Biological markers of fetal lead exposure at each stage of pregnancy

Translational toxicoepigenetic Meta-Analyses identify homologous gene DNA methylation reprogramming following developmental phthalate and lead exposure in mouse and human offspring

Although toxicology uses animal models to represent real-world human health scenarios, a critical translational gap between laboratory-based studies and epidemiology remains. In this study, we aimed to understand the toxicoepigenetic effects on DNA methylation after developmental exposure to two common toxicants, the phthalate di(2-ethylhexyl) phthalate (DEHP) and the metal lead (Pb), using a translational paradigm that selected candidate genes from a mouse study and assessed them in four human birth cohorts. Data from mouse offspring developmentally exposed to DEHP, Pb, or control were used to identify genes with sex-specific sites with differential DNA methylation at postnatal day 21. Associations of human infant DNA methylation in homologous mouse genes with prenatal DEHP or Pb were examined with a meta-analysis. Differential methylation was observed on 6 cytosines (adjusted-p < 0.05) and 90 regions (adjusted-p < 0.001). This translational approach offers a unique method that can detect conserved epigenetic differences that are developmentally susceptible to environmental toxicants.

Polysaccharide from Sparassis latifolia alleviates intestinal barrier dysfunction in mice exposed to lead

Exposure to lead can have harmful effects on the intestines and gut microbiota, leading to toxicity. This study aimed to explore the protective role of Sparassis latifolia polysaccharide (SLP) in safeguarding the intestinal barrier of Kunming mice exposed to lead. The findings indicated that SLP effectively alleviates intestinal lesions, increases the density of cupped cells in the intestine, and reduces inflammation in both serum and the small intestine. Furthermore, SLP maintains the expression of key genes such as ZO-1, Occludin, Claudin-1, Lyz, Ang4, and ZO-2, as well as proteins like claudin-1 and Occludin-1. Furthermore, SLP positively impacts the diversity and richness of microorganisms in the mouse gut microbiota at both the genus and gate levels. It also increases the levels of short-chain fatty acids (SCFAs), including acetic acid, butyric acid, and propionic acid, to varying degrees. In summary, SLP plays a role in alleviating the impaired small intestinal barrier in lead-exposed mice by modulating the intestinal flora, which is consistent with reduced lead absorption. This modulation enhances the integrity of the intestinal barrier, suppresses inflammation, and facilitates the excretion of lead.

Development of a physiologically based toxicokinetic model for lead in pregnant women: The role of bone tissue in the maternal and fetal internal exposure

Epidemiological studies have shown associations between prenatal exposure to lead (Pb) and neurodevelopmental effects in young children. Prenatal exposure is generally characterized by measuring the concentration in the umbilical cord at delivery or in the maternal blood during pregnancy. To assess internal Pb exposure during prenatal life, we developed a pregnancy physiologically based pharmacokinetic (p-PBPK) model that to simulates Pb levels in blood and target tissues in the fetus, especially during critical periods for brain development. An existing Pb PBPK model was adapted to pregnant women and fetuses. Using data from literature, both the additional maternal bone remodeling, that causes Pb release into the blood, and the Pb placental transfers were estimated by Bayesian inference. Additional maternal bone remodeling was estimated to start at 21.6 weeks. Placental transfers were estimated between 4.6 and 283 L.day-1 at delivery with high interindividual variability. Once calibrated, the p-PBPK model was used to simulate fetal exposure to Pb. Internal fetal exposure greatly varies over the pregnancy with two peaks of Pb levels in blood and brain at the end of the 1st and 3rd trimesters. Sensitivity analysis shows that the fetal blood lead levels are affected by the maternal burden of bone Pb via maternal bone remodeling and by fetal bone formation at different pregnancy stages. Coupling the p-PBPK model with an effect model such as an adverse outcome pathway could help to predict the effects on children's neurodevelopment.

Maternal Iron Deficiency and Environmental Lead (Pb) Exposure Alter the Predictive Value of Blood Pb Levels on Brain Pb Burden in the Offspring in a Dietary Mouse Model: An Important Consideration for Cumulative Risk in Development

Maternal iron deficiency (ID) and environmental lead (Pb) exposure are co-occurring insults that both affect the neurodevelopment of offspring. Few studies have investigated how ID affects brain-region-specific Pb accumulations using human-relevant Pb concentrations. Furthermore, how these Pb exposures impact blood and brain Fe levels remains unclear. Importantly, we also wanted to determine whether the use of blood Pb levels as a surrogate for the brain Pb burden is affected by underlying iron status. We exposed virgin Swiss Webster female mice to one of six conditions differing by iron diet and Pb water concentration (0 ppm, 19 ppm, or 50 ppm lead acetate) and used Inductively Coupled Plasma Mass Spectrometry to measure the maternal and offspring circulating, stored, and brain Pb levels. We found that maternal ID rendered the offspring iron-deficient anemic and led to a region-specific depletion of brain Fe that was exacerbated by Pb in a dose-specific manner. The postnatal iron deficiency anemia also exacerbated cortical and hippocampal Pb accumulation. Interestingly, BPb levels only correlated with the brain Pb burden in ID pups but not in IN offspring. We conclude that ID significantly increases the brain Pb burden and that BPb levels alone are insufficient as a clinical surrogate to make extrapolations on the brain Pb burden.

