Photochemical Formation of Long-Lived Oxidative Organic Radicals from Algal-Derived Dissolved Organic Matter under...

Algal-derived dissolved organic matter (ADOM) released by algal blooms is an important photosensitizer in natural water bodies and participates in a variety of photochemical processes. This study investigates the formation and reactivity of photochemically generated long-lived reactive species (LLRSs, specifically oxidative organic radicals herein) from ADOM and compares it with that from terrestrial dissolved organic matter (SRDOM) under full spectra, ultraviolet (UV) portion (290-420 nm), and visible portion (420-710 nm) of solar irradiation. The LLRSs from ADOM exhibited higher one-electron reduction potentials (1.00-1.06 V in solar full spectrum; 0.91-1.00 V in visible light) than those from SRDOM (0.91-1.00 V in solar full spectrum; 0.85-0.91 V in visible light). The apparent quantum yield of LLRSs (Φ_LLRSs^app) from ADOM was 2.2 × 10^-4 under full spectra of solar irradiation, slightly higher than that of SRDOM (1.8 × 10^-4). Although Φ_LLRSs^app from ADOM under visible light (1.3 × 10^-4) was about five times lower than that under UV irradiation (6.3 × 10^-4), their formation rates were comparable (1.7 × 10^-9 M s^-1 for visible light vs. 2.6 × 10^-9 M s^-1 for UV), owing to the stronger light absorption in the visible range. The formation of LLRSs was classified into dissolved oxygen (DO)-inhibited and DO-promoted pathways, with DO-inhibited processes accounting for 98% and 87% of the total LLRSs formation in SRDOM and ADOM, respectively. The degradation of 27 emerging organic contaminants demonstrated greater LLRSs involvement in ADOM, especially under visible light. These results underscore the key role of LLRSs in contaminant attenuation in bloom-impacted waters and highlight the importance of visible-light-driven photochemistry in enhancing the self-purification potential of ADOM-affected waters.