Heavy metals (lead, cadmium and mercury) in maternal, cord blood and placenta of healthy women

Relationships of chemical concentrations in maternal and cord blood: a review of available data

The developing fetus is likely to be exposed to the same environmental chemicals as the mother during critical periods of growth and development. The degree of maternal-fetal transfer of chemical compounds will be affected by chemical and physical properties such as lipophilicity, protein binding, and active transport mechanisms that influence absorption and distribution in maternal tissues. However, these transfer processes are not fully understood for most environmental chemicals. This review summarizes reported data from more than 100 studies on the ratios of cord:maternal blood concentrations for a range of chemicals including brominated flame-retardant compounds, polychlorinated biphenyls (PCB), polychlorinated dibenzodioxins and dibenzofurans, organochlorine pesticides, perfluorinated compounds, polyaromatic hydrocarbons, metals, and tobacco smoke components. The studies for the chemical classes represented suggest that chemicals frequently detected in maternal blood will also be detectable in cord blood. For most chemical classes, cord blood concentrations were found to be similar to or lower than those in maternal blood, with reported cord:maternal ratios generally between 0.1 and 1. Exceptions were observed for selected brominated flame-retardant compounds, polyaromatic hydrocarbons, and some metals, for which reported ratios were consistently greater than 1. Careful interpretation of the data in a risk assessment context is required because measured concentrations of environmental chemicals in cord blood (and thus the fetus) do not necessarily imply adverse effects or risk. Guidelines and recommendations for future cord:maternal blood biomonitoring studies are discussed.

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.

Levels of prenatal mercury exposure and their relationships to neonatal anthropometry in Wujiang City, China

We determined the levels of prenatal Hg exposure in Wujiang City, located in the southeast of Taihu Lake in China's Jiangsu Province, and analyze the relationship between prenatal exposure to Hg and neonatal anthropometry, including birth weight, body length, and head circumference. From June 2009 to July 2010, a total of 213 mother-infant pairs were enrolled. The geometric means of Hg levels in maternal hair, fetal hair, placentas, and cord blood were 496.76 μg/kg, 233.94 μg/kg, 3.58 μg/kg, and 1.54 μg/L, respectively. The Hg levels detected in our study were significantly lower than those reported by previous studies. In addition, no significant correlations were found between Hg levels in maternal hair, fetal hair, placenta, or cord blood and neonatal anthropometrics. Together, our findings may be important for understanding the effects of prenatal exposure to Hg on newborns' development and have implications concerning the recommended dose for Hg.

Mercury concentrations in human placenta, umbilical cord, cord blood and amniotic fluid and their relations with body parameters of newborns

Studies were conducted on samples taken from giving birth women (n = 40) living in Poland, representing three age groups: 19-25, 26-30 and 31-38 years old. Mercury concentrations were measured with CV-AAS in placenta, umbilical cord, cord blood and amniotic fluid. The placentas weight did not exceed the 750 g value and was heavier than 310 g. Mean values of Hg concentrations in blood, placenta and umbilical cord were similar (c.a. 9 μg/g). High levels of mercury were noted in cord blood which in 75% of all observations exceeded (up to 17 μg/L) the safe dose set by US EPA (5.8 μg/L). No statistically significant differences in medium level of Hg in all the studied tissues among age groups of women were observed. Positive correlations between Hg concentrations in placenta and umbilical cord and cord blood were revealed as well as some negative ones between mercury concentrations and pregnancy parameters.

