Environmental Engineering Reference
In-Depth Information
groups of DOM that are responsible for complex formation with trace metals are
thus susceptible to alter M-DOM complexation in natural waters.
In addition, accumulation of metals by plants (phytoremediation) can reduce
the toxicity and content of metals (Tabak et al.
2005
; Salt et al.
1995
,
1998
; Raskin
et al.
1997
; Pulford and Watson
2003
; Schwitzguébel et al.
2002
) and, as a conse-
quence, the metal complexation with DOM in the aquatic environments. The key
processes are: (i) phytoextraction; the use of metal-accumulating plants to remove
toxic metals from soil; (ii) rhizofiltration; the use of plant roots to remove toxic
metals from polluted waters; and (iii) phytostabilization or phytoremediation; the
use of plants to eliminate the bioavailability of toxic metals in soil.
5.7 Effects of Freshwater and Marine Water (Salinity)
The ionic strength and the occurrence of trace elements can affect the complexation
between DOM and trace metals and can induce structural modifications of DOM in
waters (Wu et al.
2004a
,
c
; Fu et al.
2007
; Harper et al.
2008
). Sea water is mostly
a solution of NaCl where Na and Cl contribute for more than 86 % of the salt con-
tent by mass. The order of the other cations is Mg
2
+
> Ca
2
+
> K
+
> Sr
2
+
and the
other main anions are SO
4
2
−
, HCO
3
, Br
−
, and F
−
(Livingstone
1963
; Carpente
and Manella
1973
; Hem
1985
). Comparison of river and sea water shows that Na
+
,
Ca
2
+
, Mg
2
+
, K
+
, HCO
3
−
, Cl
−
and SO
4
2
−
in the sea are typically 1670 times, 27
times, 330 times, 170 times, 2.4 times, 2,400 times and 245 times, respectively,
higher than in rivers (Livingstone
1963
; Hem
1985
). Recently it has been shown that
the affinity of EPS for complexing Pu
4
+
decreases in the order of
Clostridium
sp. >
S. putrefaciens
>
P. fluorescens
, although the concentrations of carboxylic groups in
EPS isolated in laboratory cultures decrease in the order of
P. fluorescens
>
S. putre-
faciens
>
Clostridium
sp. (Harper et al.
2008
). The deprotonated carboxylic sites of
EPS from
P. fluorescens
are mostly bound by Na
+
at a ionic strength of 0.1 M NaCl,
which might be caused by a much stronger affinity of the Na
+
ion for the EPS from
P. fluorescens
compared to other EPS (Harper et al.
2008
). The high quantities of
cations in sea water can induce more rapid complex formation in DOM, even with
metals that are relatively less effective in fresh waters. Therefore, DOM is expected
to form more complexes with cations in sea waters than in fresh waters.
−
6 Shifts in Fluorescence Spectral Patterns Due
to Metal-DOM Complexation
The complexation of trace elements with fulvic and humic acid (extracted from
sewerage sludge) can shift the excitation-emission wavelengths to longer wave-
length regions during the initial complexation process (Wu et al.
2004a
,
c
; Plaza
et al.
2006
). During the Hg-DOM complexation, both excitation and emission
