fe as a mediator of the association between metal mixtures and neurodevelopment.

OBJECTIVE

We assessed Fe status as a mediator of a mixture of Pb, Mn, Cr and Cu in relation to verbal learning and memory in a cohort of Italian adolescents.

METHODS

We used cross-sectional data from 383 adolescents (10-14 years) in the Public Health Impact of Metals Exposure Study. Metals were quantified in blood (Pb) or hair (Mn, Cr, Cu) using ICP-MS, and three markers of Fe status (blood hemoglobin, serum ferritin and transferrin) were quantified using luminescence assays or immunoassays. Verbal learning and memory were assessed using the California Verbal Learning Test for Children (CVLT-C). We used Bayesian Kernel Machine Regression Causal Mediation Analysis to estimate four mediation effects: the natural direct effect (NDE), natural indirect effect (NIE), controlled direct effect (CDE) and total effect (TE). Beta (β) coefficients and 95 % credible intervals (CIs) were estimated for all effects.

RESULTS

The metal mixture was jointly associated with a greater number of words recalled on the CVLT-C, but these associations were not mediated by Fe status. For example, when ferritin was considered as the mediator, the NIE for long delay free recall was null (β = 0.00; 95 % CI = -0.22, 0.23). Conversely, the NDE (β = 0.23; 95 % CI = 0.01, 0.44) indicated a beneficial association of the mixture with recall that operated independently of Fe status.

CONCLUSION

An industry-relevant metal mixture was associated with learning and memory, but there was no evidence of mediation by Fe status. Further studies in populations with Fe deficiency and greater variation in metal exposure are warranted.

Early-life manganese exposure during multiple developmental periods and adolescent verbal learning and memory

BACKGROUND

Manganese (Mn) is both an essential and toxic metal, and associations with neurodevelopment depend on exposure timing. Prospective data examining early life Mn with adolescent cognition are sparse.

METHODS

We enrolled 140 Italian adolescents (10-14 years old) from the Public Health Impact of Metals Exposure study. Mn in deciduous teeth was measured using laser ablation-mass spectrometry to represent prenatal, postnatal and early childhood exposure. The California Verbal Learning Test for Children (CVLT-C) was administered to assess adolescent verbal learning and memory. Multivariable regression models estimated changes in CVLT-C scores and the odds of making an error per doubling in dentine Mn in each exposure period. Multiple informant models tested for differences in associations across exposure periods.

RESULTS

A doubling in prenatal dentine Mn levels was associated with lower odds of making an intrusion error (OR = 0.23 [95% CI: 0.09, 0.61]). This beneficial association was not observed in other exposure periods. A doubling in childhood Mn was beneficially associated with short delay free recall: (ß = 0.47 [95% CI: -0.02, 0.97]), which was stronger in males (ß = 0.94 [95% CI: 0.05, 1.82]). Associations were null in the postnatal period.

CONCLUSION

Exposure timing is critical for understanding Mn-associated changes in cognitive function.

Correlates of whole blood metal concentrations among reproductive-aged Black women

BACKGROUND

Metals may influence reproductive health, but few studies have investigated correlates of metal body burden among reproductive-aged women outside of pregnancy. Furthermore, while there is evidence of racial disparities in exposure to metals among U.S. women, there is limited research about correlates of metal body burden among Black women.

OBJECTIVE

To identify correlates of whole blood metal concentrations among reproductive-aged Black women.

METHODS

We analyzed cross-sectional data from a cohort of 1664 Black women aged 23-35 years in Detroit, Michigan, 2010-2012. We collected blood samples and questionnaire data. We measured concentrations of 17 metals in whole blood using inductively-coupled plasma-mass spectrometer-triple quadrupole and total mercury using Direct Mercury Analyzer-80. We used multivariable linear regression models to identify sociodemographic, environmental, reproductive, and dietary correlates of individual metal concentrations.

RESULTS

In adjusted models, age was positively associated with multiple metals, including arsenic, cadmium, and mercury. Education and income were inversely associated with cadmium and lead. Current smoking was strongly, positively associated with cadmium and lead. Alcohol intake in the past year was positively associated with arsenic, barium, copper, lead, mercury, vanadium, and zinc. Having pumped gasoline in the past 24 h was positively associated with cadmium, chromium, and molybdenum. Having lived in an urban area for the majority of residence in Michigan was positively associated with arsenic, lead, and nickel. Higher water intake in the past year was positively associated with several metals, including lead. Fish intake in the past year was positively associated with arsenic, cesium, and mercury. We also observed associations with body mass index, season, and other environmental, reproductive, and dietary factors.

SIGNIFICANCE

We identified potential sources of exposure to metals among reproductive-aged Black women. Our findings improve understanding of exposures to metals among non-pregnant reproductive-aged women, and can inform policies in support of reducing disparities in exposures.

IMPACT STATEMENT

There are racial disparities in exposures to metals. We analyzed correlates of blood metal concentrations among reproductive-aged Black women in the Detroit, Michigan metropolitan area. We identified sociodemographic, anthropometric, lifestyle, environmental, reproductive, and dietary correlates of metal body burden. Age was positively associated with several metals. Education and income were inversely associated with cadmium and lead, indicating socioeconomic disparities. We identified potential exposure sources of metals among reproductive-aged Black women, including smoking, environmental tobacco smoke, pumping gasoline, living in an urban area, and intake of alcohol, water, fish, and rice.

A prospective ultrasound study of cigarette smoking and uterine leiomyomata incidence and growth

BACKGROUND

Uterine leiomyomata (fibroids) are common, benign neoplasms that contribute substantially to gynecologic morbidity. Some existing epidemiologic studies indicate that cigarette smoking is associated with lower uterine leiomyomata risk. However, no prospective studies have systematically screened an entire study population for uterine leiomyomata using transvaginal ultrasound or evaluated the association between cigarette smoking and uterine leiomyomata growth.

OBJECTIVE

This study aimed to examine the association between cigarette smoking and uterine leiomyomata incidence and growth in a prospective ultrasound study.

STUDY DESIGN

We enrolled 1693 residents from the Detroit metropolitan area into the Study of Environment, Lifestyle, and Fibroids during 2010 to 2012. Eligible participants were aged 23 to 34 years, had an intact uterus but no previous diagnosis of uterine leiomyomata, and self-identified as Black or African American. We invited participants to complete a baseline visit and 4 follow-up visits over approximately 10 years. At each visit, we used transvaginal ultrasound to assess uterine leiomyomata incidence and growth. Participants provided extensive self-reported data throughout follow-up including exposures to active and passive cigarette smoking in adulthood. We excluded participants who did not return for any follow-up visits (n=76; 4%). We fit Cox proportional hazards regression models to estimate hazard ratios and 95% confidence intervals for the association between time-varying smoking history and incidence rates of uterine leiomyomata. We fit linear mixed models to estimate the percentage difference and 95% confidence intervals for the association between smoking history and uterine leiomyomata growth. We adjusted for sociodemographic, lifestyle, and reproductive factors. We interpreted our results based on magnitude and precision rather than binary significance testing.

RESULTS

Among 1252 participants without ultrasound evidence of uterine leiomyomata at baseline, uterine leiomyomata were detected in 394 participants (31%) during follow-up. Current cigarette smoking was associated with a lower uterine leiomyomata incidence rate (hazard ratio, 0.67; 95% confidence interval, 0.49-0.92). Associations were stronger among participants who had smoked for longer durations (≥15 years vs never: hazard ratio, 0.49; 95% confidence interval, 0.25-0.95). The hazard ratio for former smokers was 0.78 (95% confidence interval, 0.50-1.20). Among never smokers, the hazard ratio for current passive smoke exposure was 0.84 (95% confidence interval, 0.65-1.07). Uterine leiomyomata growth was not appreciably associated with current (percent difference, -3%; 95% confidence interval, -13% to 8%) or former (percent difference, -9%; 95% confidence interval, -22% to 6%) smoking.

CONCLUSION

We provide evidence from a prospective ultrasound study that cigarette smoking is associated with lower uterine leiomyomata incidence.

Associations of an industry-relevant metal mixture with verbal learning and memory in Italian adolescents: The modifying role of iron status

BACKGROUND

Biomarker concentrations of metals are associated with neurodevelopment, and these associations may be modified by nutritional status (e.g., iron deficiency). No prior study on associations of metal mixtures with neurodevelopment has assessed effect modification by iron status.

OBJECTIVES

We aimed to quantify associations of an industry-relevant metal mixture with verbal learning and memory among adolescents, and to investigate the modifying role of iron status on those associations.

METHODS

We used cross-sectional data from 383 Italian adolescents (10-14 years) living in proximity to ferroalloy industry. Verbal learning and memory was assessed using the California Verbal Learning Test for Children (CVLT-C), and metals were quantified in hair (manganese, copper, chromium) or blood (lead) using inductively coupled plasma mass spectrometry. Serum ferritin, a proxy for iron status, was measured using immunoassays. Covariate-adjusted associations of the metal mixture with CVLT subtests were estimated using Bayesian Kernel Machine Regression, and modification of the mixture associations by ferritin was examined.

RESULTS

Compared to the 50th percentile of the metal mixture, the 90th percentile was associated with a 0.12 standard deviation [SD] (95% CI = -0.27, 0.50), 0.16 SD (95% CI = -0.11, 0.44), and 0.11 SD (95% CI = -0.20, 0.43) increase in the number of words recalled for trial 5, long delay free, and long delay cued recall, respectively. For an increase from its 25th to 75th percentiles, copper was beneficially associated the recall trials when other metals were fixed at their 50th percentiles (for example, trial 5 recall: β = 0.31, 95% CI = 0.14, 0.48). The association between copper and trial 5 recall was stronger at the 75th percentile of ferritin, compared to the 25th or 50th percentiles.

CONCLUSIONS

In this metal mixture, copper was beneficially associated with neurodevelopment, which was more apparent at higher ferritin concentrations. These findings suggest that metal associations with neurodevelopment may depend on iron status, which has important public health implications.

Environmental Metal Exposure, Neurodevelopment, and the Role of Iron Status: a Review

PURPOSE OF REVIEW

Exposure to environmental metals, like lead (Pb), manganese (Mn), and methylmercury (Me-Hg), has consistently been implicated in neurodevelopmental dysfunction. Recent research has focused on identifying modifying factors of metal neurotoxicity in childhood, such as age, sex, and co-exposures. Iron (Fe) status is critical for normal cognitive development during childhood, and current mechanistic, animal, and human evidence suggests that Fe status may be a modifier or mediator of associations between environmental metals and neurodevelopment. The goals of this review are to describe the current state of the epidemiologic literature on the role of Fe status (i.e., hemoglobin, ferritin, blood Fe concentrations) and Fe supplementation in the relationship between metals and children's neurodevelopment, and to identify research gaps.

