No abstract

We determined levels of inorganic mercury (I-Hg) and methylmercury in placentas from 119 Swedish women, not selected with respect to high exposure of mercury. Our objective was to relate placental Hg species with maternal and fetal blood concentrations and to evaluate possible associations with selenium. We performed the analyses using automated alkaline solubilization/reduction and cold-vapor atomic fluorescence spectrophotometry. I-Hg levels in placenta increased with an increasing number of maternal dental amalgam fillings (p < 0.001). Despite placental accumulation (median, 1.3 microg/kg; range, 0.18-6.7 microg/kg wet weight), a substantial fraction of maternal blood I-Hg, probably as Hg(0), reached the fetus. Although MeHg transferred easily to the fetus, it also accumulated in the placenta. On average, 60% of placental Hg was in the form of MeHg. The median concentration was 1.8 microg/kg (range, 0-6.2 microg/kg wet weight), more than twice the maternal blood concentration. We found significant associations between MeHg and selenium in both maternal and umbilical cord blood but not in the placenta. The associations were particularly obvious in freshwater fish consumers, probably reflecting that fish is a source of both MeHg and selenium. We found no correlations between I-Hg and selenium. This study increases the understanding of Hg, in its different forms, in human placenta and how they are related to maternal and fetal exposure.

Mercury in blood samples was speicated from mothers and their infants up to 2 mo after delivery. There were significant correlations between umbilical cord blood and maternal blood for methylmercury (MeHg) and inorganic mercury (I-Hg) levels. The MeHg levels in cord blood were significantly higher than in maternal blood, while I-Hg levels were significantly higher than in maternal blood, while I-Hg levels were about the same. The maternal MeHg and I-Hg levels remained stable during the sampling period, whereas the MeHg concentration in infant blood decreased more than 45% between the 72-h and 2 mo sampling times. The I-Hg levels in infant blood were low at birth, and remained low during the sampling period. The results of the present study do not support I-Hg absorption through milk as a significant source of exposure. However, the number of observations is small, and a larger study is warranted in order to verify the data.