Order of Functionality Loss during Photodegradation of Aquatic Humic Substances

• Published in: Journal of environmental quality 2010-07, Vol.39 (4), p.1416-1428
• Main Authors: Thorn, Kevin A, Younger, Steven J, Cox, Larry G
• Format: Article
• Language: English
• Subjects: Acetates; acetic acid; Aquatic ecosystems; aquatic environment; aromatic hydrocarbons; Benzopyrans - chemistry; Bicarbonates; Carbon; carbon compounds; Carbon Isotopes; Carbonyl compounds; Carbonyls; carboxylic acids; decarboxylation; Environmental Monitoring; Experiments; formic acid; Fulvic acids; geographical variation; Humic acids; humic substances; Humic Substances - analysis; Irradiation; Ketones; Mercury; Microorganisms; Molecular weight; NMR; Nuclear magnetic resonance; nuclear magnetic resonance spectroscopy; Photodegradation; Photolysis; provenance; Pyrvinium Compounds; qualitative analysis; succinic acid; temporal variation; Ultraviolet radiation; Water - chemistry; Water Pollutants, Chemical - chemistry; Water Pollutants, Chemical - radiation effects; Water Purification - methods; Water treatment; XAD-4 acids
• ISSN: 0047-2425; 1537-2537; 1537-2537
• DOI: 10.2134/jeq2009.0408

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 13C 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 15N 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.