RECENT FINDINGS

We identified 30 studies in PubMed and EMBASE that assessed Fe status as a modifier, mediator, or co-exposure of associations of Pb, Me-Hg, Mn, copper (Cu), zinc (Zn), arsenic (As), or metal mixtures measured in early life (prenatal period through 8 years of age) with cognition in children. In experimental studies, co-supplementation of Fe and Zn was associated with better memory and cognition than supplementation with either metal alone. Several observational studies reported interactions between Fe status and Pb, Mn, Zn, or As in relation to developmental indices, memory, attention, and behavior, whereby adverse associations of metals with cognition were worse among Fe-deficient children compared to Fe-sufficient children. Only two studies quantified joint associations of complex metal mixtures that included Fe with neurodevelopment, though findings from these studies were not consistent. Findings support memory and attention as two possible cognitive domains that may be both vulnerable to Fe deficiency and a target of metals toxicity. Major gaps in the literature remain, including evaluating Fe status as a modifier or mediator of metal mixtures and cognition. Given that Fe deficiency is the most common nutritional deficiency worldwide, characterizing Fe status in studies of metals toxicity is important for informing public health interventions.

Waxing activity as a potential source of exposure to per- and polyfluoroalkyl substances (PFAS) and other environmental contaminants among the US ski and snowboard community

BACKGROUND

Skiers and snowboarders apply waxes and solvents to their equipment to enhance glide across the snow. Waxing results in exposures to per- and polyfluoroalkyl substances (PFAS) and particulate matter, which have been associated with adverse health effects among professional wax technicians in Scandinavia. However, little is known about exposure among people who participate at other levels of sport, including recreationally, in other regions.

OBJECTIVE

We sought to characterize wax-related exposures among US skiers and snowboarders who participate across numerous levels of sport to expand scientific understanding of environmental health risks among this population.

METHODS

We used an anonymous electronic survey to evaluate wax-related exposures among US cross-country and downhill skiers and snowboarders. Specifically, we assessed (Fang et al., 2020): duration of time involved with each sport in any role (Freberg et al., 2013), intensity of wax-related exposures based on time spent in waxing areas, wax use, and wax type (Rogowski et al., 2007), frequency of fluorinated wax application, and (Freberg et al., 2010) use of exposure interventions.

RESULTS

Participants tended to be long-term winter sports enthusiasts (e.g., median downhill skiing duration: 31 years). Nearly all (92%) participants personally applied some wax to their skis/snowboards and most applied waxes containing PFAS (67%) and solvents (62%). Ski professionals waxed the most pairs of skis with fluorinated waxes annually (median (IQR): 20 (1, 100)), though individuals participating recreationally also applied fluorinated waxes regularly. Exposure interventions were not widely used.

SIGNIFICANCE

Waxing activities may pose significant risk of exposure to PFAS and other environmental contaminants among the US ski and snowboard community. Efforts are needed to reduce these exposures through changes to wax use patterns and broader adoption of exposure reduction strategies.

Correlates of non-persistent endocrine disrupting chemical mixtures among reproductive-aged Black women in Detroit, Michigan

Some studies indicate that Black women have higher exposure to multiple non-persistent endocrine disrupting chemicals (EDCs) than white women, but little is known about correlates of exposure to EDC mixtures. Using baseline data from a prospective cohort study of reproductive-aged Black women (N = 751), we characterized profiles of EDC mixtures and identified correlates of exposure. At baseline, we quantified biomarkers of 16 phthalates, 7 phenols, 4 parabens, and triclocarban in urine and collected covariate data through self-administered questionnaires and interviews. We used principal component (PC) analysis and k-means clustering to describe EDC mixture profiles. Associations between correlates and PCs were estimated as the mean difference (β) in PC scores, while associations between correlates and cluster membership were estimated as the odds ratio (OR) of cluster membership. Personal care product use was consistently associated with profiles of higher biomarker concentrations of non-persistent EDCs. Use of nail polish, menstrual and vaginal products (e.g., vaginal powder, vaginal deodorant), and sunscreen was associated with a mixture of phthalate and some phenol biomarkers using both methods. Current vaginal ring use, a form of hormonal contraception placed inside the vagina, was strongly associated with higher concentrations of high molecular weight phthalate biomarkers (k-means clustering: OR = 2.42, 95% CI = 1.28, 4.59; PCA: β = -0.32, 95% CI = -0.71, 0.07). Several dietary, reproductive, and demographic correlates were also associated with mixtures of EDC biomarkers. These findings suggest that personal care product use, diet, and contraceptive use may be sources of exposure to multiple non-persistent EDCs among reproductive-aged Black women. Targeted interventions to reduce exposure to multiple EDCs among Black women are warranted.

Multiple metals in children's deciduous teeth: results from a community-initiated pilot study

BACKGROUND

Characterizing retrospective exposure to toxicants during multiple early-life developmental periods is challenging, yet critical for understanding developmental effects.

OBJECTIVE

To characterize early-life metal exposure using deciduous teeth in a community concerned about past exposures.

METHODS

Naturally shed teeth were collected from 30 children ages 5-13 years who resided in Holliston, Massachusetts since conception. We estimated weekly prenatal and postnatal (up to 1 year of age) exposure to 12 metals by measuring dentine concentrations using laser ablation-inductively coupled plasma-mass spectrometry. Multivariable linear mixed models were used to explore sociodemographic, dietary, and behavioral correlates of dentine metal concentrations.

RESULTS

Temporal trends in dentine levels differed by metal. Source of milk during the first year of life was associated with dentine barium (Ba) levels, where being fed predominantly breastmilk was associated with 39% (95% CI: -57%, -13%) lower dentine Ba compared to predominantly formula use. Females had higher prenatal and postnatal dentine Mn and Pb, compared to males (e.g., % difference, postnatal Mn: 122% (17%, 321%); postnatal Pb: 60% (95% CI: -8%, 178%)).

SIGNIFICANCE

Deciduous teeth provide retrospective information on dose and timing of early-life metals exposure at high resolution. We demonstrate their utility in a community-based study with known past contamination of drinking water.

IMPACT STATEMENT

We conducted a community-initiated pilot study in a community concerned with historical exposure to multiple metals. Using deciduous teeth, a novel noninvasive biomarker, we characterized early-life exposure to 12 metals in approximately weekly increments during sensitive developmental periods, thus demonstrating the utility of this biomarker in communities concerned with past exposures.

Associations of a metal mixture with iron status in U.S. adolescents: Evidence from the National Health and Nutrition Examination Survey

Iron is needed for normal development in adolescence. Exposure to individual environmental metals (e.g., lead) has been associated with altered iron status in adolescence, but little is known about the cumulative associations of multiple metals with Fe status. We used data from the 2017-2018 National Health and Nutrition Examination Survey (NHANES) to examine associations between a metal mixture (lead, manganese, cadmium, selenium) and iron status in 588 U.S. adolescents (12-17 years). We estimated cumulative and interactive associations of the metal mixture with five iron status metrics using Bayesian Kernel Machine Regression (BKMR). Higher concentrations of manganese and cadmium were associated with lower log-transformed ferritin concentrations. Interactions were observed between manganese, cadmium, and lead for ferritin and the transferrin receptor, where iron status tended to be worse at higher concentrations of all metals. These results may reflect competition between environmental metals and iron for cellular uptake. Mixed metal exposures may alter normal iron function, which has implications for adolescent development.

Bayesian kernel machine regression-causal mediation analysis

Greater understanding of the pathways through which an environmental mixture operates is important to design effective interventions. We present new methodology to estimate natural direct and indirect effects and controlled direct effects of a complex mixture exposure on an outcome through a mediator variable. We implement Bayesian Kernel Machine Regression (BKMR) to allow for all possible interactions and nonlinear effects of (1) the co-exposures on the mediator, (2) the co-exposures and mediator on the outcome, and (3) selected covariates on the mediator and/or outcome. From the posterior predictive distributions of the mediator and outcome, we simulate counterfactuals to obtain posterior samples, estimates, and credible intervals of the mediation effects. Our simulation study demonstrates that when the exposure-mediator and exposure-mediator-outcome relationships are complex, BKMR-Causal Mediation Analysis performs better than current mediation methods. We applied our methodology to quantify the contribution of birth length as a mediator between in utero co-exposure to arsenic, manganese, and lead, and children's neurodevelopmental scores, in a prospective birth cohort in Bangladesh. Among younger children, we found a negative (adverse) association between the metal mixture and neurodevelopment. We also found evidence that birth length mediates the effect of exposure to the metal mixture on neurodevelopment for younger children. If birth length were fixed to its 75 t h percentile value, the harmful effect of the metal mixture on neurodevelopment is attenuated, suggesting nutritional interventions to help increase fetal growth, and thus birth length, could potentially block the harmful effect of the metal mixture on neurodevelopment.

Correlates of plasma concentrations of per- and poly-fluoroalkyl substances among reproductive-aged Black women

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals used in commercial and consumer goods. Black women are underrepresented in studies of PFAS exposure.

METHODS

We performed a cross-sectional analysis of correlates of plasma PFAS concentrations among 1499 Black women aged 23-35 participating in the Study of Environment, Lifestyle, and Fibroids (SELF), a Detroit-based cohort study. At baseline (2010-2012), participants provided questionnaire data on socio-demographics; behaviors; diet; and menstrual, contraceptive, and reproductive histories. Using mass spectrometry in non-fasting plasma samples collected at enrollment, we quantified several PFAS, including perfluorohexane sulfonate (PFHxS), perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), perfluorononanoate (PFNA), perfluorodecanoate (PFDA), perfluoroundecanoate (PFUnDA), and 2-N-methyl-perfluorooctane sulfonamido acetate (MeFOSAA). We used linear regression to calculate percentage differences (%D) and 95 % confidence intervals (CIs) for associations between selected correlates and PFAS concentrations, adjusting for all other correlates.

