Oxidative stress and DNA damage status in couples undergoing in vitro fertilization treatment.

This study examined the status of oxidative stress in 599 couples undertaking in vitro fertilization (IVF) treatment and its association with reproductive hormones, smoking, and outcomes. Oxidative stress biomarkers such as malondialdehyde, 8-hydroxy-2-deoxyguanosine, hydrogen peroxide (H2O2), catalase (CAT), and total antioxidant capacity (TAC) were determined in follicular fluid and seminal plasma. Tail moment (TM) was used to evaluate DNA damage in the sperm and granulosa cells. Reproductive hormones in serum and cotinine (COT) in urine, follicular fluid, and seminal plasma samples were determined. Separate multivariate linear regression was used to assess associations between levels of each oxidative stress biomarker and each hormone and smoking parameter (modeled as natural log-transformed). The findings indicate that some oxidative stress and DNA damage biomarkers played a role in disrupting certain reproductive hormones in women and their male partners either by overproducing reactive oxygen species or reducing antioxidant defense capacity. Although women were nonsmokers, COT levels > 50 and 10 µg/L in urine and follicular were observed in 5.7 and 1.7%, respectively. Levels of follicular fluid COT were positively associated with H2O2 and TM. We used log-binomial multivariate regression to estimate relative risks for the association between oxidative stress/DNA damage and IVF binary outcomes (fertilization rate > 50%, biochemical pregnancy, clinical pregnancy, and live birth). An increase in the CAT levels of follicular fluid was associated with a 48 and 41% decrease in the risk of poor fertilization rate (≤50%) and unsuccessful live birth, respectively. After the models were adjusted for hormonal factors, the associations remained the same, except that the elevated TAC in follicular fluid became significantly associated with a decrease of 42% in the risk of poor fertilization rate (≤50%). The higher antioxidant activity (CAT and TAC) in follicular fluid might positively impact specific IVF outcomes. LAY SUMMARY: Oxidative stress occurs when antioxidant molecules are insufficient in the body to destroy free radicals that can damage the cells, proteins and DNA, causing different health conditions, including infertility. The role of oxidative stress in female infertility has not received as much attention as male infertility, and research is still limited. This study explored whether the overproduction of free radicals can impact the success of in vitro fertilization (IVF) treatment using several biological markers such as hydrogen peroxide, catalase, and total antioxidant capacity. Our findings revealed that the high antioxidant levels in the fluid surrounding the egg were linked with a high fertilization rate. Additionally, oxidative stress status in couples was associated negatively with several reproductive hormones and smoking status. Biomarkers of oxidative stress and DNA damage might have potential applications in evaluating IVF patients' clinical characteristics such as causes of infertility, hormonal profile, fertilization rate, implantation and live birth.

Effects of early and recent mercury and lead exposure on the neurodevelopment of children with elevated mercury and/or developmental delays during lactation: A follow-up study.

This follow-up study of 82 children investigated the potential impact of early and recent exposure to mercury and lead on their neurodevelopmental performance at 5-8 years of age (2017-2018). Early exposure of these children to mercury, methylmercury, and lead was assessed during lactation at 3-12 months old, as well as their mother's exposure using measurements from a cross-sectional study (2011-2013). Only infants who failed to pass the neurodevelopment screening tools and/or had elevated mercury were included in this study. Urine and hair were sampled during the follow-up study to assess the children's recent exposure to mercury, methylmercury, and lead. Their cognitive performance and visual-motor integration were also measured using the Test of Non-Verbal Intelligence (TONI) and the Beery-Visual-Motor Integration (Beery VMI), respectively. The association between alterations in urinary porphyrins excretion and exposure to metals was analyzed and their influence on the children's neurodevelopment was explored. Linear regression models revealed a significant negative association between the infants' mercury exposure during lactation and the TONI Quotient (ß = -0.298, 95%CI = -4.677, -0.414) and Beery VMI Age Equivalent scores at age 5-8 (ß = -0.437, 95%CI = -6.383, -1.844). The mothers' blood methylmercury was inversely and significantly associated with their children's TONI Quotient (ß = -0.231, 95%CI = -8.184, -0.331). In contrast, the children's Beery VMI Age Equivalent scores were positively and significantly associated with the hair methylmercury of the mothers (ß = 0.214, 95%CI = 0.088, 3.899) and their infants (ß = 0.256, 95%CI = 0.396, 4.488). These relationships suggest the presence of negative confounding that we did not take into account. Unlike mercury, there was some evidence that lead in breast milk had an inverse relationship with the children's visual-motor coordination skills. Our study did not show a clear association between children's recent exposure to metals and neurodevelopment. However, a significant inverse association was observed between the TONI Quotient and the interaction of hair methylmercury × ∑porphyrins (ß = -0.224, 95%CI = -0.86, -0.049), implying that porphyrins are a sensitive measure of low body-mercury burden. Although lead induced higher ∑porphyrins excretion in urine (ß = 0.347, 95%CI = 0.107, 0.525), their interaction did not influence children's neurodevelopmental scores. The interactions between metals and porphyrins might provide insights into their potential contributory role in the pathogenesis associated with neurological disorders or other diseases. Despite the small sample size of the present study, its findings about the association between toxic metal exposure and the high risk of poor neurodevelopmental performance are worrying, particularly at an early age, and additional research is needed using larger sample sizes.