Childhood lead exposure of Amerindian communities in French Guiana: an isotopic approach to tracing sources

In French Guiana were detected high lead (Pb) levels in blood of Amerindian people. Lead exposure is a serious hazard that can affect the cognitive and behavior development. People can be exposed to Pb through occupational and environmental sources. Fingerprinting based on stable Pb isotopes in environmental media is often used to trace natural and anthropogenic sources but is rarely paired with blood data. The objective of this study was to determine the main factors associated with high Blood Lead Levels (BLL). Soil, manioc tubers, food bowls, beverages, wild games, lead pellets and children blood were sampled in small villages along the Oyapock River. children BLL ranged between 5.7 and 35 µg dL^-1, all exceeding 5 µg dL^-1, the reference value proposed in epidemiologic studies for lead poisoning. Among the different dietary sources, manioc tubers and large game contained elevated Pb concentrations while manioc-based dishes were diluted. The isotopes ratios (²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb) of children blood overlapped these of lead shots and meals. These first results confirm for the first time, the diary consumption of manioc-based food as the main contributor to Amerindian children's BLL in French Guiana, but don't exclude the occasional exposure to lead bullets by hunting activities. This is a specific health concern, since previous studies have shown that these same villagers present high levels of mercury (Hg). These communities are indeed subject to a double exposure to neurotoxic metals, Hg and Pb, both through their diet. The farming activity is based on manioc growing, and explaining that this ancestral practice can induce serious health risks for the child's development may seriously affect their food balance and cultural cohesion.

Prenatal Lead (Pb) Exposure and Peripheral Blood DNA Methylation (5mC) and Hydroxymethylation (5hmC) in Mexican Adolescents from the ELEMENT Birth Cohort

BACKGROUND

Gestational lead (Pb) exposure can adversely affect offspring health through multiple mechanisms, including epigenomic alterations via DNA methylation (5mC) and hydroxymethylation (5hmC), an intermediate in oxidative demethylation. Most current methods do not distinguish between 5mC and 5hmC, limiting insights into their individual roles.

OBJECTIVE

Our study sought to identify the association of trimester-specific (T1, T2, T3) prenatal Pb exposure with 5mC and 5hmC levels at multiple cytosine-phosphate-guanine sites within gene regions previously associated with prenatal Pb (HCN2, NINJ2, RAB5A, TPPP) in whole blood leukocytes of children ages 11-18 years of age.

METHODS

Participants from the Early Life Exposure in Mexico to Environmental Toxicants (ELEMENT) birth cohorts were selected (n=144) for pyrosequencing analysis following oxidative or standard sodium bisulfite treatment. This workflow directly quantifies total methylation (5mC+5hmC) and 5mC only; 5hmC is estimated by subtraction.

RESULTS

Participants were 51% male, and mean maternal blood lead levels (BLL) were 6.43±5.16μg/dL in Trimester 1 (T1), 5.66±5.21μg/dL in Trimester 2 (T2), and 5.86±4.34μg/dL in Trimester 3 (T3). In addition, 5hmC levels were calculated for HCN2 (mean±standard deviation(SD), 2.08±4.18%), NINJ2 (G/C: 2.01±5.95; GG: 0.90±3.97), RAB5A (0.66±0.80%), and TPPP (1.11±6.67%). Furthermore, 5mC levels were measured in HCN2 (81.3±9.63%), NINJ2 (heterozygotes: 38.6±7.39%; GG homozygotes: 67.3±9.83%), RAB5A (1.41±1.21%), and TPPP (92.5±8.03%). Several significant associations between BLLs and 5mC/5hmC were identified: T1 BLLs with 5mC in HCN2 (β=-0.37, p=0.03) and 5hmC in NINJ2 (β=0.49, p=0.003); T2 BLLs with 5mC in HCN2 (β=0.37, p=0.03) and 5hmC in NINJ2 (β=0.27, p=0.008); and T3 BLLs with 5mC in HCN2 (β=0.50, p=0.01) and NINJ2 (β=-0.35, p=0.004) and 5hmC in NINJ2 (β=0.45, p<0.001). NINJ2 5mC was negatively correlated with gene expression (Pearson r=-0.5, p-value=0.005), whereas 5hmC was positively correlated (r=0.4, p-value=0.04).

DISCUSSION

These findings suggest there is variable 5hmC in human whole blood and that prenatal Pb exposure is associated with gene-specific 5mC and 5hmC levels at adolescence, providing evidence to consider 5hmC as a regulatory mechanism that is responsive to environmental exposures. https://doi.org/10.1289/EHP8507.