Tobacco smoke exposure during pregnancy increases maternal blood lead levels affecting neonate birth weight

To assess the effect of lead exposure from cigarette smoke on fetal growth, blood lead concentrations were measured using inductively coupled plasma mass spectrometry in 150 healthy pregnant women. Mean lead concentrations in plasma and whole blood were significantly higher in the smoking group compared with the nonsmoking group in each trimester of pregnancy (p < 0.001). Logistic regression analysis showed the highest impact of the number of cigarettes smoked per day for serum lead concentration (β = 0.238; p < 0.05), while in whole blood, it was duration of smoking before conception (β = 0.297; p < 0.001). Birth weight of the smoking mothers' infants was significantly lower (mean ± SEM, 3,192 ± 50.8 and 3,569 ± 49.6 g, respectively; p < 0.001) and negatively correlated with lead levels in plasma (r = -0.38; p < 0.001) and in whole blood (r = -0.27; p < 0.001). Therefore, it is suggested that smoking during pregnancy increases lead concentrations in maternal blood. Fetal exposure to low doses of lead in utero may be a serious risk factor causing lower birth weight.

Differences in prenatal exposure to mercury in South African communities residing along the Indian Ocean

Mercury is a persistent environmental pollutant that has the potential to adversely affect human health, particularly, foetal neurodevelopment. The purpose of the study was to investigate prenatal mercury (Hg) exposure in the population in three sites along the South Africa coast. Study subjects included women (n=350) who were admitted for delivery at the local hospitals. Maternal and cord blood samples were collected to measure total mercury and each participant was required to answer a questionnaire. The 90th percentile of mercury levels in maternal and cord blood of the total population was 1.15 μg/l and 1.67 μg/l, respectively. Site 1 (Manguzi) participants had the highest maternal geometric mean (GM) values of 0.93 μg/l, which was significantly different from Site 2 (Port Shepstone) (0.49 μg/l) and Site 3 (Empangeni) (0.56 μg/l) (ANOVA test, p<0.001). Umbilical cord blood GM Hg level for Site 1 (1.45 μg/l) was more than double the GM Hg level in Site 2 (0.70 μg/l) and Site 3 (0.73 μg/l). Univariate analysis indicated that the following maternal characteristics were positive predictors for elevated umbilical cord Hg levels: maternal blood Hg levels, living with a partner, residing in Site 1, living in informal housing, using wood and gas for cooking, borehole water as a drinking source, and a member of the household being involved in fishing. Maternal dietary predictors of elevated Hg levels in umbilical cord blood included consuming fresh fish, tinned fish, fruit or dairy products, daily. This study provides baseline data and reveals that 2% of the study population were above the EPA's reference value (5.8 μg/l) suggesting low level exposure to mercury in pregnant women and the developing foetus in South Africa. Further research is required to explore the sources of elevated Hg levels in Site 1.

Cadmium, lead and mercury exposure in non smoking pregnant women

Recent literature suggests that exposure to low concentrations of heavy metals may affect both maternal and child health. This study aimed to determine the biological heavy metals concentrations of pregnant women as well as environmental and dietary factors that may influence exposure concentrations. One hundred and seventy three pregnant women were recruited from Western Australia, each providing a sample of blood, first morning void urine, residential soil, dust and drinking water samples. Participants also completed a questionnaire which included a food frequency component. All biological and environmental samples were analysed for heavy metals using ICP-MS. Biological and environmental concentrations of lead and mercury were generally low (Median Pb Drinking Water (DW) 0.04 µg/L; Pb soil <3.0 µg/g; Pb dust 16.5 µg/g; Pb blood 3.67 µg/L; Pb urine 0.55; µg/L Hg DW <0.03; Hg soil <1.0 µg/g; Hg dust <1.0 µg/g; Hg blood 0.46 µg/L; Hg urine <0.40 µg/L). Cadmium concentrations were low in environmental samples (Median CdDW 0.02 µg/L; Cdsoil <0.30 ug/g; Cddust <0.30) but elevated in urine samples (Median 0.55 µg/L, creatinine corrected 0.70 µg/g (range <0.2-7.06 µg/g creatinine) compared with other studies of pregnant women. Predictors of increased biological metals concentrations in regression models for blood cadmium were residing in the Great Southern region of Western Australia and not using iron/folic acid supplements and for urinary cadmium was having lower household annual income. However, these factors explained little of the variation in respective biological metals concentrations. The importance of establishing factors that influence low human exposure concentrations is becoming critical in efforts to reduce exposures and hence the potential for adverse health effects.