The extent and predictors of phthalate exposure among couples undergoing in vitro fertilization treatment.

Phthalates are chemicals used as plasticizers and solvents in many consumer products but are suspected of disrupting the endocrine system and are known for their reproductive/developmental health risks. This study examined the extent and predictors of phthalate exposure among 599 couples undergoing in vitro fertilization. A questionnaire was administered to obtain sociodemographic, health, and lifestyle data, and two spot urine samples were collected from the couples to analyze eight phthalate metabolites, cotinine (COT) as a smoking index, and creatinine to adjust for urine dilution. Seven phthalate metabolites were detected in > 94% of the urine samples, and monobenzyl phthalate (MBzP) was found in 24% of the women and 26% of their male partners. Median phthalate levels were highest for monoethyl phthalate (MEP), at 333.26 µg/l in women and 290 µg/l in male partners, and lowest for MBzP, at 1.17 µg/l in women and 1.14 µg/l in male partners. Correlation coefficients of ≥ 0.4 between the women and their male partners for the eight urinary phthalate metabolites may indicate a shared source of exposure. A multivariate regression model was used to assess the association between predictors and each urinary phthalate metabolite. Several potential predictors for the variations in specific urinary phthalate metabolites were identified, including the body mass index, age, socioeconomic status, and regional distribution for both women and their male partners but with slightly different patterns. Women with a history of breastfeeding, using bottled water for cooking and storing food in plastic bags had lower MEP (8.7%), mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP) (9.2%), and both mono-iso-butyl phthalate and MECPP (8.2 and 8.1%). A history of contraceptive use was associated with an increase in MECPP (8.7%), mono-(2-ethyl-5-hydroxyhexyl) phthalate (11.4%), mono-(2-ethyl-5-oxohexyl) phthalate (7.6%), and the molar sum of bis (2-ethylhexyl) phthalate metabolites (8.9%). Urinary COT levels were associated with an increase of 10-16% in all urinary metabolites in women but of only 10.5% in mono-(2-ethylhexyl) phthalate in male partners. More than 95% of the couples reported the use of cosmetics, perfumes, and personal-care products, but we were not able to find associations with urinary phthalate metabolites, perhaps due to their short half-lives. MEP levels associated with the use of household cleaning products were 11.2% higher in male partners. Our levels were generally higher than those reported elsewhere, perhaps due to different lifestyles, cultural practices, dietary habits, use of personal-care products, and governmental legislation.

Couples exposure to phthalates and its influence on in vitro fertilization outcomes.

This prospective study examined the associations between the levels of eight urinary phthalate metabolites in 599 couples and in vitro fertilization (IVF) outcomes. We used log-binomial multivariate regression to estimate relative risks (RR) for the association between phthalate concentration and IVF binary outcomes (fertilization rate >50%, biochemical pregnancy, clinical pregnancy and live birth) for each woman after adjusting the model for the concentration in a male partner and each relevant confounders. RR was expressed per unit increase in log-transformed urinary metabolite concentration. The percentage of bis-2-ethylhexyl phthalate (DEHP) metabolites excreted as mono-2-ethylhexyl phthalate (MEHP) was calculated as %MEHP. Urinary MEHP in women was associated with an increased risk of biochemical pregnancy (RR = 1.35; p = 0.04), failed clinical pregnancy (RR = 1.56; p = 0.006) and live birth (RR = 1.54; p = 0.011). An increase in monoethyl phthalate was associated with a high risk of failed clinical pregnancy (RR = 1.25; p = 0.03) and live birth (RR = 1.35; p = 0.006). An increase in %MEHP was associated with an increase in the risk of biochemical pregnancy (RR = 1.55; p = 0.05), failed clinical pregnancy (RR = 1.73; p = 0.02) and live birth (RR = 1.65; p = 0.046). Our results demonstrated that exposure to some phthalates may adversely affect IVF outcomes, particularly when couples' exposure was jointly modeled, emphasizing the importance of a couple-based approach in assessing fertility outcomes. The associations between IVF outcomes and DEHP metabolites were stronger in women whose %MEHP was >75th percentile which may be due to their less efficient metabolism and excretion of DEHP and/or MEHP.

