Degradation of aqueous tris(2-chloroisopropyl) phosphate by electrochemical oxidation process: Mechanisms, toxicity and ecological risks of intermediate products

Abstract

In this study, we investigated the electrochemical oxidation of the organophosphate flame retardant tris(2-chloroisopropyl) phosphate (TCPP). The results demonstrated the effective elimination of TCPP following pseudo-first order kinetics. The degradation efficiency of TCPP attained 98.4 % and the corresponding reaction rate constant (k) was 0.0502 min−1, with the initial concentration of 1 mg/L, current density of 10 mA/cm2, and Na2SO4 of 10 mM. Quenching experiments revealed that ·OH played a vital role, with a contribution rate of 91.3 %. Environmental indicators in water significantly influenced the degradation efficiency, where Cl− had an inhibitory effect, while humic acid (HA), NO3−, and HCO3− enhanced degradation at lower concentrations. A total of six intermediates (C6H13Cl2O4P, C3H8ClO4P, C9H18Cl3O5P, C9H17Cl2O6P, C6H12ClO6P, and C3H8ClO5P) were generated through oxidation, dichlorination and hydrolysis reactions. TCPP induced cell apoptosis of Escherichia coli (E. coli), with the proportions of apoptotic cells decreasing from 33.3 % to 1.6 % after 180 min of degradation. Furthermore, the ecological toxicity was predicted to decrease during the electrochemical oxidation using ECOSAR software. TCPP did not induce the microbial community composition at the phylum level, while the bacterial abundance at genus level significantly changed. The dominant genus Methylotenera, accounting for 15.6 % in the control, decreased to 6.8 % in the presence of TCPP, and subsequently increased to 9.3 % in the 120 min products exposure groups. Electrochemical oxidation process could effectively degrade and detoxify TCPP, as well as reduce the ecological risks.