Sex differences in the effects of prenatal lead exposure on birth outcomes

Gender-Specific Effects on the Cardiorespiratory System and Neurotoxicity of Intermittent and Permanent Low-Level Lead Exposures

Lead exposure is a significant health concern, ranking among the top 10 most harmful substances for humans. There are no safe levels of lead exposure, and it affects multiple body systems, especially the cardiovascular and neurological systems, leading to problems such as hypertension, heart disease, cognitive deficits, and developmental delays, particularly in children. Gender differences are a crucial factor, with women's reproductive systems being especially vulnerable, resulting in fertility issues, pregnancy complications, miscarriages, and premature births. The globalization of lead exposure presents new challenges in managing this issue. Therefore, understanding the gender-specific implications is essential for developing effective treatments and public health strategies to mitigate the impact of lead-related health problems. This study examined the effects of intermittent and permanent lead exposure on both male and female animals, assessing behaviours like anxiety, locomotor activity, and long-term memory, as well as molecular changes related to astrogliosis. Additionally, physiological and autonomic evaluations were performed, focusing on baro- and chemoreceptor reflexes. The study's findings revealed that permanent lead exposure has more severe health consequences, including hypertension, anxiety, and reactive astrogliosis, affecting both genders. However, males exhibit greater cognitive, behavioural, and respiratory changes, while females are more susceptible to chemoreflex hypersensitivity. In contrast, intermittent lead exposure leads to hypertension and reactive astrogliosis in both genders. Still, females are more vulnerable to cognitive impairment, increased respiratory frequency, and chemoreflex hypersensitivity, while males show more reactive astrocytes in the hippocampus. Overall, this research emphasizes the importance of not only investigating different types of lead exposure but also considering gender differences in toxicity when addressing this public health concern.

Dust to Feed, Dust to Gray: The Effect of in Utero Exposure to the Dust Bowl on Old-Age Longevity

Intensive agriculture and deep plowing caused topsoil erosion and dust storms during the 1930s, affecting agricultural income and land values for years. Given the growing literature on the relevance of in utero and early-life exposures, it is surprising that studies focusing on links between the Dust Bowl and later-life health have produced inconclusive and mixed results. We reevaluate this literature and study the long-term effects of in utero and early-life exposure to topsoil erosion caused by the 1930s Dust Bowl on old-age longevity. Specifically, using Social Security Administration death records linked with the full-count 1940 census, we conduct event studies with difference-in-differences designs to compare the longevity of individuals in high- versus low-topsoil-erosion counties before versus after 1930. We find intent-to-treat reductions in longevity of approximately 0.85 months for those born in high-erosion counties after 1930. We show that these effects are not an artifact of preexisting trends in longevity. Additional analyses suggest that the effects are more pronounced among children raised in farm households, females, and those whose mothers had lower education. We also provide suggestive evidence that reductions in adulthood income are a likely mechanism for the effects we document.

Sex-specific relationships between prenatal exposure to metal mixtures and birth weight in a Chinese birth cohort

Birth weight is an indicator linking intrauterine environmental exposures to later-life diseases, and intrauterine metal exposure may affect birth weight in a sex-specific manner. We investigated sex-specific associations between prenatal exposure to metal mixtures and birth weight in a Chinese birth cohort. The birth weight of 1296 boys and 1098 girls were recorded, and 10 metals in maternal urine samples collected during pregnancy were measured using inductively coupled plasma mass spectrometry. Bayesian Kernel Machine Regression was used to estimate the association of individual metals or metal mixtures and birth weight for gestational age (BW for GA). The model showed a sex-specific relationship between prenatal exposure to metal mixtures and BW for GA with a significant negative association in girls and a non-significant positive association in boys. Cadmium (Cd) and nickel (Ni) were positively and negatively associated with BW for GA in girls, respectively. Moreover, increasing thallium (Tl) concentration lowered the positive association between Cd and BW for GA and enhanced the negative association between Ni and BW for GA in girls. When exposure to other metals increased, the positive association with Cd diminished, whereas the negative association with Ni or Tl increased. Our findings provide evidence supporting the complex effects of intrauterine exposure to metal mixtures on the birth weight of girls and further highlight the sex heterogeneity in fetal development influenced by intrauterine environmental factors.

Individual, Independent, and Joint Associations of Toxic Metals and Manganese on Hypertensive Disorders of Pregnancy: Results from the MIREC Canadian Pregnancy Cohort

BACKGROUND

Toxic metals, such as lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg), may be associated with a higher risk of gestational hypertension and preeclampsia, whereas manganese (Mn) is an essential metal that may be protective.

OBJECTIVES

We estimated the individual, independent, and joint associations of Pb, Cd, As, Hg, and Mn on the risk of developing gestational hypertension and preeclampsia in a cohort of Canadian women.

METHODS

Metal concentrations were analyzed in first and third trimester maternal blood (n=1,560). We measured blood pressure after 20 wk gestation to diagnose gestational hypertension, whereas proteinuria and other complications defined preeclampsia. We estimated individual and independent (adjusted for coexposure) relative risks (RRs) for each doubling of metal concentrations and examined interactions between toxic metals and Mn. We used quantile g-computation to estimate the joint effect of trimester-specific exposures.

RESULTS

Each doubling of third trimester Pb (RR=1.54; 95% CI: 1.06, 2.22) and first trimester blood As (RR=1.25; 95% CI: 1.01, 1.58) was independently associated with a higher risk of developing preeclampsia. First trimester blood As (RR=3.40; 95% CI: 1.40, 8.28) and Mn (RR=0.63; 95% CI: 0.42, 0.94) concentrations were associated with a higher and lower risk, respectively, of developing gestational hypertension. Mn modified the association with As such that the deleterious association with As was stronger at lower concentrations of Mn. First trimester urinary dimethylarsinic acid concentrations were not associated with gestational hypertension (RR=1.31; 95% CI: 0.60, 2.85) or preeclampsia (RR=0.92; 95% CI: 0.68, 1.24). We did not observe overall joint effects for blood metals.