The relationships between urinary phthalate metabolites, reproductive hormones and semen parameters in men attending in vitro fertilization clinic.

Evidence from previous studies has shown that phthalates may play a role in male reproductive function; however, results are still inconclusive, and the mechanism remains unclear. In this study, we first assessed whether exposure to phthalates is associated with altered reproductive hormones and semen parameters in 599 men attending an in vitro fertilization clinic. Secondly, we evaluated whether reproductive hormones could play a mediating role in the association between phthalates and sperm parameters. Eight phthalate metabolites were measured in two different spot urine samples: mono­n­butyl phthalate, mono-isobutyl phthalate (MiBP), monoethyl phthalate (MEP), monobenzyl phthalate, and four oxidative metabolites of di­(2­ethylhexyl) phthalate (DEHP) [i.e., mono­(2­ethylhexyl) phthalate (MEHP), mono­(2­ethyl­5­hydroxyhexyl) phthalate (MEHHP), mono­(2­ethyl­5­oxohexyl) phthalate (MEOHP), and mono­(2­ethyl­5­carboxypentyl) phthalate (MECPP)]. Semen parameters (concentration, volume, motility, and morphology) and reproductive hormones, i.e., follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid-stimulating hormone, estradiol (E2), testosterone (TEST) and prolactin (PROL) were also determined and considered the main study outcomes. Separate multivariate linear regression was used to assess associations between levels of each urinary phthalate metabolite, molar sum of DEHP metabolites (∑DEHP), percentage of MEHP to ∑DEHP (%MEHP), and each outcome (natural log-transformed). Inverse associations were observed between TEST and MiBP (ß = -0.099), FSH and MEHHP (ß = -0.087), and PROL and MEOHP (ß = -0.102), while a positive relationship was seen between E2 and MEP (ß = 0.098). %MEHP was associated positively with FSH (ß = 0.118) and LH (ß = 0.099), but negatively with TEST/LH (ß = -0.086) and TEST/E2 (ß = -0.109). Sperm concentration was associated positively with MECPP (ß = 0.131), MEHHP (ß = 0.117), MEOHP (ß = 0.107) and ∑DEHP (ß = 0.111), but negatively with %MEHP (ß = -0.135). All p-values were <0.05. Sobel's test indicated that FSH mediated significantly up to 60% of the positive relationship between sperm concentration and MEHHP, while FSH and LH mediated respectively 15 and 12% of the inverse association between sperm concentration and %MEHP. Further research on this topic is warranted.

Exposure to phthalates in couples undergoing in vitro fertilization treatment and its association with oxidative stress and DNA damage.

