The Migration,transformation Of Metformin In The Municipal Wastewater And Its Ecotoxicological Study

Diabetes is one of the most common chronic diseases,there are currently more than 551million patients worldwide,and about 90%of them have type 2 diabetes.China has about 116million patients,the country with the largest number of diabetics.Metformin?MEF?as the first choice and the whole-course drug in the treatment of diabetes,its consumption is also increasing.With the development of detection technology,MEF has been frequently detected in municipal wastewater,surface water,groundwater,activated sludge,sediment,and drinking water.Although the concentration level of MEF was ng/L-?g/L,its impact on the ecological environment cannot be ignored.Therefore,MEF was used to investigate its stability in wastewater and sewers after being discharged from human,adsorption and biodegradation behavior in activated sludge,and UV oxidation degradation mechanism and pathway.Finally,zebrafish was used to explore the ecotoxicological effects of MEF discharged into natural water,and related simulation calculations were carried out.The research content and results are as follows:?1?Attenuation of MEF in municipal sewers.Under different temperature,p H,and biofilm types,the stability of MEF was evaluated by its adsorption/degradation in the transportation of wastewater and biofilm sewers.The results found that the decay percentage of MEF in wastewater increased with temperature,and its decay in wastewater was less than20%.In the lab-scale aerobic and anaerobic sewers,the decay percentage of MEF within 24hours was also less than 20%,and the degradation of the drugs in the sewers with aerobic and anaerobic biofilms was higher than that of the wastewater without biofilms.Therefore,the concentration of MEF was basically stable during the migration process in the municipal sewer.?2?Adsorption and biodegradation of MEF in the sludge system of wastewater treatment plant.The adsorption and biodegradation of MEF in the different types of sludge were studied.The results showed that the removal rates of metformin by sludge in the secondary settling tank,aerobic tank and anaerobic tank were 92.4%,86.4%and 58.2%,of which biodegradation accounted for 67.5%,61.6%and 40.2%,which played a leading role.The adsorption capacity and biodegradation efficiency of MEF in the secondary settling tank were higher than that of the aerobic and anaerobic tank,which was positively related to the content of activated sludge organic matter.Low temperature??15 ^oC?was conducive to the adsorption of MEF in three types of sludge,and the isothermal adsorption model on activated sludge conformed to the Langmuir model.And 25 ^oC was the optimal temperature for the biodegradation of MEF in the sludge system.?3?UV oxidation degradation of MEF.The influence of environmental factors?Cl^-,NO₃^-,HCO₃^-and FA?contained in the water on the ultraviolet oxidative degradation of MEF was investigated,and the degradation mechanism and photolysis pathway were explored.The results show that the hydroxyl radical?·OH?has the largest contribution rate in the process of UV degradation,reaching 73%in the effluent of the secondary sedimentation tank.Triplet-excited state organics?³OM^*?and singlet oxygen?¹O₂?also played a role in the oxidation process.The reaction rates of·OH and ¹O₂with MEF were?6.45±0.4?×10⁹and?5.4±0.7?×10⁶L/?mol·s?,respectively.The presence of NO₃^-promoted the photolysis of MEF,HCO₃^-and FA played an inhibitory role due to the light shielding effect.The photo reactivity of environmental factors in the water was the reason for the different photodegradation of MEF.The by products of MEF under UV light were detected by UPLC/Q-TOF as methylbiguanide?MBG?,2,4-diamino-1,3,5-triazine?2,4-DAT?,biguanide?BGN?,1,1-dimethylguanidine?1,1-Di MBG?,4-amino-2-imino-1-methyl-1,2-dihydro-1,3,5-triazine?4,2,1-AIMT?,and 2-amino-4-methylamino-1,3,5-triazine?2,4-AMT?.Density functional theory?DFT?was used for the first time to calculate the frontline electron density of MEF to predict the main sites of·OH attack were N10 and N12,and the results were consistent with the corresponding product detection.?4?Aquatic ecotoxicological effects of MEF.The accumulation of MEF in the gills,guts,and livers of zebrafish could be observed after dietary exposure to 0.1,1,10,100,and 1000?g/L of MEF solution,and the bioaccumulation capacity was gut>liver>gill.After a 30-day recovery period,MEF could still be detected in zebrafish tissues in the exposure groups of?10?g/L.The results of RT-Q-PCR showed that the exposure of MEF could induce the abnormal expression of CYP3A65,GSTM1,p53 and DNMT1 genes in the livers,which was related to the hydrogen bonding between MEF and the protein residues of related genes.LC/MS/MS results found that liver was the main target site of DNA methylation.When the exposure was stopped,DNA methylation restored in the livers was slower that of guts and gills.Molecular dynamics simulation results showed MEF could induce conformational changes in the 3D structure of DNMT1,thereby reducing the catalytic activity of DNMT1.The results explain the molecular mechanism of MEF dietary exposure is the induction of DNA methylation.