Dissolved organic matter (DOM) composition influences its ability to form photochemically produced reactive intermediates (PPRIs). In sunlit surface waters, PPRIs can be essential to the degradation of organic contaminants via indirect photolysis. To investigate relationships between DOM composition, PPRI formation, and contaminant transformation in a wide variety of waters, we collected an extensive sample set: oligotrophic, mesotrophic, and eutrophic lakes, dystrophic bogs, rivers and streams impacted by agricultural runoff and wastewater effluent, and waters in highly urbanized watersheds. DOM was characterized using Fourier-transform ion cyclotron resonance mass spectrometry and bulk analyses including ultraviolet-visible spectroscopy and measurements of electron-donating capacity. Chemical probes were used to quantify steady-state concentrations and quantum yields for several PPRIs: triplet-state DOM (3DOM), singlet oxygen (1O2), and radical species (e.g. hydroxyl radical, ●OH). Photolysis rate constants of selected pharmaceuticals and pesticides were measured using a photoreactor (365 nm bulbs). Quenchers 1,4-diazabicyclo[2.2.2]octane (1O2 quencher), isopropanol (radical quencher), and sorbic acid (3DOM quencher) in oxygenated and nitrogen-sparged samples were used to determine relative contributions of the PPRIs to the photolysis of each target contaminant. Which PPRI(s) dominate(s) contaminant fate depends on the target molecule, but in most cases contaminant transformation rates are more efficient per mg-C L-1 of DOM for DOM derived from aquatic systems.

Linking dissolved organic matter composition to photochemical reactivity and contaminant transformation

ACS Spring Meeting 2021

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