Trimester-Specific Associations of Prenatal Lead Exposure With Infant Cord Blood DNA Methylation at Birth

Gestational exposure to lead (Pb) adversely impacts offspring health through multiple mechanisms, one of which is the alteration of the epigenome including DNA methylation. This study aims to identify differentially methylated CpG sites associated with trimester-specific maternal Pb exposure in umbilical cord blood (UCB) leukocytes. Eighty-nine mother-child dyads from the Early Life Exposure in Mexico to Environmental Toxicants (ELEMENT) longitudinal birth cohorts with available UCB samples were selected for DNA methylation analysis via the Infinium Methylation EPIC BeadChip, which quantifies methylation at >850 000 CpG sites. Maternal blood lead levels (BLLs) during each trimester (T1: 6.56 ± 5.35 µg/dL; T2: 5.93 ± 5.00 µg/dL; T3: 6.09 ± 4.51 µg/dL), bone Pb (patella: 11.8 ± 9.25 µg/g; tibia: 11.8 ± 6.73 µg/g), a measure of cumulative Pb exposure, and UCB Pb (4.86 ± 3.74 µg/dL) were measured. After quality control screening, data from 786 024 CpG sites were used to identify differentially methylated positions (DMPs) and differentially methylated regions (DMRs) by Pb biomarkers using separate linear regression models, controlling for sex and estimated UCB cell-type proportions. We identified 3 DMPs associated with maternal T1 BLL, 2 with T3 BLL, and 2 with tibia bone Pb. We identified one DMR within PDGFRL associated with T1 BLL, one located at chr6:30095136-30095295 with T3 BLL, and one within TRHR with tibia bone Pb (adjusted P-value < .05). Pathway analysis identified 15 overrepresented gene pathways for differential methylation that overlapped among all 3 trimesters with the largest overlap between T1 and T2 (adjusted P-value < .05). Pathways of interest include nodal signaling pathway and neurological system processes. These data provide evidence for differential methylation by prenatal Pb exposure that may be trimester-specific.

Early Life Exposure in Mexico to ENvironmental Toxicants (ELEMENT) Project

PURPOSE

The Early Life Exposure in Mexico to ENvironmental Toxicants (ELEMENT) Project is a mother-child pregnancy and birth cohort originally initiated in the mid-1990s to explore: (1) whether enhanced mobilisation of lead from maternal bone stores during pregnancy poses a risk to fetal and subsequent offspring neurodevelopment; and (2) whether maternal calcium supplementation during pregnancy and lactation can suppress bone lead mobilisation and mitigate the adverse effects of lead exposure on offspring health and development. Through utilisation of carefully archived biospecimens to measure other prenatal exposures, banking of DNA and rigorous measurement of a diverse array of outcomes, ELEMENT has since evolved into a major resource for research on early life exposures and developmental outcomes.

PARTICIPANTS

n=1643 mother-child pairs sequentially recruited (between 1994 and 2003) during pregnancy or at delivery from maternity hospitals in Mexico City, Mexico.

FINDINGS TO DATE

Maternal bone (eg, patella, tibia) is an endogenous source for fetal lead exposure due to mobilisation of stored lead into circulation during pregnancy and lactation, leading to increased risk of miscarriage, low birth weight and smaller head circumference, and transfer of lead into breastmilk. Daily supplementation with 1200 mg of elemental calcium during pregnancy and lactation reduces lead resorption from maternal bone and thereby, levels of circulating lead. Beyond perinatal outcomes, early life exposure to lead is associated with neurocognitive deficits, behavioural disorders, higher blood pressure and lower weight in offspring during childhood. Some of these relationships were modified by dietary factors; genetic polymorphisms specific for iron, folate and lipid metabolism; and timing of exposure. Research has also expanded to include findings published on other toxicants such as those associated with personal care products and plastics (eg, phthalates, bisphenol A), other metals (eg, mercury, manganese, cadmium), pesticides (organophosphates) and fluoride; other biomarkers (eg, toxicant levels in plasma, hair and teeth); other outcomes (eg, sexual maturation, metabolic syndrome, dental caries); and identification of novel mechanisms via epigenetic and metabolomics profiling.

FUTURE PLANS

As the ELEMENT mothers and children age, we plan to (1) continue studying the long-term consequences of toxicant exposure during the perinatal period on adolescent and young adult outcomes as well as outcomes related to the original ELEMENT mothers, such as their metabolic and bone health during perimenopause; and (2) follow the third generation of participants (children of the children) to study intergenerational effects of in utero exposures.

TRIAL REGISTRATION NUMBER

NCT00558623.

Maternal stress modifies the effect of exposure to lead during pregnancy and 24-month old children's neurodevelopment

BACKGROUND

Lead and psychosocial stress disrupt similar but not completely overlapping mechanisms. Exposure during the prenatal period to each of these insults singularly has been found to alter normal neurodevelopment; however, longitudinal associations with stress modifying the effect of lead have not been sufficiently analyzed in epidemiologic studies.

OBJECTIVE

To evaluate prenatal stress as an effect modifier of gestational lead neurotoxicity.