This prospective study of 599 couples seeking fertility treatment and who were recruited between 2015 and 2017 was conducted to (a) explore the associations between phthalate exposure and in vitro fertilization (IVF) outcomes; and (b) examine the implication of oxidative stress as a mediator of these. We measured eight phthalate metabolites in two spot urine samples; oxidative stress biomarkers such as malondialdehyde, 8-hydroxy-2-deoxyguanosine, hydrogen peroxide, catalase (CAT), and total antioxidant capacity in follicular fluid and seminal plasma. We also examined DNA damage in sperm and granulosa cells. Couples were exposed to a broad range of phthalate compounds and seven metabolites were detected in over 94% of the urine samples, whereas monobenzyl phthalate was found in only 24% of women and 26% of men. Our results showed high levels of seven urinary phthalate metabolites (except monobenzyl phthalate) and a notable increase in many oxidative stress markers in both follicular fluid and seminal plasma. However, their associations with exposure were rather limited. Multivariate binomial regression modeling showed higher levels of follicular CAT levels reduced the probability of fertilization rate (≤ 50%) [Adjusted relative risk (RRadj) = 0.52, p = 0.005] and unsuccessful live birth (RRadj = 0.592, p = 0.023). We observed a 46% decrease in the probability of clinical pregnancy in association with an elevated percentage of DNA in the tail (RRadj = 0.536, p = 0.04). There was a 32% and 22% increase in the probability of clinical pregnancy and unsuccessful live birth associated with higher levels of mono-(2-ethylhexyl) phthalate (RRadj = 1.32, p = 0.049) and monoethyl phthalate (RRadj = 1.22, p = 0.032) in women, respectively. In contrast, the probability of clinical pregnancy reduced by 20% with higher levels of mono-(2-ethyl-5-carboxypentyl) phthalate (RRadj = 0.797, p = 0.037) and 19.6% with mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) (RRadj = 0.804, p = 0.041) in men. Other oxidative stress biomarkers or urinary phthalate metabolites showed suggestive relationships with certain IVF outcomes. Lastly, our results demonstrated that elevated levels of CAT in follicular fluid might have a positive impact on fertilization rate ≥ 50% and successful live birth. CAT seems to play a potential role in mediating the relationship between the risk of poor fertilization rate and MEOHP and mono-isobutyl phthalate. Additional data are required to understand the clinical implications of oxidative stress and its contribution to the reproductive toxicity of phthalate exposure.

Risk assessment of environmental exposure to heavy metals in mothers and their respective infants.

Exposure to heavy metals can cause renal injury, which has been well documented in occupational exposure. Studies of low exposure in the general population, however, are still scarce, particularly for vulnerable populations such as mothers and young children. This study evaluated exposure to heavy metals, and biomarkers of renal function and oxidative stress in 944 lactating mothers and their infants and investigated the role of the interaction between heavy metals and oxidative stress in altering renal function. Mother and infant urine samples were analyzed to measure mercury (Hg), cadmium (Cd), and lead (Pb) concentrations for determining body-burden exposure; N-acetyl-ß-d-glucosaminidase (NAG), α1-microglobulin (α1-MG), albumin (ALB), and creatinine (Cr) concentrations for determining early renal injury; and 8-hydroxy-2-deoxyguanosine (8-OHdG) and malondialdehyde (MDA) concentrations for determining oxidative stress. The median concentrclearlyations in mothers presented as µg/g Cr (infants as µg/l) for Hg, Cd, and Pb were 0.695 (0.716), 0.322 (0.343), and 3.97 (5.306) respectively. The mothers and their infants had clearly been exposed to heavy metals and had levels higher than the reference values reported for the general populations of USA, Germany, and Canada. Multiple regression analyses clearly demonstrated associations between urinary heavy metals in quartiles and several renal and oxidative biomarkers in mothers and to a lesser extent their infants. ß coefficients for urinary excretions of MDA, 8-OHdG, ALB, α1-MG, NAG, and Cr in mothers were high in the highest quartile of Hg (1.183-51.29µg/g Cr or 1.732-106.95µg/l), Cd (0.565-765.776µg/g Cr or 0.785-1347.0µg/l), and Pb (6.606-83.937µg/g Cr or 9.459-80.826µg/l), except Pb was not associated with ALB. Infants in the highest Pb quartile (9.293-263.098µg/l) had the highest ß coefficients of urinary excretion of MDA, 8-OHdG, ALB, NAG, and Cr. Significant increasing trend in biomarkers across the quartiles of the three metals was seen in both mothers and infants (ptrend <0.001). A receiver operating characteristic analysis supported the predictive abilities of the four renal biomarkers in discriminating between low versus high metal quartiles. The interaction between heavy metals and oxidative stress contributed to the high excretions of renal biomarkers, but the mechanism remains unclear. These findings add to the limited evidence that low exposure to heavy metals in the general population is associated with alterations in renal function that could eventually progress to renal damage if exposure continues and that children are more susceptible due to the immaturity of their body organs.

Evaluating the potential genotoxicity of phthalates esters (PAEs) in perfumes using in vitro assays.

