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stable with regard to metal-exchange reactions, thus the cited metals (Cd and Zn ions)
are less bioavailable (Koukal et al. 2003 ). Chemodynamic modeling suggests that
the enhancement of the metal uptake flux in the presence of HA originates from an
increasing amount of metal bound to the internalization sites, through ternary com-
plex formation between metal—HA complex and internalization sites (Lamelas et al.
2009 ). Cell wall speciation calculations indicate that the metal—humic acid complex
is the predominant species in the cell wall layer in algae, while for some other metals
[e.g. Cu(II) and Cd(II)] the binding to the internalization (Cu) and adsorption (Cd)
sites significantly dominates over the M HA complexes (Lamelas et al. 2009 ).
2.1 Fluorescence Characteristics of the M-DOM
Complexation
Allochthonous fulvic acids of vascular plant origin are generally composed of two
fluorescence excitation-emission (Ex/Em) peaks (or maxima) such as the peak C at
the peak C-region (280-400/380-550 nm) and the peak A at the peak A-region (215-
280/380-550 nm) (see chapter Fluorescent Dissolved Organic Matter in Natural
Waters ” for detailed description) (Fig. 1 a) (Mostofa et al. 2005 , 2009a ; Coble 1996 ;
Mostofa and Sakugawa 2009 ; Mounier et al. 2011 ; Yamashita and Jaffe 2008 ; Coble
2007 ). In contrast, allochthonous humic acids of vascular plant origin are composed
of three or more fluorescence Ex/Em peaks such as the peak C at the peak C-region
(280-400/380-550 nm) and the peak A at the peak A-region (215-280/380-550 nm)
(Fig. 1 b; see also chapter Fluorescent Dissolved Organic Matter in Natural Waters )
(Mostofa et al. 2005 , 2009a ; Mostofa and Sakugawa 2009 ; Yamashita and Jaffe 2008 ).
Similarly, the fluorescence Ex/Em peaks of autochthonous fulvic acids of algal ori-
gin resemble those of allochthonous fulvic acids (Fig. 1 c, d) (Parlanti et al. 2000 ;
Mostofa and Sakugawa 2009 ; Zhang et al. 2009 ; Stedmon et al. 2007 ). The trypto-
phan (or protein-like) component shows two fluorescence peaks such as the peak T at
the peak T-region (260-285/290-380 nm) and the peak T UV at the peak T UV T-region
(215-260/280-380 nm) (Fig. 1 e; see chapter Fluorescent Dissolved Organic Matter in
Natural Waters ”). The fluorophores or functional groups in fluorescent DOM are sus-
ceptible to show their fluorescent properties as well as to interact with metals via com-
plex formation. Therefore, the fluorescence intensity of M-DOM is either enhanced or
quenched compared to the original fluorescent DOM (Saar and Weber 1980 ; Ryan and
Weber 1982a ; Cabaniss and Shuman 1988 ; Grimm et al. 1991 ; Cabaniss 1992 ; dasilva
et al. 1995 , 1996 , 1997 , 1998 ; Smith and Kramer 1998 ; Lu and Jaffe 2001 ; Wu and
Tanoue 2001a ; Wu et al. 2004a ; b ; Dudal et al. 2006 ; Plaza et al. 2006 ; Fu et al. 2007 ;
Antunes et al. 2007 ; Ohno et al. 2008 ; Manciulea et al. 2009 , 2011 ).
Many studies show that complexation of DOM with trace elements often decreases
the overall fluorescence intensity of DOM (peak C, peak A, peak T and peak T UV ), after
addition of metal ions and with increasing their concentration. On the other hand, ele-
ments such as Al 3 + , Be 3 + , actinides (ca. Cm 3 + ), Ca 2 + and Mg 2 + are responsible for
an enhancement of the fluorescence intensity of organic ligands (fulvic acid, humic
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