Organophosphorus flame retardants (OPFRs) are commonly applied in many consumer products, resulting in their widespread distribution in water, soil and indoor air. It is in urgent need of developing efficient and safe removal methods for OPFRs. The degradation kinetics and mechanism of tris(2-chloroethyl) phosphate (TCEP), a representative OPFR, by ultraviolet-persulfate (UV/PS) were explored, and the toxicological assessment of degrading intermediate mixture was performed using isobaric tags for relative and absolute quantitation proteomic technology. The results indicated that UV/PS had a high transformation efficiency of TCEP ([TCEP](0) = 3.5 mu M, [S2Og2-](0) = 175 mu M, apparent rate constant reached 0.1272 min(-1)) with the generations of three primary intermediates, including C4H9Cl2O4P (m/z 222.97, 224.97), C6H13Cl2O5P (m/z 266.99, 268.99) and C2H6ClO4P (m/z 160.98, 162.97), through the selective electron-transfer reactions induced by activated sulfate radical. Compared to that of TCEP, the Escherichia coli ATCC11303 exposed to intermediate mixture expressed 64 up-regulated proteins those primarily associated with nutrient import, energy generation, DNA protection and signal transduction. The 86 down-regulated proteins were related to DNA repair, protein turnover and stress response, suggesting that the toxicity of the degrading intermediate mixture decreased significantly. The current study provided insights into the molecular mechanisms of TCEP and its degrading intermediate mixture on E. coli, clarifying that the UV/PS degradation is an alternative efficient and safe treatment method for TCEP. (C) 2016 Elsevier B.V. All rights reserved.