DISCUSSION

Our results confirm that even low blood Pb concentrations are a risk factor for preeclampsia. Women with higher blood As concentrations combined with lower Mn in early pregnancy were more likely to develop gestational hypertension. These pregnancy complications impact maternal and neonatal health. Understanding the contribution of toxic metals and Mn is of public health importance. https://doi.org/10.1289/EHP10825.

Sex-specific associations between cord blood lead and neurodevelopment in early life: The mother-child cohort (Shanghai, China)

The extent to which neurodevelopment is affected by prenatal lead exposure has not been conclusive. In addition, studies on the effects of sex on these relationships are inconsistent. The aim of this study was to investigate the impact of cord blood lead on neurodevelopment in children within sex subgroups. A total of 275 mother-child pairs from the Shanghai mother-child cohort were included. Umbilical cord blood lead was measured using graphite furnace atomic absorption spectrophotometry. The Bayley Scales for Infant Development-III (BSID-III) was used to measure the neurodevelopment of infants at the age of 18 ± 1.5 months. The median and interquartile range of cord blood lead levels in the total participants, male, and female children were 44.0 (24.5) μg/L, 44.0 (24.3) μg/L, and 46.0 (24.0) μg/L, respectively. According to multiple linear regression, cord blood lead concentrations showed a negative association with fine motor scores in all models associated with female children (β = -1.5; 95%confidence interval: -2.6, -0.4). However, prenatal lead levels were not associated with any of the BSID-III scores in male children. In addition, cord serum DHA was found positively related to fine motor scores in male children. Our findings suggest that prenatal lead exposure could lead to decreased motor function, although this phenomenon was only observed in female children. And DHA may be a protective factor against lead exposure in boys. Thus, further studies are needed to investigate the associations between prenatal lead exposure and neurobehavioral development, as well as the mechanism of sex differences.

Lead Exposure in Infancy and Subsequent Growth in Beninese Children

Studies suggest that elevated postnatal blood lead levels (BLLs) are negatively associated with child growth. This study aimed to investigate the associations of childhood BLLs at age one year and growth outcomes at age six years (n = 661) in a cohort of children in Allada, Benin. The growth outcomes studied are weight-for-age Z-score (WAZ), height-for-age Z-score (HAZ), BMI-for-age Z-score (BMIZ), weight-for-height Z-score (WHZ), head circumference (HC), growth velocities, underweight, stunting, and wasting. Multivariable regression models examined the associations between BLLs and growth outcomes, with adjustment for potential confounders. The geometric mean BLLs was 59.3 μg/L and 82% of children had BLLs >35 μg/L at the age of 12.8 months. After adjusting for confounding factors, no overall association was found between BLL quartiles and HAZ, WAZ, BMIZ, WHZ, growth velocities, wasting, and underweight. However, boys in the highest quartile had a 1.02 cm lower HC (95% CI: [−1.81, −0.24]) as compared to the lowest quartile. Furthermore, an increased odds of being stunted was observed in children in the highest quartile of exposure compared to the first (OR: 2.43; 95% CI: [1.11−5.33]) which remained statistically significant only among girls in sex-specific strata. Blood lead was found to be associated with an increased risk of childhood stunting and a lower head circumference in a resource-limited setting.

Joint associations among prenatal metal mixtures and nutritional factors on birth weight z-score: Evidence from an urban U.S. population

The benefits of nutritional factors on birth outcomes have been recognized, however, limited studies have examined the role of nutritional factors in mitigating the detrimental effects of metals exposure during gestation. We used data collected from 526 mother-infant dyads enrolled in the Programming of Intergenerational Stress Mechanisms longitudinal pregnancy cohort to examine the joint effects of prenatal exposure to metals and maternal nutrition on birth weight for gestational age (BWGA) z-scores. We measured concentrations of twelve metals and trace elements in urine samples collected during pregnancy. Maternal nutritional intake was measured using the Block98 Food Frequency Questionnaire and converted into energy-adjusted consumption of individual nutrients. Using multivariable linear regression and Bayesian Kernel Machine Regression, we found that three metals [cobalt (Co), nickel (Ni), and lead (Pb)] and five metals [barium (Ba), caesium (Cs), copper (Cu), Ni, and zinc (Zn)] were associated with BWGA z-score in male and female infants, respectively. When examining the sex-specific interactions between these metals and nutrient groups [macro nutrients, minerals, A vitamins, B vitamins, anti-oxidant, methyl-donor nutrients, and inflammatory (pro- and anti-)] using a Cross-validated Kernel Ensemble model, we identified significant interactions between the macro nutrients and Co (p = 0.05), minerals and Pb (p = 0.04), and A vitamins and Ni (p = 0.001) in males. No significant interactions were found in females. Furthermore, three minerals (phosphorus, iron, potassium) and vitamin A were found to be more crucial than other nutrients in modifying the association between each respective metal and BWGA z-score in males. A better understanding of the sex-specific interactions between nutrients and metals on birth weight can guide pregnant women to protect their neonates from the adverse health impacts of metal exposures by optimizing nutrient intakes accordingly.

