Environmental Engineering Reference
In-Depth Information
the solubility in water, sediment and soil environments (Shcherbina et al.
2007
;
Sekaly et al.
2003
; Lippold and Lippmann-Pipke
2009
). The complexation of
trace metal ions with specific binding sites in fulvic acid can result in confor-
mational folding, thereby changing the outer appearance of the molecule and
affecting its mobility (Chakraborty et al.
2007
). (iv) Toxic metals and radionu-
clides can form complexes with humic substances (fulvic and humic acids) in
natural aquatic ecosystems (Tabak et al.
2005
; Mantoura et al.
1978
; Choppin
1988
; Higgo et al.
1993
; Christensen et al.
1996
; Lenhart et al.
2000
; Freyer
et al.
2009
). These trace metals can subsequently undergo facilitated trans-
port with natural DOM via groundwater into the biosphere. As an alternative,
they can remain in waters under both oxic and anoxic conditions by forming
various soluble complexes with DOM (Francis and Dodge
2008
; Fletcher et
al.
2010
; Kim and Czerwinski
1996
; Kim et al.
1994
; McCarthy et al.
1998
;
Bernier-Latmani et al.
2010
; Freyer et al.
2009
; Artinger et al.
1998
; Schussler
et al.
2001
; Ranville et al.
2007
). These results suggest that the complexation
of DOM with toxic metals, actinides and radionuclides may affect mobility,
toxicity and fate of these elements in the contaminated subsurface environ-
ments. (v) Due to the steady-state existence of DOM as M-DOM complexes
in natural waters, DOM itself may substantially enhance the production of
H
2
O
2
by rapid charge transfer, excited-state electron transfer or intramolecu-
lar energy transfer in natural waters (Mostofa and Sakugawa
2009
; Fujiwara
et al.
1993
; Dalrymple et al.
2010
). The H
2
O
2
upon irradiation of river DOM
is substantially increased (from 15 to 368 nM h
−
1
) with increasing salinity at
circumneutral pH values (Osburn et al.
2009
). Therefore, M-DOM complexa-
tion plays a significant role in the initiation of photoinduced processes in natu-
ral waters. (vi) The M-DOM complexes are highly susceptible to inducing the
photo-Fenton reaction, in the presence of the H
2
O
2
produced photolytically in
surface waters. Such a process is a potential pathway to produce the hydroxyl
radical (HO
•
) (Mostofa and Sakugawa
2009
; Fujiwara et al.
1993
; Zepp et al.
1992
; Vermilyea and Voelker
2009
). The photo-Fenton reaction for iron can be
depicted as follows (Zepp et al.
1992
):
H
→
FE
3
+
+
HO
•
+
OH
−
FE
2
+
+
H
2
O
2
(6.1)
Fe
3
+
+
h
ν/
H
2
O
•
/
O
−•
→
Fe
2
+
+
O
2
+
H
+
↓
(6.2)
2
Recycling of reaction 6. 1
Therefore, the M-DOM complexation can regulate the photoinduced degrada-
tion processes of DOM and other solutes in natural waters. (vii) Production of
pure chemicals in petrochemical industry for extraction, separation and recy-
cling of metals from aqueous and organic phases, where the M-DOM complexes
are selectively dissolved (Mostofa et al.
2011
; Bhattacharyya et al.
2010
). (viii)
Metal-organic ligand complexes are less bioavailable than metals and thus
are less toxic to a variety of aquatic species (Koukal et al.
2003
; Knezovich
