Environmentally Relevant Concentrations of Nanomaterials Drive Photochemical Production of Reactive Species and Pollutant Degradation in Surface Waters

Reactive intermediates in surface waters are widely attributed to dissolved organic matter (DOM). Natural, incidental, or engineered nanomaterials simultaneously occur at parts per billion and can function as photocatalysts, yet the photochemical role of nanomaterials at environmentally relevant concentrations remains overlooked in surface water photochemistry. Here, we quantify reactive intermediates from TiO2 nanomaterials (1–100 μg L−1) and DOM (1–5 mgC L−1) under 222, 265, and 365 nm. Despite lower concentrations relative to DOM, TiO2 produces hydroxyl radical (HO•) rates 10× to 100× higher per unit mass, resulting in comparable HO• formation. DOM plus nanomaterial mixtures shows synergistic behavior, with HO• formation 16-21% above additive predictions. DOM has limited impact in the degradation of 6PPD-quinone whereas nanomaterials enhanced its degradation due to elevated [HO•]ss. These results demonstrate nanomaterials can contribute to or exceed DOM in HO• driven micropollutant degradation in surface waters or engineered ultraviolet-light water treatment systems. Environmentally relevant nanomaterial concentrations can rival dissolved organic matter in driving pollutant transformation under sunlight or UV-based water treatment.