Free Cortisol Mediates Associations of Maternal Urinary Heavy Metals with Neonatal Anthropometric Measures: A Cross-Sectional Study

Prenatal exposure to heavy metals is known to be associated with adverse birth outcomes and oxidative stress biomarkers. In this study, we examined whether maternal free cortisol or 8-Hydroxy-2-Deoxyguanosine (8-OHdG) could mediate associations between maternal heavy metal exposure and birth outcomes. A total of 182 healthy pregnant women were recruited. Heavy metals (including Pb, Hg, and Cd), free-cortisol, and 8-OHdG were analyzed in urine at delivery. Birth outcomes including birth weight, length, Ponderal index, and head circumference were measured. To examine associations of maternal urinary heavy metals with biomarkers and birth outcomes, generalized linear models were employed. Birth length was positively associated with Pb (β = 0.78, 95% CI: 0.09−1.46) and Hg (β = 0.84, 95% CI: 0.23−1.45) (both p < 0.05). The Ponderal index, a measure of a newborn’s leanness, was negatively associated with maternal urinary Pb (β = −0.23, 95% CI: −0.46−−0.07) and Hg (β = −0.26, 95% CI: −0.44−−0.08) (both p < 0.05). No association between maternal Cd and birth outcomes was observed. Most heavy metals showed positive associations with free cortisol and 8-OHdG. Free cortisol was identified as a mediator underlying the observed relationship between Hg and birth length or Ponderal index. This study observed adverse birth outcomes from maternal exposures to Pb and Hg. Increased free cortisol related to Hg exposure was suggested as a possible causal pathway from Hg exposure to birth outcomes such as the Ponderal index.

Gestational exposure to polybrominated diphenyl ethers and social skills and problem behaviors in adolescents: The HOME study

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) are persistent environmental pollutants used as flame retardants. Gestational PBDE exposure has been associated with a variety of behavior problems in children, but little is known about its impact into adolescence, particularly on social skills, which are important for achieving social competence, establishing identity, and forming lasting relationships.

OBJECTIVE

We investigated associations between gestational exposure to PBDEs and social skills and problem behaviors in early adolescence in a longitudinal pregnancy and birth cohort in Cincinnati, Ohio (recruited 2003-2006).

METHODS

We measured maternal serum concentrations of five PBDE congeners during gestation. At age 12, we measured social skills and problem behaviors scores for 243 adolescents using self- and caregiver-report on the Social Skills Improvement System (SSiS). We used multivariable linear regression models to estimate associations between maternal PBDE concentrations and SSiS scores, controlling for potential covariates. We report associations for the five congeners and a summary exposure variable (∑5BDE: the sum of BDE- 28, 47, 99, 100, and 153, n = 197).

RESULTS

We found sex-specific associations of ∑5BDE concentrations with adolescent-reported Problem Behaviors (∑5BDE × sex pint = 0.02) and caregiver-reported Social Skills (∑5BDE × sex pint = 0.02). In sex-stratified models, log10 transformed data revealed increased maternal ∑5BDE concentration among males was associated with decreased caregiver-reported Social Skills composite score (β = -10.2, 95% CI: -19.5, -1.0), increased adolescent-reported Problem Behaviors composite score (β = 12.1, 95% CI: 5.4, 18.8), and increased caregiver-reported Problem Behaviors composite score (β = 6.2, 95% CI: 0.7, 11.7). Further analysis on SSiS subscales revealed similar patterns in significant associations among males. There were no statistically significant associations in stratified models among females despite higher ∑5BDE exposure (Female GM=40.15 ng/g lipid, GSE=1.10; Male GM=35.30 ng/g lipid, GSE=1.09).

DISCUSSION

We found gestational PBDE exposure in males was associated with poorer behavioral outcomes, extending previous findings among this cohort into early adolescence.

Metal exposure and bone remodeling during pregnancy: Results from the PROGRESS cohort study

Pregnancy is characterized by high bone remodeling and might be a window of susceptibility to the toxic effects of metals on bone tissue. The aim of this study was to assess associations between metals in blood [lead (Pb), cadmium (Cd)and arsenic (As)] and bone remodeling during pregnancy. We studied pregnant woman from the PROGRESS Cohort (Programming Research in Obesity, Growth, and Environment and Social Stress). We measured concentrations of metals in blood and obtained measures of bone remodeling by quantitative ultrasound (QUS) at the radius in the second and third trimester of pregnancy. To account for chronic lead exposure, we measured lead in tibia and patella one-month postpartum with K-shell X-ray fluorescence. We assessed cross-sectional and longitudinal associations between multiple-metal concentrations and QUS z-scores using linear regression models and linear mixed models adjusted for potential confounders. Third trimester blood Cd concentrations were marginal associated with lower QUS z-scores [-0.16 (95% CI: -0.33, 0.007); P-Value = 0.06]. Mixed models showed that blood Cd was longitudinally and marginally associated with an average of -0.10 z-score (95% CI: -0.21, 0.002; P-Value = 0.06) over the course of pregnancy. Associations for Pb and As were all inverse however none reached significance. Additionally, bone Pb concentrations in patella, an index of cumulative exposure, were significantly associated with -0.06 z-score at radius (95% CI: -0.10, -0.01; P-Value = 0.03) during pregnancy. Pb and Cd blood levels are associated with lower QUS distal radius z-scores in pregnant women. Bone Pb concentrations in patella were negatively associated with z-score at radius showing the long-term effects of Pb on bone tissue. However, we cannot exclude the possibility of reverse causality for patella Pb and radius z-score associations. Our results support the importance of reducing women's metal exposure during pregnancy, as metals exposure during pregnancy may have consequences for bone strength later in life. The main finding of our study is the association between Cd blood levels and radius z-score during pregnancy. Bone lead in patella was also negatively associated with radius z-scores.

Placental chemical elements concentration in small fetuses and its relationship with Doppler markers of placental function

INTRODUCTION

In this study, we aimed at quantifying placental concentrations of 22 chemical elements in small fetuses (SGA) as compared with normally grown fetuses (AGA), and to assess the relationship with Doppler markers of placental function.