METHODS

We used a structural equations modeling approach with a trivariate response to evaluate cognitive, language and motor scores of the Bayley Scales of Infant Development-III in 24month-old children (n=360). Maternal blood lead levels were measured at the 2nd and 3rd trimester and psychosocial stress during pregnancy was assessed using a negative life events (NLE) scale derived from the CRYSIS questionnaire.

RESULTS

3rd trimester lead (mean 3.9±3.0 SDμg/dL) and stress (median=3 NLE) were negatively associated with Bayley III scores. Using the model's results we generated profiles for 0, 2, 4 and 6 NLE across lead levels (up to 10μg/dL) and observed a dose-response for the developmental scores when lead levels were below 2μg/dL. Each NLE curve had a different shape across increasing lead levels. Higher stress (NLE=6) resulted in lower cognitive scores for both sexes, in lower language scores in girls but not boys. In the absence of stress we saw a negative association with lead for all scores, however for language and motor scores, higher stress seemed to mask this association.

CONCLUSIONS

Our work examined and confirmed prenatal stress exposure as a modifier of the well-known neurotoxic effects of prenatal lead. It adds to the existing evidence pointing at the importance of studying the co-exposure of chemical and non-chemical exposures, specifically of considering the emotional environment of children at early developmental stages of life.

Glazed clay pottery and lead exposure in Mexico: Current experimental evidence

OBJECTIVES

Lead exposure remains a significant environmental problem; lead is neurotoxic, especially in developing humans. In Mexico, lead in human blood is still a concern. Historically, much of the lead exposure is attributed to the use of handcrafted clay pottery for cooking, storing and serving food. However, experimental cause-and-effect demonstration is lacking. The present study explores this issue with a prospective experimental approach.

METHODS

We used handcrafted clay containers to prepare and store lemonade, which was supplied as drinking water to pregnant rats throughout the gestational period.

RESULTS AND DISCUSSION

We found that clay pots, jars, and mugs leached on average 200 µg/l lead, and exposure to the lemonade resulted in 2.5 µg/dl of lead in the pregnant rats' blood. Neonates also showed increased lead content in the hippocampus and cerebellum. Caspase-3 activity was found to be statistically increased in the hippocampus in prenatally exposed neonates, suggesting increased apoptosis in that brain region. Glazed ceramics are still an important source of lead exposure in Mexico, and our results confirm that pregnancy is a vulnerable period for brain development.

Maternal blood lead concentrations, DNA methylation of MEG3 DMR regulating the DLK1/MEG3 imprinted domain and early growth in a multiethnic cohort

Prenatal exposure to lead (Pb) is known to decrease fetal growth; but its effects on postnatal growth and mechanistic insights linking Pb to growth are not clearly defined. Genomically imprinted genes are powerful regulators of growth and energy utilization, and may be particularly vulnerable to environmental Pb exposure. Because imprinting is established early and maintained via DNA methylation, we hypothesized that prenatal Pb exposure alters DNA methylation of imprinted genes resulting in lower birth weight and rapid growth. Pb was measured by inductively coupled plasma mass spectrometry (ICP-MS) in peripheral blood of 321 women of the Newborn Epigenetic STudy (NEST) obtained at gestation ~12 weeks. Linear and logistic regression models were used to evaluate associations between maternal Pb levels, methylation of differentially methylated regions (DMRs) regulating H19, MEG3, PEG3, and PLAGL1, measured by pyrosequencing, birth weight, and weight-for-height z score gains between birth and age 1yr, ages 1-2yrs, and 2-3yrs. Children born to women with Pb levels in the upper tertile had higher methylation of the regulatory region of the MEG3 DMR imprinted domain (β= 1.57, se= 0.82, p= 0.06). Pb levels were also associated with lower birth weight (β= -0.41, se= 0.15, p= 0.01) and rapid gains in adiposity (OR= 12.32, 95%CI=1.25-121.30, p= 0.03) by age 2-3 years. These data provide early human evidence for Pb associations with hypermethylation at the MEG3 DMR regulatory region and rapid adiposity gain-a risk factor for childhood obesity and cardiometabolic diseases in adulthood.

Blood Lead Levels in Andean Infants and Young Children in Ecuador: An International Comparison

Lead (Pb) exposure in infants and children remains an international health concern. Blood lead (PbB) levels of a cohort of 130 Ecuadorian infants and young children aged 0.33 to 5.8 yr were compared to values reported for similar age groups in Africa, Asia, Europe, Latin America, and the United States. The mean PbB level for the total group of 130 Ecuadorian infants and young children in this study was 29.4 μg/dl (SD: 24.3; range: 3.0-128.2; median: 21.7; geometric mean: 20.7 μg/dl). The mean PbB level for the 0-2 yr age group (infants) was 33.6 μg/dl (SD: 28.9; median: 22.0; range: 3.9-119.7; geometric mean: 23.6 μg/dl), while the average PbB level for the 3-5 yr age group (young children) was 27.9 μg/dl (SD: 22.5: median: 22; range: 3-128.2; geometric mean: 19.8 μg/dl). The difference between the mean PbB levels for the infants and young children was not statistically significant. The average PbB level of 32.6 μg/dl for males was not statistically different from the mean PbB level of 26.3 μg/dl for females. The PbB levels observed in Ecuadorian infants and young children in this investigation were elevated above the World Health Organization (WHO) level of concern of 10 μg/dl and Centers for Disease Control and Prevention (CDC) current reference value of 5 μg/dl. Values were comparable to concentrations found in Pakistan, where occupational use of Pb is prevalent. These findings further indicate that infants and young children exposed to Pb from Pb glazing of ceramics in Andean Ecuadorian villages exhibit greater potential metal-mediated poisoning than children of similar ages in Asia, Europe, other Latin American countries, and the United States.