We previously reported high levels of phthalate esters (PAEs) added as solvents or fixatives in 47 brands of perfumes. Diethyl phthalate was the most abundant compound (0.232-23,649 ppm), and 83.3% of the perfumes had levels >1 ppm, the threshold limit cited by a Greenpeace investigation. All samples had dimethyl phthalate levels higher than its threshold limit of 0.1 ppm, and 88, 38, and 7% of the perfumes had benzyl butyl phthalate, di(2-ethylhexyl) phthalate, and dibutyl phthalate levels, respectively, above their threshold limits. The role of PAEs as endocrine disruptors has been well documented, but their effect on genotoxic behavior has received little attention. We used in vitro single-cell gel electrophoresis (comet) and micronucleus (MN) assays with human lymphoblastoid TK6 cells to evaluate the genotoxic potency of 42 of the same perfumes and to determine its association with PAEs. All perfumes induced more DNA damage than a negative control (NEG), ≥ 90% of the samples caused more damage than cells treated with the vehicles possibly used in perfume's preparations such as methanol (ME) and ethanol (ET), and 11.6% of the perfumes caused more DNA damage than a positive control (hydrogen peroxide). Chromosome breakage expressed as MN frequency was higher in cells treated with 71.4, 64.3, 57.1, and 4.8% of the perfumes than in NEG, cells treated with ME or ET, and another positive control (x-rays), respectively. The genotoxic responses in the comet and MN assays were not correlated. The comet assay indicated that the damage in TK6 cells treated with five PAEs at concentrations of 0.05 and 0.2 ppm either individually or as a mixture did not differ significantly from the damage in cells treated with the perfumes. Unlike the comet assay, the sensitivity of the MN assay to PAEs was weak at both low and high concentrations, and MN frequencies were generally low. This study demonstrates for the first time the possible contribution of PAEs in perfumes to DNA damage and suggests that their use as solvents or fixatives should be regulated. Other ingredients with mutagenic/genotoxic properties, however, may also have contributed to the DNA damage. Future studies should focus on applying a series of assays that use different cellular models with various endpoints to identify the spectrum of genotoxic mechanisms involved.

Alterations in biochemical markers due to mercury (Hg) exposure and its influence on infant's neurodevelopment.

This study examined the role of oxidative stress due to mercury (Hg) exposure on infant's neurodevelopmental performance. A total of 944 healthy Saudi mothers and their respective infants (aged 3-12 months) were recruited from 57 Primary Health Care Centers in Riyadh City. Total mercury (Hg) was measured in mothers and infants urine and hair samples, as well as mother's blood and breast milk. Methylmercury (MeHg) was determined in the mothers and infants' hair and mother's blood. Urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), malondialdehyde (MDA), and porphyrins were used to assess oxidative stress. The infant's neurodevelopment was evaluated using Denver Developmental Screening Test II (DDST-II) and Parents' Evaluation of Developmental Status. The median total Hg levels in mother's urine, infant's urine, mother's hair, infant's hair, and mother's blood and breast milk were 0.995µg/l, 0.716µg/l, 0.118µg/g dw, 0.101µg/g dw, 0.635µg/l, and 0.884µg/l respectively. The median MeHg levels in mother's hair, infant's hair, and mother's blood were 0.132µg/g dw, 0.091µg/g dw, and 2.341µg/l respectively. A significant interrelationship between mothers and infants Hg measures in various matrices was noted. This suggests that mother's exposure to different forms of Hg (total and/or MeHg) from various sources contributed significantly to the metal body burden of their respective infants. Even though Hg exposure was low, it induced high oxidative stress in mothers and infants. The influence of multiplicative interaction terms between Hg measures and oxidative stress biomarkers was tested using multiple regression analysis. Significant interactions between the urinary Hg levels in mothers and infants and oxidative stress biomarkers (8-OHdG and MDA) were noted. The MeHg levels in mother-infant hair revealed similar interaction patterns. The p-values for both were below 0.001. These observations suggest that the exposure of our infants to Hg via mothers either during pregnancy and/or neonatal life, promoted oxidative stress that might have played a role in infant neurodevelopmental delays that we reported previously. The results confirmed that the interaction between infant's MeHg in hair and 8-OHdG and MDA levels was significantly associated with a delay in DDST-II performance (ß=-0.188, p=0.028). This finding provides an insight into the potential consequences of Hg-induced oxidative stress to infant's cognitive neurodevelopment for the first time. This observation still needs future studies to be validated. Given the low MeHg levels in our population, these findings are of particular importance.

Mercury (Hg) exposure and its effects on Saudi breastfed infant's neurodevelopment.