METHODS

Prospective cohort study, including 71 SGA fetuses (estimated fetal weight < 10th percentile) and 96 AGA fetuses (estimated fetal weight > 10th percentile), recruited in the third trimester of gestation. The placental concentration of 22 chemical elements was determined by inductively coupled plasma optical emission spectrophotometer (ICP-OES, ICAP 6500 Duo Thermo): aluminum (Al), beryllium (Be), bismuth (Bi), calcium (Ca), cadmium (Cd), cobalt (Co), chrome (Cr), copper (Cu), magnesium (Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), phosphorus (P), lead (Pb), rubidium (Rb), sulfur (S), strontium (Sr), titanium (Ti), thallium (Tl), antimony (Sb), selenium (Se), and zinc (Zn). Placental function was assessed by measuring the following fetal-maternal parameters: Uterine artery Pulsatility Index (UtA PI), Umbilical artery Pulsatility Index (UA PI) and Middle Cerebral artery Pulsatility Index (MCA PI). The association between the chemical elements concentration and study group and the association with Doppler measures were evaluated.

RESULTS

SGA was associated with significantly (p < 0.05) lower concentrations of Al (AGA 21.14 vs SGA 0.51 mg/kg), Cr (AGA 0.17 vs SGA 0.12 mg/kg), Cu (AGA 0.89 vs SGA 0.81 mg/kg), Mg (AGA 0.007 vs SGA 0.006 g/100g), Mn (AGA 0.60 vs SGA 0.47 mg/kg), Rb (AGA 1.68 vs SGA 1.47 mg/kg), Se (AGA 0.02 vs SGA 0.01 mg/kg), Ti (AGA 0.75 vs SGA 0.05 mg/kg) and Zn (AGA 9.04 vs SGA 8.22 mg/kg). Lower placental concentrations of Al, Cr, Mn, Se, Ti were associated with abnormal UtA, UA and MCA Doppler.

DISCUSSION

Lower placental concentrations of Al, Cr, Cu, Mn, Rb, Se, Ti and Zn are associated with SGA fetuses and abnormal fetal-maternal Doppler results. Additional studies are required to further understand how chemical elements affect fetal growth and potentially find strategies to prevent SGA.

Exposure to toxic metals and per- and polyfluoroalkyl substances and the risk of preeclampsia and preterm birth in the United States: a review

Preeclampsia and preterm birth are among the most common pregnancy complications and are the leading causes of maternal and fetal morbidity and mortality in the United States. Adverse pregnancy outcomes are multifactorial in nature and increasing evidence suggests that the pathophysiology behind preterm birth and preeclampsia may be similar-specifically, both of these disorders may involve abnormalities in placental vasculature. A growing body of literature supports that exposure to environmental contaminants in the air, water, soil, and consumer and household products serves as a key factor influencing the development of adverse pregnancy outcomes. In pregnant women, toxic metals have been detected in urine, peripheral blood, nail clippings, and amniotic fluid. The placenta serves as a "gatekeeper" between maternal and fetal exposures, because it can reduce or enhance fetal exposure to various toxicants. Proposed mechanisms underlying toxicant-mediated damage include disrupted placental vasculogenesis, an up-regulated proinflammatory state, oxidative stressors contributing to prostaglandin production and consequent cervical ripening, uterine contractions, and ruptured membranes and epigenetic changes that contribute to disrupted regulation of endocrine and immune system signaling. The objective of this review is to provide an overview of studies examining the relationships between environmental contaminants in the US setting, specifically inorganic (eg, cadmium, arsenic, lead, and mercury) and organic (eg, per- and polyfluoroalkyl substances) toxicants, and the development of preeclampsia and preterm birth among women in the United States.

Prenatal lead exposure and cord blood DNA methylation in the Korean Exposome Study

BACKGROUND

Prenatal lead exposure has been reported to affect infant growth and nervous system development, as well as to influence DNA methylation. We conducted an epigenome-wide association study to identify associations between prenatal lead exposure and cord blood DNA methylation in Korean infants.

METHODS

Cord blood samples were assayed with the Illumina HumanMethylationEPIC BeadChip kits, and maternal blood lead levels during early and late pregnancy, as well as cord blood lead level, were measured. The association between CpG methylation and lead level was analyzed using the limma package, with adjusting for infant sex, maternal pre-pregnancy body mass index, and estimated leukocyte composition.

RESULTS

Among 364 blood samples (182 males and 182 females), those for which maternal and cord blood lead concentrations during early and later pregnancy was known were used for analysis. Maternal lead concentration in blood during early pregnancy was significantly associated with the methylation status of specific positions. After data stratification by infant sex, we found that, in males, the level of maternal blood lead was associated with 18 CpG sites during early pregnancy, and with one CpG site near the NBAS gene, during late pregnancy. In female samples, there was no significant association between DNA methylation and lead concentrations.

CONCLUSIONS

Prenatal lead exposure was associated with altered, gender-specific patterns of DNA methylation in Korean infants.

Biomonitoring of Lead Exposure in Children from Two Fishing Communities at Northern Colombia

Lead (Pb) exposure is a growing concern in developing countries, especially in vulnerable children. The objective of this study was to evaluate blood lead levels (BLL) in children from two fishing populations at Northern Colombia, Loma de Arena and Tierrabomba, as well as their association with morphometric parameters, markers of hematological status, liver function, and mRNA expression of genes related to Pb toxicity. A total of 198 blood samples were collected from participants aged 5-16 years old. The mean (± standard error) BLL for the studied sample was 3.6 ± 0.3 μg/dL, and the 97.5th percentile was 21.0 μg/dL. The participants of Loma de Arena and Tierrabomba presented BLL of 3.9 ± 0.5 and 2.9 ± 0.3 μg/dL, respectively. Children born preterm had greater BLL than those born at full term. Boys had greater BLL than girls, which also occurred for participants between 12 and 16 years old, compared with those aged 5-11 years old. The BLL were negatively correlated with body mass index in children from Loma de Arena, but an opposite behavior was observed for Tierrabomba. In Loma de Arena, the mRNA expression of interferon gamma, a pro-inflammatory cytokine, increased with the BLL, but that of δ-aminolevulinic acid dehydrogenase, a sensor for Pb poisoning, decreased. In Tierrabomba, gene expression did not change with BLL. These results show that in fishing communities, lead exposure promotes different health impacts depending on age, sex, and other site-specific factors. In any case, appropriate educational and intervention programs should be carried out to minimize Pb exposure in children.

