Detection Of Microplastics In Water And Study On Its Adsorption Behavior Of Six Antibiotics And Trichlorophenol

According to the new pollution control action plan issued by the General Office of the State Council（Guobanfa[2022]No.15）,microplastics（MPs）have become the focus of my country’s new pollutant control actions.Because of their physical and chemical properties such as large specific surface area,strong hydrophobicity,and complex surface functional groups,MPs in the water environment not only directly pose a health threat,but also act as a carrier for pollutants to adsorb various toxic and harmful substances in water,changing the environmental behavior of pollutants and toxic effects,causing more complex hazards to ecological security.In recent years,with the large-scale use of human and veterinary antibiotics and pesticides,fungicides,wood preservatives,etc.containing chlorophenols（CPs）,the water environment has been polluted,and the direct harm to health and compound hazard with MPs has also been aggravated.At present,there is no limit for MPs in Chinese“Standards for Drinking Water Quality”（GB5749-2006）,the pretreatment techniques and testing methods for MPs in water are different.Moreover,the adsorption mode of antibiotics in MPs is still unclear and the variety of MPs could lead to the adsorption of different antibiotics.Furthermore,the hazard mechanism of compound pollutant caused by CPs and their isomers needs more investigation.And there is no corresponding water treatment technology to remove more and more pollutant compounds to ensure safety of drinking water.To solve the problems mentioned above,in this paper,we firstly explored the optimization of silver filter membrane utilized for polyethylene（PE）,polyethylene terephthalate（PET）and polyamide 66（PA-66）and the digestion of MPs,the detection of MPs combined with Raman spectroscopy.The suitable pretreatment methods were employed in our study to ensure the stable physicochemical properties and relative high extraction efficiency of MPs,so that the abundance distribution of MPs in water samples can be observed visually and accurately.Besides,we explored the adsorption behavior pattern and adsorption mechanism of three MPs,i.e.,PA-66,PE and PET,on antibiotics and CPs in water,which could not only provide references for pretreatment technologies in MPs research and some scientific theoretical and technical support for a reasonable assessment of the environmental fate and ecological risk of MPs in water,but also afford scientific theoretical and technical support for the improvement of water treatment process and water quality standards.The main research contents and results are listed as follows:（1）the scanning electron microscopy and micro-Raman spectroscopy were employed to determine the effects of different digestion conditions(i.e.,30%H₂O_2,Fenton’s reagent,HF acid,heating after digestion,sonication,potassium borohydride oxidation reduction and Na HCO₃ or Na₂CO₃ assisted sonication to remove residual H₂O₂)on filtered water samples with silver filter membrane and three MPs.The effect of pretreatment conditions was optimized as a basis for the detection and evaluation of microplastic contamination in disposable paper cups and noodle boxes to investigate the contamination of microplastics in daily life.The results showed that 30%H₂O₂ solution had less effect on the silver filter membrane,and 6g/L Na HCO₃ solution-assisted sonication was able to remove all H₂O₂ from the ablated residue.The three MPs,i.e.,PA-66,PE,and PET,were ablated by 6 m L of 30%H₂O₂ solution for 2 d,following by 3 m L of 52 g/L aqueous Na HCO₃ solution-assisted sonication for 6 h to remove H₂O₂ and 25%v/v ethanol to disperse.The number of PET,PA-66 and PE with particle size≥10μm was found to decrease from 44.33±7.07,37.40±7.25 and 42.20±6.25 to 22.20±5.16,29.20±5.54 and 40.07±6.32 before and after the digestion,respectively.The results of t-test showed that the changes in the number of PET and PA-66 particles before and after ablation were all p-values<0.05,which were statistically significant,and the changes in PE were p-values>0.05,which were not statistically significant.The shape of the peaks changed;PET showed new characteristic peaks at 1065,1519 cm^-1 and the characteristic peak at 1105 cm^-1 disappeared;PE did not change significantly and its overall dispersion was good under electron microscopy.The PE was detected in the samples of disposable paper cups and noodle boxes simulating daily use using the above method,indicating that the method is suitable for the detection and analysis of PE in water samples.（2）The concentration of antibiotics and six chlorophenols in water samples was determined by high performance liquid chromatography-mass spectrometry（HPLC-MS/MS）,and the effects of pretreatment factors such as pipetting with different materials,protection from light,storage time,centrifugation,and filtration with different membranes on the concentration determination were analyzed.The conditions determined from the previous experiments were used to systematically carry out the effects of three MPs on cinoxacin（CIN）,oxolinic acid（OXO）,penicillin G（Pen G）,penicillin V（Pen V）,sulfamethoxazole（SMX）,sulfamethoxydiazine（SMD）,and 2,3,6-TCP,2,4,6-TCP,2,3,4-TCP,2,4,5-TCP,2,3,5-TCP,3,4,5-TCPs,the kinetics,adsorption isotherms,adsorption thermodynamics,and the effect of different salinity and p H environmental conditions on the adsorption were investigated to study the adsorption behavior and mechanism by means of adsorption kinetic model,adsorption isotherm model,adsorption thermodynamics model and micro-Raman spectroscopy.The results showed that partial antibiotic loss in water was caused by aspiration via polyethylene