Cadmium human placenta, levels

Epidemiological studies in humans have so far not shown any embryo-toxicity of cadmium. Traces of cadmium have been detected in aborted human material. In contrast to mercury and lead the concentrations of cadmium in human placentae are very high. This is demonstrated by Fig. 8, which was taken from a publication of Roels and coworkers (1978). These data show that the concentration of cadmium in the human placenta is nearly 10-times higher than cadmium concentrations in maternal and fetal blood. In further determinations cadmium concentrations in mother s milk were considerably lower than maternal blood levels. 

Goyer and Cherian (1992) measured cadmium, zinc and copper, and metallothionein content of human placentas from 55 uncomplicated, full-term deliveries. The mothers ages ranged from 22 to 39 years, mean 29 years. All were current nonsmokers, but 16 (30%) acknowledged smoking in the past. None were on medication apart from iron and vitamin supplements. For 43 it was the first delivery, for 9 the second, for 1 the third, and for 2 the fourth. Samples of maternal and fetal blood were not obtained. Metals were measured by atomic absorption spectrophotometry and metallothionein by a silver saturation method (Scheuhammer and Cherian 1986). The results are shown in Table 1. Zinc levels of placentas were almost the same as those in the Kuhnert et al. (1988) study, but copper levels were considerably lower. No other comparable measurements of metallothionein were found in the literature. There is a strongly positive correlation between... 

Umbilical cord blood levels of cadmium tend to be 40%-70% of maternal blood levels, indicating that the placenta provides an incomplete barrier to fetal cadmium exposure. However, one study has shown a positive correlation between maternal blood cadmium levels and placental cadmium concentration. Human infants are born with very low tissue levels of cadmium. 

Experimental studies have shown that cadmium can induce metallothionein synthesis in the placenta, particularly in trophoblasts. Metallothionein in the placenta binds the essential trace metals, zinc and copper. The mechanism whereby essential metals are preferentially transported to the fetus and cadmium retained is not known. Experimental studies have shown that exposure of pregnant animals to high levels of cadmium early in pregnancy is teratogenic. Human studies suggest maternal cadmium exposure may reduce fetal birth weight and that this may be an indirect effect of zinc deprivation that occurs with cadmium exposure. 

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