Prenatal exposure to multiple metals and birth outcomes: An observational study within the National Children's Study cohort

BACKGROUND

Prenatal exposure to metals may play an important role in fetal growth. However, the epidemiologic evidence for certain metals is sparse, and most of the existing research has focused on evaluating single metals in highly exposed target populations.

OBJECTIVES

We evaluated associations of cadmium, lead, manganese, selenium, and total mercury exposures during pregnancy with fetal growth using data from mother-infant pairs participating in the National Children's Study.

METHODS

Prenatal metal exposures were measured using maternal blood collected from 6 to 32 weeks of gestation. Birth outcomes, including gestational age, birthweight, birth length, head circumference, and ponderal index, were ascertained through physical measurement at birth or abstraction from medical records. Regression coefficients and their 95% confidence intervals were estimated from multivariable linear regression models in the overall study population as well as among male and female infants. We further evaluated pairwise metal-metal interactions.

RESULTS

Sex-specific associations were observed for lead, with inverse associations for birthweight, birth length, head circumference, and gestational age observed only among female infants. Sex-specific associations were also observed for selenium, with a positive association for birthweight observed among male infants; selenium was also positively associated with ponderal index and inversely associated with birth length among female infants. Overall, total mercury was inversely associated with birthweight and ponderal index, and the association with birthweight was stronger among female infants. No significant associations were observed with cadmium and manganese. In the metal-metal interaction analyses, we found evidence of a synergistic interaction between lead and total mercury and antagonistic interaction between selenium and total mercury with selected birth outcomes.

CONCLUSIONS

Our findings suggest that prenatal exposure to metals may be related to birth outcomes, and infant sex may modify these associations.

Association between blood lead level during pregnancy and birth weight: A meta-analysis

BACKGROUND

We aimed to provide a quantitative summary of evidence for a relationship between prenatal lead (Pb) exposure and birth weight.

METHODS

PubMed and Web of Science databases were searched for eligible epidemiological studies. We transformed findings in eligible studies with different effect-size metrics to standardized regression coefficients, and used fixed-effects or random-effects models to assess the pooled effects of prenatal Pb exposure on birth weight.

RESULTS

There was a significant negative association between prenatal Pb exposure and birth weight. Birth weight reduction was associated with elevated lead levels in maternal blood (β = -0.094; 95% confidence interval [CI]: -0.157 to -0.030) and cord blood (β = -0.120; 95% CI: -0.239 to -0.001).

CONCLUSIONS

This meta-analysis is the first to provide a quantitative assessment of Pb exposure during pregnancy and an increased risk of lower birth weight.

Exposure to uranium and co-occurring metals among pregnant Navajo women

Navajo Nation residents are at risk for exposure to uranium and other co-occurring metals found in abandoned mine waste. The Navajo Birth Cohort Study (NBCS) was initiated in 2010 to address community concerns regarding the impact of chronic environmental exposure to metals on pregnancy and birth outcomes. The objectives of this paper were to 1) evaluate maternal urine concentrations of key metals at enrollment and delivery from a pregnancy cohort; and 2) compare the NBCS to the US general population by comparing representative summary statistical values. Pregnant Navajo women (N = 783, age range 14-45 years) were recruited from hospital facilities on the Navajo Nation during prenatal visits and urine samples were collected by trained staff in pre-screened containers. The U.S. Centers for Disease Control and Prevention (CDC), National Center for Environmental Health's (NCEH) Division of Laboratory Sciences (DLS) analyzed urine samples for metals. Creatinine-corrected urine concentrations of cadmium decreased between enrollment (1st or 2nd trimester) and delivery (3rd trimester) while urine uranium concentrations were not observed to change. Median and 95th percentile values of maternal NBCS urine concentrations of uranium, manganese, cadmium, and lead exceeded respective percentiles for National Health and Nutrition Evaluation Survey (NHANES) percentiles for women (ages 14-45 either pregnant or not pregnant.) Median NBCS maternal urine uranium concentrations were 2.67 (enrollment) and 2.8 (delivery) times greater than the NHANES median concentration, indicating that pregnant Navajo women are exposed to metal mixtures and have higher uranium exposure compared to NHANES data for women. This demonstrates support for community concerns about uranium exposure and suggests a need for additional analyses to evaluate the impact of maternal metal mixtures exposure on birth outcomes.

Low-level maternal exposure to cadmium, lead, and mercury and birth outcomes in a Swedish prospective birth-cohort

Observational studies have indicated that low-to-moderate exposure to cadmium (Cd), lead (Pb), and mercury (Hg) adversely affects birth anthropometry, but results are inconclusive. The aim of this study was to elucidate potential impact on birth anthropometry of exposure to Cd, Pb, and Hg in pregnant women, and to identify the main dietary sources. In the NICE (Nutritional impact on Immunological maturation during Childhood in relation to the Environment) birth-cohort in northern Sweden, blood and urine were collected from pregnant women in early third trimester. Cd, Pb and Hg were measured in erythrocytes (n = 584), and Cd also in urine (n = 581), by inductively coupled plasma mass spectrometry. Dietary data were collected through a semi-quantitative food frequency questionnaire administered in mid-third trimester. Birth anthropometry data were extracted from hospital records. In multivariable-adjusted spline regression models, a doubling of maternal erythrocyte Cd (median: 0.29 μg/kg) above the spline knot of 0.50 μg/kg was associated with reduced birth weight (B: -191 g; 95% CI: -315, -68) and length (-0.67 cm; -1.2, -0.14). The association with birth weight remained when the analysis was restricted to never-smokers. Likewise, a doubling of erythrocyte Hg (median 1.5 μg/kg, mainly MeHg) above 1.0 μg/kg, was associated with decreased birth weight (-59 g; -115, -3.0), and length (-0.29 cm; -0.54, -0.047). Maternal Pb (median 11 μg/kg) was unrelated to birth weight and length. Erythrocyte Cd was primarily associated with intake of plant derived foods, Pb with game meat, tea and coffee, and Hg with fish. The results indicated that low-level maternal Cd and Hg exposure were associated with poorer birth anthropometry. Further prospective studies in low-level exposed populations are warranted.

