Adrienne S. Ettinger

Fetal Lead Exposure at Each Stage of Pregnancy as a Predictor of Infant Mental Development

Background The impact of prenatal lead exposure on neurodevelopment remains unclear in terms of consistency, the trimester of greatest vulnerability, and the best method for estimating fetal lead exposure. Objective We studied prenatal lead exposure’s impact on neurodevelopment using repeated measures of fetal dose as reflected by maternal whole blood and plasma lead levels. Methods We measured lead in maternal plasma and whole blood during each trimester in 146 pregnant women in Mexico City. We then measured umbilical cord blood lead at delivery and, when offspring were 12 and 24 months of age, measured blood lead and administered the Bayley Scales of Infant Development. We used multivariate regression, adjusting for covariates and 24-month blood lead, to compare the impacts of our pregnancy measures of fetal lead dose. Results Maternal lead levels were moderately high with a first-trimester blood lead mean (± SD) value of 7.1 ± 5.1 μg/dL and 14% of values ≥10 μg/dL. Both maternal plasma and whole blood lead during the first trimester (but not in the second or third trimester) were significant predictors (p < 0.05) of poorer Mental Development Index (MDI) scores. In models combining all three trimester measures and using standardized coefficients, the effect of first-trimester maternal plasma lead was somewhat greater than the effect of first-trimester maternal whole blood lead and substantially greater than the effects of second- or third-trimester plasma lead, and values averaged over all three trimesters. A 1-SD change in first-trimester plasma lead was associated with a reduction in MDI score of 3.5 points. Postnatal blood lead levels in the offspring were less strongly correlated with MDI scores. Conclusions Fetal lead exposure has an adverse effect on neurodevelopment, with an effect that may be most pronounced during the first trimester and best captured by measuring lead in either maternal plasma or whole blood.

Influence of prenatal lead exposure on genomic methylation of cord blood DNA.

Background Fetal lead exposure is associated with adverse pregnancy outcomes and developmental and cognitive deficits; however, the mechanism(s) by which lead-induced toxicity occurs remains unknown. Epigenetic fetal programming via DNA methylation may provide a pathway by which environmental lead exposure can influence disease susceptibility. Objective This study was designed to determine whether prenatal lead exposure is associated with alterations in genomic methylation of leukocyte DNA levels from umbilical cord samples. Methods We measured genomic DNA methylation, as assessed by Alu and LINE-1 (long interspersed nuclear element-1) methylation via pyrosequencing, on 103 umbilical cord blood samples from the biorepository of the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) study group. Prenatal lead exposure had been assessed by measuring maternal bone lead levels at the mid-tibial shaft and the patella using a spot-source 109Cd K-shell X-ray fluorescence instrument. Results We found an inverse dose–response relationship in which quartiles of patella lead correlated with cord LINE-1 methylation (p for trend = 0.01) and and tibia lead correlated with Alu methylation (p for trend = 0.05). In mixed effects regression models, maternal tibia lead was negatively associated with umbilical cord genomic DNA methylation of Alu (β= −0.027; p = 0.01). We found no associations between cord blood lead and cord genomic DNA methylation. Conclusions Prenatal lead exposure is inversely associated with genomic DNA methylation in cord blood. These data suggest that the epigenome of the developing fetus can be influenced by maternal cumulative lead burden, which may influence long-term epigenetic programming and disease susceptibility throughout the life course.

Urinary phthalate metabolites in relation to preterm birth in Mexico City.

Background Rates of preterm birth have been rising over the past several decades. Factors contributing to this trend remain largely unclear, and exposure to environmental contaminants may play a role. Objective We investigated the relationship between phthalate exposure and preterm birth. Methods Within a large Mexican birth cohort study, we compared third-trimester urinary phthalate metabolite concentrations in 30 women who delivered preterm (< 37 weeks of gestation) with those of 30 controls (≥ 37 weeks of gestation). Results Concentrations of most of the metabolites were similar to those reported among U.S. females, although in the present study mono-n-butyl phthalate (MBP) concentrations were higher and monobenzyl phthalate (MBzP) concentrations lower. In a crude comparison before correcting for urinary dilution, geometric mean urinary concentrations were higher for the phthalate metabolites MBP, MBzP, mono(3-carboxylpropyl) phthalate, and four metabolites of di(2-ethyl-hexyl) phthalate among women who subsequently delivered preterm. These differences remained, but were somewhat lessened, after correction by specific gravity or creatinine. In multivariate logistic regression analysis adjusted for potential confounders, elevated odds of having phthalate metabolite concentrations above the median level were found. Conclusions We found that phthalate exposure is prevalent among this group of pregnant women in Mexico and that some phthalates may be associated with preterm birth.

