Environmental Engineering Reference
In-Depth Information
The complexation between DOM and trace elements depends on the nature and
quantity of DOM in natural waters (Sonke and Salters
2006
; Iskrenova-Tchoukova
et al.
2010
; Sanchez-Marin et al.
2010
; Cao et al.
2004
; Kaiser
1998
; Reszat and
Hendry
2007
; Jansen et al.
2003
; Naka et al.
2006
).
Extracted humic acid shows a 65-fold higher affinity for lanthanide metals than
SRFA, which suggests that affinity depends on the sources and nature of fulvic
and humic acids (Sonke and Salters
2006
). Allocthonous fulvic and humic acids
have poly-carboxylic, phenolic (catechol), iminodiacetic and aminocarboxylic
functionalities in their molecular structures; furthermore, the quantity of the func-
tional groups and the aromaticity are significantly varied between them (Malcolm
1985
; Senesi
1990
; Morel and Hering
1993
; Leenheer et al.
1998
; Steelink
2002
;
Sonke and Salters
2006
; Fimmen et al.
2007
). Each SRFA molecule has ~3 car-
boxylic sites available for coordination that can be judged from the carboxyl site
density in SRFA (Sonke and Salters
2006
; Ritchie and Perdue
2003
). The study
of SRFA complexation with the lanthanide series hypothesizes that poly-dentate
carboxylic, phenolic, and N-containing carboxylic binding sites may be involved
under environmental conditions (Sonke and Salters
2006
). Correspondingly,
autochthonous DOM of phytoplankton or algal origin is composed of amino and
sulfidic functional groups, although its exact structure remains unknown (Xue and
Sigg
1993
; Xue et al.
1995
). The conditional stability constants of the M-DOM
complexation are thus significantly variable for different DOM sources, even for
the same metal ion (Table
1
).
DOM in sediment elutriates and sewage-influenced water (i) was enriched by
1.4-1.7 times in DOC; (ii) absorbed and reemitted more light; and (iii) presented
higher Cu complexation capacities than the natural seawater (Sanchez-Marin et al.
2010
)
.
This suggests that differences in DOC and DOM may control the metal tox-
icity in natural waters (Sanchez-Marin et al.
2010
). The total DOC concentrations
decrease slightly when the C/metal ratio is less than 10, particularly for Al
3
+
and
Fe
3
+
. Hydrophilic DOC increases and hydrophobic DOC decreases with increasing
concentrations of polyvalent metal cations in the order Ca
2
+
<Al
3
+
<Fe
3
+
, whilst
Na
+
remains unaltered (Fig.
8
) (Kaiser
1998
). Such an effect is more pronounced
at low DOC concentrations and high pH values (Fig.
8
). This result suggests that
the formation of insoluble M-DOM complexes is susceptible to reduce DOC con-
centrations, whilst soluble metal-DOM complexes may induce an alteration of the
distribution between hydrophilic and hydrophobic DOC in natural waters (Kaiser
1998
). Therefore, the polyvalent cations and their concentrations can considerably
affect the distributions of the DOM fractions and their contents, determined using
XAD-8 resins, particularly at low DOC and high pH (Kaiser
1998
).
The interaction of several elements (Cu, Mn, Mo, Ni, Sr, U, and Zn) with high
dissolved organic carbon (DOC) concentrations (21-143 mg C L
−
1
) showed that
only U and Zn can form complexes with all DOC samples. The in situ associa-
tion constant (
K′
d
) for U decreases with depth in pore waters (Reszat and Hendry
2007
). It is also suggested that minor amounts of U and Zn (less than or equal
to 4 % of total) can form complexes with this DOC under in situ pH condi-
tions. Competitive complexation by other ligands may limit the importance of