This cross-sectional study analyzed mercury (Hg) levels in healthy Saudi mothers and their infants (age 3-12 months) and examined the influence of Hg on the infants' neurodevelopment using screening tools, such as the Denver Developmental Screening Test II (DDST-II) and Parents' Evaluation of Developmental Status (PEDS). A total of 944 mothers and their 944 infants were recruited from 57 Primary Health Care Centers (PHCCs) in Riyadh. The total Hg (THg) levels were measured in the mothers' and infants' urine (UTHg-M and UTHg-I) and hair (HTHg-M and HTHg-I) samples and in the breast milk and mothers' blood. Methylmercury (MeHg) levels were determined in hair samples from the mothers (MeHg-M) and infants (MeHg-I). Only 40.1% of the infants were breast-fed when enrolled, and 59.9% had stopped breastfeeding. Only 1.8% of the mothers and 0.3% of the infants had MeHg levels above the Environmental Proection Agency (EPA) reference dose (1 µg/g), with low medians of 0.132 and 0.091 µg/g dw, respectively, but the MeHg levels were significantly associated with infant DDST-II performance. The levels of corrected UTHg-M for creatinine (Cr), HTHg-M, HTHg-I, and HMeHg-M, however, displayed an association with infant PEDS performance. The medians and percentage of the tested population that exceeded the recommended limits for Hg in urine and hair set by the World Health Organization (5 µg/g Cr) and EPA (1 µg/g) were 0.695 µg/g Cr and 3% UTHg, 0.118 µg/g dw and 4.1% HTHg-M, 0.101 µg/g dw and 2.8% HTHg-I, and 0.132 µg/g dw and 1.8% HMeHg-M. Our study provides evidence of an association between some Hg measures and delays in infant neurodevelopment, despite their low levels and regardless of the infant's breastfeeding status. The results are of potential concern, because delayed psychomotor or mental performance in infants could be an indicator of later neurocognitive development in children, which may persist into adulthood, as shown in other studies. The absence of local standardization of the DDST-II and PEDS screening tools might raise some questions, although the DDST-II has been used in local institutions for a number of years. The development of effective standardized developmental screening tools is necessary to ensure that all children at risk of neurodevelopmental problems early in life are identified so that they can receive appropriate and timely intervention.

The extent of mercury (Hg) exposure among Saudi mothers and their respective infants.

A total of 1016 healthy Saudi mothers and their respective infants (aged 3-12 months) were recruited from 57 Primary Health Care Centers (PHCCs) in Riyadh, Saudi Arabia, to evaluate the extent of mercury (Hg) exposure and predict its sources in the healthy Saudi population. Total Hg levels were measured in maternal urine, breast milk, blood, and hair and in the infants' urine and hair. Only 1.9% of the mothers had urinary Hg (UHg)>10 µg/l, the limit for asymptomatic adults recommended by the World Health Organization, but the median (0.99 µg/l) was higher than in other countries. Also, 49.3% of the mothers had UHg>1 µg/l, the German reference value for adults. Median infant UHg was 0.729 µg/l, and 77 and 93 % of the infants had levels higher than 0.4 and 0.1 µg/l, the reference values of the Centers for Disease Control and Prevention and for Germany, respectively. The median Hg level in breast milk was 0.884 µg/l. Even though 43.2% of the milk samples were above the background level for Hg in human milk (1 µg/l), our results were lower than those reported from other countries. Median maternal total Hg in blood was 0.637 µg/l, and only 0.4 and 6.9% of samples were higher than the Hg reference levels of 5.8 µg/l of the Environmental Protection Agency (EPA) and of 2 µg/l for Germany, respectively. Total Hg levels in hair (HHg) varied widely among mothers and infants, but only 3.9% of the mothers and 2.8% of the infants had HHg>1 µg/g (the EPA reference level). Median HHg values were 0.117 µg/g dry weight in mothers and 0.1 µg/g dry weight in infants; both were lower than in other countries. The Hg levels in mothers and their respective infants were relatively low, but our results were consistent with other studies indicating that dental amalgam fillings and fish consumption were the main predictors of maternal Hg exposure. Among the several biomarkers of Hg exposure, Hg levels in maternal hair and urine were the strongest predictors of infant exposure. The lack of an association between Hg in breast milk and Hg in infant urine and hair suggested that the infants were exposed to Hg predominately during pregnancy rather than during breastfeeding. We expect that our data can serve as a baseline for further biomonitoring and follow-up studies, particularly of the long-term impact of Hg on childhood neurodevelopment.