Kinetics and degradation mechanism of tris (1-chloro-2-propyl) phosphate in the UV/H2O2 reaction

Abstract Tris (1-chloro-2-propyl) phosphate (TCPP) is a chlorinated organic phosphate used in various applications as a flame retardant and plasticizer. TCPP is a known suspected carcinogen and is not effectively removed by traditional water treatments such as biological, chlorination, and UV irradiation. In this study, the UV/H2O2 reaction was employed to degrade TCPP in water. TCPP was effectively degraded in the UV/H2O2 reaction by pseudofirst-order kinetics. The second-order rate constant of the reaction between the TCPP and OH radical was determined to be 4.35 (±0.13) × 108 M−1 s−1 using the competition kinetics with nitrobenzene as a reference compound. The degradation of TCPP was affected by the amount of H2O2, pH, and coexisting water components such as HCO3−, NO3−, and humic acid. Approximately 64.2% of total organic carbon (TOC) in TCPP was mineralized in 12 h during the UV/H2O2 reaction, whereas chloride (Cl−) and phosphate (PO43−) ions were identified as ionic byproducts with the recoveries of 96% chlorine (Cl) and 50% phosphorus (P). Five organic transformation products (TPs) of TCPP were also identified using LC-qTOF/MS. Considering the identified TPs, the main degradation pathway of TCPP during the UV/H2O2 reaction was found to be OH-radical-induced hydroxylation. Finally, a 70% decrease in bioluminescence inhibition in Vibrio fischeri was observed during the UV/H2O2 reaction, and the time-toxicity profile was similar to the time-peak area profile of TPs. The result of this study implies that TCPP can be efficiently removed with significant mineralization and toxicity reduction by the UV/H2O2 process.