RESULTS

PFHxS, PFOS, PFOA, and PFNA were detected in ≥97 % of women; PFDA in 86 %; MeFOSAA in 70 %; and PFUnDA in 52 %. Age, income, education, and intakes of water, alcohol, and seafood were positively associated with several PFAS. Current smoking was positively associated with MeFOSAA. Body mass index was inversely associated with most PFAS, except PFHxS. Strong inverse associations (%D; 95 % CI) were observed between parity (≥3 vs. 0 births) and PFHxS (-34.7; -43.0, -25.1) and PFOA (-33.1; -39.2, -26.3); breastfeeding duration (≥6 months vs. nulliparous) and PFOA (-31.1; -37.8, -23.7), PFHxS (-24.2; -34.5, -12.3), and PFOS (-18.4; -28.3, -7.1); recent birth (<2 years ago vs. nulliparous) and PFOA (-33.1; -39.6, -25.8), PFHxS (-29.3; -39.0, -18.1), PFNA (-25.2; -32.7, -16.8), and PFOS (-18.3; -28.3, -6.9); and intensity of menstrual bleed (heavy vs. light) and PFHxS (-18.8; -28.3, -8.2), PFOS (-16.4; -24.9, -7.1), PFNA (-10.5; -17.8, -2.6), and PFOA (-10.0; -17.2, -2.1). Current use of depot medroxyprogesterone acetate (DMPA) was positively associated with PFOS (20.2; 1.4, 42.5), PFOA (16.2; 1.5, 33.0), and PFNA (15.3; 0.4, 32.4).

CONCLUSIONS

Reproductive factors that influence PFAS elimination showed strong associations with several PFAS (reduced concentrations with parity, recent birth, lactation, heavy menstrual bleeding; increased concentrations with DMPA use).

Prospective associations of mid-childhood plasma per- and polyfluoroalkyl substances and pubertal timing

BACKGROUND

Exposure to per- and polyfluoroalkyl substances (PFAS) may disrupt pubertal timing. Higher PFAS plasma concentrations have been associated with later pubertal timing in girls, but cross-sectional findings may be explained by reverse causation.

OBJECTIVES

To assess prospective associations between PFAS plasma concentrations in mid-childhood and markers of pubertal timing in male and female adolescents.

METHODS

We studied 640 children in Project Viva, a Boston-area prospective cohort. We examined associations of plasma concentrations of 6 PFAS measured at mean 7.9 (SD 0.8) years (2007-2010) with markers of pubertal timing. Parents reported a 5-item pubertal development score at early adolescence (mean 13.1 (SD 0.8) years) and reported age at menarche annually. We calculated age at peak height velocity using research and clinical measures of height. We used sex-specific linear and Cox proportional hazards regression to estimate associations of single PFAS with outcomes, and we used Bayesian Kernel Machine Regression (BKMR) to estimate associations of the PFAS mixture with outcomes.

RESULTS

Plasma concentrations were highest for perfluorooctane sulfonate (PFOS) [median (IQR) 6.4(5.6) ng/mL], followed by perfluorooctanoate (PFOA) [4.4(3.0) ng/mL]. In early adolescence, girls were further along in puberty than boys [pubertal development score mean (SD) 2.9 (0.7) for girls and 2.2(0.7) for boys; age at peak height velocity mean (SD) 11.2y (1.0) for girls and 13.1y (1.0) for boys]. PFAS was associated with later markers of pubertal timing in girls only. For example, each doubling of PFOA was associated with lower pubertal development score (-0.18 units; 95% CI: -0.30, -0.06) and older age at peak height velocity (0.23 years; 95% CI: 0.06, 0.40)]. We observed similar associations for PFOS, perfluorodecanoate (PFDA), and the PFAS mixture. PFAS plasma concentrations were not associated with age at menarche or markers of pubertal timing in boys.

DISCUSSION

Higher PFAS plasma concentrations in mid-childhood were associated with later onset of puberty in girls.

Prospective Associations of Early Pregnancy Metal Mixtures with Mitochondria DNA Copy Number and Telomere Length in Maternal and Cord Blood

BACKGROUND

Metal exposure during pregnancy influences maternal and child health. Oxidative stress and inflammation may mediate adverse effects of heavy metals, whereas essential metals may act as antioxidants. Mitochondrial DNA is a prime target for metal-induced oxidative damage. Telomere dysfunction is attributed to imbalances between reactive oxidant species and antioxidants.

OBJECTIVES

We evaluated individual and joint associations of prenatal metals with mitochondrial DNA copy number (mtDNAcn) and telomere length (TL) in maternal and cord blood as biomarkers of inflammation and oxidative stress.

METHODS

We measured six nonessential metals (arsenic, barium, cadmium, cesium, lead, mercury) and four essential metals (magnesium, manganese, selenium, zinc) in first-trimester maternal red blood cells in Project Viva, a U.S. prebirth cohort. We measured relative mtDNAcn (n=898) and TL (n=893) in second-trimester maternal blood and mtDNAcn (n=419) and TL (n=408) in cord blood. We used multivariable linear regression and quantile g-computation to estimate associations between prenatal metals and the biomarkers. We used generalized additive models and Bayesian kernel machine regression to examine nonlinearity and interactions.

RESULTS

A 2-fold increase in maternal magnesium was associated with lower maternal [β=-0.07, 95% confidence interval (CI): -0.10, -0.01] and cord blood (β=-0.08, 95% CI: -0.20, -0.01) mtDNAcn. Lead was associated with higher maternal mtDNAcn (β=0.04, 95% CI: 0.01, 0.06). Selenium was associated with longer cord blood TL (β=0.30, 95% CI: 0.01 0.50). An association was observed between the nonessential metal mixture and higher maternal mtDNAcn (β=0.04, 95% CI: 0.01, 0.07). There was a nonlinear relationship between cord blood mtDNAcn and magnesium; maternal mtDNAcn and barium, lead, and mercury; and maternal TL and barium.

DISCUSSION

Maternal exposure to metals such as lead, magnesium, and selenium was associated with mtDNAcn and TL in maternal second trimester and cord blood. Future work will evaluate whether these biomarkers are associated with child health. https://doi.org/10.1289/EHP9294.

Correlates of Persistent Endocrine-Disrupting Chemical Mixtures among Reproductive-Aged Black Women

Black women are exposed to multiple endocrine-disrupting chemicals (EDCs), but few studies have examined their profiles of exposure to EDC mixtures. We identified biomarker profiles and correlates of exposure to EDC mixtures in a cross-sectional analysis of data from a prospective cohort study of 749 Black women aged 23-35 years. We quantified plasma concentrations of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), organochlorine pesticides (OCPs), and per- and polyfluoroalkyl substances (PFAS) in nonfasting samples collected at baseline. Demographic, behavioral, dietary, and reproductive covariates were also collected at baseline. We used k-means clustering and principal component analysis (PCA) to describe concentration profiles of EDC mixtures (17 PCBs, 6 PBDEs, 4 OCPs, 6 PFAS), followed by multinomial logistic and multivariable linear regression to estimate mean differences in PCA scores (β) and odds ratios (ORs) of cluster membership with their respective 95% confidence intervals (CIs). Older age (per 1 year increase: β = 0.47, CI = 0.39, 0.54; OR = 1.27, CI = 1.20, 1.35), lower body mass index (per 1 kg/m² increase: β = -0.14, CI = -0.17, -0.12; OR = 0.91, CI = 0.89, 0.94), and current smoking (≥10 cigarettes/day vs never smokers: β = 1.37, CI = 0.20, 2.55; OR = 2.63, CI = 1.07, 6.50) were associated with profiles characterized by higher concentrations of all EDCs. Other behaviors and traits, including dietary factors and years since last birth, were also associated with EDC mixtures.

Early pregnancy essential and non-essential metal mixtures and gestational glucose concentrations in the 2nd trimester: Results from project viva

Metals are involved in glucose metabolism, and some may alter glycemic regulation. However, joint effects of essential and non-essential metals on glucose concentrations during pregnancy are unclear. This study explored the joint associations of pregnancy exposures to essential (copper, magnesium, manganese, selenium, zinc) and non-essential (arsenic, barium, cadmium, cesium, lead, mercury) metals with gestational glucose concentrations using 1,311 women enrolled 1999-2002 in Project Viva, a Boston, MA-area pregnancy cohort. The study measured erythrocyte metal concentrations from 1st trimester blood samples and used glucose concentrations measured 1 h after non-fasting 50-gram glucose challenge tests (GCT) from clinical gestational diabetes screening at 26-28 weeks gestation. Bayesian Kernel Machine Regression (BKMR) and quantile-based g-computation were applied to model the associations of metal mixtures-including their interactions-with glucose concentrations post-GCT. We tested for reproducibility of BKMR results using generalized additive models. The BKMR model showed an inverse U-shaped association for barium and a linear inverse association for mercury. Specifically, estimated mean glucose concentrations were highest around 75th percentile of barium concentrations [2.1 (95% confidence interval: -0.2, 4.4) mg/dL higher comparing to the 25th percentile], and each interquartile range increase of erythrocyte mercury was associated with 1.9 mg/dL lower mean glucose concentrations (95% credible interval: -4.2, 0.4). Quantile g-computation showed joint associations of all metals, essential-metals, and non-essential metals on gestational glucose concentrations were all null, however, we observed evidences of interaction for barium and lead. Overall, we found early pregnancy barium and mercury erythrocytic concentrations were associated with altered post-load glucose concentrations in later pregnancy, with potential interactions between barium and lead.

Prenatal exposure to a mixture of elements and neurobehavioral outcomes in mid-childhood: Results from Project Viva

BACKGROUND

Lead (Pb), manganese (Mn), selenium (Se) and methylmercury (MeHg) can be neurotoxic individually, despite Mn and Se also being essential elements. Little is known about the joint effects of essential and non-essential elements on neurobehavior, particularly for prenatal exposures.

OBJECTIVES

To evaluate associations of prenatal exposure to multiple elements with executive function and neurobehavior in children.

METHODS

Participants included 1009 mother-child pairs from the Project Viva pre-birth cohort. We estimated maternal erythrocyte Pb, Mn, Se, and Hg concentrations prenatally. In 6-11-year old children (median 7.6 years), parents and teachers rated children's executive function-related behaviors using the Behavior Rating Inventory of Executive Function (BRIEF) Global Executive Composite score and behavioral difficulties using the Strengths and Difficulties Questionnaire (SDQ) total difficulties score. We evaluated associations of element mixtures with neurobehavior using Bayesian kernel machine regression (BKMR), multivariable linear regression, and quantile g-computation.

