Environmental Engineering Reference
In-Depth Information
Richardson 2007 ; Singh and Singa 2002 ; Miller et al. 2002 ; Hama et al. 2004 ;
McCallister et al. 2006 ; Prince et al. 2008 ). Most of these autochthonous sub-
stances have been extensively discussed in earlier studies (Mostofa et al. 2009a ).
“Autochthonous fulvic acids” of algal or phytoplankton origin are molecularly
heterogeneous, with molecular weight ranging from less than 100 to over 1,898
Daltons. They are optically active, biogenic, highly photoreactive, microbially
refractory and yellow-colored organic acids (Mostofa et al. 2009b , Mostofa KMG
et al., unpublished data; Zhang et al. 2009 ; Johannessen et al. 2007 ; Amon and
Benner 1994 ; McKnight et al. 1991 , 1994 ; Ogawa et al. 2001 ; Aoki et al. 2004 ,
2008 ; Nagai et al. 2005 ; Williams and Druffel 1987 ; Fimmen et al. 2007 ; Barber
1968 ; Ogura 1972 ). Autochthonous fulvic acids or DOM in freshwater and seawa-
ter have relatively high contents of dissolved organic N compared to organic C, i.e.
low C:N atomic ratios (ca. 8-36, but lower in surface waters and higher in deeper
waters). They are rich in S, highly aliphatic in nature and have low contents of
aromatic carbon (ca. 5-21 % of total carbon) (Wetzel 1983 ; McKnight et al. 1991 ,
1994 , 1997 , 2001 ; Ogawa et al. 1999 , 2001 ; Meyers-Schulte and Hedges 1986 ;
Aluwihare et al. 2002 ; Fimmen et al. 2007 ; McCallister et al. 2006 ; Nissenbaum
and Kaplan 1972 ; Carder et al. 1989 ; Karl et al. 1991 ; Midorikawa and Tanoue
1996 , 1998 ; McCarthy et al. 1997 ; Engel and Passow 2001 ; Carlson et al. 2000 ;
Church et al. 2002 ). Autochthonous fulvic acids have higher nitrogen content
(C:N = 8-36) than allochthonous standard fulvic and humic acids (C:N = 44-78).
This may indicate that autochthonous fulvic acids are less refractory than alloch-
thonous fulvic and humic acids, probably because autochthonous DOM has fewer
aromatic compounds and relatively more proteins and lipids, which decreases
its carbon to nitrogen ratio compared to allochthonous DOM (McCallister et al.
2006 ). Cyanobacteria may contain significant quantities of lipids (fats and oil)
which are esters of fatty acids and alcohols that comprise a large group of struc-
turally distinct organic compounds including fats, waxes, phospholipids, glycolip-
ids etc. (Singh and Singa 2002 ). The lipids of some cyanobacterial species are
also rich in essential fatty acids such as the C 18 linoleic (18:2 ω 6) and y-linolenic
(18:3 ω 3) acids and their C 20 derivatives, eicosapentaenoic acids (20:5 ω 3) and
arachidonic acid (20:4 ω 6) (Singh and Singa 2002 ). These fatty acids are essential
components of the diet of humans and animals and are becoming important feed
additives in aquaculture (Borowitzka 1988 ).
Spectroscopic studies of isolated autochthonous fulvic acids show that they
are composed of methylated isomers of hydroxy-benzenes and hydroxy-benzoic
acids, aliphatic acids, carbohydrate OH, protein amide and amine groups; they
also contain Schiff-base derivatives (-N = C-C = C-N-), fatty acid methyl esters
(heptanedioic acid, octanedioic acid, nonanedioic acid, methyl tetradecanoate,
12-methyl-tetradecanoic acid, 7-hexadecenoic acid, and hexadecanoic acid), N- and
S-containing amino and sulfidic functional groups. The latter include 3-(methylthio)-
propanoic acid; dimethyl sulfone; N,N-dimethyl-2-butanamine, N-methyl pro-
line; N-methyl aniline; 3-piperidinemethanol; 1-methyl-2,5-pyrrolidinedione;
1-methyl-2-piperidinone; caprolactam; 3-ethyl-1,3-dimethyl-2,5-pyrrolidinedione;
2-amino-5,6-dihydro-4,4,6-trimethyl-4
H-1,3-oxazine;
3-ethyl-2,6-piperidinedi-
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