Environmental Engineering Reference
In-Depth Information
Likewise, TF values of essential elements Cu, Mo, Zn, and nonessential elements
Ag, Au, La, Ba and Cs are not influenced by supplies of other elements. Transporta-
tion of Cu cannot be compared to those of other elements (DaSilva and Williams
2001
), because it usually involves special, Cu-specific proteins (metallochaperons)
in order to avoid toxic effects from the very strong binding of Cu
2+
to a multitude
of ligands. This strong coordination is the probable reason for the highest TF of any
di- or higher valent ion observed with Cu (TF
Cu
= 0.156 d/kg). Molybdenum (Mo) is
taken up and resorbed as molybdate ion by means of the sulfate carrier (Anke and
Angelov
2004
); hence Mo is unlikely to compete with “genuine” cations for their
carriers.
The interaction of an element with itself is particularly interesting because it
bears some information on both homoeostasis and deposition within in-body depots
(e.g., bones). Figure
6.3
shows that several elements absorbed in larger amounts
(Rb, Sr, Ti), which are neither toxicologically relevant nor essential, display a pro-
nounced negative self-correlation (light grey coloured), while, though other authors
postulate homoeostatic regulation for this element, there is no relationship between
supply and TF for example for zinc. Up to now, this can only be noted as a kind
of phenomenon which warrants further explanation, as do the many different in-
terelemental interactions which influence TFs of Ni and Mn. TF values of Ni and
Mn depend on the uptake rates of following elements (cp. the last two columns of
Fig.
6.3
):
TF
Mn
depends on supply of elements: Cu Zn Co Cd La
TF
Ni
depends on supply of elements: Cu Zn Co Cd La Ce Mn Mo Rb
Mn is affected by increasing supplies of Zn, Cu or Cd (pronounced negative cor-
relation in each case); possibly these metals which are known to induce oxidative
stress by radical chain reactions (Huang et al.
1994
) induce oxidation of manganese
to Mn(III), causing stronger retention to transferrin. Cobalt (Co), more than 90 % of
its total not being absorbed as cobalamine (vitamine B
12
) but as Co
2+
aquaion or some
complexes far less stable than cobalamine, does correlate negatively with uptakes
of La and Ce. La and Ce, in turn, are coordinated to transferrine, like some heavier
REEs (Nd, Sm, Yb) Hirano and Suzuki,
1996
), yet not as strongly as trivalent Fe,
Mn or Y do. This strongly suggests a competition for (protein) carrier binding sites.
Figure
6.4
symbolizes the modes of interaction for the two metals distinguished by
lowest TF values, namely, Mn and Mo. Whereas Mn responds to increased allow-
ances of many other elements with a decreased TF (see above), Mo does not do
because it is resorbed as an oxoanion by means of the sulfate carrier (Williams and
Da Silva
1996
) and thus is not perturbed by cation carrier competition.
Mother's milk contains low amounts of Mn and Mo. As both are essential, one
is required for depots built up in the foetus before delivery (Rossipal et al.
2000
)
analyzed blood samples from both arteries and vein of the umbilical cord for con-
tents of Zn, Mo, Mn, Sn, Ca, Mg, Co, Se, and Cu. Taking differences of concentra-
tions of Mn in arteries and vein, the irreversible part of Mn transfer from mater-
nal blood into the fetus-placenta amounted to 0.4 mg/l blood serum (16.2 % of a
primary 2.4 µg/l content); the corresponding value for Mo is 0.12 µg/l (16.7 % of
0.7 µg/l). Considering the fact that these values were measured at the very end of