RESULTS

Median erythrocyte Pb, Mn, Se, and Hg concentrations were 1.1 μg/dL, 33.1 μg/L, 204.5 ng/mL, and 3.1 ng/g, respectively. Findings from BKMR and quantile g-computation models both showed worse (higher) parent-rated BRIEF and SDQ z-scores with higher concentrations of the mixture, although estimates were imprecise. When remaining elements were set at their median within BKMR models, increases in Pb and Se from the 25th to 75th percentile of exposure distributions were associated with 0.08 (95% CI: 0.02, 0.19) and 0.07 (95% CI: 0.03, 0.16) standard deviation increases in parent-rated BRIEF scores, and 0.08 (95% CI: 0.02, 0.17) and 0.05 (95% CI: 0.03, 0.13) standard deviation increases in SDQ scores, respectively. There was no evidence of element interactions.

DISCUSSION

Although associations were small in magnitude, we found a trend of worsening neurobehavioral ratings with increasing prenatal exposure to an element mixture. However, we may be observing a limited range of dose-dependent impacts given the levels of exposure within our population.

Critical windows of susceptibility in the association between manganese and neurocognition in Italian adolescents living near ferro-manganese industry

INTRODUCTION

Understanding the neurodevelopmental effects of manganese (Mn) is complicated due to its essentiality for growth and development. While evidence exists for the harmful effects of excess Mn, pediatric epidemiologic studies have observed inconsistent associations between Mn and child cognition.

OBJECTIVE

We sought to estimate prospective associations between Mn measured in three different early-life time windows with adolescent cognition using deciduous teeth biomarkers.

METHODS

Deciduous teeth were collected from 195 participants (ages 10-14 years) of the Public Health Impact of Manganese Exposure (PHIME) study in Brescia, Italy. Measurements of tooth Mn represented prenatal (∼14 weeks gestation - birth), early postnatal (birth - 1.5 years) and childhood (∼1.5 - 6 years) time windows. Neuropsychologists administered the Wechsler Intelligence Scale for Children, 3rd edition (WISC-III), to obtain composite IQ and subtest scores. Associations between tooth Mn at each time window and adolescent WISC-III scores were estimated using multivariable linear regression. We tested differences in associations between Mn and outcomes across time windows using multiple informant models. Sex-specific associations were explored in stratified models.

RESULTS

Adjusted associations between tooth Mn and composite IQ scores were positive in the prenatal period and negative in the childhood period. Associations were strongest for subtest scores that reflect working memory, problem solving, visuospatial ability and attention: prenatal Mn was positively associated with Digits backward [SD change in score per interquartile range increase in Mn: β = 0.20 (95 % CI: 0.02, 0.38)] and Block design [β = 0.21 (0.01, 0.41)] and early postnatal Mn was positively associated with Digits forward [β = 0.24 (0.09, 0.40)], while childhood Mn was negatively associated with Coding [β = -0.14 (-0.28, -0.001)]. Sex-stratified analyses suggested different Mn-cognition associations for boys and girls and was also dependent on the time window of exposure.

CONCLUSION

Our results suggest that exposure timing is critical when evaluating Mn associations between Mn and cognition. Higher prenatal Mn was beneficial for adolescent cognition; however, these beneficial associations shifted towards harmful effects in later time windows. Cognitive domains most sensitive to Mn across time windows included visuospatial ability, working memory, attention and problem-solving.

Urinary concentrations of phenols, parabens, and triclocarban in relation to uterine leiomyomata incidence and growth

OBJECTIVE

To examine the association of urinary concentrations of phenols, parabens, and triclocarban with incidence and growth of uterine leiomyomata (UL; fibroids).

DESIGN

Case-cohort study, nested within the Study of Environment, Lifestyle, and Fibroids, a prospective cohort study.

SETTING

Clinic visits at baseline and every 20 months for 60 months.

PATIENT(S)

754 Black women aged 23-35 years residing in the Detroit, Michigan area (enrolled during 2010-2012).

INTERVENTION

None.

MAIN OUTCOME MEASURE(S)

At each study visit, women underwent transvaginal ultrasound for measurement of UL incidence and growth and provided urine specimens in which we quantified concentrations of seven phenols, four parabens, and triclocarban. We used Cox proportional hazards regression to estimate hazard ratios and 95% confidence intervals (CIs) characterizing the relation of urinary biomarker concentrations with UL incidence during the 60 months of follow-up. In a subset of UL detected and measured at multiple time points, we used linear regression to assess the associations between biomarker concentrations and UL growth.

RESULT(S)

Urinary biomarker concentrations were generally inversely associated with UL incidence, but the associations were weak and nonmonotonic. For example, hazard ratios comparing concentrations ≥90th with <50th percentile were 0.77 (95% CI: 0.46, 1.27) for bisphenol A, 0.72 (95% CI: 0.40, 1.28) for bisphenol S, and 0.76 (95% CI: 0.43, 1.33) for methylparaben. Biomarker concentrations were not strongly associated with UL growth.

CONCLUSION(S)

In this study of reproductive-aged Black women, urinary phenols, parabens, and triclocarban biomarkers were neither strongly nor consistently associated with UL incidence and growth.

Joint Associations of Multiple Dietary Components With Cardiovascular Disease Risk: A Machine-Learning Approach

The human diet consists of a complex mixture of components. To realistically assess dietary impacts on health, new statistical tools that can better address nonlinear, collinear, and interactive relationships are necessary. Using data from 1,928 healthy participants in the Coronary Artery Risk Development in Young Adults (CARDIA) cohort (1985-2006), we explored the association between 12 dietary factors and 10-year predicted risk of atherosclerotic cardiovascular disease (ASCVD) using an innovative approach, Bayesian kernel machine regression (BKMR). Employing BKMR, we found that among women, unprocessed red meat was most strongly related to the outcome: An interquartile range increase in unprocessed red meat consumption was associated with a 0.07-unit (95% credible interval: 0.01, 0.13) increase in ASCVD risk when intakes of other dietary components were fixed at their median values (similar results were obtained when other components were fixed at their 25th and 75th percentile values). Among men, fruits had the strongest association: An interquartile range increase in fruit consumption was associated with -0.09-unit (95% credible interval (CrI): -0.16, -0.02), -0.10-unit (95% CrI: -0.16, -0.03), and -0.11-unit (95% CrI: -0.18, -0.04) lower ASCVD risk when other dietary components were fixed at their 25th, 50th (median), and 75th percentile values, respectively. Using BKMR to explore the complex structure of the total diet, we found distinct sex-specific diet-ASCVD relationships and synergistic interaction between whole grain and fruit consumption.

MCR: Open-Source Software to Automate Compilation of Health Study Report-Back

Sharing individualized results with health study participants, a practice we and others refer to as "report-back," ensures participant access to exposure and health information and may promote health equity. However, the practice of report-back and the content shared is often limited by the time-intensive process of personalizing reports. Software tools that automate creation of individualized reports have been built for specific studies, but are largely not open-source or broadly modifiable. We created an open-source and generalizable tool, called the Macro for the Compilation of Report-backs (MCR), to automate compilation of health study reports. We piloted MCR in two environmental exposure studies in Massachusetts, USA, and interviewed research team members (n = 7) about the impact of MCR on the report-back process. Researchers using MCR created more detailed reports than during manual report-back, including more individualized numerical, text, and graphical results. Using MCR, researchers saved time producing draft and final reports. Researchers also reported feeling more creative in the design process and more confident in report-back quality control. While MCR does not expedite the entire report-back process, we hope that this open-source tool reduces the barriers to personalizing health study reports, promotes more equitable access to individualized data, and advances self-determination among participants.

Validation of Electrochemical Sensor for Determination of Manganese in Drinking Water

Manganese (Mn) is an essential nutrient for metabolic functions, yet excessive exposure can lead to neurological disease in adults and neurodevelopmental deficits in children. Drinking water represents one of the routes of excessive Mn exposure. Both natural enrichment from rocks and soil, and man-made contamination can pollute groundwater that supplies drinking water for a substantial fraction of the U.S. population. Conventional methods for Mn monitoring in drinking water are costly and involve a long turn-around time. Recent advancements in electrochemical sensing, however, have led to the development of miniature sensors for Mn determination. These sensors rely on a cathodic stripping voltammetry electroanalytical technique on a miniaturized platinum working electrode. In this study, we validate these electrochemical sensors for the determination of Mn concentrations in drinking water against the standard method using inductively coupled plasma mass spectrometry (ICP-MS). Drinking water samples (n = 78) in the 0.03 ppb to 5.3 ppm range were analyzed. Comparisons with ICP-MS yielded 100% agreement, ∼70% accuracy, and ∼91% precision. We envision the use of our system for rapid and inexpensive point-of-use identification of Mn levels in drinking water, which is especially valuable for frequent monitoring where contamination is present.

Correlates of urinary concentrations of phthalate and phthalate alternative metabolites among reproductive-aged Black women from Detroit, Michigan

BACKGROUND

Phthalates are endocrine-disrupting chemicals that are widely present in consumer products. In the United States, Black women are more highly exposed to phthalates than other racial/ethnic groups, yet information on predictors of phthalate exposure among Black women is limited.

OBJECTIVE

We evaluated the association of demographics, lifestyle, reproductive history, and personal care product use with urinary concentrations of phthalate and phthalate alternative metabolites, using cross-sectional data from a study of 754 Black women from Detroit, Michigan (2010-2012).

METHODS

Women completed questionnaires and provided urine specimens which were analyzed for 16 phthalate and phthalate alternative metabolites. We used linear regression models to estimate mean percentage differences and 95% confidence intervals (CIs) in concentrations across levels of correlates.

RESULTS

Monoethyl phthalate (MEP) and MBP concentrations were positively associated with personal care product use, particularly nail products. Educational attainment was positively associated with high molecular weight phthalate concentrations but inversely associated with monobenzyl phthalate (MBzP) concentrations. Parity was positively associated with MBzP concentrations and inversely associated with concentrations of MEP and high molecular weight phthalates.

SIGNIFICANCE

We found that sociodemographics, reproductive characteristics, and use of certain personal care products were associated with urinary phthalate concentrations among Black women. Our results emphasize the importance of examining exposure determinants among multiply marginalized populations.

Prenatal metal mixtures and fetal size in mid-pregnancy in the MADRES study

BACKGROUND

Fetal growth is predictive of health later in life. Both toxic and essential metals influence fetal growth, but most studies have focused on these elements individually and used birth weight as an indicator of fetal growth. The objective of the current study was to investigate the impact of a mixture of metals on fetal size in mid-pregnancy in a predominately lower income Hispanic pregnancy cohort in Los Angeles.