Environmental factors predicting blood lead levels in pregnant women in the UK: the ALSPAC study

Background

Lead is a widespread environmental toxin. The behaviour and academic performance of children can be adversely affected even at low blood lead levels (BLL) of 5–10 µg/dl. An important contribution to the infant's lead load is provided by maternal transfer during pregnancy.

Objectives

Our aim was to determine BLL in a large cohort of pregnant women in the UK and to identify the factors that contribute to BLL in pregnant women.

Methods

Pregnant women resident in the Avon area of the UK were enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC) in 1991–1992. Whole blood samples were collected at median gestational age of 11 weeks and analysed by inductively coupled plasma dynamic reaction cell mass spectrometry (n = 4285). Self-completion postal questionnaires were used to collect data during pregnancy on lifestyle, diet and other environmental exposures. Statistical analysis was carried out with SPSS v19.

Results

The mean±SD BLL was 3.67±1.47 (median 3.41, range 0.41–19.14) µg/dl. Higher educational qualification was found to be one of the strongest independent predictor of BLL in an adjusted backwards stepwise logistic regression to predict maternal BLL <5 or ≥5 µg/dl (odds ratio 1.26, 95% confidence interval 1.12–1.42; p<0.001). Other predictive factors included cigarette smoking, alcohol and coffee drinking, and heating the home with a coal fire, with some evidence for iron and calcium intake having protective effects.

Conclusion

The mean BLL in this group of pregnant women is higher than has been found in similar populations in developed countries. The finding that high education attainment was independently associated with higher BLL was unexpected and currently unexplained. Reduction in maternal lead levels can best be undertaken by reducing intake of the social drugs cigarettes, alcohol and caffeine, although further investigation of the effect of calcium on lead levels is needed.

Mercury (Hg) exposure in breast-fed infants and their mothers and the evidence of oxidative stress

The objective of this work was to assess exposure to mercury (Hg) and its induction of oxidative stress in 155 healthy lactating Saudi mothers and their infants. Samples of breast milk and blood were collected from the mothers, while urine was taken from both infants and mothers. Both urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) and malondialdehyde (MDA) were measured in mothers and infants as biomarkers of oxidative stress. The mean concentration of Hg in breast milk was 1.19 μg/L (range 0.012-6.44 μg/L) with only one mother having Hg >4 μg/L, the upper limit established by the US Agency for Toxic Substance and Disease Registry. However, 57.4 % had Hg ≥1 μg/L, the background level for Hg in human milk. The mean urinary Hg corrected for creatinine (Hg-C) in mothers and infants was 1.47 and 7.90 μg/g creatinine, respectively, with a significant correlation between the two (p < 0.001). Urinary Hg levels over 5 μg/g creatinine (the background level in an unexposed population) were found in 3.3 % of mothers and 50.1 % of infants. None of the mothers had total blood Hg above the US Environmental Protection Agency's maximum reference dose of 5.8 μg/L. No correlation was noted between urinary Hg in infants and Hg in breast milk (p > 0.05). Hg in breast milk, though, was associated with Hg in blood (p < 0.001), suggesting the efficient transfer of Hg from blood to milk. Hg in the breast milk of mothers and in the urine of infants affected the excretion of urinary MDA and 8-OHdG, respectively, in a dose-related manner. These findings reveal for the first time lactational exposure to Hg-induced oxidative stress in breast-fed infants, which may play a role in pathogenesis, particularly during neurodevelopment. This will also contribute to the debate over the benefits of breast milk versus the adverse effects of exposure to pollutants. Nevertheless, breastfeeding should not be discouraged, but efforts should be made to identify and eliminate the source of Hg exposure in the population.

