Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 53, Issue 20, Pages 11725-11734Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.9b03007
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Funding
- Wisconsin Sea Grant [R/HCE-31]
- University of St. Thomas Undergraduate Research Opportunities Program (UROP)
- Wisconsin partnership funds
- NIH [S10OD018475]
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Dissolved organic matter (DOM) composition influences its ability to form photochemically produced reactive intermediates (PPRI). While relationships have been established between bulk DOM properties and triplet DOM ((DOM)-D-3) and singlet oxygen (O-1(2)) quantum yields, contradictory evidence exists for hydroxyl radical ((OH)-O-center dot) and hydroxylating species. Furthermore, little is known about these relationships at the molecular level. We evaluated DOM composition and photochemical reactivity of water samples from a wastewater treatment plant and the St. Louis River in Minnesota and Wisconsin, U.S.A. Bulk characterization using ultraviolet-visible spectroscopy demonstrates that color and apparent size of DOM decrease downstream, while molecular composition analysis using Fourier-transform ion cyclotron resonance mass spectrometry reveals that saturation and chemodiversity is highest near Lake Superior. (DOM)-D-3 quantum yield coefficients and O-1(2) quantum yields increase downstream and correlate strongly with saturated formulas. Similar results are observed for carbon-normalized photodegradation rate constants of atorvastatin, carbamazepine, and venlafaxine, which react primarily with (DOM)-D-3 and O-1(2). In contrast, (OH)-O-center dot quantum yields are lowest downstream and correlate with less saturated, more oxygenated DOM, suggesting that (DOM)-D-3 is not its major precursor. Mixed relationships are observed for DEET, which reacts with multiple PPRI. Molecular-level compositional data reveal insights into the differing formation pathways of individual PPRI, but information about specific contaminants is needed to predict their photochemical fate.
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