Oxidation degradation of tri(dichloropropyl) phosphate by UV/H2O2 system: Degradation pathways and risk assessment of intermediates

In this work, 5 mg/L of tri(dichloropropyl) phosphate (TDCP) was degraded by UV/H2O2 system in aqueous solution. At 900 min, the removal rate of total organic carbon (TOC), pH values, concentrations of Cl- and PO43- reached 31.7 %, 3.5, 0.09 mg/L, and 0.10 mg/L for TDCP, respectively. The degradation process of TDCP obeyed the pseudo-first-order kinetic formula with a reaction rate constant k of 0.0021 min(-1). The intermediates of the degradation of TDCP were detected, which contained some dechlorinated and hydroxylated products. The degradation pathway of TDCP in the UV/H2O2 system was proposed based on the intermediates and calculations of density functional theory (DFT). For the first time, the environmental risks of the intermediates of TDCP were estimated via the "ecological structure-activity relationships" (ECOSAR) program, and acute and chronic toxicity changes of intermediate products were pointed out. The measurement of the luminescence inhibition rate suggested that the intermediates of TDCP degraded by UV/H2O2 system were more toxic than TDCP because of the production of Cl-containing compounds. The study of the environmental behavior of TDCP helps to deepen the understanding of organic phosphorus flame retardants, and provides a scientific basis for the comprehensive prevention and control of such substances and the formulation of environmental regulations.