Early postnatal blood manganese levels and children's neurodevelopment.

Background: Recent evidence suggests that low-level environmental exposure to manganese adversely affects child growth and neurodevelopment. Previous studies have addressed the effects of prenatal exposure, but little is known about developmental effects of early postnatal exposure. Methods: We studied 448 children born in Mexico City from 1997 through 2000, using a longitudinal study to investigate neurotoxic effects of early-life manganese exposure. Archived blood samples, collected from children at 12 and 24 months of age, were analyzed for manganese levels using inductively coupled plasma mass spectrometry. Mental and psychomotor development were scored using Bayley Scales of Infant Development at 6-month intervals between 12 and 36 months of age. Results: At 12 months of age, the mean (SD) blood manganese level was 24.3 (4.5) &mgr;g/L and the median was 23.7 &mgr;g/L; at 24 months, these values were 21.1 (6.2) &mgr;g/L and 20.3 &mgr;g/L, respectively. Twelve- and 24-month manganese concentrations were correlated (Spearman correlation = 0.55) and levels declined over time (&bgr; = −5.7 [95% CI = −6.2 to −5.1]). We observed an inverted U-shaped association between 12-month blood manganese and concurrent mental development scores (compared with the middle 3 manganese quintiles, for the lowest manganese quintile, &bgr; = −3.3 [−6.0 to −0.7] and for the highest manganese quintile, &bgr; = −2.8 [−5.5 to −0.2]). This 12-month manganese effect was apparent but diminished with mental development scores at later ages. The 24-month manganese levels were not associated with neurodevelopment. Conclusions: These results suggest a possible biphasic dose-response relationship between early-life manganese exposure at lower exposure levels and infant neurodevelopment. The data are consistent with manganese as both an essential nutrient and a toxicant.

Maternal Blood Manganese Levels and Infant Birth Weight

Background: Manganese is both an essential element and a known neurotoxicant to children. High manganese exposures have been associated with negative reproductive outcomes in animals, but few epidemiologic studies have examined the effects of human fetal manganese exposure. Methods: We studied the association between maternal and umbilical cord blood manganese levels and birth weight in a cohort of 470 mother-infant pairs born at term (≥37 weeks gestation) in Ottawa County, Oklahoma. Nonlinear spline and quadratic regression models were used to test the hypothesis of an inverted U-shaped relationship between manganese levels and birth weight. Results: Mean (standard deviation) concentration of manganese was 2.4 (0.95) &mgr;g/dL in the maternal blood and 4.2 (1.6) &mgr;g/dL in the cord blood. Umbilical cord manganese was not associated with birth weight. A nonlinear relationship was observed between maternal manganese and birth weight after adjusting for potential confounders. Birth weight increased with manganese levels up to 3.1 &mgr;g/L, and then a slight reduction in weight was observed at higher levels. Compared with the 3.1-&mgr;g/L point of inflection, birth weight estimates at the 5th (1.3 &mgr;g/L) and 95th (4.0 &mgr;g/L) percentiles of exposure were −160 g (95% confidence interval = −286 to −33) and −46 g (−38 to 131), respectively. Conclusions: Maternal blood manganese levels during pregnancy are associated with birth weight in a nonlinear pattern in full-term infants. These findings suggest that manganese may affect fetal growth. Possible detrimental effects of elevated manganese levels on the fetus should be further examined in more highly exposed populations.

