Photosensitized degradation of caffeine: Role of fulvic acids and nitrate Laura E. Jacobs b,1 , Linda K. Weavers a , Erika F. Houtz a , Yu-Ping Chin b,⇑ a Department of Civil and Environmental Engineering and Geodetic Science, The Ohio State University, 470 Hitchcock Hall, 2070 Neil Avenue, Columbus, OH 43210, USA b School of Earth Sciences, The Ohio State University, 125 South Oval Mall, 275 Mendenhall Laboratory, Columbus, OH 43210, USA article info Article history: Received 15 June 2011 Received in revised form 2 September 2011 Accepted 30 September 2011 Available online 4 November 2011 Keywords: Caffeine Photolysis Wastewater Dissolved organic matter Fulvic acid abstract The photolysis of caffeine was studied in solutions of fulvic acid isolated from Suwannee River, GA (SRFA) and Old Woman Creek Natural Estuarine Research Reserve, OH (OWCFA) with different chemical amend- ments (nitrate and iron). Caffeine degrades slowly by direct photolysis (>170 h in artificial sunlight), but we observed enhanced photodegradation in waters containing the fulvic acids. At higher initial concen- trations (10 lM) the indirect photolysis of caffeine occurs predominantly through reaction with the hydroxyl radical (OH Å ) generated by irradiated fulvic acids. Both rate constant estimates based upon mea- sured OH Å steady-state concentrations and quenching studies using isopropanol corroborate the impor- tance of this pathway. Further, OH Å generated by irradiated nitrate at concentrations present in wastewater effluent plays an important role as a photosensitizer even in the presence of fulvic acids, while the photo-Fenton pathway does not at neutral or higher pH. At lower initial concentrations (0.1 lM) caffeine photolysis reactions proceed even more quickly in fulvic acid solutions and are influ- enced by both short- and long-lived reactive species. Studies conducted under suboxic conditions suggest that an oxygen dependent long-lived radical e.g., peroxyl radicals plays an important role in the degra- dation of caffeine at lower initial concentration. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The xanthine alkaloid compound, caffeine (1,3,7-trimethylxan- thine) is used as a molecular tracer of wastewater contributions to surface waters (Seiler et al., 1999; Buerge et al., 2003; Strauch et al., 2008; Bruton et al., 2010) due to its ubiquity. Further it does not sorb strongly to suspended solids because of its very low octanol–water partition coefficient (log K o/w 0.01) and high aqueous solubility (22 mg mL 1 ) (Gossett and Brown, 1983). Indeed, caffeine is one of the most popular drugs in the world as it is contained in coffee, tea, chocolate, soft drinks (Bunker and McWilliams, 1979; Ogunseitan, 1996) and pharmaceuticals (pre- scription and over the counter) (Graham, 1978). Once ingested, approximately 3% of the total caffeine intake is excreted in urine (Tang-Liu et al., 1982). Despite this small amount and efficient (>99%) wastewater treatment removal (Buerge et al., 2003; Thomas and Foster, 2005; Strauch et al., 2008) caffeine has been documented extensively in the environment. For example, Buerge et al. (2003) found levels ranging from 0.03 to 1.28 nM of caffeine in Swiss surface waters while caffeine in German surface waters ranges from 0.05 to 0.5 nM (Strauch et al., 2008). Caffeine is also present in coastal waters where Gardinali and Zhao (2002) reported between 0.03 and 0.2 nM in Biscayne Bay, FL, Caffeine is also found in groundwater with concentrations ranging from 0.05 to 1.2 nM (Seiler et al., 1999; Strauch et al., 2008). Buerge et al. (2003) evaluated caffeine as an anthropogenic marker of wastewater contamination in surface waters and found indirect photolysis via reaction with the hydroxyl radical (OH Å ) as the primary pathway of its degradation. This was based upon the magnitude of caffeine’s 2nd-order rate constant (6  10 9 M 1 s 1 ) with OH Å (k OH Å ) as well as observed degradation in both natural sunlight and a batch photo-reactor. Despite this important removal mechanism for caffeine in sunlit waters, the authors were still able to correlate caffeine concentrations to wastewater loadings into Swiss lakes and rain events. Nonetheless they identified a need for more precise information regarding the compound’s behavior in natural waters. Finally, they only investigated caffeine’s photo- chemical fate in one lake water sample (Greifensee) with no knowledge regarding its dissolved organic matter (DOM) composi- tion. In a different study Lam et al. (2004) demonstrated that pho- tolysis is the principal removal mechanism for caffeine in surface waters based upon sterile and unsterile pond water experiments in the presence and absence of light. They similarly attribute caf- feine’s degradation to reactions with the hydroxyl radical. The hydroxyl radical is produced from various photosensitizers present in natural waters including nitrate (NO  3 ) and dissolved or- ganic matter. It is also produced by the photo-Fenton pathway 0045-6535/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2011.09.052 ⇑ Corresponding author. Tel.: +1 614 292 6953; fax: +1 614 292 7688. E-mail address: yo@geology.ohio-state.edu (Y.-P. Chin). 1 Present address: The National Academies, 500, 5th Street NW, Washington, DC 20001, USA. Chemosphere 86 (2012) 124–129 Contents lists available at SciVerse ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere