Effect Of PBS Microplastics On The Migration And Transformation Of Heavy Metals And Antibiotics In Water And Soil And Its Remediation

In recent years,with the promulgation of policies restricting the use of conventional plastics in various countries,using degradable plastics as a substitute for non-degradable plastics has become a general trend.Compared with conventional nondegradable plastics,the effects of degradable plastic-derived microplastics on the migration and transformation of pollutants in water and soil are complex and unexplored,which requires in-depth research.In this study,poly(butylene succinate)derived-microplastics(PBS-MPs)were selected as model degradable microplastics,while Pb(Ⅱ)and sulfamethazine(SM2)that commonly found in the environment were selected as model heavy metal and antibiotic pollutants.The effects of the degradation process of PBS-MPs on the Pb(Ⅱ)and SM2 adsorption on PBS-MPs in the aquatic environment and the relevant mechanisms were studied.The changes of antibiotic resistance genes(ARGs)under the coexistence of PBS-MPs,Pb(Ⅱ)and SM2 in soil were further investigated.On this basis,the digestion liquid(DL),digested food waste(DFW)and digested food waste derived biochar(DFW-BC)that derived from food waste were used as organic fertilizers or soil amendment for the remediation of PBSMPs,Pb(Ⅱ),and SM2 co-contaminated soil,and the effect of these amendments on PBS-MPs,Pb(Ⅱ),SM2 and ARGs systems and the relevant mechanisms were investigated.The main conclusions of this study are as follows:(1)The biodegraded-PBS-MPs(B-PBS)and photoaged-PBS(P-PBS)were prepared,and the adsorption behavior of Pb(Ⅱ)and SM2 on the pristine PBS-MPs,BPBS and P-PBS in Pb(Ⅱ)/SM2 single and combined polluted water were compared.Results showed that the physicochemical properties(such as the surface morphology,crystallinity,hydrophobicity,and the surface functional groups)of PBS-MPs changed during its bio-degradation and photoaging process,the amount of hydrophilic oxygencontaining groups and active adsorption sites on the surface of PBS-MPs increased,which resulted in the significant enhancement for the adsorption of Pb(Ⅱ)and SM2 on PBS-MPs in a water environment.In the Pb(Ⅱ)and SM2 sole system,the maximum adsorption capacity of Pb(Ⅱ)could increase from 64.13 μg/g for the pristine PBS-MPs to 647.09 μg/g for B-PBS and 362.06 μg/g for P-PBS,respectively.The maximum adsorption capacity of SM2 could increase from 76.52 μg/g for the pristine PBS-MPs to 316.58 μg/g for B-PBS and 351.49 μg/g for P-PBS,respectively.The results of desorption experiments indicated that the adsorption-desorption hysteresis of Pb(Ⅱ)and SM2 on B-PBS was the most significant.The co-existence of humic acid in water could further enhance the adsorption of Pb(Ⅱ)and SM2 on PBS-MPs,B-PBS,and P-PBS.In Pb(Ⅱ)-SM2 binary system,the competitive and synergistic adsorption of Pb(Ⅱ)and SM2 on PBS-MPs were both observed,and their adsorption behavior was affected by both the amount of the adsorption activity sites on the surface of PBS-MPs and the affinity among Pb(Ⅱ),SM2,and PBS-MPs.The bio-degradation and photoaging process of PBS-MPs significantly affected the simultaneous adsorption of Pb(Ⅱ)and SM2.Under the experimental conditions,the co-existed SM2 inhibited the adsorption of Pb(Ⅱ)on PBS-MPs,B-PBS,and P-PBS;while the co-existed Pb(Ⅱ)promoted the adsorption of SM2 on PBS-MPs and P-PBS,but inhibited the adsorption of SM2 on PBS-MPs and P-PBS.(2)Various methods,such as the x-ray photoelectron spectroscopy,threedimensional fluorescence spectroscopy,scanning electron microscope and Fourier transform infrared spectroscopy,were used to explore the adsorption mechanism of Pb(Ⅱ)and SM2 by PBS-MPs during its biodegradation and photoaging.The results showed that the mechanism of Pb(Ⅱ)adsorbed on the pristine PBS-MPs was electrostatic interaction,while for B-PBS,the main mechanisms of Pb(Ⅱ)adsorption involved the complexation with the extracellular polymeric substances(EPS)on the biofilm loaded on B-PBS,surface complexation,and electrostatic interaction,for PPBS,the main mechanisms of Pb(Ⅱ)adsorption involved surface complexation,electrostatic interaction,and pore-filling/diffusion.The main mechanism of SM2 adsorbed on the pristine PBS-MPs was non-bonding forces such as Vander Waals force,while for B-PBS,the main mechanisms of SM2 adsorption involved the coordination and complexation with the EPS components on the adhered biofilm,hydrogen bond association,van der Waals forces,and micropore filling,for P-PBS,the main mechanisms of SM2 adsorption involved hydrogen bonds and Vander Waals force.