A preliminary study on the photolysis mechanism of organophosphorus compounds driven by dissolved organic matter and reactive intermediate species in aquatic environments

Dissolved organic phosphorus (DOP) serves as a crucial phosphorus (P) reservoir in aquatic systems, regulating P biogeochemical cycling and eutrophication dynamics. In this study, five representative organic phosphorus compounds (OPs), encompassing phosphate monoesters, phosphate diesters, and phosphonates, were systematically examined under contrasting aqueous matrices, including ultrapure water, freshwater, and seawater. Their photolysis kinetics were systematically quantified, yielding apparent first-order rate constants of 1.13–2.26 × 10 −4  h −1 in ultrapure water, 0.70–1.83 × 10 −3  h −1 in seawater, and 0.60–3.13 × 10 −3  h −1 in freshwater, with phosphate esters consistently exhibiting higher photochemical reactivity than phosphonates. To elucidate environmental influences, simulated water matrices were constructed by incorporating representative inorganic ions (NO₃ − , HCO₃ − , Cl − , Br − , and SO₄ 2− ) and dissolved organic matter (DOM). DOM exhibited pronounced photochemical complexity, characterized by intrinsically heterogeneous molecular architectures and persistent associations with DOP, underscoring the necessity for targeted mechanistic investigations. Furthermore, radical quenching and probe experiments delineated DOM-mediated RIs formation pathways and reactivity, identifying 3 DOM* as the dominant photoreactive species, with 1 O₂ and ·OH contributing synergistically. Furthermore, three-dimensional correlation analyses integrating DOM compositional characteristics, RIs-driven photodegradation kinetic parameters, and experimentally determined OP photolysis rate constants revealed that DOM molecular structure and intrinsic photochemical reactivity are tightly coupled to RIs generation pathways, thereby indirectly governing OP photolysis dynamics. Collectively, these results advance mechanistic understanding of the abiotic transformation processes and environmental fate of OPs in natural aquatic systems, with direct implications for P risk assessment and evidence-based water management strategies.