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 (3DOM) and singlet oxygen (1O2) quantum yields, contradictory evidence exists for hydroxyl radical (•OH) 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. 3DOM quantum yield coefficients and 1O2 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 3DOM and 1O2. In contrast, •OH quantum yields are lowest downstream and correlate with less saturated, more oxygenated DOM, suggesting that 3DOM 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.

Fluorine incorporation into organic molecules has increased due to desirable changes in the molecular physiochemical properties. Common fluorine motifs include: aliphatic fluorines and −CF 3 , or −F containing groups bonded directly onto an aromatic (Ar−CF 3 and Ar−F) or heteroaromatic ring. Photolysis of these compounds, either in natural or engineered systems, is a potential source of new fluorinated byproducts. Given the potential persistence and toxicity of fluorinated byproducts, monitoring of product formation during photolysis of various fluorinated motifs is needed. 19 F-NMR is a means to detect and quantify these species. Ar−CF 3 and Ar−F model compounds (2-, 3-, and 4-(trifluoromethyl)phenol, 2-, 3-, 4-fluorophenol, and 2,6-, 3,5difluorophenol) were photolyzed under a variety of aqueous conditions: pH 5, pH 7, pH 10, 1 mM H 2 O 2 at pH 7 to form •OH, and 0.5 mM SO 3 2− at pH 10 to form e aq − . Pharmaceuticals with the Ar−CF 3 (fluoxetine) and Ar−F plus pyrazole-CF 3 (sitagliptin) motifs were treated similarly. Parent molecule concentrations were monitored with high pressure liquid chromatography with a UV detector. Fluorine in the parent and product molecules was quantified with 19 F-NMR and complete fluorine mass balances were obtained. High resolution mass spectrometry was used to further explore product identities. The major product for Ar−F compounds was fluoride. The Ar−CF 3 model compounds led to fluoride and organofluorine products dependent on motif placement and reaction conditions. Trifluoroacetic acid was a product of 4-(trifluoromethyl)phenol and fluoxetine. Additional detected fluoxetine products identified using mass spectrometry resulted from addition of −OH to the aromatic ring, but a dealkylation product could not be distinguished from fluoxetine by 19 F-NMR. Sitagliptin formed multiple products that all retained the pyrazole-CF 3 motif while the Ar−F motif produced fluoride. 19 F-NMR, mass spectrometry, and chromatography methods provide complementary information on the formation of fluorinated molecules by modification or fragmentation of the parent structure during photolysis, allowing screening for fluorinated photoproducts and development of fluorine mass balances.