Premium
Order of Functionality Loss during Photodegradation of Aquatic Humic Substances
Author(s) -
Thorn Kevin A.,
Younger Steven J.,
Cox Larry G.
Publication year - 2010
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2009.0408
Subject(s) - photodegradation , chemistry , humic acid , alkyl , hydroquinone , ketone , photochemistry , organic chemistry , nuclear chemistry , catalysis , photocatalysis , fertilizer
The time course photodegradation of the Nordic aquatic fulvic and humic acids and Suwannee River XAD‐4 acids subjected to UV irradiation with an unfiltered medium pressure mercury lamp was studied by liquid‐state 13 C nuclear magnetic resonance. Photodecarboxylation was a significant pathway in all cases. Decreases in ketone, aromatic, and O‐alkyl carbons were observed throughout the course of the irradiations, whereas C‐alkyl carbons resisted photodegradation. Peaks attributable to the low‐molecular‐weight photodegradation products bicarbonate, formate, acetate, and succinate grew in intensity with irradiation time. The final products of the irradiations were decarboxylated, hydrophobic, predominantly C‐alkyl and O‐alkyl materials that were resistant to further photodegradation. The total amount of carbon susceptible to loss appeared to be related mainly to the total concentration of carbonyl and aromatic carbons and partly to the concentration of O‐alkyl carbons in the fulvic, humic, and XAD‐4 acids. The carbon losses for Nordic fulvic, Nordic Humic, Suwannee fulvic, and Suwannee XAD‐4 acids were estimated to be 75, 63, 56, and 17%, respectively. More detailed analyses of the effects of irradiation on the carbonyl functionality in Nordic humic acid and Laurentian soil fulvic acid through reaction with hydroxylamine in conjunction with 15 N nuclear magnetic resonance analysis confirmed preferential photodegradation of the quinone/hydroquinone functionality over ketone groups and the loss of ester groups in Laurentian fulvic acid.