Environmental Engineering Reference
In-Depth Information
shorter wavelengths (Ex/Em
=
295-310/443-450 nm) in surface waters (0-20 m)
compared to the deep water layers (40-80 m) (Ex/Em
=
300-310/444-464 nm).
Furthermore, maxima are 320-325/422-454 nm in sea waters and 300-305/449
and 250/449 nm in irradiated river waters (Table
2
) (Mostofa KMG et al., unpub-
lished data; Mostofa et al.
2005b
; Yamashita et al.
2011
). The excitation-emis-
sion maxima of the fluorescence peak C are shifted in irradiated samples from
longer to shorter wavelength regions, which gives a blue-shift of the peak position
(Mostofa et al.
2005a
,
2007a
; Moran et al.
2000
). Such blue-shift phenomenon is
the photoinduced result of the mineralization of fluorophores that are present in
the molecular structure of fulvic acids. Irradiation decomposes the allochthonous
fulvic acid (A-like and M-like) entirely (Table
2
) (Mostofa KMG et al., unpub-
lished data). Photobleached fulvic acid is generally detected in the surface waters
of rivers, lakes, estuaries and oceans (Table
2
) (Brooks et al.
2007
; Mostofa et al.
2007a
,
2005b
; Garcia et al.
2005
; Skoog et al.
1996
; Moran et al.
2000
; Osburn
et al.
2009
; Lepane et al.
2003
; Abboudi et al.
2008
; Poiger et al.
1999
; Zhang
et al.
2009b
).
Allochthonous Humic Acids (C-like, A-like and M-like
)
The standard Suwannee River Humic Acid (SRHA) has three fluorescent com-
ponents, namely allochthonous humic acid (C-like), humic acid (A-like) and
humic acid (M-like). They can be identified using PARAFAC modeling of EEM
spectra in a variety of waters (Fig.
3
f, g; Table
2
). The allochthonous humic acid
(C-like) shows three fluorescence peaks, of which two are at Ex/Em
=
285-340/
460-480 nm (shorter wavelength) and at 350-405/480-508 nm (longer wavelength,
peak C-region). The third peak is located at Ex/Em
=
240-270/460-508 nm in
the peak A-region (Fig.
3
f; Table
2
). Allochthonous humic acid (C-like) has been
detected at Ex/Em
=
320-350/461-498 and 300/461 nm (peak C-region) and
at 255/461 nm (peak A-region) in standard SRFA dissolved in Milli-Q water; at
295-310/423-464 and 255/464 nm in extracted humic acid; at 330/456-480 and
<250/450-460 nm in river and soil waters; at 385/>500 and 256/>500 nm in estu-
aries; at 300-340/>500-510, 290-405/>500-510 and <260-270/>508 nm in bay
and marine waters; at 370-380/490-498 and <260/490-498 nm in the north Pacific
and Atlantic ocean; at 360/458-480, 300/458 and 250-260/458-480 nm in drinking
water treatment plants and municipal wastes; at 370/440 and <250/440 nm in soil;
at 351/459 and 240/459 nm in water extracted from sugar maple leaves; finally, at
350-360/460-480 nm in plant biomass, manure and soil (Fig.
3
f; Table
2
) (Coble
1996
; Mostofa et al.
2005a
; Ohno and Bro
2006
; Baker
2005
; Hunt et al.
2008
;
Kowalczuk et al.
2009
; Baghoth et al.
2010
; Chen et al.
2010
; Fellman et al.
2008
,
2010
; Guo et al.
2010
; Yu et al.
2010
; Wu et al.
2011
; Yamashita et al.
2011
;
Balcarczyk et al.
2009
; Santín et al.
2009
; Murphy et al.
2008
; Yamashita and Jaffé
2008
).
The allochthonous humic acid (A-like) can exhibit a strong shoulder (not
often a clear peak) at peak A-region in a wide range of emission wavelengths.