(3)The effects of PBS-MPs on the fate of Pb,SM2,and ARGs in soil were investigated through soil microcosm experiments.The results indicated that the presence and degradation of PBS-MPs in soil significantly increased the content of soil dissolved organic matter(DOM)and soil p H,and significantly improved the activities of soil polyphenol oxidase(PPO),but had a limited effect on the content of soil total dissolved nitrogen(TDN).The results of microbial community analysis indicated that the presence of PBS-MPs had little effect on the diversity,richness,and structure of soil microbial community at the phylum level.However,at the family level,the addition of PBS-MPs significantly decreased the abundance of Bacillaceae and Streptomycetaceae.The results of FAPROTAX functional analysis indicated that the addition of PBS-MPs significantly promoted the abundance of fermentative bacteria associated with soil carbon mineralization and organic matter degradation.Network analysis indicated that the presence of PBS-MPs enhanced the importance of Firmicutes in bacterial networks.During the 60-d incubation period,with 5% PBS-MPs addition,the concentration of acid-soluble Pb(Ⅱ)in soil increased by 11.3%,which increased the mobility of Pb(Ⅱ)in soil,while the reduction rates of water-soluble SM2 and total SM2 were increased by 2.7% and 2.4%,respectively.After 60 days of incubation,the addition of PBS-MPs reduced the relative abundances of the sulfonamides resistance genes sul1,sul2 by 31.1%and 0.2%,and reduced the relative abundances of the total sulfonamides resistance genes(sul)and the class I integron(intl1)by 28.6%,and 3.4%,respectively.The results showed that the addition of PBS MPs significantly inhibited the proliferation of sul1,but had limit effect on sul2 and intl1.Spearman correlation analysis and the redundancy analysis pointed out that the addition of PBS-MPs could promote the proliferation of fermentative bacteria and the activity of PPO enzyme by increasing soil p H,thereby promoting the degradation of water-soluble SM2 and total SM2.With the reduction of the selective pressure of SM2 on soil microbe,the abundance of some potential hosts of ARGs,such as Bacillaceae,etc.,was reduced,consequently inhibiting the spread of ARGs to a certain extent.(4)The effects of the prepared food waste derived products,i.e.,DL,DFW,and DFW-BC application on the fate of Pb,SM2,and ARGs in PBS-MPs contained soil were investigated.During the incubation,both the addition of DL,DFW,and DFW-BC could promote the transformation of Pb and SM2 from high-mobility species to lower mobility species.After 60 days of incubation,the application of DL,DFW,and DFWBC could reduce soil acid-soluble Pb(Ⅱ)by 6.6%,23.3%,and 33.7%,increase the reduction rate of water soluble SM2 by 0.7%,8.2% and 7.7%,respectively,and could increase the reduction rate of total SM2 by 1.8%,7.8%,and 7.6%,respectively.In terms of the fate of ARGs,at the end of incubation,DL amendment significantly reduced the relative abundance of intl1 and sul1 by 21.6% and 35.0%,respectively,although the relative abundance of sul2 increased,DL amendment still reduced the relative abundance of sul genes by 8.2% due to its strong inhibition effect on sul1 proliferation.DFW amendment significantly reduced the relative abundance of intl1,sul1,sul2,and the relative abundance of sul genes by 77.6%,6.0%,57.1%,and 11.6%,respectively,and the DFW-BC amendment could reduce the relative abundance of intl1,sul1,sul2 and the relative abundance of sul genes by 17.8%,5.6%,28.6%,and 8.2%,respectively.The application of DL,DFW,and DFW-BC had different effects on soil p H,while all of them could significantly increase soil DOM and TDN contents.During the incubation,the DOM contents in soil treated with DL,DFW,and DFW-BC could increase up to 5.4,18.4,and 0.13 folds,respectively,and the TDN contents of these treatments could increase up to 1.17,2.41,and 0.30 folds.For the variances of microbial communities,at the phylum level,the application of DL and DFW significantly promoted the proliferation of Firmicutes and Proteobacteria.At the family level,the application of DL and DFW made the family Clostridium became the dominant species,and could significantly increase the abundance of Clostridium by 39.6～121.6 folds and26.3～231.3 folds,respectively.However,DFW-BC application had less effect on soil bacterial composition.Besides,the results of FAPROTAX functional analysis indicated that the application of DL and DFW significantly increased the abundance of fermentative bacteria,while DFW-BC amendment increased the abundance of the functional bacteria related to hydrocarbon and aromatic compound degradation.The Network analysis suggested that the potential hosts of sul1 and intl1 mainly belong to Firmicutes and Actinobacteriota,and the family Bacillus belonging to the phyla Firmicutes was suggested to be the most important sul1 and intl1 host.Besides,the main hosts of sul1 belong to the phyla Proteobacteria.The results of Spearman correlation analysis,redundancy analysis,and stepwise regression analysis indicated that the mitigation of soil ARGs pollution by DL,DFW,and DFW-BC amendments mainly depended on its influence on microbial composition.During the incubation,the tremendous change of soil p H,TDN,DOM and water soluble SM2 contents derived the changes of soil bacterial communities.Through these methods,the reproduction of potential ARGs hosts,such as the family Bacillus,was restricted,which contributed to the mitigation of ARGs proliferation.