Sex differences in the effects of lead exposure on growth and development in young children

The adverse effects of lead exposure on children's health have been widely investigated. Physical growth is a central indicator of health in early childhood. However, studies on the associations between lead exposure and the physical growth of young children are still equivocal. This study aimed to investigate the effects of lead exposure on young children's growth. A cross-sectional survey was conducted, and a total of 1678 young children were recruited. Blood lead levels were determined by graphite furnace atomic absorption spectrophotometry and anthropometric measurements were obtained by nurses. The weight-for-age Z-score (WAZ), height-for-age Z-score (HAZ) and BMI for-age Z-score (BMIZ) of the children were calculated according to World Health Organization standards. Multivariable linear models after adjustment for potential confounders were used to evaluate the associations between lead exposure and childhood anthropometric characteristics. Meanwhile, the sex differences in these associations were also examined. The median blood lead levels in total subjects, in boys and in girls were 46.44, 49.00 and 43.27 μg/L, respectively. After adjusting for confounders, a significantly negative association of blood lead levels with WAZ and HAZ was observed. After stratification by sex, the blood lead levels in children were negatively associated with WAZ and HAZ in boys but not in girls. Meanwhile, we further provide evidence that blood lead levels below 50 μg/L may also have adverse effects on young children's HAZ. Our findings suggest that lead exposure may have sex-specific effects on physical growth in young children and that blood lead level in a low levels may also have adverse effects on children's physical growth and development.

A pilot study of mothers and infants reveals fetal sex differences in the placental transfer efficiency of heavy metals

It has been demonstrated that heavy metals cross the placental barrier and exert potentially harmful fetal effects. Although previous studies showed sex differences in response to similar intrauterine environments, little is known about fetal sex-related differences in placental transfer and accumulation of heavy metals. This study aimed to reveal the sex-specific risk of fetal exposure to heavy metals in pregnant women. We detected the exposure levels of eight heavy metals in 64 paired mother-infant maternal blood, cord blood and placental tissue samples. We found that the placental transfer efficiency (PTE) of titanium (Ti) and silver (Ag) was significantly higher in the group with male fetuses than that with female fetuses. The group with male fetuses had a larger placental:maternal blood ratio of Ag levels than the group with female fetuses, indicating fetal sex-related differences in placental transfer and accumulation of Ag. Prospective research should focus on the sex differences of adverse health effects induced by heavy metals and other pollutants.

Screening for Elevated Blood Lead Levels and Related Risk Factors among Thai Children Residing in a Fishing Community

The present study explored environmental and behavioral factors associated with elevated blood lead (Pb) levels in 311 children (151 girls and 160 boys), aged 3–7 years, who lived in a coastal fishing community of the Pakpoon Municipality, Nakhon Si Thammarat, Thailand. The geometric mean for blood Pb was 2.81 µg/dL, ranging between 0.03 and 26.40 µg/dL. The percentage of high blood Pb levels, defined as blood Pb ≥ 5 µg/dL, was 10.0% in boys and 13.9% in girls. Parental occupation in producing fishing nets with lead weights was associated with a marked increase in the prevalence odds ratio (POR) for high blood Pb (POR 17.54, 95%; CI: 7.093, 43.390; p < 0.001), while milk consumption was associated with 61% reduction in the POR for high blood Pb (POR 0.393, 95%; CI: 0.166, 0.931; p = 0.034). High blood Pb was associated with an increased risk for abnormal growth (POR 2.042, 95%; CI: 0.999, 4.174; p = 0.050). In contrast, milk consumption was associated with a 43% reduction in POR for abnormal growth (POR 0.573, 95%; CI: 0.337, 0.976; p = 0.040). After adjustment for age, the mean (standard error of mean, SE) values for blood Pb were 6.22 (0.50) μg/dL in boys and 6.72 (0.49) μg/dL in girls of parents with an occupation in making fishing nets with lead weights. These mean blood Pb values were respectively 2.3 and 2.5 times higher than similarly aged boys and girls of parents with other occupations. These data are essential for setting surveillance and programmes to prevent toxic Pb exposure, especially in children of coastal fishing communities in southern Thailand.

GM1 Ameliorates Lead-Induced Cognitive Deficits and Brain Damage Through Activating the SIRT1/CREB/BDNF Pathway in the Developing Male Rat Hippocampus

Developmental lead (Pb) exposure involves various serious consequences, especially leading to neurotoxicity. In this study, we examined the possible role of monosialoganglioside (GM1) in lead-induced nervous impairment in the developing rat. Newborn male Sprague-Dawley rat pups were exposed to lead from birth for 30 days and then subjected to GM1 administration (0.4, 2, or 10 mg/kg; i.p.) or 0.9% saline. The results showed that developmental lead exposure significantly impaired spatial learning and memory in the Morris water maze test, reduced GM1 content, induced oxidative stress, and weakened the antioxidative systems in the hippocampus. However, co-treatment with GM1 reversed these effects. Moreover, GM1 counteracted lead-induced apoptosis by decreasing the expression of Bax, cleaved caspase-3, and by increasing the level of Bcl-2 in a dose-dependent manner. Furthermore, we found that GM1 upregulated the expression of SIRT1, CREB phosphorylation, and BDNF, which underlie learning and memory in the lead-treated developing rat hippocampus. In conclusion, our study demonstrated that GM1 exerts a protective effect on lead-induced cognitive deficits via antioxidant activity, preventing apoptosis, and activating SIRT1/CREB/BDNF in the developing rat hippocampus, implying a novel potential assistant therapy for lead poisoning.

