Sakamoto Mineshi, Kubota Machi, Matsumoto Shin-ichiro, Nakano Atsuhiro, Akagi Hirokatsu
Department of Epidemiology, National institute for Minamata Disease, 4058-18 Hama, Minamata, 867-0008, Kumamoto, Japan.
Environ Res. 2002 Nov;90(3):185-9. doi: 10.1016/s0013-9351(02)00011-7.
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.
甲基汞（MeHg）除了在子宫内通过胎盘传递给胎儿外，还可通过乳汁传递给婴儿。众所周知，孕期胎儿体内甲基汞的蓄积量高于母亲，且对毒性更敏感。然而，通过母乳接触汞对婴儿体内甲基汞浓度的影响尚不清楚。本研究的目的是通过检测以母乳喂养的婴儿体内甲基汞水平的变化，基于红细胞汞浓度（RBCs-Hg）评估胎儿期和哺乳期的风险。比较了7对母婴血样在出生时和分娩后3个月时的红细胞汞浓度（RBCs-Hg）和血浆汞浓度（Plasma-Hg）。分娩时及分娩后3个月母亲的红细胞汞与血浆汞比值约为8:1，这表明她们的汞来源是食用鱼类中的甲基汞，这在日本人中很常见。在所有7例中，脐带血中的红细胞汞浓度均高于分娩时母亲的红细胞汞浓度。脐带血红细胞汞浓度的几何平均值（10.6ng/g）约为母亲红细胞汞浓度几何平均值（7.1ng/g）的1.4倍。母亲和脐带血中的红细胞汞浓度存在很强的相关性。然而，所有婴儿在整个哺乳期的汞浓度均呈下降趋势。3个月大婴儿红细胞汞浓度的几何平均值为5.8ng/g，占脐带血红细胞汞浓度的54%。因此，与分娩时的情况相反，母亲的红细胞汞浓度在3个月时超过了婴儿的红细胞汞浓度。哺乳期婴儿红细胞汞浓度的下降可以用母乳中汞的低传递率和出生后婴儿的快速生长来解释。母乳汞浓度的几何平均值较低（0.21ng/g），约为母亲血浆汞浓度的20%。3个月大婴儿的平均体重增加到出生时的约1.9倍。因此，后代在孕期和哺乳期都会接触甲基汞；孕期的风险尤其高，但在哺乳期可能会降低。
