Relationships between trace element concentrations in chorionic tissue of placenta and umbilical cord tissue: potential use as indicators for prenatal exposure.

The role of the placenta was assessed by comparing the profiles of methylmercury (MeHg), inorganic mercury (I-Hg), lead (Pb), cadmium (Cd), selenium (Se), zinc (Zn), and copper (Cu) in freeze-dried chorionic tissue of the placenta and umbilical cord tissue. The significance of the placenta and cord tissue as predictors of prenatal exposure to these trace elements in pregnant women and newborns was also examined by comparing the element profiles among placenta and cord tissue, and maternal and cord blood red blood cells (RBCs). The samples were collected from 48 mother-child pairs at birth in the general population of Japanese. The concentrations of all elements, except for MeHg, were significantly higher in placenta than in cord tissue. In particular, the Cd showed the highest placenta vs. cord tissue ratio (59:1), followed by I-Hg (2.4:1), indicating that the placental barrier works most strongly against Cd among the examined toxic elements. Contrary to the other elements, the MeHg concentration in cord tissue was significantly higher (1.6 times) than that in placenta, indicating its exceptionally high placental transfer. The MeHg in placenta showed significant correlations with total mercury (T-Hg) in maternal and cord RBCs (rs=0.80 and 0.91, respectively). The MeHg in cord tissue also showed significant correlations with T-Hg in maternal and cord RBCs (rs=0.75 and 0.85, respectively). Therefore, both placenta and cord tissue are useful for predicting maternal and fetal exposure to MeHg. The Se concentration in placenta showed significant but moderate correlations with that in maternal and cord RBCs (rs=0.38 and 0.57, respectively). The Pb, Zn, and Cu concentrations in placenta and cord tissue showed no significant correlations with those in maternal and cord RBCs. As an exception, the Cd concentration in placenta showed a moderate but significant correlation (rs=0.41) with that in maternal RBCs, suggesting that the placenta is useful for predicting maternal exposure to Cd during gestation.

Changes in body burden of mercury, lead, arsenic, cadmium and selenium in infants during early lactation in comparison with placental transfer.

The developing brains of both fetuses and infants are susceptible to environmental contaminants. However, the contribution of breast-feeding to the element body burden in infants remains unclear. The main objective of this study was to investigate the changes in body burden of elements such as methylmercury, lead, arsenic, cadmium, and selenium in infants during a 3-month breast-feeding period compared with placental transfer of the elements. Element concentrations were measured in maternal and umbilical cord (fetus) red blood cells (RBCs) at parturition and in infant RBCs at 3 months. Most of the mercury in RBCs is in the methyl form, and the total mercury concentration in RBCs reflects methylmercury exposure. The mercury level in cord RBCs was approximately 1.5 times higher than that in mothers, while in infants, it declined by approximately 60% after 3-months' breast-feeding. The cord selenium level was similar to the maternal level, but declined approximately 75% after 3-months' breast-feeding in infants. Lead and arsenic concentrations in cord RBCs were about 60% of the maternal levels, and remained constant until the 3-month study period. The cadmium level in cord RBCs was about 20% of that in maternal RBCs, and remained almost constant until the end of the 3-month study period. In conclusion, although pregnant women should pay attention to avoid high methylmercury exposure, element exposure through breast-feeding does not pose any great concern in this population.

Mercury and heavy metal profiles of maternal and umbilical cord RBCs in Japanese population.

Mercury (Hg) and other heavy metal profiles, namely, lead (Pb), arsenic (As), cadmium (Cd), and selenium (Se) were investigated in maternal and umbilical cord (cord) red blood cells (RBCs) at parturition in Japanese population. Correlation coefficients of Hg, Pb, As, Cd, and Se between maternal and cord RBCs were 0.91, 0.79, 0.89, 0.31, and 0.76, respectively, and the respective means of cord/maternal RBCs ratios were 1.63, 0.52, 0.62, 0.12, and 1.18. These results indicate that fetal exposure to these metals (excluding Cd) strongly reflected each maternal exposure level. Among these metals, the placental transfer of methylmercury (MeHg) seemed to be extremely high but that of Cd to be limited. Hg showed positive correlations with Se in maternal RBCs but not in cord RBCs, and the Se/Hg molar ratio was lower in the latter, suggesting that the protective effects of Se against MeHg are less expected in fetuses than in mothers.

Changes in mercury concentrations of segmental maternal hair during gestation and their correlations with other biomarkers of fetal exposure to methylmercury in the Japanese population.

Methylmercury (MeHg) is one of the most hazardous substances that affects the fetus through fish consumption. The objective of this study was to evaluate the changes in the level of exposure to MeHg by assessing the mercury (Hg) concentrations of the segmental hair at parturition and 3 months after parturition, and to study their correlations with the total Hg concentrations of maternal and cord red blood cells (RBCs) and neonatal hair as biomarkers of fetal exposure to MeHg at parturition. In total, 40 paired samples of maternal hair from the scalp, maternal and cord RBCs, and 21 samples of neonatal hair from the scalp were collected at parturition. In addition, 19 samples of maternal hair from the scalp were collected at 3 months after parturition. The maternal hair samples were cut into 1cm segments from the scalp end toward the tip. The geometric mean of the Hg concentrations in cord RBCs was approximately 1.6 times higher than that in the maternal RBCs, and a strong correlation coefficient (r=0.91) was found between them. The increase or decrease in the Hg concentrations of the segmental hair during gestation differed largely among individuals. The correlation coefficients between the Hg concentrations of the segmental hair and cord RBCs were the strongest (r=0.90) in the hair segment 1cm from the scalp and decreased gradually with the distance from the scalp. The correlation coefficients between the Hg concentrations of the segmental hair collected at 3 months after parturition and maternal RBCs were over 0.9 in the hair segments 5 and 6 cm from the scalp, suggesting that the time required for the incorporation of Hg from the blood into a growing hair was very short. The geometric mean of Hg concentrations in the neonatal hair at parturition was similar to that in the maternal hair 1cm from the scalp at parturition, and they exhibited a strong correlation (r=0.95). The findings of this study indicate that maternal hair close to the scalp at parturition and neonatal hair are useful biomarkers of fetal exposure to MeHg at parturition. In addition, the segmental maternal hair throughout gestation is essential to obtain important information on MeHg exposure during the different sensitive windows or bolus MeHg exposure during gestation.