Kidney biomarkers associated with blood lead, mercury, and cadmium in premenopausal women: a prospective cohort study

Certain metals are harmful to the kidney and liver at high levels, but associations with functional biomarkers at low exposure levels among premenopausal women apparently has not been evaluated. Healthy, regularly menstruating women (n = 259) were followed for up to 2 menstrual cycles with up to 16 visits. Renal and liver biomarkers were measured in serum at each clinic visit. Cadmium (Cd), lead (Pb), and mercury (Hg) were measured in whole blood at baseline. Linear mixed models were adjusted for age, body mass index (BMI), race, average calories, alcohol intake, smoking, and cycle day. Median levels of Cd, Pb, and Hg were 0.31 μg/L, 0.88 μg/dl, and 1.1 μg/L, respectively. One-third of women had diminished glomerular filtration rate (eGFR) (<90 ml/min/1.73 m(2)). Each twofold increase in Cd was associated with a negative 4.9% change in blood urea nitrogen (BUN) and bilirubin. Each twofold rise in Pb was associated with decreased eGFR and increased creatinine. A twofold elevation in Hg was associated with higher protein and reduced alkaline phosphatase. In healthy, predominantly nonsmoking women, low levels of Cd, Pb, and Hg were associated with changes in select biomarkers of kidney and liver function.

Very low maternal lead level in pregnancy and birth outcomes in an eastern Massachusetts population

PURPOSE

Maternal lead exposure is associated with poor birth outcomes in populations with moderate to high blood levels. However, no studies have looked at exposure levels commonly experienced by US women.

METHODS

We evaluated the relationship between maternal red blood cell (RBC) lead levels in midpregnancy and birth outcomes in 949 mother-child pairs in a prebirth cohort. We used multiple linear regression and logistic regression, adjusted for potential confounders including maternal age, race, prepregnancy body mass index, and smoking to relate maternal lead to infant birth size and risk for preterm birth (<37 weeks).

RESULTS

Mean RBC lead level was 1.2 μg/dL (range, 0.0-5.0). Mean (standard deviation) birthweight was 3505 (520) g, birthweight for gestational age z-score 0.22 (0.93), and length of gestation 39.5 (1.7) weeks. Mothers in the highest versus lowest lead quartile did not have higher odds (OR, 1.85; 95% confidence interval [CI], 0.79-4.34) of preterm delivery; after stratifying by child sex, there was an association among males (OR, 5.51; 95% CI, 1.21-25.15) but not females (OR, 0.82; 95% CI, 0.24-2.85). Maternal RBC lead was not associated with any continuous outcomes in combined or sex-stratified analyses.

CONCLUSIONS

Maternal lead exposure, even at very low levels, may adversely affect some childbirth outcomes, particularly preterm birth among males.

Lead levels in the breast milk of nursing andean mothers living in a lead-contaminated environment

Concentrations of lead (Pb) in breast milk (PbM) and blood (PbB) were measured in a current cohort of lactating mothers living in Andean communities where women of childbearing age engage in the occupational use of Pb, and compared to results obtained in earlier studies. Mean PbM concentration in the current group of breastfeeding mothers tested in 2012/2013 was 3.73 μg/L (SD: 7.3; range: 0.049-28.04), and significantly lower than the 9.83 μg/L (SD: 12.75; range: 0.2-49) previously observed in breastfeeding mothers in the study area from 1999 to 2007. Breastfeeding women in the current cohort showed an average PbM/PbB ratio of 3.6%, which is in agreement with other studies. The mean PbB level obtained for the current cohort was 7.8 μg/dl (SD: 5.2; range: 1.4-21), and significantly lower than the mean PbB level of 20.8 μg/dl (SD: 16.4; range: 4-73) obtained for the comparison group of breastfeeding mothers tested between 1999 and 2007. A correlation of .687 between paired PbM and maternal PbB was found, indicating that maternal PbB level is a significant predictor of PbM. Current PbM levels remain higher than international averages, but indicate that maternal Pb exposure has declined over time in the environmentally Pb-contaminated study area. The current reduction in Pb in milk and blood of breastfeeding mothers may be due to adherence to a Pb-exposure education and prevention program initiated by the authors in the study area years earlier, as well as recent improvements in local health care delivery.

Maternal blood, plasma, and breast milk lead: lactational transfer and contribution to infant exposure

BACKGROUND

Human milk is a potential source of lead exposure. Yet lactational transfer of lead from maternal blood into breast milk and its contribution to infant lead burden remains poorly understood.