METHODS

For our primary analysis, we focused on six elements that have previously been associated individually with fetal size, including arsenic (As), barium (Ba), cadmium (Cd), mercury (Hg), molybdenum (Mo), and tin (Sn), measured in maternal urine samples collected in early pregnancy (median: 12.4 weeks gestation). In an exploratory analysis, we additionally included cobalt (Co), nickel (Ni), antimony (Sb), and thallium (Tl). Using covariate-adjusted Bayesian Kernel Machine Regression (BKMR) as our main mixture modeling approach, we examined the impact of these metals on fetal biometry measures obtained between 18 and 22 weeks gestation, with a focus on estimated fetal weight (EFW).

RESULTS

BKMR identified Mo and Ba as the mixture components that contributed most to associations with EFW. Linear associations were observed for both metals. An increase in Mo from the 25th to 75th percentile was associated with a 0.114 (95% credible interval (CI): 0.019, 0.247) SD higher EFW, equivalent to a 7.4 g difference. Similar associations were observed between Mo and the other fetal measures evaluated. In contrast, an increase in Ba from the 25th to 75th percentile was associated with a -0.076 (95% CI: 0.217, 0.066) SD lower EFW, equivalent to a 4.9 g difference. Similar inverse associations were observed for Ba in relation to abdominal circumference and biparietal diameter. BKMR also identified a possible interaction between Ba and Mo in relation to head circumference, suggesting that the positive associations between Mo and this outcome may be attenuated at high levels of Ba, which was consistent with findings from linear regression (P_interaction = 0.03). In an exploratory analysis accounting for a larger mixture of metals, Mo and Ba consistently contributed most to associations with EFW. An inverse association was also identified between Sb and EFW.

CONCLUSIONS

Our results suggest that Mo may promote fetal growth, while Ba and Sb may reduce fetal growth, in this population.

A Prospective Ultrasound Study of Plasma Polychlorinated Biphenyl Concentrations and Incidence of Uterine Leiomyomata

BACKGROUND

Uterine leiomyomata, or fibroids, are hormone-dependent neoplasms of the myometrium that can cause severe gynecologic morbidity. In previous studies, incidence of these lesions has been positively associated with exposure to polychlorinated biphenyls (PCBs), a class of persistent endocrine-disrupting chemicals. However, previous studies have been retrospective in design and none has used ultrasound to reduce disease misclassification.

METHODS

The Study of Environment, Lifestyle, and Fibroids is a prospective cohort of 1,693 reproductive-aged Black women residing in Detroit, Michigan (enrolled during 2010-2012). At baseline and every 20 months for 5 years, women completed questionnaires, provided blood samples, and underwent transvaginal ultrasound to detect incident fibroids. We analyzed 754 baseline plasma samples for concentrations of 24 PCB congeners using a case-cohort study design. We used multivariable Cox proportional hazards regression to estimate hazard ratios (HRs) and 95% confidence intervals for the association between plasma PCB concentrations and ultrasound-detected fibroid incidence over a 5-year period.

RESULTS

We observed little association between PCB congener concentrations and fibroid incidence. The HR for a one-standard deviation increase in log-transformed total PCBs was 0.94 (95% CI = 0.78, 1.1). The PCB congener with the largest effect estimate was PCB 187 (HR for a one-standard deviation increase in log-transformed exposure = 0.88, 95% CI = 0.73, 1.1). Associations did not seem to vary strongly across PCB groupings based on hormonal activity.

CONCLUSIONS

In this cohort of reproductive-aged Black women, plasma PCB concentrations typical of the contemporary general population were not appreciably associated with higher risk of fibroids.

Brominated flame retardants and organochlorine pesticides and incidence of uterine leiomyomata: A prospective ultrasound study

Uterine leiomyomata (UL) are hormone-responsive benign neoplasms. Brominated flame retardants and organochlorine pesticides (OCPs) can disrupt hormones involved in UL etiology.

METHODS

The Study of Environmental, Lifestyle, and Fibroids is a Detroit-area prospective cohort of 1693 Black women 23-35 years of age. At baseline and approximately every 20 months for 5 years, women completed questionnaires and underwent transvaginal ultrasounds. Using a case-cohort study design, we selected 729 UL-free participants at baseline and analyzed baseline plasma samples for polybrominated diphenyl ethers (PBDEs), a polybrominated biphenyl ether (PBB-153), and OCPs. We used Cox proportional hazard models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

Compared with total PBDE plasma concentrations <50th percentile, adjusted HRs for the 50th-74th, 75th-89th, and ≥90th percentiles were 1.00 (95% CI = 0.68, 1.47), 1.04 (95% CI = 0.63, 1.68), and 0.85 (95% CI = 0.48, 1.50), respectively. HRs for PBB-153 plasma concentrations were generally similar to total PBDE plasma concentrations. Compared with total OCP plasma concentrations <50th percentile, HRs for the 50th-74th, 75th-89th, and ≥90th percentiles were 0.86 (95% CI = 0.57, 1.29), 0.73 (95% CI = 0.43, 1.22), and 0.58 (95% CI = 0.32, 1.04), respectively. HRs for individual PBDEs and OCPs were similar to their respective totals.

CONCLUSION

We found little support for an association between brominated flame retardant plasma concentrations and UL incidence, and some evidence of lower UL incidence with the highest OCP plasma concentrations.

Incidence of uterine leiomyoma in relation to urinary concentrations of phthalate and phthalate alternative biomarkers: A prospective ultrasound study

BACKGROUND

Numerous studies suggest that some phthalates have adverse reproductive effects. However, literature on the association between phthalates and incidence of uterine leiomyomata (UL) is limited and inconsistent, with no existing prospective studies.

OBJECTIVES

We examined the association of urinary concentrations of phthalate and phthalate alternative biomarkers with UL incidence.

METHODS

We conducted a case-cohort analysis within a subgroup of 754 participants in the Study of the Environment, Lifestyle, and Fibroids (SELF), a prospective cohort of premenopausal Black women aged 23-35 years who were recruited during 2010-2012. We quantified fourteen phthalates and two phthalate alternative [1,2-cyclohexane dicarboxylic acid, diisononyl ester (DINCH)] biomarkers in urine collected at baseline, 20 months, and 40 months. Transvaginal ultrasounds identified UL at baseline and every 20 months during 60 months of follow-up. We evaluated the individual biomarkers, molar sum of di(2-ethylhexyl) phthalate [ΣDEHP] and potency-weighted sum of anti-androgenic [WΣAA] biomarkers. We used Cox proportional hazards regression to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between biomarkers and UL incidence. We then used quantile g-computation to examine joint associations of multiple phthalate biomarkers with UL incidence.

RESULTS

Most individual biomarkers showed weak-to-moderate inverse associations with UL incidence. HRs comparing highest vs. lowest quartiles of mono-isobutyl phthalate (MiBP) and mono-hydroxyisobutyl phthalate (MHiBP) concentrations were 0.63 (95% CI: 0.40, 1.01) and 0.61 (95% CI: 0.38, 0.96), respectively. Inverse associations for specific phthalates were stronger among women with BMI ≥ 30 kg/m². HRs comparing detectable vs. nondetectable concentrations of DINCH biomarkers were 0.92 (95% CI: 0.62, 1.35) for cyclohexane-1,2-dicarboxylic acid mono hydroxyisononyl ester (MHNCH) and 0.68 (95% CI: 0.38, 1.18) for cyclohexane-1,2-dicarboxylic acid mono carboxyisoocytl ester (MCOCH). For the DEHP metabolite of mono(2-ethylhexyl) phthalate (MEHP), we observed weak-to-moderate positive associations. HRs comparing highest vs. lowest quartiles for MEHP and ΣDEHP were 1.29 (95% CI: 0.82, 2.06) and 0.96 (95% CI: 0.61, 1.50), respectively. In the mixtures analysis, the HR for a joint quartile increase in phthalate biomarker concentrations was 0.90 (95% CI: 0.73, 1.08).

DISCUSSION

In this prospective ultrasound study of reproductive-aged Black women, urinary concentrations of phthalate and DINCH biomarkers were not appreciably associated with higher risk of UL, either individually or jointly.

Integrated measures of lead and manganese exposure improve estimation of their joint effects on cognition in Italian school-age children

Every day humans are exposed to mixtures of chemicals, such as lead (Pb) and manganese (Mn). An underappreciated aspect of studying the health effects of mixtures is the role that the exposure biomarker media (blood, hair, etc.) may play in estimating the effects of the mixture. Different biomarker media represent different aspects of each chemical's toxicokinetics, thus no single medium can fully capture the toxicokinetic profile for all the chemicals in a mixture. A potential solution to this problem is to combine exposure data across different media to derive integrated estimates of each chemical's internal concentration. This concept, formalized as a multi-media biomarker (MMB) has proven effective for estimating the health impacts of Pb exposure, but may also be useful to estimate mixture effects, such as the joint effects of metals like Pb and Mn, while factoring in how the association changes based upon the biomarker media. Levels of Pb and Mn were quantified in five media: blood, hair, nails, urine, and saliva in the Public Health Impact of Metals Exposure (PHIME) project, a study of Italian adolescents aged 10-14 years. MMBs were derived for both metals using weighted quantile sum (WQS) regression across the five media. Age-adjusted Wechsler Intelligence Scale for Children (WISC) IQ scores, measured at the same time as the exposure measures, were the primary outcome and models were adjusted for sex and socioeconomic status. The levels Pb and Mn were relatively low, with median blood Pb of 1.27 (IQR: 0.84) μg/dL and median blood Mn of 1.09 (IQR: 0.45) μg/dL. Quartile increases in a Pb-Mn combination predicted decreased Full Scale IQ of 1.9 points (95% CI: 0.3, 3.5) when Pb and Mn exposure levels were estimated using MMBs, while individual regressions for each metal were not associated with Full Scale IQ. Additionally, a quartile increase in the WQS index of Pb and Mn, measured using MMBs, were associated with reductions in Verbal IQ by 2.8 points (1.0, 4.5). Weights that determine the contributions of the metals to the joint effect highlighted that the contribution of the Pb-Mn was 72-28% for Full Scale IQ and 42-58% for Verbal IQ. We found that the joint effects of Pb and Mn are strongly affected by the medium used to measure exposure and that the joint effects of the Pb and Mn MMBs on cognition were the stronger than any individual biomarker. Thus, increase power and accuracy for measuring mixture effects compared to individual biomarkers. As the number of chemicals in mixtures increases, appropriate biomarker selection will become increasingly important and MMBs are a natural way to reduce bias in such analyses.