Maternal and fetal mercury and n-3 polyunsaturated fatty acids as a risk and benefit of fish consumption to fetus.

Maternal fish consumption brings both risks and benefits to the fetus from the standpoint of methylmercury (MeHg) and n-3 PUFA (polyunsaturated fatty acids). MeHg is one of the most risky substances to come through fish consumption, and mercury concentrations in red blood cells (RBC-Hg) are the best biomarker of MeHg exposure. Docosahexaenoic acid (DHA, C22:6n-3), which is one of the most important fatty acids for normal brain development and function, is also derived from fish consumption. Our objective in this study was to examine the relationships between RBC-Hg and plasma fatty acid composition in mother and fetus at parturition. Venous blood samples were collected from 63 pairs of mothers and fetuses (umbilical cord blood) at delivery. In all cases, fetal RBC-Hg levels were higher than maternal RBC-Hg levels. The geometric mean of fetal RBC-Hg was 13.4 ng/g, which was significantly (p < 0.01) higher than that of maternal RBC-Hg (8.41 ng/g). While the average fetal/maternal RBC-Hg ratio was 1.6, the individual ratios varied from 1.08 to 2.19, suggesting considerable individual differences in MeHg concentrations between maternal and fetal circulations at delivery. A significant correlation was observed between maternal and fetal DHA concentrations (r = 0.37, p < 0.01). Further, a significant correlation was observed between RBC-Hg and plasma DHA in fetus (r = 0.35, p < 0.01). These results confirm that both MeHg and DHA which originated from fish consumption transferred from maternal to fetal circulation and existed in the fetal circulation with a positive correlation. Pregnant women in particular need not give up eating fish to obtain such benefits. However, they would do well to at least consume smaller fish, which contain less MeHg, thereby balancing the risks and benefits from fish comsumption.

Plasma fatty acid profiles in 37 pairs of maternal and umbilical cord blood samples.

OBJECTIVES AND METHODS: In order to study the fatty acid transfer from the mother to fetus, their fatty acid profiles were compared by 37 pairs of maternal and umbilical cord plasma specimens obtained from healthy Japanese women at delivery. RESULTS: The fetal/maternal fatty acid concentration ratios differed among individual fatty acids. The ratios were low for linoleic acid (LN, 0.12±0.04) and linolenic acid (LnN, 0.07±0.05) but high for arachidonic acid (AA, 0.66±0.17) and docosahexaenoic acid (DHA, 0.44±0.13). Significant correlations were observed between the maternal and fetal EPA (r=0.74) and DHA (r=0.40) concentrations. CONCLUSIONS: These results suggest that DHA and AA are preferentially transferred to the fetus. Fetal fatty acid profile reflects the maternal intake of EPA and DHA.

Declining risk of methylmercury exposure to infants during lactation.

Methylmercury (MeHg) can be transferred to infants through milk, in addition to passage through the placenta during intrauterine life. The higher MeHg accumulation and susceptibility to toxicity in the fetus than in the mother during the gestation period is well known. However, the contribution of Hg exposure through breast milk to the MeHg concentration in infants is not clear. Our objective in this study was to examine the changes in MeHg levels in infants who were reared on breast milk to evaluate the risks between fetal and breast-feeding periods based on Hg concentrations in red blood cells (RBCs-Hg). RBCs-Hg and plasma-Hg concentrations (Plasma-Hg) in seven pairs of maternal and infant blood samples were compared at birth and 3 months after parturition. RBCs to Plasma-Hg ratio was approximately 8:1 for mothers at parturition and after 3 months, suggesting that their Hg source is MeHg from consumed fish as is general in Japanese. In all seven cases, RBCs-Hg in the umbilical cords were higher than those in the mothers at parturition. The geometric mean of RBCs-Hg in umbilical cords (10.6ng/g) was about 1.4 times higher than that in the mothers (7.1ng/g). There was a strong correlation in RBCs-Hg in mothers and umbilical cords. However, all the infants showed declines in Hg concentrations throughout the breast-feeding period. The geometric mean RBCs-Hg at 3 months of age was 5.8ng/g, accounting for 54% of that in the umbilical cords. Consequently, maternal RBCs-Hg surpassed that of infants at 3 months, opposite to the situation at parturition. The decline in infant RBCs-Hg during the breast-feeding period can be explained by the low Hg transfer through breast milk and the rapid growth of infants after birth. The geometric mean Milk-Hg was low (0.21ng/g), around 20% of that in maternal Plasma-Hg. The average body weight of infants at 3 months increased to about 1.9 times of that at birth. Thus, offspring are subjected to MeHg exposure through both the gestation and the breast-feeding periods; the risk is especially high during gestation but may decrease during breast-feeding.