Efficient degradation of organophosphate esters and an aromatic phosphine oxide by UV/periodate: selective radical mechanisms, pathways, and environmental implications

Photo-assisted advanced oxidation processes (AOPs) are promising for removing emerging contaminants. A UV/periodate system (UV/PI) was evaluated for the degradation of two organophosphate esters, trimethyl phosphate (TMP) and tris(2-chloroethyl) phosphate (TCEP), and an aromatic phosphine oxide comparator, triphenylphosphine oxide (TPPO), under 254 and 365 nm irradiation. Under matched conditions, UV/PI markedly outperformed UV or periodate alone and followed pseudo-first-order kinetics. Multiple lines of evidence including radical quenching, iodide quenching and iodine speciation, high-resolution mass spectrometry, and quantum-chemical analysis, indicate that hydroxyl radicals (•OH) dominate TMP and TCEP removal, whereas iodine-centered radicals (RIS; IO 3 •/IO 4 • − ) drive TPPO transformation. The process remained effective across pH 6.0–8.5 and retained substantial activity in natural waters despite inhibition by natural organic matter and common anions. Pathway analysis revealed hydroxylation, iodination, dechlorination, and aromatic ring-opening routes. Screening-level computational toxicity estimates suggest comparable or reduced risk for most products, with transient increases for some iodinated intermediates. At 254 nm, the electrical energy per order (EEO) was approximately 270, 304, and 100 kWh·m −3 ·order −1 for TMP, TCEP, and TPPO, respectively; the lower TPPO EEO reflects selective radical attack. In matched cross-AOP tests, UV/PI gave the highest TPPO removal rate, whereas UV/persulfate was faster for the aliphatic OPEs; comparisons are substrate- and system-specific rather than universal. Overall, UV/PI emerges as a selective, non-catalytic, photo-assisted process that links structure to reactivity and energy demand. The 365 nm results demonstrate feasibility with UVA LEDs/sunlight.