Associations of Early Childhood Manganese and Lead Coexposure with Neurodevelopment

Background: Most toxicologic studies focus on a single agent, although this does not reflect real-world scenarios in which humans are exposed to multiple chemicals. Objectives: We prospectively studied manganese–lead interactions in early childhood to examine whether manganese–lead coexposure is associated with neurodevelopmental deficiencies that are more severe than expected based on effects of exposure to each metal alone. Methods: Four hundred fifty-five children were enrolled at birth in an longitudinal cohort study in Mexico City, provided blood samples, and were followed until 36 months of age. We measured lead and manganese at 12 and 24 months and assessed neurodevelopment at 6-month intervals from 12 to 36 months of age using Bayley Scales of Infant Development–II. Results: Mean (± SD) blood concentrations at 12 and 24 months were, respectively, 24.7 ± 5.9 μg/L and 21.5 ± 7.4 μg/L for manganese and 5.1 ± 2.6 μg/dL and 5.0 ± 2.9 μg/dL for lead. Mixed-effects models, including Bayley scores at five time points, showed a significant interaction over time: highest manganese quintile × continuous lead; mental development score, β = –1.27 [95% confidence interval (CI): –2.18, –0.37]; psychomotor development score, β = –0.92 (95% CI: –1.76, –0.09). Slopes for the estimated 12-month lead effect on 18-month mental development and 24- through 36-month psychomotor development scores were steeper for children with high manganese than for children with midrange manganese levels. Conclusions: We observed evidence of synergism between lead and manganese, whereby lead toxicity was increased among children with high manganese coexposure. Findings highlight the importance of understanding health effects of mixed exposures, particularly during potentially sensitive developmental stages such as early childhood.

Effect of Calcium Supplementation on Blood Lead Levels in Pregnancy: A Randomized Placebo-Controlled Trial

Background Prenatal lead exposure is associated with deficits in fetal growth and neurodevelopment. Calcium supplementation may attenuate fetal exposure by inhibiting mobilization of maternal bone lead and/or intestinal absorption of ingested lead. Objective Our goal was to evaluate the effect of 1,200 mg dietary calcium supplementation on maternal blood lead levels during pregnancy. Methods In a double-blind, randomized, placebo-controlled trial conducted from 2001 through 2003 in Mexico City, we randomly assigned 670 women in their first trimester of pregnancy to ingest calcium (n = 334) or placebo (n = 336). We followed subjects through pregnancy and evaluated the effect of supplementation on maternal blood lead, using an intent-to-treat analysis by a mixed-effects regression model with random intercept, in 557 participants (83%) who completed follow-up. We then conducted as-treated analyses using similar models stratified by treatment compliance. Results Adjusting for baseline lead level, age, trimester of pregnancy, and dietary energy and calcium intake, calcium was associated with an average 11% reduction (0.4 μg/dL) in blood lead level relative to placebo (p = 0.004). This reduction was more evident in the second trimester (−14%, p < 0.001) than in the third (−8%, p = 0.107) and was strongest in women who were most compliant (those who consumed ≥ 75% calcium pills; −24%, p < 0.001), had baseline blood lead > 5 μg/dL (−17%, p < 0.01), or reported use of lead-glazed ceramics and high bone lead (−31%, p < 0.01). Conclusion Calcium supplementation was associated with modest reductions in blood lead when administered during pregnancy and may constitute an important secondary prevention effort to reduce circulating maternal lead and, consequently, fetal exposure.

Effect of breast milk lead on infant blood lead levels at 1 month of age

Nursing infants may be exposed to lead from breast milk, but relatively few data exist with which to evaluate and quantify this relationship. This route of exposure constitutes a potential infant hazard from mothers with current ongoing exposure to lead as well as from mothers who have been exposed previously due to the redistribution of cumulative maternal bone lead stores. We studied the relationship between maternal breast milk lead and infant blood lead levels among 255 mother–infant pairs exclusively or partially breast-feeding through 1 month of age in Mexico City. A rigorous, well-validated technique was used to collect, prepare, and analyze the samples of breast milk to minimize the potential for environmental contamination and maximize the percent recovery of lead. Umbilical cord and maternal blood lead were measured at delivery; 1 month after delivery (± 5 days) maternal blood, bone, and breast milk and infant blood lead levels were obtained. Levels of lead at 1 month postpartum were, for breast milk, 0.3–8.0 μg/L (mean ± SD, 1.5 ± 1.2); maternal blood lead, 2.9–29.9 μg/dL (mean ± SD, 9.4 ± 4.5); and infant blood lead, 1.0–23.1 μg/dL (mean ± SD, 5.5 ± 3.0). Infant blood lead at 1 month postpartum was significantly correlated with umbilical cord (Spearman correlation coefficient rS = 0.40, p < 0.0001) and maternal (rS = 0.42, p < 0.0001) blood lead at delivery and with maternal blood (rS = 0.67, p < 0.0001), patella (rS = 0.19, p = 0.004), and breast milk (rS = 0.32, p < 0.0001) lead at 1 month postpartum. Adjusting for cord blood lead, infant weight change, and reported breast-feeding status, a difference of approximately 2 μg/L (ppb; from the midpoint of the lowest quartile to the midpoint of the highest quartile) breast milk lead was associated with a 0.82 μg/dL increase in blood lead for breast-feeding infants at 1 month of age. Breast milk lead accounted for 12% of the variance of infant blood lead levels, whereas maternal blood lead accounted for 30%. Although these levels of lead in breast milk were low, they clearly have a strong influence on infant blood lead levels over and above the influence of maternal blood lead. Additional information on the lead content of dietary alternatives and interactions with other nutritional factors should be considered. However, because human milk is the best and most complete nutritional source for young infants, breast-feeding should be encouraged because the absolute values of the effects are small within this range of lead concentrations.

