1129_Photodegradation of fluorescent organic matter in river waters



ESEL Paper Review_20101129 by Aamir Alaud-din
1. Title and Author

Title: Photodegradation of fluorescent organic matter in river waters

Authors: Khan M. G. Mostofa1,2, Takahito Yoshioka1, Eiichi Konohira1, and Eiichiro Tanoue1

1Institute for Hydrospheric-Atmospheric Sciences, Nagoya University, Nagoya 464-8601, Japan
2Graduate School of Biosphere Science, Department of Environmental Dynamics and Management, Hiroshima University, 1-7-1, Kagamiyama, Higashi-Hiroshima 739-8521, Japan

2. Summary of Paper
Humic substances, carbohydrates and amino acids are the major dissolved organic matter (DOM) in fresh water. Humic substances (HS) include fulvic acid (FA) and humic acid (HA) usually in the ratio of 9:1. Amino acids are combination of humic bound or colloidal and are affected by anthropogenic sources.

The upstreams, the Kago (KG) and Nishi-Mataya (NM), and the downstream, the Yasu River (YR) were the sites for water sampling. 15 samples, in quartz bottles with sealed Teflon-coated butyl rubber stoppers with aluminium caps were kept in a constant tap water flow water bath to analyze the irradiation effects on the samples. Other 15 samples were collected in glass bottles with Teflon-coated butyl rubber stoppers with aluminium caps. These bottles were covered with aluminium foil and were also kept in constant tap water flow water bath to check the effects of darkness, in spite of irradiation, on the samples.

Photodegradation of DOM was observed. There was a reduction in concentration of dissolved organic carbon (DOC), fluorescent peak intensity (FI) of FA and protein-like substances. Mineralization of DOM in the upstream samples was high as compared to those of downstream samples in irradiated samples. For samples stored in the dark, DOC concentration decreased significantly in downstream samples. FI of FA like substances decreased during 13 days of irradiation. Protein-like substances also decreased in irradiated samples, but this decrease was less than the decrease of FA like substances.

The following table shows the % decrease in DOM, FA and protein like substances in the samples stored in irradiated as well as in dark conditions alongwith the excitation and emission wavelengths used for analysis.
Table. Irradiation and darkness analysis for upstream and downstream samples to study photodegradation of DOM
Level 99?M C in KG 38?M C in NM 194?M C in YR
% Decrease in DOM in Irradiated
Samples 36% 32% 16%
% Decrease in DOM
Samples Nearly same as before analysis Nearly same as before analysis 16%
Ex/Em Data 340±3/472±5 340±5/458±3 340/435±3

This table shows clearly that DOM concentration decreased in upstream irradiated samples while photodegradation was not effective for downstream samples was not effective (16% in both cases). It was suggested that this decrease in DOM is due to microbial activitiy.

3. Contribution to ESEL
To get good results, it is necessary to analyze the samples as soon as possible so that there is no decrease in concentration of DOM in collected samples. Otherwise, DOM concentration will be changed from the collection site specification.

By: Aamir Alaud-din

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