Environmental Engineering Reference
In-Depth Information
Fig. 6.4
Influences of administration of other elements on TF values of Mn and Mo which have
the lowest TF values of all the metals investigated. The reduction of TF
Mn
may be due to competi-
tion for cation carrier sites also employed by Zn, Cu, Cd, Co or La. TF
Mo
, on the other hand, is not
influenced by intakes of other elements; presumably because it is transported by a specific carrier
non-responsive to “genuine” cations (Wünschmann
2007
; Wuenschmann et al.
2008
)
pregnancy, that period of time when weight gain of the fetus per day is largest, one
would anticipate the largest possible uptake of metals into whatever the depot is.
Moreover, metabolic activity of the going-to-be mother is increased by some 30 %
as compared to a non-pregnant woman of similar activity patterns. At low physical
activity levels, some 8-10 l of blood per minute are circulated through the body;
accordingly, the state of pregnancy will add some 2.5-3 l/min of blood circulation,
that is, about 4.000 l/day. Because Mn is not given away from the placenta by the
umbilical cord vein at all, some 1.6 mg/day
1
of manganese will remain in the fetus.
For Mo, (Rossipal et al.
2000
) detected a chance of back-transfer, rendering the
calculated uptake of some 0.4-0.5 mg/d just a conservative upper limit. Given the
very small demand even of adults for this ultratrace element (≤ 0.1 mg/d), this value
would be an extremely high uptake. This is to say that depots may be constructed
prenatally for both Mn and Mo. Given that such depots exist indeed, a supply of
either element via milk thereafter would not be required by physiology.
Unlike many other mammals (e.g. ungulates), humans are physiologically very
premature when just born and thus depends on milk nutrition entirely for a longer
period of time. On the other hand, birth weight just about doubles in humans until
breast-feeding is terminated. One can compare this situation with that of marsu-
pial mammals or monotremes (kangaroo, platypus etc.), whose youngsters are very
small when born or hatching at less than 1 g of weight (Grzimek
1965
) thus they
cannot have acquired any relevant amounts of depots before delivery. When milk-
nutrition ends in these mammals, they would grow to (at least) several hundred
1
4.000 l/day additional blood circulation times a carryover of 0.4 mg/l correspond to 1.6 mg/day,
the transfer being irreversible (see above).