Maternal arsenic exposure and impaired glucose tolerance during pregnancy.

Background Accumulating evidence has shown an increased risk of type 2 diabetes in general populations exposed to arsenic, but little is known about exposures during pregnancy and the association with gestational diabetes (GD). Objectives We studied 532 women living proximate to the Tar Creek Superfund Site to investigate whether arsenic exposure is associated with impaired glucose tolerance during pregnancy. Methods Blood glucose was measured between 24 and 28 weeks gestation after a 1-hr oral glucose tolerance test (GTT) as part of routine prenatal care. Blood and hair were collected at delivery and analyzed for arsenic using inductively coupled plasma mass spectrometry with dynamic reaction cell. Results Arsenic concentrations ranged from 0.2 to 24.1 μg/L (ppb) (mean ± SD, 1.7 ±1.5) and 1.1 to 724.4 ng/g (ppb) (mean ± SD, 27.4 ± 61.6) in blood and hair, respectively. One-hour glucose levels ranged from 40 to 284 mg/dL (mean ± SD, 108.7 ± 29.5); impaired glucose tolerance was observed in 11.9% of women when using standard screening criterion (> 140 mg/dL). Adjusting for age, Native-American race, prepregnancy body mass index, Medicaid use, and marital status, women in the highest quartile of blood arsenic exposure had 2.8 higher odds of impaired GTT than women in the lowest quartile of exposure (95% confidence interval, 1.1–6.9) (p-trend = 0.008). Conclusions Among this population of pregnant women, arsenic exposure was associated with increased risk of impaired GTT at 24–28 weeks gestation and therefore may be associated with increased risk of GD.

Cohort Profile: The Maternal-Infant Research on Environmental Chemicals Research Platform

BACKGROUND The Maternal-Infant Research on Environmental Chemicals (MIREC) Study was established to obtain Canadian biomonitoring data for pregnant women and their infants, and to examine potential adverse health effects of prenatal exposure to priority environmental chemicals on pregnancy and infant health. METHODS Women were recruited during the first trimester from 10 sites across Canada and were followed through delivery. Questionnaires were administered during pregnancy and post-delivery to collect information on demographics, occupation, life style, medical history, environmental exposures and diet. Information on the pregnancy and the infant was abstracted from medical charts. Maternal blood, urine, hair and breast milk, as well as cord blood and infant meconium, were collected and analysed for an extensive list of environmental biomarkers and nutrients. Additional biospecimens were stored in the studys Biobank. The MIREC Research Platform encompasses the main cohort study, the Biobank and follow-up studies. RESULTS Of the 8716 women approached at early prenatal clinics, 5108 were eligible and 2001 agreed to participate (39%). MIREC participants tended to smoke less (5.9% vs. 10.5%), be older (mean 32.2 vs. 29.4 years) and have a higher education (62.3% vs. 35.1% with a university degree) than women giving birth in Canada. CONCLUSIONS The MIREC Study, while smaller in number of participants than several of the international cohort studies, has one of the most comprehensive datasets on prenatal exposure to multiple environmental chemicals. The biomonitoring data and biological specimen bank will make this research platform a significant resource for examining potential adverse health effects of prenatal exposure to environmental chemicals.