Co-transport Behavior Of Polystyrene Nanoplastics And Sulfadiazine In Saturated Porous

Nanoplastics,as an emerging environmental pollutant,have been widely reported that it posed a threat to ecological safety and human health.Compared with microplastics,nanoplastics particles have smaller particles,larger specific surface area,and stronger hydrophobicity.They have characteristics such as high environmental abundance,strong diffusion ability,and high biological toxicity in soil environments.Antibiotics are widely present in soil environments due to their widespread use.They are easily soluble and have strong migration ability under acidic and alkaline conditions.The coexistence of nanoplastics and antibiotics in soil may lead to more complex environmental hazard.The issue of composite contamination by their interactions has been rarely reported.At present,there are many studies on the single migration of pollutants such as nanoplastics,heavy metals,and antibiotics in porous media,while the co-migration behavior of polystyrene nanoplastics(PSNPs)and sulfonamide antibiotics(SDZ)in porous media has not been reported.Iron oxides are widely present in soil and can be coated on the surface of porous media,which significantly affects the migration behavior of nanoplastics and antibiotics in soil.In this study,using bare quartz sand(BQS)and goethite-coated quartz sand(GQS)as the media,using sand column migration experiments,model fitting and DerjaguinLandau-Verwey-Overbeek(DLVO)theoretical calculation,combined with Zeta potential analysis,electron microscope analysis,Fourier transform infrared spectroscopy and other techniques,to study the co-migration behavior and microscopic mechanism of PSNPs and SDZ under different p H value and ionic strength.The research results will help predict to understand the co-migration behavior and mechanism of PSNPs and SDZ in soil porous media,and provide scientific basis for predicting and evaluating the complex pollution of nanoplastics and sulfonamide antibiotics in soil and groundwater.The main conclusions achieved in this study are as follows:(1)The migration rate of PSNPs in BQS is significantly higher than that in GQS,mainly due to the presence of goethite on the surface of GQS,which increases the surface roughness and deposition sites of GQS;At the same time,the Zeta potential value of GQS is lower than that of BQS,which reduces the electrostatic repulsion between PSNPs and GQS,resulting in a lower migration rate of PSNPs in GQS than in BQS.(2)The mobility of PSNPs in BQS is greatly affected by ionic strength and p H value,while the mobility of PSNPs in GQS is less affected by ionic strength and p H value,but the mobility of PSNPs in BQS and GQS will decrease with the increase of ionic strength,and increase with the increase of p H value.Under p H 9 and 10 mmol/L KCl conditions,the migration rate of PSNPs in BQS can reach 0.85,while the migration rate of PSNPs in GQS is only 0.11.TSM fitting showed that with the increase of ionic strength and the decrease of p H value,the distribution coefficient Kd value and retardation factor Rd value of PSNPs in BQS also decreased.(3)When PSNPs co migrate with SDZ,the addition of SDZ can improve the migration rate of PSNPs.The addition of SDZ will compete with PSNPs for deposition sites on BQS and GQS;FTIR characterization shows that the addition of SDZ increases the negatively charged functional groups on the surface of PSNPs,thereby increasing the electrostatic repulsion between PSNPs and BQS or GQS;DLVO theoretical calculations show that the presence of SDZ can increase the potential barrier value between PSNPs and BQS or GQS,thereby increasing the mobility of PSNPs on BQS and GQS.(4)When PSNPs and SDZ co migrate,the addition of ionic strength and PSNPs has little effect on the mobility of SDZ,while the change of p H value has a greater effect on the mobility of SDZ;An increase in p H value will significantly increase the migration rate of SDZ.SDZ has a higher migration rate under p H 9 conditions,with a maximum value of 1.00.This is mainly attributed to the fact that when the p H value is 9,both BQS and GQS have the highest number of negative charges on the surface.SDZ is mainly in an anionic form at p H 9,and the electrostatic repulsion between BQS or GQS and SDZ is the highest,thereby promoting the migration of SDZ.