Mechanisms of the Impacts of Anions on Tris(2-Chloroelthy) Phosphate (Tcep) Degradation by Uv/Peroxydisulfate (Pds)

Tris(2-chloroethyl) phosphate (TCEP), a substitute for bromide flame retardants, is frequently detected in aqueous environments. Previous studies proved anions affect TCEP pseudo-first-order degradation constants ( kobs ) based on sulfate radical-based advanced oxygen processes (SR-AOPs), they were concentrated on qualitative major radical species rather than quantitative radical concentration. In this article, radical steady-state concentration and carbon isotope enrichment factor ( εC ) were coupled to express TCEP degradation mechanisms. In the absence of extra anions, SO4−• was the dominant radical attributed to 92% of the TCEP degradation and yielded εC of −1.6 ± 0.2 ‰ . Meanwhile, three intermediates (C6H13Cl2O5P, C6H11Cl2O6P and C4H9Cl2O4P) were identified and generated via hydroxylation and dechlorination. When Cl− was present, Cl2−• was the dominant radical instead of SO4−•, and Cl− had no obvious effects on kobs values. In the presence of HCO3− , kobs gradually declined with increasing HCO3− because of an increase inhibitor CO3−•. In contrast, HPO42– accelerated TCEP degradation, with nearly a 2-fold higher k obs than that observed without HPO42– , which could mostly be attributed to HPO4−•. Additionally, the εC values reached in the presence of extra anions ranged from −1.5 ± 0.3‰ to −2.7 ± 0.2‰, and they were independent of the anion type and concentration. Stable εC were achieved in this study, which may be a better parameter for evaluating TCEP field remediation replaced fluctuation kobs