Associations of metals and neurodevelopment: a review of recent evidence on susceptibility factors

PURPOSE OF REVIEW

Epidemiologic evidence exists that many metals are associated with adverse neurobehavioral effects in young children, including lead (Pb), methylmercury (meHg), manganese (Mn) and arsenic (As)5-8. Importantly, chemical insult can vary depending on host factors and exposure circumstance. This systematic review summarizes the recent literature investigating modifying factors of the associations between metals and neurodevelopment, including immutable traits (sex or genetics) or exposure conditions (timing or co-exposures).

RECENT FINDINGS

Of the 53 studies included in this review, the number investigating modification of exposure effects were: 30 for sex, 21 for co-exposures, 12 for timing of exposure, and six for genetic modifiers. Sex-specific effects of metal-neurobehavioral associations were inconclusive for all metals, likely due to the heterogeneity of outcome domains assessed and the exposure time points measured. Seven studies evaluated both sex and exposure timing as modifying factors using deciduous teeth or other biomarkers with repeated measures to characterize metals exposure over time. Only five studies used statistical methods for mixtures to evaluate associations of more than two metals with neurobehavioral domains.

SUMMARY

Despite the expansion of research on susceptibility to the neurodevelopmental effects of metals exposure, considerable gaps remain. This work remains critical, as characterizing susceptible subpopulations can aid in identifying biological mechanisms and is fundamental for the protection of public health.

Identification of novel loci associated with infant cognitive ability

It is believed that genetic factors play a large role in the development of many cognitive and neurological processes; however, epidemiological evidence for the genetic basis of childhood neurodevelopment is very limited. Identification of the genetic polymorphisms associated with early-stage neurodevelopment will help elucidate biological mechanisms involved in neuro-behavior and provide a better understanding of the developing brain. To search for such variants, we performed a genome-wide association study (GWAS) for infant mental and motor ability at two years of age with mothers and children recruited from cohorts in Bangladesh and Mexico. Infant ability was assessed using mental and motor composite scores calculated with country-specific versions of the Bayley Scales of Infant Development. A missense variant (rs1055153) located in the gene WWTR1 reached genome-wide significance in association with mental composite score (meta-analysis effect size of minor allele βmeta = -6.04; 95% CI: -8.13 to -3.94; P = 1.56×10-8). Infants carrying the minor allele reported substantially lower cognitive scores in both cohorts, and this variant is predicted to be in the top 0.3% of most deleterious substitutions in the human genome. Fine mapping and region-based association testing provided additional suggestive evidence that both WWTR1 and a second gene, LRP1B, were associated with infant cognitive ability. Comparisons with recently conducted GWAS in intelligence and educational attainment indicate that our phenotypes do not possess a high genetic correlation with either adolescent or adult cognitive traits, suggesting that infant neurological assessments should be treated as an independent outcome of interest. Additional functional studies and replication efforts in other cohorts may help uncover new biological pathways and genetic architectures that are crucial to the developing brain.

Prenatal Metal Mixtures and Birth Weight for Gestational Age in a Predominately Lower-Income Hispanic Pregnancy Cohort in Los Angeles

BACKGROUND

Reduced fetal growth increases the risk for adverse health outcomes. Growing evidence suggests that metal exposures contribute to reduced fetal growth, but little is known about the effects of complex metal mixtures.

OBJECTIVES

We investigated the impact of a complex mixture of metals on birth weight for gestational age (BW for GA) in the Maternal and Developmental Risks from Environmental and Social Stressors study, a predominately lower-income Hispanic pregnancy cohort in Los Angeles, California.

METHODS

Cadmium (Cd), cobalt (Co), mercury (Hg), nickel (Ni), molybdenum (Mo), lead (Pb), antimony (Sb), tin (Sn), and thallium (Tl) were measured by inductively coupled plasma mass spectrometry (ICP-MS) in maternal urine samples collected in early pregnancy (median GA: 13.1 wk). Speciated urinary arsenic (As) (inorganic+monomethyl+dimethyl As) was measured by high-performance liquid chromatography coupled to ICP-MS. Primary analyses focused on a mixture of seven metals that have previously been associated individually with fetal growth (i.e., As, Cd, Co, Hg, Ni, Pb, Tl) (n=262). In exploratory analyses, we additionally examined three metals that have been less studied in relation to fetal growth (i.e., Mo, Sb, Sn). Covariate-adjusted Bayesian kernel machine regression was used to investigate metal mixture associations with BW for GA z-scores.

RESULTS

In primary analyses, Hg and Ni ranked highest as predictors of BW for GA. An inverse linear association was estimated for Hg, whereas a positive association was estimated for Ni at low-to-moderate concentrations. A potential interaction between Hg and Ni was also identified. In our exploratory analysis, Sb ranked highest as a predictor of BW for GA, followed by Hg and Ni.

CONCLUSIONS

Our findings suggest that in this understudied population, Hg may reduce fetal growth, whereas Ni may promote fetal growth. We also identified Sb as a potential metal of concern for this population, which merits additional investigation. https://doi.org/10.1289/EHP7201.

Associations of a Metal Mixture Measured in Multiple Biomarkers with IQ: Evidence from Italian Adolescents Living near Ferroalloy Industry

BACKGROUND

Research on the health effects of chemical mixtures has focused mainly on early life rather than adolescence, a potentially important developmental life stage.

OBJECTIVES

We examined associations of a metal mixture with general cognition in a cross-sectional study of adolescents residing near ferromanganese industry, a source of airborne metals emissions.

METHODS

We measured manganese (Mn), lead (Pb), copper (Cu), and chromium (Cr) in hair, blood, urine, nails, and saliva from 635 Italian adolescents 10-14 years of age. Full-scale, verbal, and performance intelligence quotient (FSIQ, VIQ, PIQ) scores were assessed using the Wechsler Intelligence Scale for Children-III. Multivariable linear regression and Bayesian kernel machine regression (BKMR) were used to estimate associations of the metal mixture with IQ. In secondary analyses, we used BKMR's hierarchical variable selection option to inform biomarker selection for Mn, Cu, and Cr.

RESULTS

Median metal concentrations were as follows: hair Mn, 0.08 μ g / g ; hair Cu, 9.6 μ g / g ; hair Cr, 0.05 μ g / g ; and blood Pb, 1.3 μ g / dL . Adjusted models revealed an inverted U-shaped association between hair Cu and VIQ, consistent with Cu as an essential nutrient that is neurotoxic in excess. At low levels of hair Cu (10th percentile, 5.4 μ g / g ), higher concentrations (90th percentiles) of the mixture of Mn, Pb, and Cr (0.3 μ g / g , 2.6 μ g / dL , and 0.1 μ g / g , respectively) were associated with a 2.9 (95% CI: - 5.2 , - 0.5 )-point decrease in VIQ score, compared with median concentrations of the mixture. There was suggestive evidence of interaction between Mn and Cu. In secondary analyses, saliva Mn, hair Cu, and saliva Cr were selected as the biomarkers most strongly associated with VIQ score.

DISCUSSION

Higher adolescent levels of Mn, Pb, and Cr were associated with lower IQ scores, especially at low Cu levels. Findings also support further investigation into Cu as both beneficial and toxic for neurobehavioral outcomes. https://doi.org/10.1289/EHP6803.

Prenatal exposure to per- and polyfluoroalkyl substances and maternal and neonatal thyroid function in the Project Viva Cohort: A mixtures approach

BACKGROUND

Maternal and neonatal thyroid function is critical for growth and neurodevelopment. Exposure to individual per- and polyfluoroalkyl substances (PFAS) can alter circulating thyroid hormone levels, but few studies have investigated effects of combined exposure to multiple PFAS.

OBJECTIVES

Estimate associations of exposure to multiple PFAS during early pregnancy with maternal and neonatal thyroid function.

METHODS

The study population consisted of 726 mothers and 465 neonates from Project Viva, a Boston, Massachusetts area longitudinal pre-birth cohort. We measured six PFAS [perfluorooctanoate (PFOA), perfluorooctane sulfonate (PFOS), perfluorononanoate (PFNA), perfluorohexane sulfonate (PFHxS), 2-(N-ethyl-perfluorooctane sulfonamido)acetate (EtFOSAA), and 2-(N-methyl-perfluorooctane sulfonamido)acetate (MeFOSAA)] and thyroxine (T₄), Free T₄ Index (FT₄I), and thyroid stimulating hormone (TSH) in maternal plasma samples collected during early pregnancy, and neonatal T₄ in postpartum heel sticks. We estimated individual and joint effects of PFAS exposure with thyroid hormone levels using weighted quantile sum (WQS) regression and Bayesian kernel machine regression (BKMR), and evaluated potential non-linearity and interactions among PFAS using BKMR.

RESULTS

Higher concentrations of the PFAS mixture were associated with significantly lower maternal FT₄I, with MeFOSAA, EtFOSAA, PFOA, and PFHxS contributing most to the overall mixture effect in BKMR and WQS regression. In infants, higher concentrations of the PFAS mixture were associated with lower T₄ levels, primarily in males, with PFHxS and MeFOSAA contributing most in WQS, and PFHxS contributing most in BKMR. The PFAS mixture was not associated with maternal T₄ or TSH levels. However, in maternal BKMR analyses, ln-PFOS was positively associated with T₄ levels (Δ25^th to 75th percentile: 0.21 µg/dL; 95% credible interval: -0.03, 0.47) and ln-PFHxS was associated with a non-linear effect on TSH levels.

CONCLUSIONS

These findings support the hypothesis that there may be combined effects of prenatal exposure to multiple PFAS on maternal and neonatal thyroid function, but the direction and magnitude of these effects may vary across individual PFAS.

Correlates of organochlorine pesticide plasma concentrations among reproductive-aged black women

BACKGROUND

Organochlorine pesticides (OCPs) are lipophilic persistent organic pollutants associated with adverse health outcomes. Black women have higher body burdens compared with other U.S. populations and research on their correlates is limited.

METHODS

Using baseline data from a prospective cohort study of Black women aged 23-35 years from the Detroit, Michigan metropolitan area (enrolled 2010-2012), we examined correlates of plasma concentrations of the following OCPs: dichlorodiphenyltrichloroethane (p,p'-DDE), hexachlorobenzene (HCB), oxychlordane, and trans-nonachlor. At enrollment, we collected non-fasting blood samples from 742 participants. We also collected data on demographic, behavioral, dietary, occupational, and medical history factors via self-administered questionnaires, telephone interviews, and in-person clinic visits. We fit linear regression models to calculate percent (%) differences across categories of each correlate and 95% confidence intervals (CIs).