Birth outcome measures and maternal exposure to heavy metals (lead, cadmium and mercury) in Saudi Arabian population

This cross-sectional study was conducted to assess the association between exposure to heavy metals (lead, cadmium and mercury) during pregnancy and birth outcomes in 1578 women aged 16-50 years who delivered in Al-Kharj hospital, Saudi Arabia, in 2005 and 2006. The levels of lead, cadmium and mercury were measured in umbilical cord blood, maternal blood and the placenta. Outcome variables were anthropometric measures taken at birth, along with the risk of being small-for-gestational age (SGA). We selected the 10th percentile as the cutoff for dichotomizing measures of birth outcome. Cadmium, despite its partial passage through the placenta had the most prominent effect on several measures of birth outcome. After adjustment for potential confounders, logistic regression models revealed that crown-heel length (p=0.034), the Apgar 5-minute score (p=0.004), birth weight (p=0.015) and SGA (p=0.049) were influenced by cadmium in the umbilical cord blood. Significant decreases in crown-heel length (p=0.007) and placental thickness (p=0.022) were seen with higher levels of cadmium in maternal blood. As placental cadmium increased, cord length increased (p=0.012) and placental thickness decreased (p=0.032). Only lead levels in maternal blood influenced placental thickness (p=0.011). Mercury in both umbilical cord and maternal blood was marginally associated with placental thickness and placental weight, respectively. Conversely, placental mercury levels significantly influenced head circumference (p=0.017), the Apgar 5-minute score (p=0.01) and cord length (p=0.026). The predictions of these models were further assessed with the area under the curve (AUC) of the receiver operating curves (ROCs), which were modest (larger than 0.5 and smaller than 0.7). The independence of gestational age or preterm births on the observed effect of metals on some measures of birth outcome, suggested detrimental effects of exposure on fetal development. The magnitude of the estimated effects might not necessarily be of clinical significance for infants but may have a considerable public-health relevance given the high prevalence of exposure to heavy metals. Further research should be conducted to confirm these findings and to evaluate their long-term risks, if any.

Association between prenatal exposure to cadmium and atopic dermatitis in infancy

Our objective was to evaluate the relationship between intrauterine exposure to cadmium and the presence of atopic dermatitis in infants 6 months of age, adjusted for covariates including exposure to other heavy metals. The present research is a component of the Mothers' and Children's Environmental Health (MOCEH) study, a multi-center birth cohort project conducted in Korea. Study subjects were restricted to pregnant women in whom cadmium and lead levels were measured at delivery and whose infants were assessed for the presence of atopic disease at 6 months of age. The odds ratio (OR) for the presence of atopic dermatitis in 6-month-old infants whose cord blood had elevated cadmium levels, after adjustment for other covariates, was 2.350 (95% CI, 1.126-4.906). The OR for the presence of atopic dermatitis in infants whose cord blood had elevated lead levels was not significant. In the present study, the cord blood cadmium level was significantly associated with the presence of atopic dermatitis in 6-month-old infants; this was not true of the cord blood lead level. To the best of our knowledge, this is the first prospective study to show a relationship between prenatal exposure to cadmium and atopic dermatitis in infancy.

Systems biology and birth defects prevention: blockade of the glucocorticoid receptor prevents arsenic-induced birth defects

BACKGROUND

The biological mechanisms by which environmental metals are associated with birth defects are largely unknown. Systems biology-based approaches may help to identify key pathways that mediate metal-induced birth defects as well as potential targets for prevention.

OBJECTIVES

First, we applied a novel computational approach to identify a prioritized biological pathway that associates metals with birth defects. Second, in a laboratory setting, we sought to determine whether inhibition of the identified pathway prevents developmental defects.

METHODS

Seven environmental metals were selected for inclusion in the computational analysis: arsenic, cadmium, chromium, lead, mercury, nickel, and selenium. We used an in silico strategy to predict genes and pathways associated with both metal exposure and developmental defects. The most significant pathway was identified and tested using an in ovo whole chick embryo culture assay. We further evaluated the role of the pathway as a mediator of metal-induced toxicity using the in vitro midbrain micromass culture assay.

