Photooxidation and Its Effects on the Carboxyl Content of Dissolved Organic Matter in Two Coastal Rivers in the Southeastern United States
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- 作者：Huixiang Xie ; Oliver C. Zafiriou ; Wei-Jun Cai ; Richard G. Zepp ; and Yongchen Wang
- 刊名：Environmental Science & Technology
- 出版年：2004
- 出版时间：August 1, 2004
- 年：2004
- 卷：38
- 期：15
- 页码：4113 - 4119
- 全文大小：105K
- 年卷期：v.38,no.15(August 1, 2004)
- ISSN：1520-5851
文摘
Photodecarboxylation (often stoichiometrically expressedas RCOOH + <SUP>1/2O2 
ROH + CO2) has long been postulatedto be principally responsible for generating CO2 fromphotooxidation of dissolved organic matter (DOM). In thisstudy, the quantitative relationships were investigatedamong O2 consumption, CO2 production, and variation ofcarboxyl content resulting from photooxidation of DOM innatural water samples obtained from the freshwaterreaches of the Satilla River and Altamaha River in thesoutheastern United States. In terms of loss of dissolvedorganic carbon (DOC), loss of optical absorbance, andproduction of CO2, the rate of photooxidation of DOM wasincreased in the presence of Fe redox chemistry andwith increasing O2 content. The ratio of photochemical O2consumption to CO2 photoproduction ranged from ~0.8to 2.5, depending on the O2 content, the extent of involvementof Fe, and probably the initial oxidation state of DOM aswell. The absolute concentration of carboxyl groups ([-COOH])on DOM only slightly decreased or increased over thecourse of irradiation, possibly depending on the stages ofphotooxidation, while the DOC-normalized carboxylcontent substantially increased in the presence of Feredox chemistry and sufficient O2. Both the initial [-COOH]and the apparent loss of this quantity over the courseof irradiation was too small to account for the much largerproduction of CO2, suggesting that carboxyl groups werephotochemically regenerated or that the major productionpathway for CO2 did not involve photodecarboxylation.The results from this study can be chemically rationalizedby 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 orof (b) nondecarboxylation photooxidation: CxHyOz(COOH)m+ aO2 + (metals, hv) bCO2 + cH2O2 + Cx-bHy'Oz'(COOH)m.
ROH + CO2) has long been postulatedto be principally responsible for generating CO2 fromphotooxidation of dissolved organic matter (DOM). In thisstudy, the quantitative relationships were investigatedamong O2 consumption, CO2 production, and variation ofcarboxyl content resulting from photooxidation of DOM innatural water samples obtained from the freshwaterreaches of the Satilla River and Altamaha River in thesoutheastern United States. In terms of loss of dissolvedorganic carbon (DOC), loss of optical absorbance, andproduction of CO2, the rate of photooxidation of DOM wasincreased in the presence of Fe redox chemistry andwith increasing O2 content. The ratio of photochemical O2consumption to CO2 photoproduction ranged from ~0.8to 2.5, depending on the O2 content, the extent of involvementof Fe, and probably the initial oxidation state of DOM aswell. The absolute concentration of carboxyl groups ([-COOH])on DOM only slightly decreased or increased over thecourse of irradiation, possibly depending on the stages ofphotooxidation, while the DOC-normalized carboxylcontent substantially increased in the presence of Feredox chemistry and sufficient O2. Both the initial [-COOH]and the apparent loss of this quantity over the courseof irradiation was too small to account for the much largerproduction of CO2, suggesting that carboxyl groups werephotochemically regenerated or that the major productionpathway for CO2 did not involve photodecarboxylation.The results from this study can be chemically rationalizedby 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 orof (b) nondecarboxylation photooxidation: CxHyOz(COOH)m+ aO2 + (metals, hv) bCO2 + cH2O2 + Cx-bHy'Oz'(COOH)m.