RESULTS

In models adjusted for all other correlates, a 5-year increase in age was associated with 24% higher oxychlordane (95% CI: 12%, 38%) and 26% higher trans-nonachlor (95% CI: 12%, 42%) plasma concentrations. Heavy alcohol use was associated with 7-9% higher plasma concentrations of p,p'-DDE, oxychlordane, and trans-nonachlor. Current smoking was associated with 10-19% higher plasma concentrations of all four OCPs, and was highest for current smokers of ≥10 cigarettes/day (% differences ranged from 22 to 29%). Compared with having never been breastfed during infancy, having been breastfed for ≥3 months was associated with 15% higher concentrations of p,p'-DDE (95% CI: 6%, 25%), 14% higher oxychlordane (95% CI: 5%, 24%), and 15% higher trans-nonachlor (95% CI: 5%, 27%). Consumption of ≥5 vs. ≤2 glasses/day of tap or bottled water was associated with 8-15% higher plasma concentrations of all four OCPs, and was highest for trans-nonachlor (% difference: 15%; 95% CI: 6%, 26%). No other dietary predictors were appreciably associated with plasma OCP concentrations. Obesity, parity, higher birth order, and longer lactation duration were inversely associated with plasma OCP concentrations.

CONCLUSIONS

In Black U.S. women of reproductive age, older age was an important correlate of plasma OCP concentrations. Exposure to OCPs earlier in life appears to contribute to current blood concentrations. In addition, tobacco, alcohol, and drinking water may be important sources of exposure.

Correlates of plasma concentrations of brominated flame retardants in a cohort of U.S. Black women residing in the Detroit, Michigan metropolitan area

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) and polybrominated biphenyls (PBBs) are brominated flame retardant chemicals detectable in the environment and U.S. population, and are associated with adverse health outcomes over the life course. Correlates of these organic pollutants are understudied among U.S. Black women.

METHODS

Using baseline data from a prospective cohort study of U.S. Black women aged 23-35 years from the Detroit area of Michigan (2010-2012), we examined correlates of PBDEs and PBB-153. Non-fasting blood samples were collected from 742 participants at enrollment, a subset of women selected for a case-cohort study of environmental chemicals. Data on socio-demographics, behaviors, diet, medical history, and early-life exposures were collected via self-administered questionnaires, telephone interviews, and in-person clinic visits. We fit linear regression models to calculate percent differences and 95% confidence intervals in lipid adjusted plasma concentrations of 11 individual PBDE congeners and PBB-153 for each baseline predictor.

RESULTS

In models adjusted for all other correlates, a 5-year increase in age was inversely associated with most PBDE congeners (% differences ranged from 6 to 15% lower), and was positively associated with PBB-153 (52% higher). A 5-kg/m² increase in BMI was inversely associated with PBDE-153 and PBB-153 (16% lower for both), and 6% higher for PBDE-28. Compared with having never been breastfed in infancy, ≥3 months of breastfeeding in infancy was associated with 69% higher PBB-153 concentrations. Lower education, current smoking, and heavy alcohol use were associated with higher plasma concentrations of most flame retardants. Diet was not an important predictor.

CONCLUSION

Important correlates for elevated body burdens of PBB-153 were increasing age and a history of having been breastfed in infancy. Education, smoking, and heavy alcohol use were important predictors of elevated body burdens of most flame retardants. This study fills an important gap in the environmental health literature by focusing on an understudied population.

Multi-media biomarkers: Integrating information to improve lead exposure assessment

Exposure assessment traditionally relies on biomarkers that measure chemical concentrations in individual biological media (i.e., blood, urine, etc.). However, chemicals distribute unevenly among different biological media; thus, each medium provides incomplete information about body burden. We propose that machine learning and statistical approaches can create integrated exposure estimates from multiple biomarker matrices that better represent the overall body burden, which we term multi-media biomarkers (MMBs). We measured lead (Pb) in blood, urine, hair and nails from 251 Italian adolescents aged 11-14 years from the Public Health Impact of Metals Exposure (PHIME) cohort. We derived aggregated MMBs from the four biomarkers and then tested their association with Wechsler Intelligence Scale for Children (WISC) IQ scores. We used three approaches to derive the Pb MMB: one supervised learning technique, weighted quantile sum regression (WQS), and two unsupervised learning techniques, independent component analysis (ICA) and non-negative matrix factorization (NMF). Overall, the Pb MMB derived using WQS was most consistently associated with IQ scores and was the only method to be statistically significant for Verbal IQ, Performance IQ and Total IQ. A one standard deviation increase in the WQS MMB was associated with lower Verbal IQ (β [95% CI] = -2.2 points [-3.7, -0.6]), Performance IQ (-1.9 points [-3.5, -0.4]) and Total IQ (-2.1 points [-3.8, -0.5]). Blood Pb was negatively associated with only Verbal IQ, with a one standard deviation increase in blood Pb being associated with a -1.7 point (95% CI: [-3.3, -0.1]) decrease in Verbal IQ. Increases of one standard deviation in the ICA MMB were associated with lower Verbal IQ (-1.7 points [-3.3, -0.1]) and lower Total IQ (-1.7 points [-3.3, -0.1]). Similarly, an increase of one standard deviation in the NMF MMB was associated with lower Verbal IQ (-1.8 points [-3.4, -0.2]) and lower Total IQ (-1.8 points [-3.4, -0.2]). Weights highlighting the contributions of each medium to the MMB revealed that blood Pb was the largest contributor to most MMBs, although the weights varied from more than 80% for the ICA and NMF MMBs to between 30% and 54% for the WQS-derived MMBs. Our results suggest that MMBs better reflect the total body burden of a chemical that may be acting on target organs than individual biomarkers. Estimating MMBs improved our ability to estimate the full impact of Pb on IQ. Compared with individual Pb biomarkers, including blood, a Pb MMB derived using WQS was more strongly associated with IQ scores. MMBs may increase statistical power when the choice of exposure medium is unclear or when the sample size is small. Future work will need to validate these methods in other cohorts and for other chemicals.

Evaluating associations between early pregnancy trace elements mixture and 2nd trimester gestational glucose levels: A comparison of three statistical approaches

OBJECTIVE

Studies have shown that individual trace element levels might be associated with abnormal glycemic status, with implications for diabetes. Few studies have considered these trace elements as a mixture and their impact on gestational glucose levels. Comparing three statistical approaches, we assessed the associations between essential trace elements mixture and gestational glucose levels.

METHODS

We used data from 1720 women enrolled in the Eunice Kennedy Shriver National Institute of Child Health and Human Development's Fetal Growth Study, for whom trace element concentrations (zinc, selenium, copper, molybdenum) were measured by inductively coupled plasma mass spectrometry (ICP-MS) using plasma collected during the 1st trimester. Non-fasting glucose levels were measured during the gestational diabetes mellitus (GDM) screening test in the 2nd trimester. We applied (1) Bayesian Kernel Machine Regression (BKMR); (2) adaptive Least Absolute Shrinkage and Selection Operator (LASSO) in a mutually adjusted linear regression model; and (3) generalized additive models (GAMs) to evaluate the joint associations between trace elements mixture and glucose levels adjusting for potential confounders.

RESULTS

Using BKMR, we observed a mean 2.7 mg/dL higher glucose level for each interquartile increase of plasma copper (95% credible interval: 0.9, 4.5). The positive association between plasma copper and glucose levels was more pronounced at higher quartiles of zinc. Similar associations were detected using adaptive LASSO and GAM. In addition, results from adaptive LASSO and GAM suggested a super-additive interaction between molybdenum and selenium (both p-values = 0.04).

CONCLUSION

Employing different statistical methods, we found consistent evidence of higher gestational glucose levels associated with higher copper and potential synergism between zinc and copper on glucose levels.

Prenatal lead exposure and childhood executive function and behavioral difficulties in project viva

BACKGROUND

Lead is an established neurotoxicant and early life exposure to lead is associated with detrimental impacts on IQ and several neurobehavioral domains. Less is known, however, about effects of prenatal lead exposure below 5 μg/dL on executive function and on social, emotional and self-regulatory behaviors in childhood.

OBJECTIVES

To examine the association between prenatal lead exposure and childhood executive function and social, emotional and self-regulatory behaviors.

METHODS

We included 1006 mother-child pairs from the Project Viva prospective pre-birth cohort. We measured prenatal maternal lead in second-trimester erythrocytes. In mid-childhood (median 7.7 years), parents and teachers rated executive function related behaviors using the Behavior Rating Inventory of Executive Function (BRIEF) and behavioral difficulties using the Strengths and Difficulties Questionnaire (SDQ). We used multivariable linear regression models adjusted for maternal, paternal, and child characteristics and metal co-exposures.

RESULTS

Mean maternal erythrocyte lead concentration was 1.2 μg/dL (interquartile range [IQR] 0.8-1.5 μg /dL), equivalent to approximately 0.4 μg/dL in whole blood. In adjusted models, associations with parent and teacher-rated scales were largely null, although effect estimates were consistently positive, suggesting worse scores with increasing lead levels. For an IQR increase in lead, BRIEF Global Executive Composite (GEC) was 0.73 (95% CI: -0.06, 1.52) points higher for parent-rated scores and 0.42 (95% CI: -0.39, 1.23) points higher for teacher-rated scores. Associations were strongest for parent-rated BRIEF plan/organize (β = 0.85; 95% CI: 0.12, 1.59) and shift (β = 0.88; 95% CI: 0.01, 1.75) subscales, as well as the SDQ emotional problems subscale (β = 0.18; 95% CI: 0.03, 0.33).

DISCUSSION

In this cohort with lead levels commonly experienced by U.S. women, there were few statistically significant associations with childhood executive function and behavior. However, there was a trend of worse neurobehavioral scores with increasing prenatal lead concentrations, in particular for childhood emotional problems and capacity to plan/organize and shift. Our results highlight the importance of continuing efforts to eliminate lead exposure in the general population.

Maternal blood arsenic levels and associations with birth weight-for-gestational age

BACKGROUND

Among highly exposed populations, arsenic exposure in utero may be associated with decreased birth weight, however less is known about potential effects of arsenic exposure in urban communities without contaminated sources such as drinking water.

OBJECTIVE

Investigate the association of blood arsenic levels with birth weight-for-gestational age categories within a prospective birth cohort study.

