Environmental Engineering Reference
In-Depth Information
The conditional stability constants for the complexation of hydrophobic or hydro-
philic fractions of DOM or autochthonous DOM with metal ions are 7.8-9.6 (log
10
K
1
) for Zn
2
+
-DOM; 8.92-16.3 (log
10
K
1
) and 6.87-12.9 (log
10
K
2
) for Cu
2
+
-DOM;
11.6-31.0 (log
10
K
1
) and 10.5-11.2 (log
10
K
2
) for Hg
2
+
-DOM in lakes, estuaries and
oceans (Table
1
) (Haitzer et al.
2002
; Xue and Sigg
1993
; Xue et al.
1995
; van Den
Berg et al.
1987
; Sunda and Huntsman
1991
; Sunda and Hanson
1987
; Sunda and
Ferguson
1983
; Moffett et al.
1990
; Coale and Bruland
1988
,
1990
; van Den Berg
1984
; Midorikawa and Tanoue
1996
; Benoit et al.
2001
; Drexel et al.
2002
; Gasper
et al.
2007
; Hsu and Sedlak
2003
; Sander et al.
2005
; Shank et al.
2006
). It has been
shown that the conditional stability constants between autochthonous DOM of phyto-
plankton or algal origin and Cu
2
+
are much higher (log
10
K
1
=
13.9-15.6 and log
10
K
2
=
11.8-13.4) in lakes, and they are similar to those of organic ligands of phyto-
plankton or biological sources (11.1-13.2 and 9.2-10.2, respectively) in estuaries
and seawater compared to those of allochthonous fulvic and humic acids (Table
1
)
(Xue and Sigg
1993
; Xue et al.
1995
; van Den Berg et al.
1987
; Moffett et al.
1990
;
Coale and Bruland
1988
; Coale and Bruland
1990
; Sunda
1988
). Surface water from
the Irish Sea and the Atlantic Ocean contains ligand concentrations of 1.7
×
10
−
7
and 1.1
×
10
−
7
M, with conditional stability constants (log
10
K
) of 9.84
±
0.13 and
9.86
±
0.23, respectively, at pH 8.0 (van Den Berg
1982
).
The conditional stability constants of the Hg
2
+
-DOM complexation are
significantly higher for the hydrophobic fraction of DOM or DOM in natural
surface waters (Table
1
) (Haitzer et al.
2002
,
2003
; Benoit et al.
2001
; Drexel et al.
2002
; Gasper et al.
2007
; Hsu and Sedlak
2003
; Ravichandran et al.
1998
;
1999
;
Lamborg et al.
2003
,
2004
; Waples et al.
2005
). The high affinity of the Hg
2
+
-
DOM complexation is responsible for the reduced S-containing binding sites (thiol
and disulfide/disulfane functional groups) bound in DOM, presumably autochtho-
nously produced in natural waters (Haitzer et al.
2002
; Benoit et al.
2001
; Gasper
et al.
2007
; Dyrssen and Wedborg
1986
; Schuster
1991
; Guentzel et al.
1996
;
Wallschlager et al.
1996
; Xia et al.
1999
). The possible complexation reaction
can be written as [Hg
2
+
+
R-SH
n
−
=
HgR-S
(n
−
1)
−
+
H
+
] (Benoit et al.
2001
;
Dyrssen and Wedborg
1991
).
The conditional stability constants for the complexation of the two major binding
sites of tryptophan with metal ions are 4.88-4.90 (log
10
K
1
) for Cu
2
+
-tryptophan;
7.82-9.56 for Cu
2
+
-tryptophan; and 4.99-5.33 for Hg
2
+
-tryptophan for peak T at
Ex/Em
=
275-285/330-360 nm in aqueous solution (Table
1
) (Fu et al.
2007
; Hays
et al.
2004
; Wu and Tanoue
2001b
).
The conditional stability constants (log
10
K
1
and log
10
K
2
) for the complex-
ation of two major binding sites of EPS with metal ions are 3.98-4.12 (log
10
K
1
) and 4.28-4.48 (log
10
K
2
) for Hg
2
+
-EPS; 0.45-4.9 (log
10
K
1
) and 3.2-4.6
(log
10
K
2
) for Pb
2
+
-EPS; 1.54-3.5 (log
10
K
1
) and 2.7-3.8 (log
10
K
2
) for Cd
2
+
-
EPS; 3.0-4.4 (log
10
K
1
) for Cu
2
+
-EPS; and 2.6-3.0 (log
10
K
1
) for Ni
2
+
-EPS
in aqueous solution (Table
1
) (Zhang et al.
2010
; Guibaud et al.
2004
,
2006
;
Comte et al.
2006
). The conditional stability constants of Hg
2
+
-EPS com-
plexes are relatively low (3.98-4.12: log
10
K
1
) at peak T (Ex/Em
=
275-
280/328-334 nm) compared to those (4.28-4.48: log
10
K
2
) at peak T
UV
(Ex/
