Adsorption Of Copper And Tetracycline Onto Microplastics In Water And Soil And The Corresponding Control Method

Heavy metals and antibiotics were the major selective factors for the generation and spread of antibiotic resistance genes(ARGs)in the environments.The emergence of microplastics further aggravated the impacts of heavy and antibiotics on ARGs.Thus,the treatment of this kind of combined pollution was arduous and necessary.This study investigated the adsorption of heavy metal(Cu(Ⅱ))and antibiotics(tetracycline)by polyethylene(PE)microplastics and the impacts of PE microplastics on ARG abundances in soil.Besides,the effects of struvited-loaded zeolite(S-NZ)on the combined pollution of PE microplastics,Cu(Ⅱ),tetracycline(TC)and ARGs were also investigated.The adsorption behaviors of Cu(Ⅱ)and TC onto virgin microplastics(V-PE-MPs)and microplastics exposed to air with UV light(A-PE-MPs),water environments(WPE-MPs)and soil environments(S-PE-MPs)were investigated.The optical microscope,field emission scanning electron microscope(SEM),X-ray diffraction(XRD),Fourier infrared spectroscopy(FT-IR),etc.were used to characterize microplastics.The Freundlich adsorption isotherm,Langmuir adsorption isotherm and Temkin adsorption isotherm were used to describe the adsorption behavior of Cu(Ⅱ)and TC on the four microplastics.The Cu(Ⅱ)and TC adsorption data of V-PE-MPs and A-PE-MPs were best fitted by the Freundlich model,while the adsorption data of W-PE-MPs and S-MPMPs were best described by the Langmuir model.The maximum adsorption capacities of V-PE-MPs,A-PE-MPs,W-PE-MPs and S-PE-MPs for Cu(Ⅱ)were 42.6 μg/g,423μg/g,120 μg/g and 318 μg/g,respectively,and for TC were 148 μg/g,193 μg/g,264μg/g and 240 μg/g,respectively.The adsorption on W-PE-MPs and S-PE-MPs was dominated by film diffusion,while the adsorption on V-PE-MPs and A-PE-MPs was additionally affected by intra-particle diffusion.The irreversibility of Cu(Ⅱ)and TC adsorption onto four microplastics followed the order of S-PE-MPs> W-PE-MPs> APE-MPs> V-PE-MPs.The adsorption mechanism was explored by using FT-IR,XPS and GC-MS.W-PE-MPs and S-PE-MPs were colonized by microorganisms and biofilms were formed on their surface,which enhanced the adsorption capacities of WPE-MPs and S-PE-MPs by complexation with surface functional groups,hydrogen bond and π–π interaction.After the exposure to air with UV light,the plastic additives,such as the phthalates,were released,which enhanced Cu(Ⅱ)adsorption by phthalateCu complex generation and bridge effects.The effects of microplastics with long-time exposure to soil environments(A-MPs)on the combined pollution of Cu(Ⅱ),TC in soil were investigated.In batch adsorption experiments,the addition of 1% A-MPs had no significant effects on the adsorption and desorption of Cu(Ⅱ)and TC in the soil environment.However,this treatment increased soil pH and soluble organic matter,resulting in lower TC degradation and higher bioavailable copper(Bio-Cu)and TC(Bio-TC)concentrations in soil environments.The removal mechanism of Cu(Ⅱ)and TC by S-NZ in water was comprehensively investigated by comparing with the adsorption onto natural zeolite(NZ).S-NZ and NZ were characterized by using SEM,XRD,FT-IR,etc.In the sole-pollutant systems,the maximum removal capacities of S-NZ and NZ for Cu(Ⅱ)were 2181.95 mM/kg and31.88 mM/kg,respectively,and for TC were 66.00 mM/kg and 29.06 mM/kg,respectively.In the binary-pollutant systems,the maximum removal capacities of S-NZ and NZ for Cu(Ⅱ)were 379.42 mM/kg and 42.86 mM/kg,respectively,and for TC were197.53 mM/kg and 102.49 mM/kg,respectively.3% S-NZ addition increased the maximum adsorption capacity of the soil for Cu(Ⅱ)and TC from 6.85 mg Cu(Ⅱ)/g and19.9 mg TC/g to 13.9 mg Cu(Ⅱ)/g and 41.7 mg TC /g,respectively,and at the same time stabilized Cu(Ⅱ)and TC in the soil environment.When S-NZ and A-MPs coexisted,due to competition effects,S-NZ could reduce the distribution of Cu(Ⅱ)and TC in A-MPs and soil particles.The Langmuir model is more suitable than the Freundlich model to describe the adsorption isotherms of S-NZ,indicating the homogeneous monolayer adsorption by S-NZ.The pseudo-second-order kinetic equation was more suitable for fitting the adsorption data of S-NZ,indicating that Cu(Ⅱ)and TC were mainly removed through surface chemical adsorption by S-NZ.S-NZ had the best TC removal efficiency in the pH range of 5.5-6.5.When Zn(Ⅱ)coexisted with Cu(Ⅱ)and TC,the competition between Zn(Ⅱ)and Cu(Ⅱ)reduced the adsorption performance of S-NZ for Cu(Ⅱ),TC and Zn(Ⅱ).The adsorption mechanism was explored by using FT-IR,XPS and XRD.The adsorption of Cu(Ⅱ)on S-NZ was mainly through surface phosphate precipitation and electrostatic adsorption.In the binarypollutant system,Cu(Ⅱ)increased the adsorption capacity of S-NZ for TC through ion bridge effects and the surface complexation of TC and copper-bearing precipitate.The impacts of S-NZ on the combined pollution of Cu(Ⅱ)and TC in soil containing A-MPs were investigated.In the soil microcosm experiments,3% S-NZ amendment significantly reduced the concentrations of bio-Cu and bio-TC in microplasticcontained soil by 74.2%-76.0% and 71.4%-78.5%,respectively.Most ARGs,such as tetB,tetQ,tetG,tetX,sul1,and sul2 were significantly correlated with Bio-Cu and BioTC,and some ARGs(sul1,tetX and tetG),heavy metal resistance genes(copA and czcA)could coexist in the class Ⅰ integrin.Thus,the total relative abundances of ARGs were further reduced by 0.77-0.81 times with 3% S-NZ amendment in soil containing A-MPs.In addition,the addition of S-NZ could effectively reduce the total abundance of ARGs in A-MPs by more than 0.36 times and alleviate the negative effects of microplastics on the soil microbial community,as well as lower the relative abundances of potential hosts of ARGs in soil.