Relation of prenatal low-level mercury exposure with early child neurobehavioral development and exploration of the effects of sex and DHA on it

BACKGROUND

The extent to which low-level, in utero mercury exposure affects child neurobehavioral development during early childhood has been inconclusive. In addition, the effects of sex and docosahexaenoic acid (DHA) on these relationships remain unclear and controversial.

OBJECTIVES

This study aimed to explore the associations between prenatal low-level mercury exposure and child neurobehavioral development during the neonatal and toddler periods and to examine the potential confounding or interactive effects of sex and DHA status on these relationships.

METHODS

This longitudinal study included 286 mother-child pairs in Shanghai, China, whose cord blood samples were analyzed for total mercury, DHA, other nutrients and coexposure contaminants possibly due to maternal consumption of seafood. Children's neurobehavioral development was assessed with the Neonatal Behavioral Neurological Assessment (NBNA) three days after birth and the Bayley Scales of Infant and Toddler Development, Third Edition (BSID-III) at 18 months of age.

RESULTS

Cord blood mercury concentration, with geometric mean of 2.00 μg/l, was related to poorer NBNA performance but unrelated to BSID-III scores with adjustment for DHA and other covariates. Cord serum DHA was positively associated with motor development assessed by the BSID-III. The interaction was found between mercury and DHA on the NBNA score, and the inverse relation of cord blood mercury with NBNA was significant only among the children with lower DHA levels (<45.54 μg/ml). Additional adjustment for DHA didn't change the associations between cord blood mercury and neurodevelopmental outcomes substantially. The mercury by sex interaction for language of BSID-III was borderline significant.

CONCLUSIONS

Our research provides initial evidence for the negative effects of prenatal low-level mercury exposure on neonates' neurobehavioral development. Prenatal DHA status may modify the relationship between cord blood mercury level and neonatal neurobehavioral development, but the confounding effects of DHA were not observed. Further studies are warranted before the causality of the observed associations can be determined.

In utero metal exposures measured in deciduous teeth and birth outcomes in a racially-diverse urban cohort

A growing number of studies have examined associations of metal exposures with birth outcomes, however, results from these studies have been inconsistent, and hampered by methodological limitations. We measured direct fetal exposure to three metals (lead, manganese and zinc) during the second and third trimester and examined its association with birth weight and gestational age at delivery. Participants in the Wayne County Health, Environment, Allergy and Asthma Longitudinal Study (WHEALS), a population-based birth cohort established between September 2003 and December 2007, were invited to donate teeth to the study. Lead, manganese and zinc during the second and third trimesters were measured via high-resolution microspatial mapping of dentin growth rings, a validated biomarker for prenatal metal exposure. Gestational age at delivery and infant birth weight were obtained from the delivery medical record. A total of 145 children had tooth metal measurements and birth outcome data. Mean birth weight was 3431 ± 472 g and mean gestational age at delivery was 39.0 ± 1.3 weeks. Overall, there was a positive association between second (β = 0.21, 95% CI: 0.05, 0.37, P = 0.01) and third trimester (β = 0.21, 95% CI: 0.05, 0.37, P = 0.01) tooth manganese and birth weight Z-score; this remained statistically significant after covariate adjustment. There was also a negative association between second trimester tooth lead level and birth weight Z-score (β = -0.20, 95% CI: -0.38, -0.02, P = 0.02), however, this was attenuated after adjusting for covariates. Mixture analysis revealed similar findings. There was evidence for a sex-specific effect of manganese with birth weight Z-score, with the association stronger in female compared to male infants. Overall, we found evidence suggesting that higher in utero manganese is associated with larger birth weight Z-scores and that these associations may vary by infant sex.

Effects of lead, mercury, aluminium and manganese co-exposure on the serum BDNF concentration of pre-school children in Taizhou, China

Previous studies have shown that toxic metal exposure can have adverse effects on the nervous system of children, but the toxicology of metal co-exposure on neurodevelopment remains to be clarified. Brain derived neurotrophic factor (BDNF) plays an important role in nervous system development, but the possible effects of metal co-exposure on the serum BDNF concentrations of children remain unknown. A total of 561 children living in Taizhou City, China were recruited to participate in our cross-sectional multicenter survey. We measured their blood Pb, Hg, Al and Mn levels and serum BDNF concentrations as well as determined their associations in the total and within sex subgroups. The geometric means of the blood Pb, Hg, Al and Mn levels in all the participants were 67.18 μg/L, 1.01 μg/L, 52.03 μg/L and 18.26 μg/L, respectively. The serum BDNF concentration in children was 19.45 ng/mL. After adjusting for confounders, the blood Pb levels were significantly negatively associated with the serum BDNF concentrations in all the subjects and boys but not in girls. In addition, a significantly negative interaction between blood Pb and blood Hg and a positive interaction between blood Pb and blood Al on serum BDNF concentrations were also observed in boys but not in girls. Our findings highlight the toxic effects of metal co-exposure on serum BDNF levels in pre-school children and indicate that these effects might differ by gender, which suggest that special attention should be paid to the sex-specific effects of metal exposure.

