Environmental Engineering Reference
In-Depth Information
fluorophores need photon absorption for their initial excitation, thus they are fun-
damentally the chromophores in the respective organic molecule. The fluorophores
present in allochthonous fulvic acid can have two fluorescence peaks at peak
C-region and peak A-region, but allochthonous humic acid shows several peaks at
peak C-region.
On the other hand, allochthonous fulvic acid generally exhibits monotonous
absorption spectra whilst allochthonous humic acid has a shoulder at around
400 nm in aqueous media (Hayase and Tsubota 1985 ; Zepp and Scholtzhauer
1981 ; Ishiwatari 1973 ; Lawrence 1980 ). In addition, CDOM generally exhibits
low absorbance at longer wavelengths and the absorbance increases with decreas-
ing wavelength from 700 to 200 nm (Hayase and Tsubota 1985 ).
Allochthonous fulvic and humic acids, as well as autochthonous fulvic acids
are part of the colored DOM (CDOM) and absorb radiation at 200-800 nm.
Along with them, also FDOM, protein-like, tryptophan-like, tyrosine-like,
FWAs-like and other fluorescent components absorb radiation at 200-800 nm.
In addition, there is a vast number of allochthonous and autochthonous non-
fluorescent organic substances. They do not display fluorescence properties,
but absorb radiation at specific wavelength ranges. For example, acetaldehyde
absorb light at 208-224 nm (Mopper et al. 1991 ; Kieber et al. 1990 ), acetate
at 204-270 nm (Wetzel et al. 1995 ; Dahlén et al. 1996 ), formaldehyde at 207-
250 nm (Mopper et al. 1991 ; Kieber et al. 1990 ), glyoxal at <240 nm (Mopper
et al. 1991 ), malonate at 225-240 nm (Dahlén et al. 1996 ) and so on. All these
organic molecules are termed as CDOM but they do not belong to FDOM
because as they do not show fluorescence properties. Therefore 'all fluorescent
DOM (FDOM) is colored or chromophoric DOM (CDOM), but not all CDOM
is also FDOM'.
7 Scope of the Future Challenges
Autochthonous fulvic acids (C-like and M-like) of algal origin show fluorescence
properties at peak C- and A- regions, for which they show a similar behavior as
allochthonous fulvic and humic acids. Researchers did not distinguish between
the photoinduced and microbial degradation of the autochthonous DOM (fulvic
acids) nor its differentiation with terrestrial fulvic acid, and this should be a key
focus for future research. Two types of autochthonous fulvic acids (C-like and
M-like) can be distinguished based on the presence of fluorophores. This mate-
rial is originated from algal biomass or phytoplankton biomass. Among these two
fulvic acids, the C-like fulvic acid is produced photolytically and microbially and
undergoes rapid photoinduced degradation, therefore it does not appear as a key
component in natural waters. However, it is important to extract the autochthonous
fulvic acids from water, to identify them using other spectroscopic methods and to
make relationship with fluorescence properties. The extraction of autochthonous
fulvic acids, which represent key DOM sources in lake and marine waters, and the
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