BackgroundSparse research exists on predictors of element concentrations measured in deciduous teeth.ObjectiveTo estimate associations between maternal/child characteristics, elements measured in home tap water during pregnancy and element concentrations in the dentin of shed deciduous teeth.MethodsOur analysis included 152 pregnant person-infant dyads followed from the second trimester through the end of the first postnatal year from the New Hampshire Birth Cohort Study. During pregnancy and early infancy, we collected dietary and sociodemographic information via surveys, measured elements in home tap water, and later collected naturally exfoliated teeth from child participants. We measured longitudinal deposition of elements in dentin using LA-ICP-MS. Multivariable linear mixed models were used to estimate associations between predictors and dentin element concentrations.ResultsWe measured 12 elements in dentin including those previously reported (Ba, Mn, Pb, Sr, Zn) and less frequently reported (Al, As, Cd, Cu, Hg, Li, and W). A doubling of Pb or Sr concentrations in water was associated with higher dentin Pb or Sr respectively in prenatally formed [9% (95%CI: 3%, 15%); 3% (1%, 6%)] and postnatally formed [10% (2%, 19%); 6% (2%, 10%)] dentin. Formula feeding from birth to 6 weeks or 6 weeks to 4 months was associated with higher element concentrations in postnatal dentin within the given time period as compared to exclusive human milk feeding: Sr: 6 weeks: 61% (36%, 90%) and 4 months: 85% (54%, 121%); Ba: 6 weeks: 35% (3.3%, 77%) and 4 months: 42% (10%, 83%); and Li: 6 weeks: 61% (33%, 95%) and 4 months: 58% (31%, 90%).SignificanceThese findings offer insights into predictors of dentin elements and potential confounders in exposure-health outcome relationships during critical developmental periods.

Background: Per- and polyfluoroalkyl substances (PFAS) are a class of persistent synthetic chemicals that are found in human milk and are associated with negative health effects. Research suggests that PFAS affect both lactation and the human metabolome. Methods: We measured perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) in the milk of 425 participants from the New Hampshire Birth Cohort Study using liquid chromatography-tandem mass spectrometry (LC-MS/MS). A nontargeted metabolomics assay was performed using LC with high-resolution MS, and metabolites were identified based on in-house database matching. We observed six metabolic profiles among our milk samples using self-organizing maps, and multinomial logistic regression was used to identify sociodemographic and perinatal predictors of these profiles, including infant sex, parity, participant body mass index, participant age, education, race, smoking status, gestational weight gain, and infant age at time of milk collection. Results: Elevated PFOA was associated with profiles containing higher amounts of triglyceride fatty acids, glycerophospholipids and sphingolipids, and carnitine metabolites, as well as lower amounts of lactose and creatine phosphate. Lower concentrations of milk PFOS were associated with lower levels of fatty acids. Conclusion: Our findings suggest that elevated PFOA in human milk is related to metabolomic profiles consistent with enlarged milk fat globule membranes and altered fatty acid metabolism. Further, our study supports the theory that PFAS share mammary epithelial membrane transport mechanisms with fatty acids and associate with metabolic markers of reduced milk production.

Fish consumption is one of the main sources of mercury (Hg) exposure, but few studies have examined Hg exposure from fish consumption among children. This study aimed to assess the frequency of fish intake and associations with Hg and other element concentrations among 700 three-year-old children from the New Hampshire Birth Cohort Study. Usual fish intake was derived from a validated food frequency questionnaire (Block Questionnaire for ages 2-7) and toenail element concentrations were determined using ICP-MS. Multiple linear regression analysis was used to assess the association between fish intake and toenail element concentrations. A mixture analysis, using Weighted quantile sum (WQS) regression, was used to estimate the relative contribution of fish consumption to element exposures. Twenty-three percent of children were reported to consume at least one fish meal/week on average during the previous 6 months. In adjusted linear regression models, children with any type of fish consumption versus no consumption had 108% (95% confidence interval (CI: 68%, 153%)) higher toenail Hg concentrations. To a lesser extent, children consuming “other fish (not fried) including tuna” and “fried fish or fish sticks” had 120% (95% CI: 82%, 164%), and 23% (95% CI: 2%, 51%) higher toenail concentrations, respectively, than those consuming no fish. Using WQS regression, Hg was the element most strongly related to fish consumption. Fish intake among young children was related to Hg exposure even at low levels of consumption. Future studies will need to determine the health consequences of this exposure.