RESULTS

The glucocorticoid receptor pathway was computationally predicted to be a key mediator of multiple metal-induced birth defects. In the chick embryo model, structural malformations induced by inorganic arsenic (iAs) were prevented when signaling of the glucocorticoid receptor pathway was inhibited. Further, glucocorticoid receptor inhibition demonstrated partial to complete protection from both iAs- and cadmium-induced neurodevelopmental toxicity in vitro.

CONCLUSIONS

Our findings highlight a novel approach to computationally identify a targeted biological pathway for examining birth defects prevention.

Heavy metals in canned tuna from Italian markets

Fish is a good source of nutrients for humans but can pose a risk to human health because of the possible presence of some xenobiotics such as heavy metals and persistent organic contaminants. Constant monitoring is needed to minimize health risks and ensure product quality and consumer safety. The aim of the present study was to use atomic absorption spectrometry to determine the concentrations of some heavy metals (Hg, Pb, and Cd) in tuna packaged in different kinds of packages (cans or glass) in various countries (Italy and elsewhere). Concentrations of Cd and Hg were within the limits set by European Commission Regulation (EC) No 1881/2006 and in many samples were below the detection limit. Pb concentrations exceeded European limits in 9.8% of the analyzed samples. These results are reassuring in terms of food safety but highlighted the need to constantly monitor the concentrations of heavy metals in fish products that could endanger consumer health.

Placental concentrations of heavy metals in a mother-child cohort

Heavy metals are environmental contaminants with properties known to be toxic for wildlife and humans. Despite strong concerns about their harmful effects, little information is available on intrauterine exposure in humans. The aim of this study was to evaluate prenatal exposure to As, Cd, Cr, Hg, Mn, and Pb and its association with maternal factors in a population-based mother-child cohort in Southern Spain. Between 2000 and 2002, 700 pregnant women were recruited and 137 placentas from the cohort were randomly selected and analyzed for the selected metals by atomic absorption. Maternal sociodemographic and lifestyle factors were obtained by questionnaire after delivery. Bivariate analysis and multivariate linear regression were performed. Cd and Mn concentrations were detected in all placentas, while Cr, Pb, and Hg were found in 98.5%, 35.0%, and 30.7% of samples, respectively. The highest concentrations were observed for Pb (mean: 94.80 ng/g wet weight of placenta), followed by Mn (63.80 ng/g), Cr (63.70 ng/g), Cd (3.45 ng/g), and Hg (0.024 ng/g). Arsenic was not detected in any sample. Gestational age and smoking during pregnancy were associated with placental Cd concentrations, while no factor appeared to influence concentrations of Cr, Hg, Mn, or Pb. In comparison to results of European studies, these concentrations are in a low-intermediate position. Studies are required to investigate the factors contributing to early exposure to heavy metals and to determine how placental transfer of these toxic compounds may affect children's health.

Effect of pregnancy on the levels of urinary metals for females aged 17-39 years old: data from National Health and Nutrition Examination Survey 2003-2010

Data from National Health and Nutrition Examination survey for the years 2003-2010 were used (n = 1565) to evaluate the effect of age, parity, body mass index (BMI), race/ethnicity, pregnancy, iron (Fe) storage status, smoking status, and fish/shellfish consumption on the levels of urine barium (Ba), cadmium (Cd), cesium (Cs), cobalt (Co), molybdenum (Mo), lead (Pb), antimony (Sb), thallium (TI), tungsten (W), uranium (U), and mercury (Hg) for females aged 17-39 yr old. Regression analysis was used to fit models for each of the 11 metals. For Cd, Cs, TI, and Hg, age was positively associated with levels of these metals. Body mass index was negatively associated with levels of Cs, Co, and TI. Levels of Co, Mo, and W increased over the period 2003-2010. Over the same period, levels of Pb, Sb, and Hg declined. Non-Hispanic blacks showed lower levels of almost all metals compared to either Mexican American or other unclassified race/ethnicities. Non-Hispanic whites displayed higher levels than non-Hispanic blacks for 9 of 11 metals. Smokers displayed significantly higher levels of Pb, Sb, W, and U than nonsmokers but significantly lower levels of Cd and Mo than nonsmokers. Pregnancy was found to be associated with higher levels of Ba, Cs, Co, Mo, Pb, W, and Hg compared to nonpregnant females. Levels of Mo, Cs, and Cd declined significantly during the pregnancy period but levels of Co rose during the same period.

