| With the development of technology,electronic products,and electrical equipment have appeared in family around the world.Brominated flame retardant(BFRs),as an additive in electronic products and plastic polymer,could reduce the ignition point of products and the rate of fire.Tetrabromobisphenol A(TBBPA),as one of the largest and most widely used BFRs,has been widely detected in environmental and received extensive attention from scientific researchers.Mangrove wetland is an important ecosystem,located in the intertidal zone,and mangrove sediment is a sink of many organic pollutants.Up to now,researchers on the pollution level and distribution characteristics of TBBPA in mangrove sediment,on the uptake and accumulation,biotransformation and physiological response of TBBPA in mangrove plants,and the effect of mangrove plants on the removal of TBBPA in sediment and the associated microbial mechanism were still unknown.Therefore,the present study firstly focuses on the pollution level and distribution characteristics of TBBPA and the related microbial community composition in mangrove sediments.Secondly,hydroponic experiments were conducted to explore the uptake and accumulation,biotransformation,and physiological response of mangrove plants to TBBPA.Thirdly,we investigated the impact of mangrove plants on the dissipation of TBBPA in a pot experiment and the association microbial mechanism.The main findings are as follows:1.The pollution levels and distribution characteristics of TBBPA in three mangrove sediments were investigated and the main results as follows:(1)The range and averages concentrations of TBBPA in mangrove sediments from Zhangjiang estuary,Jiulongjiang estuary and Quanzhou bay were nd-20.46 and 7.78 ng g-1 dw,3.4740.77 and 11.63 ng g-1 dw,nd-19.83 and 9.67 ng g-1 dw,respectively;(2)Main pollution source of TBBPA was agricultural pollution discharge,meanwhile the levels of TBBPA was affect by urbanization and industrialization;(3)Relative analysis indicated that TBBPA concentrations was significantly correlated with TOC in mangrove sediment from Jiulongjiang and Zhangjiangko,there was no positive correlation between TBBPA and TOC in sediments from Quanzhou bay;(4)There was significantly correlated between TOC and TN in sediment,indicated that TOC and TN had the same pollution sources with TBBPA;(5)Some reasons for the lower TBBPA concentration in mangrove sediments,on the one hand,mangroves are located in downstream of the river,part of TBBPA was deposited in river sediments during the surface runoff;on the other hand,TBBPA was easily migrate from sediments to the overlying water under periodically intertidal conditions;thirdly,TBBPA was reductive dehalogenation by anaerobic microorganisms under hypoxic and anaerobic conditions;(6)16S rRNA high-throughput sequencing results shown that the main phylum microbia contain Proteobacteria,Chloroflexi,Actinobacteria,Firmicutes,Acidobacteria,Bacteroidetes;the main genus include Anaerolineaceae,Sulfurovum,Chloroflexi,Acidobacteria,Thiobacillus,Nitrospira,Desulfobulbus,Chlostridium,Gracilibacteria,Actinobacteria,Thioalkalispira,Robiginitalea;some genus are responsible for the elimination of aromatic and halogenated organic contaminants.2.A hydroponic experiments was conducted to investigated the uptake,transcolation,biotransformation and physiological response of K.obovata and A.marina to TBBPA,the main conclusions as followed:(1)K.obovata and A.marina could uptake TBBPA from solution,and them translocate to stems and leaves;the high TBBPA concentrations significantly increase TBBPA concentrations in roots,stems and leaves of K.obovata and A.marina seedlings,TBBPA was mainly accumulate in roots of two mangroves plants;(2)Bioaccumulation factor(BCFr)of TBBPA in K.obovata seedling roots was significantly higher than that in A.marina roots,while the translocation factor(TFs-1)of TBBPA in A.marina seedlings was greater than that in K.obovata seedlings;(3)After 14-days treatment with high TBBPA concentrations,the total biomass,chlorophyll a,chlorophyll b and total chlorophyll content of K.obovata seedlings were significantly reduced,on the contrary,there has no impact on the grow of A.marina seedlings;(4)Electron paramagnetic resonance spectroscopy(EPR)detection results indicated that TBBPA induced the production of quinone radicals in roots and leaves of K.obovata and A.marina seedlings;(5)Exposure to the high TBBPA concentrations for 14-days significantly increased the content of malondialdehyde(MDA)in roots and leaves of K.obovata seedlings;(6)At 7-days and 14-days of TBBPA exposure treatments,the activities of superoxide dismutase(SOD)and peroxidase(POD)in roots and leaves of K.obovata seedlings increased firstly and then decreased,and the activity of catalase(CAT)in roots and leaves of K.obovata seedlings increased during the experiments;(7)Activities of SOD,POD,CAT in A.marina seedlings roots and leaves were activated,which could eleminate the oxidative stress caused by TBBPA;(8)UPLC-MS/MS analysis indicated that the biotransformation products of TBBPA in mangrove plants include hydroxylationtetrabromobisphenol A(OH-TBBPA),tribromobisphenol A(TriBBPA),monobromobisphenol A(MonoBBPA)and bisphenol A(BPA),revealed that the biotransformation pathway of TBBPA in mangrove plant including hydroxylation and reductive dehalogenation.3.A pot experiment was carried out to explore the key role of TBBPA removal in the rhizosphere process of mangrove plants and the interaction mechanism between plant and microbial.The following conclusions were shown:(1)Removal of TBBPA was mainly owing to the microbial degradation in mangrove sediments,the planting K.obovata and A.marina promote the degradation of TBBPA,and the degradation efficiency of TBBPA was higher in K.obovata rhizosphere than that in A.marina rhizosphere;(2)TBBPA undergoes a reduction dehalogenation process in mangrove sediments,the dehalogenation products include TriBBPA,DiBBPA,MonoBBPA and BPA,the transformation of DiBBPA to MonoBBPA was the limiting link of reduction dehalogenation;(3)K.obovata and A.marina could uptake,accumulate and translocate TBBPA to the above-ground part from sediment,the larger TBBPA contents accumulates in roots and stems;(4)The bioaccumulation sediment factor(BSCFr)of TBBPA in K.obovata roots was greater than that of A.marina roots,while TBBPA stem-leaf translocation factor(TFs-1)in A.marina was greater than TFs-1 in K.obovata;(5)Mass balance results shown that the fate of TBBPA were bound residue,plant accumulation and microbial degradation,and the removal of TBBPA mainly due to the biodegradation,biotransformation and bioaccumulation by microorganisms;(6)The activities of urease and dehydrogenase in rhizosphere sediments of K.obovata and A.marina were significantly higher than those without plant treatment.The abundance and diversity of microorganisms in rhizosphere sediments were higher than that in nonrhizosphere sediments,and the total number of bacteria in rhizosphere sediments was significantly higher than that in sediments without plants;(7)The microbial β-diversity analysis showed that the composition and evolution of the microbial community were mainly affected by mangrove species;(8)Different evolutionary processes of microbial community in rhizosphere of K.obovata and A.marina lead to the different degradation efficiency of TBBPA;(9)TBBPA degradation-related functional microorganisms(Geobacter,Pseudomonas,Flavobacterium,Azoarcus)also play an important role in the degradation of TBBPA;(10)K.obovata and A.marina could enhance the dissipation of TBBPA in sediments,and K.obovata and A.marina could be used as potential species to remediation TBBPA contamination in estuary sediment. |
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