Eur J Pediatr. 1994 Aug;153(8):607-10.
Mercury burden of human fetal and infant tissues.
Drasch G, Schupp I, Höfl H, Reinke R, Roider G.
Source: Institut für Rechtsmedizin, München, Germany.
The total mercury concentrations in the liver (Hg-L), the kidney cortex (Hg-K) and the cerebral cortex (Hg-C) of 108 children aged 1 day-5 years, and the Hg-K and Hg-L of 46 fetuses were determined. As far as possible, the mothers were interviewed and their dental status was recorded.
The results were compared to mercury concentrations in the tissues of adults from the same geographical area. The Hg-K (n = 38) and Hg-L (n = 40) of fetuses and Hg-K (n = 35) and Hg-C (n = 35) of older infants (11-50 weeks of life) correlated significantly with the number of dental amalgam fillings of the mother.
The toxicological relevance of the unexpected high Hg-K of older infants from mothers with higher numbers of dental amalgam fillings is discussed.
Future discussion on the pros and cons of dental amalgam should not be limited to adults or children with their own amalgam fillings, but also include fetal exposure.
The unrestricted application of amalgam for dental restorations in women before and during the child-bearing age should be reconsidered.
The mercury concentration in different tissues of fetuses and infants has been rarely studied and has never been related to maternal amalgam fillings. Suzuki et al.  reported the mercury concentrations in five brain and four liver specimens of fetuses and Markesbery et a1.  in two fetal, one term and three infant brains. Their results lie within the same range of concentrations that we found.
Table 2 Comparison (MannWhitney-Tsst) of the mercury concentrations (ng Hg/g, medians) in tissues of human fetuses and older infants (age: 11—50 Weeks) from mothers with either O-2 or 10 or more teeth with amalgam fillings to ageqnatched adults (age: 16-45 years) with the same number of amalgam fillings as the mothers [5, 19]
Data from earlier investigations [15, l6] are less reliable due to the limitations of analytical methods at that time. Exposure of pregnant guinea pigs to mercury vapour [25, 26] or pregnant ewes to amalgam fillings (containing radioactive  resulted in an increase of the mercury concentrations of the fetuses and the newborn. The placental transfer of mercury from the mother to the fetus depends on the maternal mercury burden [7, 10, 12, 21]. Sinee the number of dental amalgam fillings is significantly related to the mercury concentration in the maternal tissues 01° animals  and humans  the number of matemal amalgam fillings should also influence the mercury concentration in human fetal tissues. We Were able to confirm this relationship with respect to the fetal liver and kidney. The avidity of maternal kidneys for mercury documented in Table 2 can he explained by the storage function of the maternal kidney for mercury. It can be assumed that the "mobile" mercury, available for a transfer through the placenta, derives predominantly from the maternal liver (and comparable compartments) and not from the maternal kidney. Moreover, the fetal liver seems te trap the transferred mercury to some extent [8, 12, 25, 26] and thus prevents a higher accumulation in the fetal kidney. The present findings in humans compare favourably with similar results reported earlier in sheep .
The mercury concentrations in the tissues of newborns and young infants were not Well correlated with the number of maternal teeth with amalgam fillings. This may be explained by a superposition of the initial influence of the maternal dental amalgam on the mercury concentration in the infant tissues during pregnancy by a redistribution of mercury from the infant liver to the infant kidney and other tissues in the first months of life and a simultaneous new intake of mercury in this transient period of life [12, 26].
Maternal amalgam fillings appears to influence the Hg-C in older infants approximately as much as they influence Hg-C in adults. The influence on the Hg-K in older infants is approximately half so great as that of own fillings of adults (see Table 2).
Most of the babies under investigation were not nursed or nursed only for a few Weeks. Hence it follows that the higher Hg-K and Hg-C of offspring from mothers with amalgam fillings is due at least partly to an exposure derived in utero and not from breastmilk. If and to what extent nursing by mothers with multiple amalgam fillings contributes to the mercury burden of the baby should be further investigated. Dental amalgam mercury does concentrate in sheep milk , however, Klemann et al.  found no statistically significant correlation between the mercury concentration in human breastmilk and the num~ ber of amalgam fillings of the mothers.
At the present time, the toxicity of mercury vapour from dental amalgarns is being assessed through a variety of investigations [I]; however, the toxicological consequence of the relatively high mercury concentrations in the renal cortex of infants, as found in the present study, has not been determined. In contrast to the Well-known vulnerability of the developing brain to an exposure to mercury vapour (most of the mercury from dental amalgam is released in this form) or methyl-mercury, there are the other hand, current evidence suggests that the nephrotic syndrome following absorption of mercury compounds results from an immunotoxic response . Amalgam mercury has also been shown to alter several indices of kidney function in sheep . Possible differences in the binding form of the mercury in the kidney of fetuses, infants and adults, e. g. to metallothionein or selenium, are presently not known [4, 17, 18].
The present findings clearly demonstrate that further discussion on the pros and cons of dental amalgam should not be focused exclusively on adults or children with their own amalgam fillings [3, 27], but also on the offspring.
From our results it can be concluded that infants can accumulate mercury, apparently derived from maternal amalgam fillings, in their kidneys to a similar extent as older children or adults do from their own fillings. Therefore the unrestricted application of amalgam for dental restorations in Women before and during the child-bearing age should be reconsidered in analogy to the recommendation of the German Health Authorities from 1992 , which argued that because of a higher vulnerability of infants to mercury, amalgam cannot be further recommended for dental restorations for children up to 6 years and notably not during the first 3 years of life. At the very least, high numbers of amalgam fillings should be avoided for women before and during child-bearing age. In 1991, the WHO confirmed an earlier statement from 1980: "The exposure of Women of child-bearing age to mercury vapour should be as low as possible" .