plastic dropper,placed for 8 h to avoid light or not,and the loss rate was as high as 36.4%,51.7%,and 60.2%,respectively.After filtration by centrifugation or PTFE,NL66,MCE filter membrane,the recovery of some antibiotics was as low as 32.3%or less.The results of tap water matrix spiking experiments showed that the recoveries of all antibiotics,except for five macrolide antibiotics and virginiamycin S1,reached more than 78.6%after filtration by their respective optimal membranes.the recoveries of the six TCPs filtered by NL66 and MCE membranes were 0.2%～29.6%and8.4%～30.5%,respectively,and the overall recoveries of the six TCPs filtered by PTFE membranes The overall recoveries of the six TCPs by PTFE membrane filtration were 93.2%～101.9%,and the recoveries of tap water spiking experiments were more than 100.9%.It can be seen that some antibiotics in water are easily adsorbed,undergo their own degradation or photolysis,and centrifugation and filtration will cause the detection results of low concentration of antibiotics to be underestimated.Therefore,the actual test should be placed in the sample away from light,and the determination should be completed within 8 h after sampling,avoiding the use of plastic products such as polyethylene dropper and polypropylene centrifuge tube,and making it clear that the filter membrane used will not cause the loss of the substances to be tested.The adsorption processes of the three MPs on the six antibiotics with PA-66 and PET on the six TCPs could be better fitted by quasi-secondary kinetic models（R² was 0.704～0.990,0.300～0.897,0.947～0.994,respectively）,the adsorption processes of PE on the six TCPs could be better fitted by quasi-first-order kinetic models（R² was 0.867～0.976）,the adsorption capacities of the three MPs on the six antibiotics PA-66（5.063μg/g～94.804μg/g）>PET（1.398μg/g～17.487μg/g）>PE（1.296μg/g～17.896μg/g）,the adsorption capacities of the three MPs on the six TCPs PA-66（10.435μg/g～55.638μg/g）>PET（12.129μg/g～17.041μg/g）>PE（1.561μg/g～4.315μg/g）.The adsorption isotherms of the three MPs on the six antibiotics and TCPs were well fitted by the Freundlich model（R² 0.875-0.996 and 0.740-0.992,respectively）,with 1/n mostly less than 1.The adsorption of the three MPs on the six antibiotics and TCPs increased with increasing temperature,except for the adsorption of 2,4,6-TCP by PA-66,and the adsorption of TCPs by MPs decreased with increasing temperature?G value and?H value>0.The adsorption of CIN,OXO,Pen G,Pen V by PA-66 and CIN,OXO by PE was the highest at p H=7.The adsorption of CIN,OXO,Pen G,Pen V by PET was the highest at p H=6.The effect of p H on the adsorption of SMX,SMD by the three MPs was not significant.The adsorption of Pen G and Pen V by PA-66 decreased with increasing ionic strength,and the adsorption of CIN,OXO,SMX and SMD reached the maximum at an ionic strength of 0.1mol/L.The adsorption of the six antibiotics by PET reached the maximum at an ionic strength of 0.02mol/L.No pattern was found for the adsorption of the six antibiotics by PE with ionic strength.No pattern was found for the adsorption of PE on the six antibiotics with ionic strength.It was suggested that the adsorption behavior of the three MPs on the six antibiotics and TCPs was affected by hydrophobic interaction,van der Waals forces,hydrogen bonding,π-πinteractions,polar interactions,and electrostatic interactions.（3）UV irradiation atλ=340 nm was used to simulate the natural aging of microplastics in the environment,and the changes in the physical and chemical properties of microplastics such as morphological structure and functional groups were characterized by scanning electron microscopy and Raman spectroscopy for unaged and aged microplastics.It was found that UV aging led to changes in the morphology and structure of MPs,the surface was yellowed,the roughness increased significantly,the pores increased,and the hydrophilicity increased.The Raman spectra of the three unaged and aged microplastics did not produce new characteristic peaks,and there was a clear arch at 1300 cm^-1-1500 cm^-1.After aging,the adsorption of PA-66 plastic increased for CIN and OXO and decreased for Pen G,Pen V,SMX and SMD,and PE and PET increased for CIN,OXO,Pen G,Pen V,SMX and SMD;the adsorption of PA-66,PE and PET decreased for the six TCPs.It is suggested that aging MPs decrease hydrophobic interactions and electrostatic interactions,and the change of surface oxygen functional groups enhances hydrogen bonding,which is the most significant interaction affecting the adsorption of microplastics.In summary,the Raman spectrometry established in this paper can be used for the detection of microplastic PE in water.Different materials removal,light avoidance,storage time,centrifugation,different filter membrane filtration and other factors will affect the accuracy and stability of the determination.In the actual detection,the samples should be placed away from light,and the determination should be completed within 8 h after sampling,avoiding the use of plastic products,and making it clear that the filter membrane used will not cause the loss of the substances to be measured.The adsorption behavior of microplastics on antibiotics and trichlorophenols is affected by hydrophobic interactions,van der Waals forces,hydrogen bonding,π-πinteractions,polar interactions and electrostatic interactions.UV aging will change the surface morphological structure,crystallinity and other physicochemical properties of microplastics and affect their adsorption behavior.The results of the study provide a basis for assessing the environmental risks and ecological safety hazards of MPs,antibiotics and CPs,and the pollution management of environmental microplastics and related pollutants.