Effect of pregnancy on the levels of blood cadmium, lead, and mercury for females aged 17-39 years old: data from National Health and Nutrition Examination Survey 2003-2010

Data from the National Health and Nutrition Examination survey for the years 2003-2010 were used (n = 4700) to evaluate the effect of age, parity, body mass index (BMI), race/ethnicity, pregnancy, iron (Fe) storage status, smoking status, and fish/shellfish consumption on the levels of blood cadmium (Cd), lead (Pb), and total mercury (Hg)for females aged 17-39 years old. Regression analysis was used to fit models for each of the three metals. For all three metals, age was positively and BMI was negatively associated with levels of these metals in blood. Smokers had statistically significantly higher levels of Cd and Pb irrespective of race/ethnicity and Fe storage status as compared to nonsmokers. Novel to this study, pregnancy was found to be associated with significantly lower levels of Cd, Pb, and Hg irrespective of race/ethnicity and Fe storage status as compared to nonpregnant females. It is conceivable that pregnancy may thus accelerate clearance of these metals from blood. Fish/shellfish consumption was associated with higher levels of Hg but not with Cd levels.

Placental and fetal disposition of mercuric ions in rats exposed to methylmercury: role of Mrp2

Methylmercury is a prevalent environmental toxicant that can have deleterious effects on a developing fetus. Previous studies indicate that the multidrug resistance-associated protein 2 (Mrp2) is involved in renal and hepatic export of mercuric ions. Therefore, we hypothesize that Mrp2 is also involved in export of mercuric ions from placental trophoblasts and fetal tissues. To test this hypothesis, we assessed the disposition of mercuric ions in pregnant Wistar and TR(-) (Mrp2-deficient) rats exposed to a single dose of methylmercury. The amount of mercury in renal tissues (cortex and outer stripe of outer medulla), liver, blood, amniotic fluid, uterus, placentas and fetuses was significantly greater in TR(-) rats than in Wistar rats. Urinary and fecal elimination of mercury was greater in Wistar dams than in TR(-) dams. Thus, our findings suggest that Mrp2 may be involved in the export of mercuric ions from maternal and fetal organs following exposure to methylmercury.

Circulating metals and persistent organic pollutant concentrations in Canadian and non-Canadian born primiparous women from five Canadian centres: results of a pilot biomonitoring study

The developing foetus is thought to be at increased risk from exposure to environmental contaminants; however, developmental exposure data is notably lacking for many contaminants. Moreover, potential regional differences or effect of place of birth on residue levels measured in pregnant women is also unknown. Therefore, as part of a multinational biomonitoring study, 125 primiparous pregnant Canadian women were recruited from five Canadian centres (Vancouver, Calgary, Hamilton, Ottawa, and Halifax). Metals in whole blood and persistent organic pollutants (POPs) in plasma were measured by inductively coupled plasma mass spectrometry (ICPMS) and gas chromatography-mass spectrometry (GCMS), respectively. Of the 125 women recruited to this study, complete data sets were available for 123 of which 103 were Canadian born. Data were analysed by analysis of covariance and linear mixed models using age and body mass index as covariates. The metals cadmium (Cd), cobalt (Co), lead (Pb), nickel (Ni), selenium (Se), and total mercury (Hg) were detected in more than 93% of the samples tested. β-Hexachlorohexane (β-HCH), oxychlordane, trans-nonachlor, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE), polybrominated diphenyl ether (PBDE) congeners (PBDE-153, PBDE-47), polychlorinated biphenyl (PCB) congeners (PCB-138, -153, and -180), and the dioxin-like PCB congener PCB-118 were quantified in greater than 70% of the samples tested. Significant differences in the concentrations of Cd, Ni, PCB-153, and p,p'-DDE were found between the centres studied. Furthermore, foreign-born pregnant women had significantly higher concentrations of Cd, β-HCH, PBDE-47, PCB-138, -153, -180, and p,p'-DDE compared to Canadian born pregnant women. Taken together, the data suggest that there are potential regional differences in contaminant body burden and place of birth may also contribute to differences in maternal residue concentrations.

