| The emerging brominated flame retardant 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane(TBECH)and ultraviolet filter benzophenone(BP-3)are typical endocrine disruptors,which widely exist in multi-media environments.Although they often exist as micro-pollutants in the environment,they may still pose a persistent threat to ecosystems and human health.The pathways of human and organisms exposed to endocrine disruptors are varied,and the accumulation of respiration,drinking water and food chain are important exposure pathways.Therefore,understanding the environmental persistence and fate of endocrine disruptors is very important to clear the environmental risks caused by these substances.However,the transformation mechanism and half-life of TBECH and BP-3 in atmosphere and aquatic environments are still not thoroughly studied,especially the potential environmental impact of their transformation products in the environment is not clear.More importantly,the treatment effect of traditional wastewater treatment technology on some endocrine disruptors is not ideal,resulting in their residues in the aquatic environments.Advanced oxidation processes(AOPs)rely on active oxidation species with high oxidation activity,which can efficiently degrade some stubborn micro-pollutants,so they have attracted more and more attention.In recent years,AOPs has been widely studied and applied to industrial wastewater treatment.Among them,several prevailing AOPs include AOPs based on reactive oxygen species(ROS),reactive chlorine species(RCS),sulfate radical(SR)and carbonate radical(SPC).Nevertheless,the effectiveness of these AOPs for the treatment of TBECH and BP-3 in wastewater still needs to be evaluated.The aims of water treatment technology for the treatment of pollutants is not only to degrade into smaller molecules,but also low toxicity and even non-toxic are key indicators.Therefore,the effectiveness of AOPs in the treatment of TBECH and BP-3 wastewater needs to be evaluated from the half-life of target pollutants and the toxicity of transformation products,which needs to clarify the transformation mechanism,kinetics and toxicology.In this thesis,quantum chemical calculation method was used to study the transformation mechanism of typical endocrine disruptors TBECH and BP-3 initiated by oxidative active species in atmosphere and aquatic environments.The rate constants of all initiation reactions were obtained by using the transition state theory(TST).On this basis,the half lives of TBECH and BP-3 in atmosphere,surface water,seawater and various AOPs were calculated.In addition,the acute and chronic toxicity,developmental toxicity,mutagenicity,bioaccumulation effect and biomagnification effect of the transformation products were evaluated by computational toxicology.The contents and conclusions of this paper include the four parts as follows:1.Transformation mechanism and potential environmental impact of 1,2-dibromo-4-(1,2dibromoethyl)cyclohexane stereoisomers initiated by ·OH in atmosphere1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane(TBECH),as an emerging brominated flame retardant(EBFR)pollutant,has been often observed in the air,and to comprehend its fate in the environment is still challenging due to the diversity of its stereoisomers.In this work,the environmental transformation behavior and potential toxicological implications of TBECH stereoisomers under the oxidation of OH in the gas phase were investigated by computational chemistry.Our results indicate the complexity of the TBECH transformation reactions and the diversity of its transformation products in the atmosphere.Although the reactions of TBECH enantiomers with OH exhibit highly consistency,it is obvious that the reactions of the four diastereoisomers of TBECH with OH and their subsequent reactions have both specificity and similarity.The dehydrogenation intermediates produced by H-abstraction of OH in the initial reactions may undergo oxidative debromination,hydroxylation and decomposition reactions,leading to the transformation into low bromine and monohydroxy substituted compounds,as well as debrominated or unbrominated unsaturated fatty ketones.The toxicity assessments show that all transformation products are less toxic to aquatic organisms than TBECH,but some of them are still classified at toxic or harmful levels.More importantly,some transformation products still exhibit carcinogenic and teratogenic activity.This study fills the gap in the research on the transformation mechanism and potential environmental impact of TBECH in the atmosphere,and it is of great significance to understand the atmospheric chemical process and guide the rational use and emission of TBECH.2.Chemical behavior and potential environmental risks of TEBCH transformation initiated by reactive oxygen species in surface