Correlating The Spectroscopic Properties Of Organic Matter To The Photochemical Formation Of Hydroxyl Radical In Natural Waters
Townsend, Eli B 1 ; Glover, Caitlin M 2 ; Rosario-Ortiz, Fernando L 3
1 University of Colorado
The production of reactive oxygen species, including hydroxyl radical (HO•), from organic matter (OM) is a driver for the degradation of organic contaminants found almost ubiquitously in natural systems. To determine the role efficacy of OM, advanced analytical techniques are required to monitor the ROS production and quantum yield. In this study fifteen surface, ground and wastewaters samples were analyzed to determine if a correlation exists between the quantum yield of HO• and certain optical properties of water. The optical properties examined included specific UV absorbance (SUVA), E2:E3 and the Spectral Slope Ratio (SR). A positive correlation was found with the E2:E3 ratio, but a slightly better correlation was achieved when the spectral slope from 275 nm to 295 nm was coupled with this ratio. Researchers could use this optically based model to replace advanced analytical techniques for estimating quantum yield and apply it in natural systems.
Organic matter is primarily composed of fulvic, humic, and non-humic substances such as proteins or decaying lignin i.e., an intermediate in the degradation of terrestrial plant matter to organic matter. Fulvic acids are low molecular weight humic substances. Humic substances are naturally occurring multivalent acids. Fulvic acids are the major light-absorbing fraction between 800-200 nm (the UV-Vis range). These substances are hydrophobic in nature, act as proton donors or acceptors, and may act as a pH buffer (Weishaar, Aiken, Bergamaschi, Fram, Fujii, & Mopper, 2003). The difference in the source of OM leads to a difference in structure, and structure is the main factor influencing the reactivity and, therefore, the fate of OM. The information of this study may also help in clarifying the mechanism of HO• formation from organic mater, the fate in natural systems, and the intermolecular interactions of organic mater due to light exposure.
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