Placental metal concentrations and birth outcomes: The Environment and Childhood (INMA) project

OBJECTIVE

To examine the association of placental levels of arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb), manganese (Mn), and chromium (Cr) with birth outcomes (birth weight, length, and head circumference, low birth weight [LBW], gestational age, preterm delivery, and small for gestational age [SGA]) in mother-child pairs from the Environment and Childhood (INMA) Project in Spain.

METHODS

Metal concentrations were measured in placenta tissue samples randomly selected from five INMA cohorts. Data on birth outcomes were obtained from medical records. Associations were assessed in a sub-sample of 327 mother-infant pairs by regression models adjusted for confounding factors and for all metals simultaneously. Effect modification by sex was also evaluated.

RESULTS

Elevated placental Cd levels (>5.79 vs. <3.30 ng/g) were associated with reduced birth weight (-111.8 g, 95%CI = -215.6; -8.06, p-trend = 0.01) and length (-0.62 cm, 95%CI = -1.20; -0.04, p-trend = 0.02), while a 10% increase in Cd was associated with 1.21-fold increased odds (95%CI = 1.01; 1.43) of LBW in the global sample but with 14% lower odds (95%CI = 0.78; 0.96) of preterm delivery in males (P_interaction = 0.10). Detected (vs. undetected) Hg was associated with reduced head circumference (-0.49 cm, 95%CI = -1.00; 0.03) in females (P_interaction = 0.03). A 10% increase in placental Mn was associated with slight increases in gestational age (0.04 weeks, 95%CI = 0.01; 0.07) in the global sample and in head circumference (0.05 cm, 95%CI = -0.01; 0.10) in females (P_interaction = 0.03). Elevated Cr levels (>99.6 vs. <56.1 ng/g) were associated with reduced birth length (-0.68 cm, 95%CI = -1.33; -0.04, p-trend = 0.02) and slightly increased gestational age (0.35 weeks, 95%CI = -0.07; 0.77, p-trend = 0.08) in the global sample. As and Pb were detected in few placentas (27% and 13%, respectively) and were not associated with any studied birth outcome.

CONCLUSIONS

Data suggest that in utero exposure to Cd, Hg, and Cr could adversely affect fetal growth, whereas Mn and Cr appear to have a positive effect on gestational age. Given the relatively small number of subjects, sex-specific associations should be interpreted with caution.

Associations between prenatal lead exposure and birth outcomes: Modification by sex and GSTM1/GSTT1 polymorphism

Maternal lead exposure is associated with poor birth outcomes. However, modifying effects of polymorphism in glutathione S-transferases (GST) gene and infant sex remain unexplored. Our aim was to evaluate whether associations between prenatal lead and birth outcomes differed by maternal GST genes and infant sex. Prospective data of 782 mother-child pairs from Mothers and Children's Environmental Health (MOCEH) study were used. The genotyping of GST-mu 1 (GSTM1) and theta-1 (GSTT1) polymorphisms was carried out using polymerase chain reaction. Multivariable linear regression was used to examine whether the association between blood lead (BPb) level and birth outcomes (birthweight, length, and head circumference) varied by maternal GST genes and sex. We did not find a statistically significant association between prenatal BPb levels and birth outcomes; in stratified analyses, the association between higher BPb level during early pregnancy and lower birthweight (β=-224 per square root increase in BPb; 95% confidence interval (CI): -426, -21; false discovery rate p=0.036) was significant in males of mothers with GSTM1 null. Results were similar for head circumference model (β=-0.78 per square root increase in BPb; 95% CI: -1.69, 0.14, p=0.095), but the level of significance was borderline. Head circumference model showed a significant three-way interaction among BPb during early pregnancy, GSTM1, and sex (p=0.046). For combined analysis with GSTM1 and GSTT1, GSTM1 null and GSTT1 present group showed a significant inverse association of BPb with birthweight and head circumference in males. Our findings of the most evident effects of BPb on the reduced birthweight and head circumference in male born to the mother with GSTM1 null may suggest a biological interaction among lead, GST genes and sex in detoxification process during fetal development.

Reduction of in utero lead exposures in South African populations: Positive impact of unleaded petrol

Background

Prenatal exposure to lead (Pb) has been shown to have negative and irreversible health impacts on foetal and early childhood development, affecting morbidity and mortality in adulthood. This study aimed to assess in utero Pb exposure, examine birth outcomes, and identify confounding factors in the large cohort of South African population, following the legislated removal of Pb from petrol.

Methods

Lead was measured in the maternal blood, urine and cord blood using Inductive Coupled Plasma Mass spectrometry (ICP-MS). The statistical analyses included Spearman’s correlation, Wilcoxon rank sum (Mann Whitney), Kruskal-Wallis rank tests and multivariate linear regression.

Results

Overall, the geometric mean (GM) of Pb in maternal blood (PbB) was 1.32 μg/dL (n = 640; 95% CI, 1.24–1.40). In the subset cohort, the GM of paired maternal PbB and cord blood (PbC) was 1.73 μg/dL (n = 350; 95% CI, 1.60–1.86) and 1.26 μg/dL (n = 317; 95% CI, 1.18–1.35), respectively with a positive correlation between the log PbB and the log PbC (rho = 0.65, p = <0.001). Birth outcomes showed geographical differences in the gestational age (p<0.001), birth length (p = 0.028) and head circumference (p<0.001), Apgar score at 5 min (p<0.001) and parity (p<0.002). In female neonates, a positive association was found between PbC and head circumference (rho = 0.243; p<0.016). The maternal PbB levels were positively correlated with race, educational status, water sources, cooking fuels and use of pesticides at home.

Conclusions

This study has demonstrated not only the positive impact that the introduction of unleaded petrol and lead-free paint has had on in utero exposure to Pb in South Africa, but has also contributed new data on the topic, in a region where such data and scientific investigations in this field are lacking. Future research should evaluate if similar effects can be detected in young children and the adult population.