Photochemistry of excited-state species in natural waters: A role for particulate organic matter

• Published in: Water research (Oxford) 2013-09, Vol.47 (14), p.5189-5199
• Main Authors: Cottrell, Barbara A., Timko, Stephen A., Devera, Lianne, Robinson, Alice K., Gonsior, Michael, Vizenor, Ashley E., Simpson, André J., Cooper, William J.
• Format: Article
• Language: English
• Subjects: absorption; Acetal resins; Applied sciences; benzophenone; Benzophenones - chemistry; Black River; California; Chlorophyll; constructed wetlands; Construction; Dissolved organic matter; Exact sciences and technology; Excitation; Excitation spectra; Extraction plants; Fresh Water - chemistry; lakes; Laser flash photolysis; Lasers; lignin; Lignin - chemistry; Magnetic Resonance Spectroscopy; nuclear magnetic resonance spectroscopy; Particle Size; Particulate organic matter; Photochemistry; Photolysis; plant extracts; Plants - chemistry; Pollution; rivers; Rivers - chemistry; solubilization; sorbic acid; Sorbic Acid - chemistry; Spectrometry, Fluorescence - methods; Tannic acid; tannins; Tannins - chemistry; Triplet excited state; Water treatment and pollution; Wetlands
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2013.05.059

Laser flash photolysis (LFP) was used to characterize a triplet excited state species isolated from Black River and San Joaquin wetlands particulate organic matter (POM). The solubilized organic matter, isolated from POM by pH-independent diffusion in distilled water, was named PdOM. UV–visible absorption spectroscopy, excitation–emission matrix spectroscopy (EEMs), and 1H NMR were used to characterize the PdOM. While LFP of dissolved organic matter (DOM) is known to generate the solvated electron, LFP of the PdOM transient in argon-, air-, and nitrous oxide-saturated solutions indicated that this was a triplet excited state species (3PdOM*). The lifetime and the reactivity of 3PdOM* with sorbic acid, a triplet state quencher, were compared with that of the triplet excited state of benzophenone, a DOM proxy. A second excited state species (designated DOM*), with a longer lifetime, was reported in a number of previous studies but not characterized. The lifetime of DOM*, measured for seventeen organic matter isolates, lignin, tannic acid, and three wetlands plant extracts, was shown to differentiate allochthonous from autochthonous DOM. 3POM* and DOM* were also observed in lake water and a constructed wetlands' water. Aqueous extracts of fresh and aged plant material from the same wetland were shown to be one source of these excited state species. This study provides evidence of a role for POM in the photochemistry of natural and constructed wetland waters. [Display omitted] •Particulate organic matter (POM) from natural waters is photochemically reactive.•Organic matter (OM) desorbed from POM (PdOM) is chemically distinct.•Laser flash photolysis of desorbed PdOM generates a triplet excited state species.•The solvated electron is not generated by laser flash photolysis of PdOM.•Another excited state species (millisecond lifetime) is partially characterized.