water and AOPs1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane(TBECH),as an emerging pollutant,was often detected in the aquatic environments,but the chemical behavior and potential eco-toxicity of each stereoisomer are poorly understood.Here,the chemical behavior of TBECH stereoisomers under the oxidation of ROS(·OH and HO2·)in the aqueous phase was investigated by computational chemistry.Besides,the eco-toxicity effects of TBECH and representative transformation products were obtained by computational toxicology.In the natural environments,TBECH stereoisomers could be transformed under the initiation of ROS,and the key oxidation species is OH rather than HO2·in this process.DOM could indirectly promote the transformation of TBECH stereoisomers,resulting in the half-life(t1/2)of TBECH stereoisomers in less than 180 days,thus no longer maintaining environmental persistence.Although TBECH stereoisomers may show environmental persistence in natural waters,AOPs based on ·OH could bring about their rapid transformation,which predicts the effectiveness of OH-based AOPs for the treatment of TBECH wastewater.The results of the eco-toxicity assessment showed that the transformation of TBECH stereoisomers is beneficial to the reduction of toxicity,but the transformation products are not completely harmless.Thus,it is urgent to clarify the environmental behaviors and risks of these transformation products that remain toxic in the aquatic environments.The results of this study provide new insights into the environmental behavior and environmental persistence of TEBCH in surface water,and provide a theoretical reference for the application of AOPs in wastewater treatment of TEBCH.3.Study on transformation mechanism and kinetics of benzophenone-3 in atmosphere and natural watersBenzophenone-3(BP-3)is a widespread emerging organic pollutant.However,little is known about the synergistic effect of various reactive oxygen species(ROS)in natural waters and wastewater treatment plants on its transformation.In this study,the indirect photochemical behavior of BP-3 in the natural aquatic environments and the degradation process in the AOPs system were investigated by theoretical chemistry calculations.Besides the potential ecotoxicity effects,health effects,and bioaccumulation of the transformation products were assessed by computational toxicology.Results of transformation mechanism and kinetics showed that OH and 1O2 are the keys to the transformation of BP-3,whereas the role of HO2· and O3 can be ignored.AOPs based on ·OH and 1O2 could lead to the rapid transformation of BP-3,while the transformation of BP-3 in natural waters is slow,and even environmental persistence can be observed.However,dissolved organic matter(DOM)promotes the indirect phototransformation of BP-3 in natural waters.A variety of transformation products are generated under the synergistic effects of ROS,H2O,and 3O2.This study not only gives valuable insights into the indirect phototransformation of BP-3 in natural waters but also provides theoretical support for the feasibility of BP-3 degradation in industrial wastewater by AOPs based on ·OH and 1O2.4.Degradation mechanism,kinetics and toxicity evaluation of benzophenone-3 in several typical AOPs systemsThe degradation efficiency of BP-3 in wastewater treated by AOPs has been explored by experiments,but the micro-mechanism of degradation process and the evaluation of the effectiveness of AOPs based on various active oxidation species are still lacking,especially the research on the effectiveness of AOPs based on 1O2 in the treatment of BP-3 in wastewater is still blank.In addition,the synergistic effect of various active oxidation species in the subsequent reactions need to be further clarified.In this study,the transformation mechanism,kinetics,aquatic toxicity,developmental toxicity,mutagenicity and bioaccumulation of BP-3 in four AOPs(ROS-AOPs,RCS-AOPs,SR-AOPs and SPC-AOPs)were studied by using quantum chemistry and computational toxicology methods.The results show that although ROS-AOPs,RCS-AOPs,SR-AOPs and SPC-AOPs can lead to a short half-life of BP-3,ROSAOPs and RCS-AOPs seem to be more efficient than SR-AOPs and SPC-AOPs.In addition,among ROS-AOPs,1O2 is the most critical oxidation species leading to the rapid transformation of BP-3.In RCS AOPs,the most important oxidation species leading to the rapid transformation of BP-3 is Cl·.Although some products can still show toxicity,they do not have bioaccumulation effect and biomagnification effect,so all products are harmless to organisms and human health.This shows the effectiveness of ROS-AOPs,RCS-AOPs,SR-AOPs and SPC-AOPs in the treatment of BP-3 in wastewater.This study provides important theoretical support for the industrial application of the above four AOPs in the treatment of BP-3 wastewater. |