OBJECTIVES

We explored the dose-response relationships between maternal blood, plasma, and breast milk to better understand lactational transfer of lead from blood and plasma into milk and, ultimately, to the breastfeeding infant.

METHODS

We measured lead in 81 maternal blood, plasma, and breast milk samples at 1 month postpartum and in 60 infant blood samples at 3 months of age. Milk-to-plasma (M/P) lead ratios were calculated. Multivariate linear, piecewise, and generalized additive models were used to examine dose-response relationships between blood, plasma, and milk lead levels.

RESULTS

Maternal lead levels (mean±SD) were as follows: blood: 7.7±4.0 μg/dL; plasma: 0.1±0.1 μg/L; milk: 0.8±0.7 μg/L. The average M/P lead ratio was 7.7 (range, 0.6-39.8) with 97% of the ratios being >1. The dose-response relationship between plasma lead and M/P ratio was nonlinear (empirical distribution function=6.5, p=0.0006) with the M/P ratio decreasing by 16.6 and 0.6 per 0.1 μg/L of plasma lead, respectively, below and above 0.1 μg/L plasma lead. Infant blood lead level (3.4±2.2 μg/dL) increased by 1.8 μg/dL per 1 μg/L milk lead (p<0.0001, R2=0.3).

CONCLUSIONS

The M/P ratio for lead in humans is substantially higher than previously reported, and transfer of lead from plasma to milk may be higher at lower levels of plasma lead. Breast milk is an important determinant of lead burden among breastfeeding infants.

Investigation of lead concentrations in whole blood, plasma and urine as biomarkers for biological monitoring of lead exposure

Lead in blood is a major concept in biomonitoring of exposure but investigations of its alternatives are scarce. The aim of the study was to describe different lead biomarkers' variances, day-to-day and between individuals, estimating their fraction of the total variance. Repeated sampling of whole blood, plasma and urine were conducted for 48 lead-exposed men and 20 individuals under normal environmental lead exposure, in total 603 measurements. For lead workers, the fraction of the total variance attributed to differences between individuals was 91% for whole-blood lead (geometric mean 227 μg/l; geometric standard deviation (GSD): 1.55 μg/l); plasma 78% (0.57 μg/l; GSD: 1.84 μg/l); density-adjusted urine 82%; and unadjusted urine 75% (23.7 μg/l; GSD: 2.48 μg/l). For the individuals under normal lead exposure, the corresponding fractions were 95% of the total variance for whole blood (20.7 μg/l; GSD: 8.6 μg/l), 15% for plasma (0.09 μg/l; GSD: 0.04 μg/l), 87% for creatinine-adjusted urine and 34% for unadjusted (10.8 μg/l; GSD: 6.7 μg/l). Lead concentration in whole blood is the biomarker with the best ability to discriminate between individuals with different mean concentration. Urinary and plasma lead also performed acceptably in lead workers, but at low exposures plasma lead was too imprecise. Urinary adjustments appear not to increase the between-individual fraction of the total variance among lead workers but among those with normal lead exposure.

Lead, cadmium and mercury levels in pregnancy: the need for international consensus on levels of concern

For heavy metals that have any degree of transfer though the placenta to the fetus, it is unlikely that there are safe limits for maternal blood levels. The only means of reducing fetal exposure is to minimise maternal exposure. There are few recommendations for levels of concern. With the exception of US recommendations for maternal Pb levels, but there are no international levels of concern or cut-off levels specifically for pregnancy for heavy metals, so that comparisons can generally only be made with national reference values relating to similar physiological statuses or age groups. These include recommendations for Cd levels by Germany (reference value for non-smoking adults aged 18–69 years, 1 µg/l) and for Hg by Germany (reference value for adults age 18–60 years with fish intake ⩽3 times per month, 2.0 µg/l) and the USA (cut-off level for women, 5.8 µg/dl). To illustrate the lack of cohesion, we present data on blood Pb, Cd and Hg levels from pregnant women enroled in the UK Avon Longitudinal Study of Parents and Children study and compare the values with present levels of concern and recommended cut-off values. We also compare the levels with those found in other groups of pregnant women worldwide to strengthen the database for the development of levels of concern in pregnancy. The need for clarity of terminology in describing levels of concern is discussed. There is a pressing need for international consensus on levels of concern for all age groups and physiological statuses, particularly for pregnancy.

Experimental determination of the oral bioavailability and bioaccessibility of lead particles

In vivo estimations of Pb particle bioavailability are costly and variable, because of the nature of animal assays. The most feasible alternative for increasing the number of investigations carried out on Pb particle bioavailability is in vitro testing. This testing method requires calibration using in vivo data on an adapted animal model, so that the results will be valid for childhood exposure assessment. Also, the test results must be reproducible within and between laboratories. The Relative Bioaccessibility Leaching Procedure, which is calibrated with in vivo data on soils, presents the highest degree of validation and simplicity. This method could be applied to Pb particles, including those in paint and dust, and those in drinking water systems, which although relevant, have been poorly investigated up to now for childhood exposure assessment.