DESIGN/METHODS

We analyzed 730 mother-infant dyads within the Programming Research in Obesity, GRowth, Environment and Social Stressors (PROGRESS) cohort in Mexico City. Total arsenic was measured in maternal blood samples from the 2nd and 3rd trimesters, at delivery, as well as from infant umbilical cord blood samples. Multivariable, multinomial logistic regression models adjusting for maternal age at enrollment, pre-pregnancy body mass index, parity, infant sex, socioeconomic position, and prenatal environmental tobacco smoke exposure were used to calculate odds ratios of small-for-gestational age (<10th percentile, SGA) and large-for-gestational age (>90th percentile, LGA) compared to appropriate-for-gestational age (AGA) per unit increase of log-transformed arsenic.

RESULTS

Median (IQR) blood arsenic levels for maternal second trimester were 0.72 (0.33) μg/L, maternal third trimester 0.75 (0.41) μg/L, maternal at delivery 0.85 (0.70) μg/L, and infant cord 0.78 (0.65) μg/L. Maternal delivery and infant cord blood samples were most strongly correlated (spearman r = 0.65, p < 0.0001). Maternal arsenic levels at delivery were associated with significantly higher odds of both SGA (adj. OR = 1.44, 95% CI: 1.08-1.93) and LGA (adj. OR = 2.03, 95% CI: 1.12-3.67) compared to AGA. Results were similar for cord blood. There were 130 SGA infants and 22 LGA infants. Earlier in pregnancy, there were no significant associations of arsenic and birth weight-for-gestational age. However, we observed non-significantly higher odds of LGA among women with higher arsenic levels in the 3rd trimester (adj. OR = 1.46, 95% CI: 0.67-3.12).

CONCLUSION

We found that in a Mexico City birth cohort, higher maternal blood arsenic levels at delivery were associated with higher odds of both SGA and LGA. However, sources and species of arsenic were not known and the number of LGA infants was small, limiting the interpretation of this finding and highlighting the importance of future large studies to incorporate arsenic speciation. If our findings were confirmed in studies that addressed these limitations, determining modifiable factors that could be mitigated, such as sources of arsenic exposure, may be important for optimizing fetal growth to improve long-term health of children.

Assessing the contributions of metals in environmental media to exposure biomarkers in a region of ferroalloy industry

Residential proximity to ferroalloy production has been associated with increased manganese exposure, which can adversely affect health, particularly among children. Little is known, however, about which environmental samples contribute most to internal levels of manganese and other ferroalloy metals. We aimed to characterize sources of exposure to metals and evaluate the ability of internal biomarkers to reflect exposures from environmental media. In 717 Italian adolescents residing near ferromanganese industry, we examined associations between manganese, lead, chromium, and copper in environmental samples (airborne particles, surface soil, indoor/outdoor house dust) and biological samples (blood, hair, nails, saliva, urine). In multivariable regression analyses adjusted for child age and sex, a 10% increase in soil Mn was associated with increases of 3.0% (95% CI: 1.1%, 4.9%) in nail Mn and 1.6% (95% CI: -0.2%, 3.4%) in saliva Mn. Weighted-quantile-sum (WQS) regression estimated that higher soil and outdoor dust Mn accounted for most of the effect on nail Mn (WQS weights: 0.61 and 0.22, respectively, out of a total of 1.0). Higher air and soil Mn accounted for most of the effect on saliva Mn (WQS weights: 0.65 and 0.29, respectively). These findings can help inform biomarker selection in future epidemiologic studies and guide intervention strategies in exposed populations.

Lagged kernel machine regression for identifying time windows of susceptibility to exposures of complex mixtures

The impact of neurotoxic chemical mixtures on children's health is a critical public health concern. It is well known that during early life, toxic exposures may impact cognitive function during critical time intervals of increased vulnerability, known as windows of susceptibility. Knowledge on time windows of susceptibility can help inform treatment and prevention strategies, as chemical mixtures may affect a developmental process that is operating at a specific life phase. There are several statistical challenges in estimating the health effects of time-varying exposures to multi-pollutant mixtures, such as: multi-collinearity among the exposures both within time points and across time points, and complex exposure-response relationships. To address these concerns, we develop a flexible statistical method, called lagged kernel machine regression (LKMR). LKMR identifies critical exposure windows of chemical mixtures, and accounts for complex non-linear and non-additive effects of the mixture at any given exposure window. Specifically, LKMR estimates how the effects of a mixture of exposures change with the exposure time window using a Bayesian formulation of a grouped, fused lasso penalty within a kernel machine regression (KMR) framework. A simulation study demonstrates the performance of LKMR under realistic exposure-response scenarios, and demonstrates large gains over approaches that consider each time window separately, particularly when serial correlation among the time-varying exposures is high. Furthermore, LKMR demonstrates gains over another approach that inputs all time-specific chemical concentrations together into a single KMR. We apply LKMR to estimate associations between neurodevelopment and metal mixtures in Early Life Exposures in Mexico and Neurotoxicology, a prospective cohort study of child health in Mexico City.

Bayesian varying coefficient kernel machine regression to assess neurodevelopmental trajectories associated with exposure to complex mixtures

Exposure to environmental mixtures can exert wide-ranging effects on child neurodevelopment. However, there is a lack of statistical methods that can accommodate the complex exposure-response relationship between mixtures and neurodevelopment while simultaneously estimating neurodevelopmental trajectories. We introduce Bayesian varying coefficient kernel machine regression (BVCKMR), a hierarchical model that estimates how mixture exposures at a given time point are associated with health outcome trajectories. The BVCKMR flexibly captures the exposure-response relationship, incorporates prior knowledge, and accounts for potentially nonlinear and nonadditive effects of individual exposures. This model assesses the directionality and relative importance of a mixture component on health outcome trajectories and predicts health effects for unobserved exposure profiles. Using contour plots and cross-sectional plots, BVCKMR also provides information about interactions between complex mixture components. The BVCKMR is applied to a subset of data from PROGRESS, a prospective birth cohort study in Mexico city on exposure to metal mixtures and temporal changes in neurodevelopment. The mixture include metals such as manganese, arsenic, cobalt, chromium, cesium, copper, lead, cadmium, and antimony. Results from a subset of Programming Research in Obesity, Growth, Environment and Social Stressors data provide evidence of significant positive associations between second trimester exposure to copper and Bayley Scales of Infant and Toddler Development cognition score at 24 months, and cognitive trajectories across 6-24 months. We also detect an interaction effect between second trimester copper and lead exposures for cognition at 24 months. In summary, BVCKMR provides a framework for estimating neurodevelopmental trajectories associated with exposure to complex mixtures.

Dentine biomarkers of prenatal and early childhood exposure to manganese, zinc and lead and childhood behavior

BACKGROUND

Metal exposure alters neurodevelopmental outcomes; little is known about critical windows of susceptibility when exposure exerts the strongest effect.

OBJECTIVE

To examine associations between dentine biomarkers of manganese (Mn), zinc (Zn) and lead (Pb) and later childhood behaviors.

METHODS

Subjects enrolled in a longitudinal birth cohort study in Mexico City provided naturally shed deciduous teeth. We estimated weekly prenatal and postnatal dentine Mn, Zn and Pb concentrations in teeth using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and measured behavior at ages 8-11 years of age using the Behavior Assessment System for Children, 2nd edition (BASC-2). We used distributed lag models and lagged weighted quantile sum regression to identify the role of individual and combined dentine biomarkers of Mn, Zn and Pb on behavioral outcomes controlling for maternal education and gestational age.

RESULTS

Among the 133 subjects included in this study, prenatal and early postnatal dentine Mn appeared protective against childhood behavioral problems, specifically hyperactivity and attention. Postnatal dentine Mn was associated with increased reporting of internalizing problems, specifically anxiety. At 6 months, a 1-unit increase (unit = 1 SD of log concentration) in Mn was associated with a 0.18-unit (unit = 1 SD of BASC-2 score) increase in internalizing symptoms score and a 0.25-unit increase in anxiety. Postnatal Pb was associated with increasing anxiety symptoms; at 12 months, a 1-unit increase in Pb was associated with a 0.4 unit increase in anxiety symptoms. When examined as a metal mixture, we observed two potential windows of susceptibility to increased anxiety symptoms: the first window (0-8 months) appeared driven by Mn, the second window (8-12 months) was driven by the metal mixture and dominated by Pb. A 1-unit increase in the mixture index was associated with a 0.7-unit increase in SD of anxiety symptoms.

CONCLUSIONS

Childhood behaviors may demonstrate postnatal windows of susceptibility to individual and mixed metal concentrations measured in deciduous teeth. Prenatal dentine Mn may be protective, while excessive early postnatal Mn may increase risk for adverse behaviors. In combination, higher concentrations of Mn, Zn and Pb may have an adverse impact on behavior.

Statistical software for analyzing the health effects of multiple concurrent exposures via Bayesian kernel machine regression

BACKGROUND

Estimating the health effects of multi-pollutant mixtures is of increasing interest in environmental epidemiology. Recently, a new approach for estimating the health effects of mixtures, Bayesian kernel machine regression (BKMR), has been developed. This method estimates the multivariable exposure-response function in a flexible and parsimonious way, conducts variable selection on the (potentially high-dimensional) vector of exposures, and allows for a grouped variable selection approach that can accommodate highly correlated exposures. However, the application of this novel method has been limited by a lack of available software, the need to derive interpretable output in a computationally efficient manner, and the inability to apply the method to non-continuous outcome variables.

METHODS

This paper addresses these limitations by (i) introducing an open-source software package in the R programming language, the bkmr R package, (ii) demonstrating methods for visualizing high-dimensional exposure-response functions, and for estimating scientifically relevant summaries, (iii) illustrating a probit regression implementation of BKMR for binary outcomes, and (iv) describing a fast version of BKMR that utilizes a Gaussian predictive process approach. All of the methods are illustrated using fully reproducible examples with the provided R code.

RESULTS

Applying the methods to a continuous outcome example illustrated the ability of the BKMR implementation to estimate the health effects of multi-pollutant mixtures in the context of a highly nonlinear, biologically-based dose-response function, and to estimate overall, single-exposure, and interactive health effects. The Gaussian predictive process method led to a substantial reduction in the runtime, without a major decrease in accuracy. In the setting of a larger number of exposures and a dichotomous outcome, the probit BKMR implementation was able to correctly identify the variables included in the exposure-response function and yielded interpretable quantities on the scale of a latent continuous outcome or on the scale of the outcome probability.

CONCLUSIONS

This newly developed software, integrated suite of tools, and extended methodology makes BKMR accessible for use across a broad range of epidemiological applications in which multiple risk factors have complex effects on health.