Environmental Engineering Reference
In-Depth Information
constants between Cm
3
+
and 5-sulfosalicylic acid (log
10
K
=
6.44), fulvic acid
(log
10
K
=
5.90), and humic acid (log
10
K
=
6.22) are all very similar, suggest-
ing the salicylic acid-like functional groups may be present in the molecular
structure of humic substances (fulvic and humic acids) (Panak et al.
1995
). This
can be further highlighted by the observation of enhanced fluorescence intensity
in the complexes of Cm
3
+
with 5-sulfosalicylic acid, fulvic acid, and humic acid
(Panak et al.
1995
). The U
4
+
complexation with humic acids with different sul-
fur contents (1.9, 3.9, 6.9 wt %) shows that increasing sulfur (>2 wt %) leads to
an increase of the number of humic acid binding sites. This is also reflected in
increased U
4
+
loading capacities and increased total humic acid ligand concen-
trations for U
4
+
(Sachs et al.
2010
). This increase of the fraction of humic acid
binding sites for U
4
+
indicates an involvement of reduced sulfur functionalities,
such as thiol groups, in the complexation between U
4
+
and humic acid (Sachs
et al.
2010
). However, for environmentally relevant sulfur contents of humic acids
(<2 wt %), compared to the oxygen functionalities and in particular to carboxylic
groups, reduced sulfur functionalities play only a subordinate role in U
4
+
com-
plexation in the acidic pH range. Notes that reduced sulfur species such as thi-
ols, dialkylsulfides and/or disulfides are the dominating sulfur functionalities in
extracted humic acids with different sulfur contents (Sachs et al.
2010
). Therefore,
the functional groups in fulvic and humic acids that form complexes with trace
metals are phenolic OH and acidic OH groups, among which are hydroquinone-
like moieties and non-quinoid phenols, O-, N- and S-containing functional groups
or thiol groups (Lu and Allen
2002
; Schmeide and Bernhard
2009
; Haitzer et al.
2003
; Zhang et al.
2004
; Smith et al.
2002
).
Strong organic ligands for copper (II) in seawater are likely to derive from bio-
logical sources, rather than being refractory organic materials (Wu and Tanoue
2001a
,
b
; Midorikawa and Tanoue
1998
; Moffett et al.
1990
). The exudates from
certain phytoplankton and bacteria, which are important sources of protein-like
fluorescence, are strong Cu chelators (Zhang et al.
2009
; Mcknight and Morel
1980
; Determann et al.
1998
). Autochthonous DOM from phytoplankton or algal
biomass may contain amino and sulfidic functional groups in its molecular struc-
ture, which may form complexes with trace metals in water (Xue and Sigg
1993
;
Xue et al.
1995
).
EEMS of tryptophan amino acid shows two fluorescence peaks: peak T for the
amino carboxylic acid functional group [-CH-(NH
2
)-COOH] and peak T
UV
for
the -NH group in the aromatic functionality [C
8
H
5
(NH)-] (Mostofa et al.
2009a
,
2011
). Interestingly, proteins and oligopeptides are important constituents of high
molecular mass-DOM that contains primary amines in seawater (Lee and Bada
1975
; Tanoue et al.
1996
).
The EPS is primarily composed of polysaccharides, proteins, uronic acid, fatty
acids, nucleic acids and lipids containing ionizable functional groups such as car-
boxyl, phosphoric, amine, acidic amino acids, hydroxyl, phenolic, sulfates, and
organic phosphates (Beech and Sunner
2004
; Quiroz et al.
2006
; Merroun and
Selenska-Pobell
2008
; Zhang et al.
2008
; Wingender et al.
1999
; Liu and Fang
2002
,
2003
; Guibaud et al.
2003
; Merroun et al.
2003
; Sponza
2003
; Guibaud
