Document Detail

Photooxidation and its effects on the carboxyl content of dissolved organic matter in two coastal rivers in the southeastern United States.
MedLine Citation:
PMID:  15352449     Owner:  NLM     Status:  MEDLINE    
Photodecarboxylation (often stoichiometrically expressed as RCOOH + (1/2)O2 --> ROH + CO2) has long been postulated to be principally responsible for generating CO2 from photooxidation of dissolved organic matter (DOM). In this study, the quantitative relationships were investigated among O2 consumption, CO2 production, and variation of carboxyl content resulting from photooxidation of DOM in natural water samples obtained from the freshwater reaches of the Satilla River and Altamaha River in the southeastern United States. In terms of loss of dissolved organic carbon (DOC), loss of optical absorbance, and production of CO2, the rate of photooxidation of DOM was increased in the presence of Fe redox chemistry and with increasing O2 content. The ratio of photochemical O2 consumption to CO2 photoproduction ranged from approximately 0.8 to 2.5, depending on the O2 content, the extent of involvement of Fe, and probably the initial oxidation state of DOM as well. The absolute concentration of carboxyl groups ([-COOH]) on DOM only slightly decreased or increased over the course of irradiation, possibly depending on the stages of photooxidation, while the DOC-normalized carboxyl content substantially increased in the presence of Fe redox chemistry and sufficient O2. Both the initial [-COOH] and the apparent loss of this quantity over the course of irradiation was too small to account for the much larger production of CO2, suggesting that carboxyl groups were photochemically regenerated or that the major production pathway for CO2 did not involve photodecarboxylation. The results from this study can be chemically rationalized by a reaction scheme of (a) photodecarboxylation/ regeneration of carboxyl: CxHyOz(COOH)m + aO2 + (metals, hv) --> bCO2 + cH2O2 + Cx-bHy'Oz'(COOH)m-b(COOH)b or of (b) nondecarboxylation photooxidation: CxHyOz(COOH)m + aO2 + (metals, hv) --> bCO2 + cH2O2 + Cx-bHy'Oz'(COOH)m.
Huixiang Xie; Oliver C Zafiriou; Wei-Jun Cai; Richard G Zepp; Yongchen Wang
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Environmental science & technology     Volume:  38     ISSN:  0013-936X     ISO Abbreviation:  Environ. Sci. Technol.     Publication Date:  2004 Aug 
Date Detail:
Created Date:  2004-09-08     Completed Date:  2005-01-31     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0213155     Medline TA:  Environ Sci Technol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  4113-9     Citation Subset:  IM    
Institut des Sciences de la Mer de Rimouski, Université du Québec à Rimouski, Québec, Canada G5L 3A1.
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MeSH Terms
Carbon Dioxide / analysis*,  chemical synthesis
Decarboxylation / radiation effects
Hydrocarbons / radiation effects
Iron / analysis,  chemistry
Oxygen / analysis*,  chemistry
Rivers / chemistry*
Time Factors
Ultraviolet Rays*
Reg. No./Substance:
0/Hydrocarbons; 124-38-9/Carbon Dioxide; 14485-07-5/carboxyl radical; 70-51-9/Deferoxamine; 7439-89-6/Iron; 7782-44-7/Oxygen

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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