Assessment of essential and nonessential metals and different metal exposure biomarkers in the human placenta in a population from the south of Portugal

The general population is exposed to metals as trace amounts of metallic compounds are present in air, water, and food. Information on background exposures and biomarker concentrations of environmental chemicals in the general Portuguese population is limited. Therefore, the purpose of this study was to determine the levels of important nonessential metals with recognized toxicity cadmium (Cd) and lead (Pb) and essential metals copper (Cu), nickel (Ni), chromium (Cr), and zinc (Zn) in placentas of mothers living in south Portugal (Algarve). Due to the difficulty in establishing the effects of chemicals in a complex and variable environment, this study also aimed to examine the response of biomarkers, such as biochemical changes that occurs at subcellular levels in the presence of contaminants. The investigated biomarkers in placentas indicative of metal exposure or damage included the metallothioneins (MT), delta-aminolevulinic acid dehydratase (ALAD) (specific for Pb), and lipid peroxidation (LPO) as an index of oxidative stress damage. Moreover, HJ-BIPLOT was applied in order to identify and categorize mothers vulnerable to environmental contamination in this region. Metal concentrations in the placenta were not excessive but within the range found in most European studies. In general, the biomarkers MT and LPO were positively correlated with metal levels, while with ALAD the opposite occurred, indicating the selected battery of biomarkers were suitable to study the effects of metals on human placenta. Further, the application of multivariate analysis with HJ-BIPLOT showed that most significant factors contributing to maternal and fetal exposures via placenta were dietary and smoking habits.

Critical windows of fetal lead exposure: adverse impacts on length of gestation and risk of premature delivery

OBJECTIVE

Research on the role of environmental lead exposure in the complex etiology of premature birth has yielded inconsistent results. We assessed the trimester-specific effect of prenatal lead exposure on gestational age and risk of premature delivery.

METHODS

We used linear and logistic regression to identify critical windows of susceptibility to lead exposure on gestational length.

RESULTS

In single-trimester models, decreases in gestational length were most strongly associated with first and second trimester blood lead. In adjusted logistic regression models, a one-standard deviation increase in second trimester blood lead was associated with an odds ratio of prematurity of 1.75 (95% CI: 1.02, 3.02).

CONCLUSIONS

Maternal whole blood lead levels measured during first and second trimesters yielded the most prominent inverse association with length of gestation and increased the risk of prematurity.

Prenatal exposure to lead in Spain: cord blood levels and associated factors

INTRODUCTION AND OBJECTIVE

Lead is a known neurotoxic. Fetuses and infants are very vulnerable to lead exposure, since their blood-brain barrier is not completely formed. Hence, there is an importance for monitoring of blood lead levels prenatally and during early infancy. The aim of this study is to evaluate the prenatal exposure to lead and its association with maternal factors in four population based mother-child cohorts in Spain. The present research was carried out within the framework of the INMA project INfancia y Medio Ambiente (Environment and Childhood).

METHODS

A total of 1462 pregnant women were recruited between 2004 and 2008. Lead was analyzed in a sample of cord blood by thermal decomposition, amalgation, and Atomic Absorption Spectrometry. Maternal sociodemographic, lifestyle and dietary factors were obtained by questionnaires during pregnancy. A multivariate logistic regression model was constructed. The dependent variable was a dichotomous lead level variable (detected vs no detected, i.e. ≥ vs < 2μg/dL).

RESULTS

A low percentage of cord blood samples with lead levels ≥ 2μg/dL were found (5.9%). Geometric mean and maximum were 1.06μg/dL and 19μg/dL, respectively. Smoking at the beginning of pregnancy, age, social class, weight gain during pregnancy, gravidity, and place of residence were the maternal factors associated with detectable cord blood lead levels. Mother's diet does not appear to be a determining factor of lead exposure. Nevertheless, daily intake of iron and zinc may act as a protective factor against having cord blood lead levels ≥ 2μg/dL.

CONCLUSION

In the different regions of Spain taking part in this study, lead levels to which newborns are exposed are low. Mobilization of lead from bones may be the main contributor to the cord blood levels.

Vitamin D receptor haplotypes affect lead levels during pregnancy

Pregnant women are particularly susceptible to toxic effects associated with lead (Pb) exposure. Pb accumulates in bone tissue and is rapidly mobilized from bones during pregnancy, thus resulting in fetal contamination. While vitamin D receptor (VDR) polymorphisms modify bone mineralization and affect Pb biomarkers including blood (Pb-B) and serum (Pb-S) Pb concentrations, and %Pb-S/Pb-B ratio, the effects of these polymorphisms on Pb levels in pregnant women are unknown. This study aimed at examining the effects of three (FokI, BsmI and ApaI) VDR polymorphisms (and VDR haplotypes) on Pb levels in pregnant women. Pb-B and Pb-S were determined by inductively coupled plasma mass spectrometry in samples from 256 healthy pregnant women and their respective umbilical cords. Genotypes for the VDR polymorphisms were determined by PCR and restriction fragment length digestion. While the three VDR polymorphisms had no significant effects on Pb-B, Pb-S or %Pb-S/Pb-B ratio, the haplotype combining the f, a, and b alleles for the FokI, ApaI and BsmI polymorphisms, respectively, was associated with significantly lower Pb-S and %Pb-S/Pb-B (P<0.05). However, maternal VDR haplotypes had no effects on Pb levels in the umbilical cords. To our knowledge, this is the first study showing that a combination of genetic polymorphisms (haplotype) commonly found in the VDR gene affects Pb-S and %Pb-S/Pb-B ratios in pregnant women. These findings may have major implications for Pb toxicity because they may help to predict the existence of a group of subjects that is genetically less prone to Pb toxicity during pregnancy.

