Environmental Engineering Reference
In-Depth Information
Em
=
220-230/322-336 nm) in aqueous solution (Zhang et al.
2010
). Note that
the fluorescence properties of EPS are similar to those of tryptophan, with higher
fluorescence intensity at peak T
UV
T-region than at peak T-region and similar Ex/
Em maxima.
The conditional stability constants (log
10
K
) for the complexation of some
standard organic and inorganic ligands with metal ions are identified in aqueous
solution as 3-6 for Cu
2
+
-carboxylic or HO group; 2.8 for Cu
2
+
-amine (NH
2
);
4.4 for Cu
2
+
-ethanol amine; 6.6 for Cu
2
+
-glycine (NH
2
-CH
2
-COOH or NH
3
+
-
CH
2
-COO
−
); 8.5 for Cu
2
+
-ethylene diamine (NH
2
-CH
2
-CH
2
-NH
2
); 7.2 for
Cu
2
+
- aspartic acid [HOOC-CH(NH
2
)-CH
2
-COOH]; 9.4 for Cu
2
+
- iminodi-
aacetic acid (HOOC-CH
2
-NH
2
-CH
2
-COOH); 8.3 for Cu
2
+
- diaminopropanol;
11.4 for Cu
2
+
- ethylenediamine-N-acetic acid; 13.0 for Cu
2
+
-diethylenetriamine;
6.27 and 11.76 for Eu
3
+
-5-sulfosalicylic acid; 6.4 and 11.99 for Cm
3
+
-5-
sulfosalicylic acid; 8.06 and 15.34 for Am
3
+
-5-sulfosalicylic acid; 8.56 and
17.51 for Pu
3
+
-5-sulfosalicylic acid; 59.65 and 14.06 for Th
4
+
- catechol; 48.51
and 64.86 for Th
4
+
-hydroquinone; and 16.98, 46.46, and 59.65 for Th
4
+
- resor-
cinol (Table
1
) (Nair and Chander
1983
; Martin and Prados
1974
; Thakur et al.
2006
; Smith
1974
). The stability constants of various standard organic substances
are similar to those of allochthonous and autochthonous DOM in natural waters,
indicating that carboxylic, phenolic and amino group-containing carboxylic acid
bound in allochthonous and autochthonous DOM may form complexes with
metal ions in aqueous solution.
The binary complexes of Cu
2
+
, Ni
2
+
, Co
2
+
and Zn
2
+
with resorcinol and
some biologically important aliphatic dicarboxylic acids (adipic, succinic,
malic, malonic, maleic, tartaric and oxalic) in aqueous solution at 25 °C and
I
=
0.1 mol dm
−
3
NaNO
3
suggest the following hypotheses (Radalla
2010
): (i)
Stability of the 1:1 binary complexes for all investigated ligands is higher than that
of the corresponding 1:2 ones. (ii) Normal 1:1 and 1:2 complexes of resorcinol are
formed with all of the metal ions studied. (iii) The order of stability constants of
the 1:1 complexes of all investigated ligands with respect to the divalent transition
metal ions follows the Irving-Williams series (Zn < Cu > Ni > Co) (Irving and
Williams
1948
). (iv) Stability of the 1:1 metal-complexes of aliphatic dicarboxylic
acids follows their basicity (p
K
a
1
+
p
K
a
2
), where
K
a
1
and
K
a
2
are the first and sec-
ond dissociation constants, respectively.
Experimental studies show that photoinduced degradation can decrease the
conditional stability constants of M-DOM complexes in stream waters (log
K
1
=
4.9 to 4.1) and in wetland waters (log
K
1
=
8.02 and log
K
2
=
6.1 to
7.61 and 5.85, respectively), whilst their values are increased in river DOM (log
K
1
=
7.59 and log
K
2
=
5.83 to 7.63 and 5.88, respectively) and in lake DOM
(log
K
1
=
16.3 to 16.8). The values remain the same (log
K
1
=
13.5) before
and after irradiation of estuarine waters (Wu et al.
2004a
; Brooks et al.
2007
;
Sander et al.
2005
; Shank et al.
2006
). The decomposition of the functional
groups in DOM is susceptible to decrease the stability constants of the M-DOM
complexes in natural waters. In contrast, the increase in stability constants of
the M-DOM complexes is likely caused by the formation of new photoproducts