Background Gut-derived metabolites, products of microbial and host co-metabolism, may inform mechanisms underlying children’s neurodevelopment. We investigated whether infant fecal metabolites were related to toddler social behavior. Methods Stool samples collected from 6-week-olds ( n = 86) and 1-year-olds ( n = 209) in the New Hampshire Birth Cohort Study (NHBCS) were analyzed using nuclear magnetic resonance spectroscopy metabolomics. Autism-related behavior in 3-year-olds was assessed by caregivers using the Social Responsiveness Scale (SRS-2). To assess the association between metabolites and SRS-2 scores, we used a traditional single-metabolite approach, quantitative metabolite set enrichment (QEA), and self-organizing maps (SOMs). Results Using a single-metabolite approach and QEA, no individual fecal metabolite or metabolite set at either age was associated with SRS-2 scores. Using the SOM method, fecal metabolites of six-week-olds organized into four profiles, which were unrelated to SRS-2 scores. In 1-year-olds, one of twelve fecal metabolite profiles was associated with fewer autism-related behaviors, with SRS-2 scores 3.4 (95%CI: −7, 0.2) points lower than the referent group. This profile had higher concentrations of lactate and lower concentrations of short chain fatty acids than the reference. Conclusions We uncovered metabolic profiles in infant stool associated with subsequent social behavior, highlighting one potential mechanism by which gut bacteria may influence neurobehavior. Impact Differences in host and microbial metabolism may explain variability in neurobehavioral phenotypes, but prior studies do not have consistent results. We applied three statistical techniques to explore fecal metabolite differences related to social behavior, including self-organizing maps (SOMs), a novel machine learning algorithm. A 1-year-old fecal metabolite pattern characterized by high lactate and low short-chain fatty acid concentrations, identified using SOMs, was associated with social behavior less indicative of autism spectrum disorder. Our findings suggest that social behavior may be related to metabolite profiles and that future studies may uncover novel findings by applying the SOM algorithm.

BACKGROUND:Spatial elemental analysis of deciduous tooth dentin combined with odontochronological estimates can provide an early life (in utero to ~2 years of age) history of inorganic element exposure and status. OBJECTIVE:To demonstrate the importance of data normalization to a certified reference material to enable between-study comparisons, using populations with assumed contrasting elemental exposures. METHODS:We used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of dentin to derive a history of elemental composition from three distinct cohort studies: a present day rural cohort, (the New Hampshire Birth Cohort Study (NHBCS; N = 154)), an historical cohort from an urban area (1958-1970), (the St. Louis Baby Tooth Study (SLBT; N = 78)), and a present-day Nigerian cohort established to study maternal HIV transmission (Dental caries and its association with Oral Microbiomes and HIV in young children-Nigeria (DOMHaIN; N = 31)). RESULTS:We report Li, Al, Mn, Cu, Zn, Sr, Ba and Pb concentrations (µg/g) and qualitatively examine As, Cd and Hg across all three cohorts. Rates of detection were highest, both overall and for each cohort individually, for Zn, Sr, Ba and Li. Zinc was detected in 100% of samples and was stably present in teeth at a concentration range of 64 - 86 µg/g. Mercury, As and Cd detection rates were the lowest, and had high variability within individual ablated spots. We found the highest concentrations of Pb in the pre- and postnatal dentin of the SLBT cohort, consistent with the prevalent use of Pb as an additive to gasoline prior to 1975. The characteristic decline in Mn after the second trimester was observed in all cohorts. IMPACT:Spatially resolved elemental analysis of deciduous teeth combined with methods for estimating crown formation times can be used to reconstruct an early-life history of elemental exposure inaccessible via other biomarkers. Quantification of data into absolute values using an external standard reference material has not been conducted since 2012, preventing comparison between studies, a common and highly informative component of epidemiology. We demonstrate, with three contrasting populations, that absolute quantification produces data with the lowest variability, compares well with available data and recommends that future tooth biomarker studies report data in this way.

