Identification Method Of New Siloxane Compounds In Typical Regional Environment And Its Generation / Degradation Mechanism

This dissertation mainly focused on the identification methods,generation and degradation mechanisms of new siloxanes,including modified and transformed products of methylsiloxanes in typical industrial and residential environments.It consisted of the following five chapters:In the first chapter,the research progress of environmental emission,fatesand toxic effects of methylsiloxanes in recent years were reviewed.Meanwhile,based on several preliminary studies,this part also introduced the application and environmental occurrence of modified methylsiloxanes?phenylsiloxanes and trifluoropropylsiloxanes?and transformed?halogenated?methylsiloxanes.In the second chapter,based on GC-MS,the pretreatment and analysis methods of phenylmethysiloxanes,trifluoropropylmethylsiloxanes and bromomethysiloxanes in landfill gas,liquid samples?sewage and leachate?,and solid samples?sludge,dust and soil?were developed.Additionally,each target compound has a good linear relationship in the range of 0.010-2.00?g/mL,with correlation coefficients greater than 0.99.The limits of quantification of target compounds were 3.82-8.23 ng/m³for gas,0.189-0.359 ng/L for liquids,and 0.185-0.451 ng/g for solids,respectively.In three types of matrices,the recoveries of all target compounds were 83-99%,with relative standard deviation?RSD?being within 10%.In the third chapter,during 20-d leaching experiment,mean concentrations of total P3 and P4 isomers[??P3+P4?]were 140 to 1255 ng/L in simulated leachates immersing electronic wastes?printed wire boards and light emitting diodes?collected from one Chinese landfill.From January 2017 to December 2018,two P3 isomers?cis-P3 and trans-P3?and four P4 isomers?cis-P4 and trans-P4a,b,c?were detected in raw leachates from active cell[<LOD-989 ng/L,detection frequency?df?=67-100%]and closed cell?LOD-281 ng/L,df=2.1-98%?of this landfill.Generally,mass loads of??P3+P4?in active cell were largest in summer?380 mg/d?,followed by winter?mean=295 mg/d?,spring?mean=178 mg/d?and autumn?mean=108 mg/d?,while they had a decreasing trend?from 36.1 mg/d to<LOD?in closed cell in the entire period.In the coupled leachate treatment system,sorption by sludge?64.0-84.4%?and Fenton treatment?8.5-25%?had dominant contributions to P3 and P4 removal.Fenton experiments indicated that hydroxylation half-lives were1.26-1.45 h for P3 isomers and 0.64-0.87 h for P4 isomers,which were 15-92 times faster than their hydrolysis half-lives?21.8-59.0 h,pH=3.5?.Furthermore,mono-hydroxylated P4 isomers with hydroxyphenyl group had larger?3.2-3.9 times?concentrations than those with methanol group,meaning that the phenyl group may be more likely to be hydroxylated than methyl group.In the fourth chapter,based on sludge and sewage samples taken from 29wastewater treatment plants?WWTP?located in 25 Chinese cities,the nationwide occurrence and composition profiles of phenylmethylsiloxanes?P3 and P4?and trifluoropropylmethylsiloxanes?D3F and D4F?was systematically investigated.cis-and trans-isomers of P3,P4,D3F and D4F were detected in 58 digested sludges[<LOD-188 ng/g dw?dry weight?,detection frequencies?df?=0-96.6%],while only P3 and P4 were detected in paired raw sewage samples[<LOD–13.5 ng/L for aqueous phase?df=1.72-96.6%?,and<LOD-165 ng/g dw for solid phase?df=22.4-96.6%?].Adsorption onto sludge had dominant contribution?up to 99%?to phenylmethylsiloxanes removal in WWTP.The emissions of phenylmethylsiloxanes in sludge in each region,except for the Southwest,were correlated with the reported consumption volume?R²=0.81?.Meanwhile,phenylmethylsiloxanes emission slightly correlated with regional per capita gross domestic products?GDP??R²=0.20?,while strongly correlated with the annual average temperature of the studied cities?R²=0.63?.Risk quotient values?RQ<0.01?of phenylmethylsiloxanes and trifluoropropylmethylsiloxanes in sludge indicated that there were low ecological risks in soils undergoing one year sludge-fertilization.In the fifth chapter,this part study investigated sources and fates of methylsiloxanes and their brominated products in one e-waste recycling area of China.During thermal?30-1000 ^oC?recycling experiments for printed circuit boards?PCBs?,besides volatile methylsilxoanes?D4,D5 and D6?,their mono-brominated products,i.e.,D3D?CH₂Br?,D4D?CH₂Br?and D5D?CH₂Br?,were also found by Q-TOF GC/MS,with 2-3 orders of magnitudes lower emissions?0.307-1.26?g/g?than those?18.1-866?g/g?of parent methylsiloxanes.Overall,the fastest emissions of methylsiloxanes and bromo-methylsiloxanes respectively occurred at 300-400 ^oC and400-500 ^oC,accounting for 35.3-51.0%and 39.4-82.1%of their total emission.In the e-waste recycling area,concentrations of D4-D6 were 1.14-75.0?g/g dw[detection frequency?df?=100%)]in 31 dusts from PCBs treatment workshops while<LOD-683 ng/g dw?df=69-100%?in 48 surrounding soils,which were up to 3orders of magnitudes higher than those in reference areas.Meanwhile,D3D?CH₂Br?-D5D?CH₂Br?were detected in both dusts?<LOD-1.18?g/g dw,df=48-52%?and soils?<LOD-70.3 ng/g dw,df=23-77%?from e-waste recycling area,while not found in reference samples.Simulating experiments showed that hydrolysis?9.01-378 d?and volatilization?8.55-1007 d?half-lives of mono-brominated D4-D6 in soils were 1.6-5.0 times longer than those of their parent methylsiloxanes.