A Study On The Removal Mechanism Of Sulfonamide By Vallisneria Natans(Lour.)Hara

In recent years,the extensive application of sulfonamides?SAs?in the fields of medicine and aquaculture raises concern regarding its negative environmental effects to aquatic ecosystems and its remediation have become of increasing concern to government and industry.Phytoremediation is considered as the most promising approach for the remediation of soil or water pollution.It is a new technology that uses plants to degrade,assimilate,metabolize or detoxify pollutants and an important research front in many disciplines.Submerged plants,at the bottom of the food chain,are exposed to both overlying water and sediment,and because they are all located below the water layer,their growth is closely related to the water environment.To explore the removal effect and mechanism of submerged plants on antibiotics,to develop cheap,efficient and environmentally friendly phytoremediation technology for SAs in water bodies,to provide suitable species resources,and to provide reference basis for other varieties of antibiotics to repair pollution.In this paper,the common submerged plant Vallisneria natans?Lour.?Hara was taken as the research object,and the mechanism of the submerged plant to remove?SN?in the water was studied systematically.The main results were as follows:?1?Experimental results of toxicological response of V.natans to SN showed that The toxic effect and oxidative stress caused by SN resulted in a reduction of total chlorophyll?chl.a and b?and autofluorescence of chloroplast.Meanwhile,the levels of reactive oxygen species?ROS,including O₂^-and H₂O₂?and peroxidase?POD?increased with increasing SN concentration and duration of exposure.After 20 days'exposure,a reduction in the relative growth rate?RGR?and leaf length of V.natans was found under SN stress,but SN had only a weak effect on root length.Although high SN concentrations had toxic effects on the growth of V.natans,the plant was overall resistant to the SN doses that we used.?2?The presence of SN had a negative effect on the removal of nitrogen and phosphorus nutrients from the water by V.natans.After 15 days,the TN and TP removal rates of the control group?CK?and treatment group?SD-T?reached 93.5%,70.1%,43.1%,and 29.2%,respectively.The reason why the effect of V.natans on the removal of nitrogen and phosphorus nutrients is different was that on the one hand,SN had a stress effect on the V.natans itself,destroying its normal physiological state and affecting its absorption function of nitrogen and phosphorus;SN also had a strong bactericidal effect,and its existence destroys the community structure of the root microbial community of V.natans and affects its normal function of removing nitrogen and phosphorus.?3?This study mainly explored the rule of removing SN from V.natans based on four aspects:p H,light intensity,SN concentration and water temperature.The main conclusions were as follows:1.The decline rate of SN in each p H treatment group was significantly lower than neutral and alkaline under acidic conditions?p<0.05?.Under neutral conditions?p H=7?,the leaves had the highest chlorophyll content,followed by alkaline conditions?p H=9?,and the lowest under acidic conditions?p H=9?.The chlorophyll content in neutral conditions was significantly greater than the chlorophyll content in V.natans leaves under alkaline and acidic conditions?p<0.05?;2.The stronger the light intensity,the greater the degradation rate of SN and the lower the SN concentration in the water;3.The SN in the low-concentration SN treatment group was first degraded,and the treatment group with V.natans in each concentration treatment group was degraded before the treatment group without V.natans;4.The degradation rate of SN was slowest in the 10?treatment group.However,the concentration of SN in the treatment group with V.natans was lower than that in the treatment group without V.natans;the concentration of SN in the treatment group at 30?decreased the fastest.Compared with the treatment group without V.natans,the treatment group with V.natans had faster SN degradation.?4?Enrichment,transformation and distribution of SN in V.natans showed that the content of SN(?g kg^-1)in V.natans was 3 orders of magnitude higher than that of the other four N4 acetyl metabolites(ng kg^-1).The accumulation of SN in V.natans was gradually increasing with time.SN was converted into 4 kinds of N4 acetyl metabolites after being enriched into the body by V.natans:Ac-SDZ?N4-acetyl sulfadiazine?,Ac-SMX?N4-acetyl sulfamethoxazole?,Ac-SMZ1?N4-acetyl sulfamerazine?,Ac-SMZ2?N4-acetyl sulfamethazine?,the content of metabolites was greater in the root than in the leaves.?5?Epiphytic algae are important primary producers in water bodies,to recognize community succession rules of epiphytic algae in the antibiotics pollute water body,macroscope counting method was used to study the responses of epiphytic algae on submerged macrophyte Vallisneria natans to sulfonamide?SN?supply by static incubation test.Results showed that colonization process and community composition of epiphytic algae varied with SN levels.Ulothrix and Oscillatoria are easier to colonize on the surface of leaves of V.natans than other algae populations,and the relative abundance of Ulothrix and Oscillatoria show a decreasing trend with time in the treatment group added with SN;High concentrations of SN(30 mg L^-1and 50 mg L^-1)promoted the colonization and growth of Chlorella;SN showed"low promotion and high suppression"in the colonization of Nitzschia,the lower concentration of SN(10 mg L^-1)stimulated the colonization and growth of Nitzschia,and high concentration of SN(30 mg L^-1and 50 mg L^-1)inhibited the colonization and growth of Nitzschia;The principal co-ordinates analysis?PCo A?indicated that the structure of the algae community on the surface of V.natans was also changed under the condition of SN stress,and the difference between the groups gradually decreased in the later period,which also indicated that the negative impact of SN decreased with time.?6?The effect of SN on the community structure of eukaryotic microorganisms attached to the leaves of V.natans showed that the Venn diagram showed that there were more types of microorganisms in the control group?Control?than in the SN treatment group?treated?.PCo A analysis showed significant differences between the microbial communities in each treatment group?p<0.05?.The relative abundance of species in different treatment groups showed that the abundance of Vorticella was greater in the Treated group,while the relative abundance of Paramecium and Oxytricha in the Control group was higher.The correlation network diagram and network structure characteristic data showed that the treatment of SN increases the stability of the eukaryotic microbial community attached to the leaves and the complexity of the network structure.?7?We studied the effect of V.natans on sulfonamide removal in an additional13-day exposure experiment with focus on the dynamics of dissolved oxygen?DO?,the oxidation-reduction potential?ORP?and microbial communities in the water column,as well as in the periphyton on V.natans surfaces.The results show that presence of V.natans significantly improved the SN removal efficiency likely by increasing DO,ORP and bacterial diversity in the water column.The presence of V.natans led to higher relative abundances of Saccharimonadales and Rhizoniales.Lefse analysis showed that Saccharimonadales,Micrococcales,Sphingobacteriales,Bacteroidales,Obscuribacterales,Flavobacteriales,Pseudomonadaceae and Myxococcales,which are considered to be SN-resistant bacteria,increased significantly in the V+S+?V.natans and SN?treatment compared with the V+S-?V.natans and no SN?treatment and V-S+?no V.natans and SN?treatment.Therefore,they were considered to be SN-resistant bacteria and played an important role in the removal of SN from water bodies.?8?Through the simulation of large barrels in the field,V.natans cultivated in different types of water was selected to carry out the removal experiment of SN.Our research results found that in the initial stage,no matter whether the microbial community in the water body or the leaves of V.natans are attached to microorganisms,there were significant differences between the treatment groups,and the composition of the microbial species in each treatment group was also different.Over time,the differences in the community structure of the microorganisms attached to the water body or the leaves of V.natans among the treatment groups gradually decreased.In the W treatment group,Sphingobacteriales and Flavobacteriales had relatively high abundance,which played a certain role in the removal of SN.