Photodegradation of fluorescent dissolved organic matter in river waters

Abstract

Photodegradation of dissolved organic matter (DOM), collected from two upstream and one downstream sites in the Lake Biwa watershed in Japan, was investigated using fluorescence properties of three-dimensional excitation emission matrix (3-D EEM). Solar irradiation caused a decrease in the dissolved organic carbon (DOC) concentration and in the fluorescence peak intensity (FI) of fulvic acid (FA)-and protein-like substances in DOM. Mineralization of DOC during an irradiation period (13 days) was observed to be higher in upstream samples (32-36%) compared to that in downstream sample (16%). DOC concentration in samples stored in the dark significantly decreased in the downstream sample (16%), while those in upstream samples hardly decreased (1-8%). The FI of FA-like substance decreased by 72-84% during 13-days irradiation (integrated solar intensity = 176 MJ m -2 ). The protein-like fluorescence was only observed in the downstream sample and the net decrease in the FI was 59% in the irradiated sample. The first-order reaction kinetics was applied to analyze the photodegradation of DOM. Two-step photodegradation was suggested for the fluorescent DOM (FDOM), while not for the DOC. Results obtained here suggested that FA-like FDOM is more susceptible to photodegradation compared with those of protein-like substances and DOC.Keywords: dissolved organic carbon, fulvic acid-like fluorescence, protein-like fluorescence, photodegradation, streams as benzene containing carboxyl, methoxylate and phenolic groups, hydroxycoumarin-like structures, and fluorophores containing the Schiff-base system, chromone, xanthone, and quinoline derivatives (Senesi, 1990;Leenheer and Croue, 2003). On the other hand, amino acids in freshwaters have been detected in a combined form, mostly humic bound or colloidal in river waters (Volk et al., 1997;Baker et al., 2007) and affected by anthropogenic sources (Baker, 2001(Baker, , 2002a(Baker, , 2002bMostofa et al., 2005a). FA-and protein-like substances are the major components of the fluorescent dissolved organic matter (FDOM) in natural waters (Senesi, 1990;Coble, 1996; Yamashita and Tanoue, 2003 and references therein). The florescent components such as FA-and protein-like substances have been investigated by the three-dimensional excitation emission matrix (3-D EEM). Due to simplicity of the 3-D EEM technique, it is now widely used for characterization of FDOM and for determinations of the nature, sources and quantity of FDOM in natural waters (Baker, 2001(Baker, , 2002aCoble, 1996;Yamashita and Tanoue, 2003;Mostofa, 2005; Mostofa et al., 2005a, b). The 3D-EEM of FA-or humiclike substances in the aquatic DOM, in general, has been shown a major fluorescence peak within a range of excitation/emission (Ex/Em) wavelengths of 320-390/420-490 nm (Coble et al

Photochemical, microbial and metal complexation behavior of fluorescent dissolved organic matter in the aquatic environments

“…It has been demonstrated that photoirradiation reduces the fluorescence intensity by decomposing fulvic and humic acids (Moran et al, 2000;Wu et al, 2005), tryptophan-like component (Moran et al, 2000;Mostofa et al, 2007b), and FWAs or household detergents (Poiger et al, 1999;Mostofa et al, 2005aMostofa et al, , 2010 in natural waters. On the other hand, microbial degradation has been observed to either enhance or decrease the fluorescence intensity in natural waters.…”

“…On the other hand, microbial degradation has been observed to either enhance or decrease the fluorescence intensity in natural waters. This is mainly the consequence of the complex interactions between micro-organisms and fulvic and humic acids (Moran et al, 2000;Ma and Green, 2004;Mostofa et al, 2007a), detergent components (Table 1) and tryptophan-like compounds (Moran et al, 2000;Baker and Inverarity, 2004;Mostofa et al, 2007b; Table 1). The photochemical and microbial processing of FDOM yields a variety of photo-and microbial transformation intermediates in natural waters (Amador et al, 1989;Allard et al, 1994;Amon and Benner, 1996;Kramer et al, 1996;Ma and Green, 2004; Table 1 and references therein).…”

“…In particular: (i) Photochemical degradation modifies the physical, chemical and optical properties of water (Moran et al, 2000;Vähätalo et al, 2000;Twardowski and Donaghay, 2002;Kopáček et al, 2003;Mostofa et al, 2005aMostofa et al, , 2007aMostofa et al, , 2007b, the DOM molecular structure (Kramer et al, 1996;Kulovaara, 1996;Bertilsson and Allard, 1996) as well as its molecular weight (Allard et al, 1994;Twardowski and Donaghay, 2002;Kaiser and Sulzberger, 2004); (ii) Photodegradation processes can affect the acidity-alkalinity balance and the consumption of dissolved oxygen at the epilimnion level in both lacustrine and oceanic environments (Amon and Benner, 1996;Gao and Zepp, 1998;Kopáček et al, 2003); (iii) Photochemical degradation decreases the absorbance of CDOM (and/or FDOM), which can result in water discoloration (Reche et al, 1999 and references therein) and increases the water-column transparency. A notable consequence is the increased penetration of photosynthetically active radiation (PAR, 400-700 nm) but also of damaging UV radiation (280-400 nm) in the water column (Laurion et al, 2000 and references therein).…”

Sources, factors, mechanisms and possible solutions to pollutants in marine ecosystems

“…Despite very different mechanisms involved, microbial processes have several analogies with photochemical ones as far as the final products are concerned (Köhler et al, 2002;Ma and Green, 2004;Millero, 2007;Moran et al, 2000;Mostofa et al, 2007;Mostofa and Sakugawa, 2009;Zhang et al, 2009;Letscher et al, 2013;Mostofa et al, 2011Mostofa et al, , 2013bMostofa et al, , 2013d The compounds formed from DOM and POM because of photochemical and microbial processes would be substantially increased due to increased temperature following global warming. These compounds act as nutrients, enhancing photosynthesis and, as a consequence, primary production as summarized in earlier reports ( Fig.…”

First Photolysis of Benzidine Schiff Base in Non Aqueous Solvents

“…A number of papers have been published on the direct photolysis of chemicals in water using the Hg-lamp (K. G. Mostafa, 2007, J.P. Escalanda, 2008, S.T. Ong, 2009).…”