Study On Chlorination Of β-N-methylamino-L-alanine And 2,4-diaminobutyric Acid

β-N-methylamino-L-alanine(BMAA)and 2,4-diaminobutyric acid(DAB)are chemically stable,widely distributed algal toxins,which show high biological accumulation and amplification.They are accumulated in human bodies through the ingestion of foods containing neurotoxin.In this study,the degradation of BMAA and DAB and the resulting disinfection byproducts(DBPs)during chlorination were investigated,which provided fundamental data for the health risk assessment of BMAA and DAB in drinking water sources.In this study,an analytical method for the determination of BMAA and DAB was established,which employed HPLC-MS/MS for qualitative and quantitative analysis.The recoveries were between 90%and 105%,and the detection limit was 0.2 μg/L and 1.4 μg/L for BMAA and DAB,respectively.For the analysis of DBPs,gas chromatography(GC-ECD)was used for the qualitative and quantitative analysis.For all the DBPs in this study,the detection limits were in the range of 0.56-2.34 μg/L,and the recoveries were 84-95%.By using the established methods,water samples from Taihu Lake were detected.BMAA and DAB were detected in all the collected samples,indicating that these two algal toxins were widely present in Taihu Lake.For the samples collected in October2015,the concentrations of BMAA were in the range ofo.8-230.8 ng/L.For the samples collected in January 2016,the concentrations were significantly lower,which were in the range of 1.7-24.2 ng/L.The concentrations of DAB were generally low,which were below 2 ng/LMoreover,it was found that both BMAA and DAB underwent degradation during chlorination.Longer contact times,higher temperatures,acidic conditions and higher chlorine dosesenhanced the degradation of BMAA and DAB.The DBPs resulting from BMAA and DAB included THM(TCM),HANs(TCAN,DCAN),HAAs(TCAA,DCAA),and some other DBPs(1,1,1-TCP,TCNM).1,1,1-TCP and TCNM were not detected in chlorinated BMAA samples.For the chlorinated BMAA samples,the formation of TCM,DCAA and TCAA increased with time.In addition,due to the hydrolysis,DCAN and TCAN first increased and then decreased with time.Higher temperature resulted in the increasing formation of TCM,DCAA and TCAA and the decreasing formation of TCAN and DCAN.The alkaline conditions resulted in the decreasing formation of HANs and HAAs,and the increasing formation of TCM.Meanwhile,increasing the chlorine dose increased the formation of all the DBPs except TCM.For the chlorinated DBA samples,the formation of TCM,DCAA,TCAA,1,1,1-TCP and TCNM increased with time.Owing to the hydrolysis,DCAN and TCAN also first increased and then decreased with time.Higher temperatures resulted in the increasing formation of TCM,DCAA,TCAA,1,1,1-TCP and TCNM,and the decreasing formation of DCAN and TCAN.The alkaline conditions reduced the generation of HANs and HAAs and increased the formation of TCM,1,1,1-TCP and TCNM.Higher chlorine doses resulted in the increasing formation of all the DBPs.Finally,the formation pathways of the DBPs from BMAA and DAB were proposed in this study.During chlorination of BMAA and DAB,TCM was generated from chloral chloride as an intermediate product,or was formed by the hydrolysis of DCAN.HANs generate nitrile further through the decomposition of intermediate chlorinated precursor,then nitrile has a reaction of chlorination.At last chain scission results HANs.DCAA is generated from intermediate chlorinated precursor,which has the structure of a cyano group and an amino group.Meanwhile,a portion of TCAA was formed through the conversion of TCAN.Since DAB has the γ-position amino group,which can be conversed to DCAN through a series of reactions,chlorination of DAB generated more DBPs than BMAA.