Research on the neurodevelopmental effects of metal(loid)s has focused mainly on outcomes assessed at one time point, even though brain development progresses over time. We investigated biomarkers of perinatal exposure to metals and changes in child behavior over time. We followed 268 participants from the prospective New Hampshire Birth Cohort Study between birth and age 5 years. We measured arsenic (As), copper (Cu), manganese (Mn), lead (Pb), selenium (Se), and zinc (Zn) in toenails from 6-week-old infants. The Behavioral Symptoms Index (BSI), externalizing, and internalizing symptoms were assessed using the Behavior Assessment System for Children, 2nd edition (BASC-2) at ages 3 and 5 years. Multivariable linear regression was used to estimate associations of metals with behavior change, calculated as the difference in symptom raw scores between 3 and 5 years, in addition to the associations for symptom scores at 3 and 5 years separately. Sex-specific associations were also explored using stratified models and a sex-metal interaction term. Adjusted associations of metals and change in behavior varied by exposure and outcome. Each 1 µg/g increase in ln toenail Cu was associated with improved behavior between 3 and 5 years [BSI: β = − 3.88 (95%CI: − 7.12, − 0.64); Externalizing problems: β = − 2.20 (95%CI: − 4.07, − 0.33)]. Increasing Zn was associated with increased externalizing behavior over time ( β = 3.42 (95%CI: 0.60, 6.25). Sex-stratified analyses suggested more pronounced associations among boys compared to girls. Perinatal exposure to metals may alter behavioral development between ages 3 and 5 years. Findings support the need for more research on associations between metals and neurodevelopment over longer time periods.

Background: Manganese (Mn) is an essential nutrient and neurotoxicant, and the neurodevelopmental effects of Mn may depend on exposure timing. Less research has quantitatively compared the impact of Mn exposure on neurodevelopment across exposure periods. Methods: We used data from 125 Italian adolescents (10–14 years) from the Public Health Impact of Metals Exposure Study to estimate prospective associations of Mn in three early life exposure periods with adolescent attention-related behaviors. Mn was quantified in deciduous teeth using laser ablation-inductively coupled plasma-mass spectrometry to represent prenatal (2nd trimester-birth), postnatal (birth ~1.5 years), and childhood (~1.5–6 years) exposure. Attention-related behavior was evaluated using the Conners Behavior Rating Scales in adolescence. We used multivariable linear regression models to quantify associations between Mn in each exposure period, and multiple informant models to compare associations across exposure periods. Results: Median tooth Mn levels (normalized to calcium) were 0.4 area under the curve (AUC) 55Mn:43Ca × 104, 0.1 AUC 55Mn:43Ca × 104, and 0.0006 55Mn:43Ca for the prenatal, postnatal, and childhood periods. A doubling in prenatal tooth Mn levels was associated with 5.3% (95% confidence intervals [CI] = −10.3%, 0.0%) lower (i.e., better) teacher-reported inattention scores, whereas a doubling in postnatal tooth Mn levels was associated with 4.5% (95% CI = −9.3%, 0.6%) and 4.6% (95% CI = −9.5%, 0.6%) lower parent-reported inattention and attention deficit/hyperactivity disorder index scores, respectively. Childhood Mn was not beneficially associated with reported attention-related behaviors. Conclusion: Protective associations in the prenatal and postnatal periods suggest Mn is beneficial for attention-related behavior, but not in the childhood period.

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.