Mercury, cadmium, and lead levels in human placenta: a systematic review

BACKGROUND

Placental tissue may furnish information on the exposure of both mother and fetus. Mercury (Hg), cadmium (Cd), and lead (Pb) are toxicants of interest in pregnancy because they are associated with alterations in child development.

OBJECTIVES

The aim of this study was to summarize the available information regarding total Hg, Cd, and Pb levels in human placenta and possible related factors.

METHODS

We performed a systematic search of PubMed/MEDLINE, EMBASE, Lilacs, OSH, and Web of Science for original papers on total Hg, Cd, or Pb levels in human placenta that were published in English or Spanish (1976-2011). Data on study design, population characteristics, collection and analysis of placenta specimens, and main results were extracted using a standardized form.

RESULTS

We found a total of 79 papers (73 different studies). Hg, Cd, and Pb levels were reported in 24, 46, and 46 studies, respectively. Most studies included small convenience samples of healthy pregnant women. Studies were heterogeneous regarding populations selected, processing of specimens, and presentation of results. Hg concentrations > 50 ng/g were found in China (Shanghai), Japan, and the Faroe Islands. Cd levels ranged from 1.2 ng/g to 53 ng/g and were highest in the United States, Japan, and Eastern Europe. Pb showed the greatest variability, with levels ranging from 1.18 ng/g in China (Shanghai) to 500 ng/g in a polluted area of Poland.

CONCLUSION

The use of the placenta as a biomarker to assess heavy metals exposure is not properly developed because of heterogeneity among the studies. International standardized protocols are needed to enhance comparability and increase the usefulness of this promising tissue in biomonitoring studies.

The potential effect of metallothionein 2A -5A/G single nucleotide polymorphism on blood cadmium, lead, zinc and copper levels

Metallothioneins (MTs) are low molecular weight, cysteine-rich, metal-binding proteins. Because of their rich thiol groups, MTs bind to the biologically essential metals and perform these metals' homeostatic regulations; absorb the heavy metals and assist with their transportation and extraction. The aim of this study was to investigate the association between the metallothionein 2A (MT2A) core promoter region -5 A/G single nucleotide polymorphism (SNP) and Cd, Pb, Zn and Cu levels in the blood samples. MT2A polymorphism was determined by the standard polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique using the 616 blood samples and the genotype frequencies were found as 86.6% homozygote typical (AA), 12.8% heterozygote (AG) and 0.6% homozygote atypical (GG). Metal levels were analyzed by dual atomic absorption spectrophotometer system and the average levels of Cd, Pb, Zn and Cu in the blood samples were 1.69±1.57 ppb, 30.62±14.13 ppb, 0.98±0.49 ppm and 1.04±0.45 ppm, respectively. As a result; highly statistically significant associations were detected between the -5 A/G core promoter region SNP in the MT2A gene and Cd, Pb and Zn levels (p=0.004, p=0.012 and p=0.002, respectively), but no association was found with Cu level (p=0.595). Individuals with the GG genotype had statistically lower Zn level and higher Cd and Pb levels in the blood samples than individuals with AA and AG genotypes. This study suggests that having the GG genotype individuals may be more sensitive for the metal toxicity and they should be more careful about protecting their health against the toxic effects of the heavy metals.