Non-target Identification And Distribution Characterization Of Organosilicon Compounds In Typical Environmental Matrices

Silicones have a unique molecular structure and show chemical properties like both organic and inorganic compounds.Silicones can be applied in many industrial and daily-life actives.Among the compounds,methylsiloxane is used widely and investigated in depth.Due to the unique chemical properties,methylsiloxane is found in various kinds of industrial and household products,resulting in numerous routines to enter the surrounding environment.Meanwhile,modified siloxanes were also developed and applied to meet specific industrial requirements,and their discharge in environment should also be considered.In addition,a number of silicon-containing intermediates and products are generated in natural matrix,since siloxanes could be degraded or reacted with other substances.Therefore,in typical silicone-producing areas,an understandof methylsiloxanes,modified siloxanes,and their transformation products are crucial for a comprehensive evaluation of the environmental risk of organosilicon compounds.However,little relevant studies focused on this field.This work established a target/non-target identification method for organosilicon compounds in environmental media.Four typical silicone factories and their surrounding residential areas were chosen for the research to investigate the concentration profiles and distribution characteristics of methyl siloxanes and modified siloxanes in atmospheric particulate matter.A non-target screening method was established for organosilicon compounds in nature and used for the non-targeted screening of degradation products of cyclic siloxanes（D4-D6）in atmospheric and organosilicon compounds in the natural environment.The thesis is divided into five chapters:In Chapter 1,this thesis provides an overview of siloxanes in production and domestic applications;the fugacity and environmental behavior in the natural environment;bioaccumulation,toxicity and degradation;and pathways in different environmental matrix.In Chapter 2,pre-treatment and instrumental analytical methods were established to determine methyl siloxanes and modified siloxanes in airborne particulates,as well as the screening of environmental silicones.In Chapter 3,it was investigated for the fugacity levels of methyl siloxanes and modified siloxane in atmospheric particulates in thermal power plants,petrochemical plants,tire plants,sewage treatment plants,and three residential areas around the pillar industries in Dongying City.The highest concentration of methyl siloxanes in particulate matter from the tire plant was found to be 466μg/g,which was 19 times higher than that in the surrounding residential area（24.4μg/g）.Linear methyl siloxanes were the main components,with L7 and L8accounting for more than 30 percent of the total concentration.Phenylsiloxane,trifluoro propyl siloxane,and vinyl siloxanes were detected to varying degrees in the WWTP,and phenylsiloxanes were also found in residential areas,but none of these modified siloxanes were found in other plants.In Chapter 4,a method for non-targeted screening of organosilicon compounds has been established using high-resolution mass spectrometry FT-ICR-MS for sample detection according to the nature of Si isotopes.In nature,Si exists in form of three isotopes,²⁸Si,²⁹Si and ³⁰Si,which present fixed values for the abundance interval in the mass spectrum:Δm/s(²⁹Si-²⁸Si)=0.999568,Δm/s(³⁰Si-²⁹Si)=0.997276,Δm/s(³⁰Si-²⁹Si)=1.996844.Based on these values,the screening could be carried out for a large number of natural environmental Si-containing contaminants.Meanwhile,abundances of Si isotopes in nature are constant,²⁸Si,²⁹Si and ³⁰Si accounting for 92.23%,4.68%,and 3.09%,respectively.The same abundances in nature can also be reflected in the mass spectra,which gives this same proportion of mass spectrometric isotope peaks in area.This would allow us to determine the number of Si in a compound by comparing the abundances.Based on this,silicone compounds are identified using Bruker Data Analysis,a data analysis software of the assay device,to complete the screening of the sample for silicone compounds.In Chapter 5,the non-targeted screening of silicone compounds was presented for atmospheric D4-D6 degradation products,and influent/effluent of a wastewater treatment plant and its receiving water bodies.Additionally,the degradation of D4,D5,and D6 under natural light was simulated using Si O₂nanoparticles as catalysts,respectively,and,13,10,and10 degradation products were identifiedwith the non-targeted screening,respectively.Structure speculation was carried out based on parent siloxanes.A total of 99 organosilicon compounds were identified in the water column after the non-targeted screening of the influent/effluent and the river water.