Background A community residing along a flight path to Boston International Airport raised concerns about increased air traffic leading to increased soil pollutant deposition. These depositions may contain metals that are harmful to human health such as Pb, Zn, Cu, Fe, and Ni. Objective To conduct a pedagogical pilot exposure assessment study of measuring elements in soil across areas of Milton, MA with varying air traffic on approach to Boston International Airport. Methods As part of a Boston University School of Public Health graduate class in collaboration with a community organization, soil samples were collected from 17 different locations within and outside of the located flight path and analyzed for a suite of 30 elements using X-ray fluorescence spectroscopy. To evaluate the relationship between flight path and soil concentrations, samples were denoted as either within the flight path or outside the flight path. Differences between element concentrations within and outside the flight path were determined using Wilcoxon Rank Sum tests and correlations were compared using spearman correlations. Results Median soil metal concentrations of selected metals most associated with air traffic within vs. outside flight path were respectively: Pb: 73 (49) ppm vs. 108 (75) ppm, Zn: 45 (26) ppm vs. 38 (46) ppm, Cu: 16 (11) ppm vs. 18 (8) ppm, Fe: 12,926 (2,425) ppm vs. 11,222 (2,429) ppm. Conclusions Correlations between elements were higher and more positive within the flight path compared to outside the flight path which suggests a potential contribution from aircraft emission sources.

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.

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. 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.

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.

BACKGROUND AND AIM: Research on the neurodevelopmental effects of metals has focused mainly on outcomes assessed at one time point, even though brain development progresses over time. We investigated biomarkers of prenatal exposure to metals and changes in child behavior over time. METHODS: We followed 268 participants from the New Hampshire Birth Cohort Study between birth and age five years. We measured arsenic (As), copper (Cu), manganese (Mn), lead (Pb), selenium (Se) and zinc (Zn) in toenails from 6-week-old infants. The Behavioral Symptoms Index (BSI), externalizing, and internalizing symptoms were assessed using the Behavior Assessment System for Children, 2nd edition (BASC-2) at ages 3 and 5 years. Multivariable linear regression and Bayesian Kernel Machine Regression were used to estimate associations of the metal mixture with behavior change, calculated as the change in raw score from 3 to 5 years. Sex specific associations were explored in stratified models. RESULTS:Adjusted associations of metals with behavior varied by metal, sex, and outcome. Among boys, higher ln-Pb was associated with increased overall behavioral problems, externalizing symptoms, and internalizing symptoms over time as compared to girls [ boys: β= 4.3 (95%CI: -0.5, 9.0) vs. girls: -3.8 (-7.8,0.3); 1.8 (-1.1, 4.6) vs. -2.5 (-5.0, 0.01); 1.1 (-1.7,3.9) vs. -2.9 (-5.6, -0.2); sex-Pb interaction term p-values0.05]. Among boys, higher ln-Cu was associated with decreased overall behavioral problems, externalizing symptoms, and internalizing symptoms over time as compared to girls [boys: -6.4 (-10.9, -2.0) vs. girls: 1.1 (-4.0, 6.1); -3.6 (-6.2, -0.9) vs. 0.7 (-2.4, 3.8); -2.4 (-5.0, 0.3) vs. 1.3 (-2.1,4.6); sex-Cu interaction term p-values0.05]. CONCLUSIONS:Prenatal exposure to metals may alter symptoms of maladaptive behavior between ages 3 and 5 years. Findings support the need for more research on sex differences in associations between metals and neurodevelopment over longer time periods and at multiple time points. KEYWORDS: Metals, neurodevelopment, pediatric, mixtures, sex-differences

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: 13 = 0.20 (95 % CI: 0.02, 0.38)] and Block design [13 = 0.21 (0.01, 0.41)] and early postnatal Mn was positively associated with Digits forward [13 = 0.24 (0.09, 0.40)], while childhood Mn was negatively associated with Coding [13 = -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.

