Geoscience Reference
In-Depth Information
et al.,
2008
), was responsible, in part, for the fluorescence signal commonly defined as
the T-peak for samples from the South Platte River downstream from a water treatment
plant near Denver, Colorado. In other work, Hernes et al. (
2009
) noted that the regions
of EEMs spectra most useful for the prediction of lignin phenols were those commonly
assigned to both tyrosine and tryptophan, but most notably with tyrosine. Lignin (discussed
in
Section 2.4.6
) contains no amino acids and samples thought to be derived from ligna-
ceous sources have been found to contain low amounts of nitrogen (McKnight and Aiken,
1998
). Hernes et al. (
2009
) ascribed the strong relationship between protein-like regions
and lignin phenols to the chemical similarities of fluorophores associated with the amino
acids and the propylphenol monomers associated with lignin. Many fluorescence studies
of natural waters and aquatic systems influenced by wastewaters refer to signals in tyrosine
region as “tyrosine-like” (e.g., Hudson et al.,
2007
), a term that suggests chemical compo-
sition, without the measurement of either tyrosine or other compounds that also fluoresce
in this region.
2.4.3 Indoles
Indole (2,3-benzopyrrole;
Figure 2.4b
) is a precursor compound for the biosynthesis of
tryptophan, some alkaloids, and other biomolecules (Lehninger,
1970
; Robinson,
1991
). It
is found in coal tar, oil shale, and feces (The Merck Index,
1996
), and is a major product
of the degradation of tryptophan. Indole and its simple derivatives (e.g., 3-methyl-1H-
indole) are also constituents in personal care products and pharmaceuticals. Indoles are
commonly found in wastewaters associated with agricultural feed lots (Harden,
2009
),
municipal wastewater treatment effluents (Goldberg and Weiner,
1993
; Tertuliani at al.,
2008
) and oil shale and coal mining operation wastewaters (Gu and Berry,
1991
). As for the
case of phenols and flavanols, indole is also of interest in the production of wine, where its
presence can be determined using fluorescence (Bonerz et al.,
2008
). Indole and 3-methyl-
1H-indole fluoresce strongly and overlap significantly with the fluorescence of tryptophan,
which is an indole-containing compound.
The indole fluorophore peak has been noted in wastewaters and is commonly referred
to as the “T-peak” or as “tryptophan-like” (Baker,
2001
; Hudson et al.,
2007
). Elliot et al.
(
2006
) demonstrated that this peak can be microbially generated in simple systems con-
taining bacteria; however, their samples were unfiltered and, as noted by the authors, the
resulting signals were the combination of bacterial biomass and exudates. Whereas many
reports of wastewater DOM fluorescence often describe this peak as “tryptophan-like,”
thereby inferring the presence of proteins and tryptophan, few actually measure for the
presence of tryptophan or hydrolyzable amino acids. Indole and 3-methyl-1H-indole, on
the other hand, are both routinely determined by direct methods in groundwater and surface
water influenced by wastewaters. In one of the few studies of its kind, Goldberg and Weiner
(
1993
) showed a good relationship between the presence of indole, measured directly, and
fluorescence response in the indole region.
