Mechanisms Study On Characterizing Chemical Oxidation And Biodegradation Of Organophosphorus Ester Flame Retardants

With the gradual restriction and phase-out partial use of flame retardants(FRs),such as polychlorinated biphenyl(PCB)and polybrominated diphenyl esters(PBDEs),and because of their persistent bioaccumulation and toxicity,the demand for FRs is increasing.Dependent on their technical characteristics,organophosphorus ester(OPE)flame retardants are major components of FRs and are suitable substituents for brominated flame retardants(BFRs).Depending on their extensive consumption in many consumer products,OPE flame retardants were widespread distribution in multi-environment matrices,such as aquatic,terrestrial and atmospheric.Considering potential adverse effects have been observed in animals exposed to OPE flame retardants,such as neurotoxicity,skin irritation and dermatitis,and are thus of increasing concern.Therefore,developing efficient and safe methods for removing OPE flame retardants is urgent.In this study,compound-specific stable isotope analysis(CSIA)and production identification analysis were both applied using chemical degradation and biodegradation to investigate the degradation mechanism of tri-(2chloroethyl)phosphate(TCEP)and tributyl phosphate(TBP),which are representative types of chlorinated and halogen-free OPE flame retardants.The liquid-liquid dichloromethne extraction method was applied in this study.The recovery of TCEP and TBP were in the range of 84.6%-99.2%and 85.1%-101.4%,respectively.The isotope shifts of carbon and hydrogen were stable under the uncertainty of carbon and hydrogen isotope compositions respectively.Hence,extraction methods and analytical isotope data were reliable in this study.Carbon and hydrogen isotope fractionation were measured in the systematic investigation of radicals(C12-·,SO4-· and·OH)through pH-dependent potassium peroxydisulfate(KPS)oxidation and UV/H2O2 process.The results indicated that the presence of Cl-efficiently decreased the degradation kinetics constants of TCEP and TBP.For the same compound,different radicals(like Cl2-·、SO4-·、and·OH)were gained identical isotope fractionation,which indicated the same degradation mechanisms causing C-H bond split.For the same radical,however,the isotope enrichment factors clearly decreased from TCEP to TBP,due to isotope "dilution"、effects.All TBP hydrolysis experiments were followed pseudo-first order kinetics,in the order of pH 12>pH 9>pH 7 ≈ pH 2.Carbon isotope fractionation was found in pH 2,pH 7 and pH 9 hydrolysis,which was in accordance with the mode of C-O bond split and causing an apparent carbon kinetic isotope effect(AKIEc)ranged from 1.045 to 1.058.The observed negligible carbon and hydrogen isotope fractionation of TBP at pH 12 highly supported a nucleophile displacement(SN2-type)leading P-O bond split.A series of pH-dependency of KPS oxidation were obversed both carbon and hydrogen isotope fractionation with an AKIEc of 1.007 to 1.011,positive supporting of C-H bond split.A TBP-degrading strain isolated from a mining area,which belonged to genera Sphingomonas according to phylogenetic analysis and identified by 16s rDNA.Results validated the intermediates of TBP including dibutyl phosphate(DnBP)and monobutyl phosphate(MnBP)were detected by liquid chromatography—time-of-flight mass spectrometry.No obvious change of carbon and hydrogen isotope composition was observed in both cell suspension and crude extract degradation,which indicated the first irreversible bond cleavage did not involve carbon or hydrogen element.