Blood lead levels among pregnant women: historical versus contemporaneous exposures

Blood lead among pregnant women, even at modest levels, may impair offspring cognitive development. We examine whether blood lead levels (BLLs) result from current versus historic exposures, among a cohort of pregnant women. Cumulative logit models were used to characterize the relationship between maternal risk factors and higher BLLs. Maternal blood lead levels more likely result from lead remobilization from historic versus contemporaneous exposures. Even if all lead sources were abated immediately, women and their fetuses would experience lead exposure for decades. This work emphasizes the importance of addressing sources of environmental lead exposure in the United States and internationally.

Effect of prenatal lead exposure on nigrostriatal neurotransmission and hydroxyl radical formation in rat neostriatum: dopaminergic-nitrergic interaction

The present study was designed to explore the role of ontogenetic lead (Pb(2+)) exposure on a putative dopaminergic-nitrergic interaction in the nigrostriatal pathway. Pregnant Wistar rats were given tap water containing 250-ppm lead acetate, for the duration of pregnancy, with regular tap water (without Pb(2+)) being substituted at birth. Control rats were derived from dams that consumed tap water throughout pregnancy, and had no exposure to Pb(2+) afterwards. At 12 weeks after birth in vivo microdialysis of the neostriatum was employed to demonstrate that maternal Pb(2+) exposure was without effect on the baseline dopamine (DA) microdialysate concentration as well as amphetamine (AMPH, 1.0mg/kg i.p.)-evoked release of striatal DA. Also, prenatal Pb(2+) exposure did not enhance AMPH- and 7-nitroindazole (neuronal nitric oxide synthase inhibitor) (7-NI, 20mg/kg i.p.)-induced hydroxyl radical (HO) formation in the striatum, as indicated by analysis of the salicylate spin-trap product 2,5-dihydroxybenzoic acid. However, in rats exposed prenatally to Pb(2+), the facilitatory effect of 7-NI on DA exocytosis was attenuated. On the basis of the current study we conclude that maternal Pb(2+) exposure distorts the dopaminergic-nitrergic interaction in the nigrostriatal pathway, but without involvement of reactive oxygen species (ROS).

Association between the plasma/whole blood lead ratio and history of spontaneous abortion: a nested cross-sectional study

Background

Blood lead has been associated with an elevated risk of miscarriage. The plasmatic fraction of lead represents the toxicologically active fraction of lead. Women with a tendency to have a higher plasma/whole blood Pb ratio could tend towards an elevated risk of miscarriage due to a higher plasma Pb for a given whole blood Pb and would consequently have a history of spontaneous abortion.

Methods

We studied 207 pregnant Mexico City residents during the 1^st trimester of pregnancy, originally recruited for two cohorts between 1997 and 2004. Criteria for inclusion in this study were having had at least one previous pregnancy, and having valid plasma and blood Pb measurements. Pb was measured in whole blood and plasma by inductively coupled plasma mass spectrometry using ultra-clean techniques. History of miscarriage in previous pregnancies was obtained by interview. The incidence rate of spontaneous abortion was defined as the proportion of previous pregnancies that resulted in miscarriage. Data were analyzed by means of Poisson regression models featuring the incidence rate of spontaneous abortion as the outcome and continuous or categorized plasma/blood Pb ratios as predictor variables. All models were adjusted for age and schooling. Additionally, logistic regression models featuring inclusion in the study sample as the outcome were fitted to assess potential selection bias.

Results

The mean number of miscarriages was 0.42 (range 0 to 4); mean Pb concentrations were 62.4 and 0.14 μg/L in whole blood and plasma respectively. Mean plasma/blood Pb ratio was 0.22%. We estimated that a 0.1% increment in the plasma/blood Pb ratio lead was associated to a 12% greater incidence of spontaneous abortion (p = 0.02). Women in the upper tertile of the plasma/blood Pb ratio had twice the incidence rate of those in the lower tertile (p = 0.02). Conditional on recruitment cohort, inclusion in the study sample was unrelated to observable characteristics such as number of abortions, number of pregnancies, blood Pb levels, age schooling, weight and height.

Conclusion

Women with a large plasma/whole blood Pb ratio may be at higher risk of miscarriage, which could be due to a greater availability of placental barrier-crossing Pb.

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 microg/dL and 14% of values >or=10 microg/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.