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-M. 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 mu g/g; hair Cu, 9.6 mu g/g; hair Cr, 0.05 mu g/g; and blood Pb, 1.3 mu 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 mu g/g), higher concentrations (90th percentiles) of the mixture of Mn, Pb, and Cr (0.3 mu g/g, 2.6 mu g/dL, and 0.1 mu 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.

Introduction: Prior studies have reported Mn-associated decrements in IQ, a composite score computed from subtests. We examined patterns of IQ subtest scores to generate hypotheses about the underlying structural changes in the brain that may be produced by early life Mn exposure among adolescents living near ferromanganese industry.Methods: We analyzed deciduous teeth from 190 Italian children ages 10-14 years. Mn was measured in the tooth matrix to represent prenatal, postnatal (0-1 year) and childhood (~1-6 years) exposure periods. Neuropsychologists administered the Wechsler Intelligence Scale for Children, 3rd edition. Multivariable linear regression and generalized additive models were used to estimate adjusted associations between ln-tooth Mn and scores on seven subtests: Arithmetic, Comprehension, Information, Similarities, Vocabulary, Digits forward and Digits backward.Results: We observed varied patterns of adjusted associations between tooth Mn and subtest performance, depending on the window of exposure. Overall, subtests associated with Mn across exposure windows measure memory, problem solving and attention, suggesting frontal system and hippocampal involvement. We found inverted U-shaped associations between prenatal Mn and Arithmetic, Comprehension, Information and Digits forward (pgam=0.18-0.39). Early postnatal Mn was associated with better performance on Arithmetic (β=0.27 (95%CI=-0.63, 1.17)), Information (β=0.35 (95%CI=-0.42, 1.13)), and Digits forward (β=0.51 (95%CI=0.21, 0.81)). However, childhood Mn was associated with lower Information scores (β=-0.35 (95%CI=-1.11, 0.41)) and non-linearly associated with Digits forward (pgam=0.06). In these data, the shape of the Mn-subtest relationship was dependent on exposure timing.Conclusion: Our results suggest that frontal cortex function may be sensitive to Mn exposure. Higher Mn may be toxic in childhood, potentially identifying a window for intervention implementation.

Introduction: Growing epidemiologic evidence suggests that environmental exposure to manganese (Mn) in childhood is associated with neurobehavioral decrements. However, substantial gaps remain in understanding Mn health risks among adolescents and in relation to varying biomarkers and timing of exposure. Methods: As part of the Public Health Impact of Manganese Exposure (PHIME) study, we measured Mn in blood, hair, nails, saliva, and urine collected from 10-14 year old Italian children (N~720) living near ferromanganese industry. Mn was also measured in deciduous teeth to represent prenatal, postnatal, and early childhood exposure periods. Neurobehavioral assessments, conducted concurrent with biological sample collection, included the Wechsler Intelligence Scale for Children, Conners Behavior Rating Scale, and California Verbal Learning Test. Multivariable models evaluated associations between each Mn biomarker and neurobehavior. Weighted quantile sum regression was used to estimate associations of a weighted cumulative Mn index and to identify the biomarker with the largest contribution to neurobehavior score. Results: We observed inverse associations between childhood Mn with cognition (e.g., saliva and verbal IQ, β=−1.4, p=0.004) and memory (saliva and short recall, β=−0.3, p=0.001). In contrast, early life Mn (teeth) was associated with improved scores of cognition (digit span backward, β=0.4, p=0.05), behavior (teacher-reported inattention, β=-0.07, p=0.04), and memory (sum of intrusions, β=-1.8, p=0.03). The weighted cumulative Mn index, which included blood, hair, nail, saliva and urine Mn, was associated with worse performance on all three neurobehavioral assessments (verbal IQ, β=−4.0, p=0.001; parent-reported inattention, β=0.05, p=0.01); saliva was the largest contributor to most associations. Conclusions: These results suggest a complex relationship between Mn and neurobehavior, whereby associations may differ by biomarker and timing of exposure.