Study On The Impact Of Metallic Nanoparticles And Nano/microplastics On The Antibiotic Resistance Genes And Its Resistance Risk Control In Landfill Leachate

The enrichment and spread of antibiotic resistance genes(ARGs)in the environments poses a potential threat to human health.Landfill leachate has been identified as a significant reservoir for ARGs and a source of ARGs spreading to the surrounding environment,which has attracted extensive attention.Meanwhile,landfill leachate is also an important hotspot for metallic nanoparticles,nanoplastics and microplastics(nano/microplastics).In recent years,the risk issues of metallic nanoparticles and microplastics were found to be compounded by the antibiotic resistance.However,the specific effects and mechanism of metallic nanoparticles and nano/microplastics on the occurrence of ARGs in the landfill system are very limited.Therefore,this study focused on the influence of metallic nanoparticles and nano/microplastics on the dissemination of ARGs in landfill leachate using a series of experimental and analytical methods including quantitative PCR,16S r DNA high-throughput sequencing and modern bioinformatics.Furthermore,the reduction and retransmission restrainment of ARGs and antibiotic resistant bacteria(ARB)in microplastics and leachate samples by chlorination disinfection and Fenton oxidation were studied.The main findings are as follows:1.The changes of ARGs in leachate separately exposed to different concentrations of two representative metallic nanoparticles,i.e.zinc oxide and zero valent iron nanoparticles(Zn O NPs and Fe⁰ NPs)were investigated.The results showed that Zn O NPs exposure promoted the proliferation of target ARGs in leachate,and the promotion effect was enhanced with the increase of exposure concentration.When the concentration of Zn O NPs was 500 mg/L,after 56 days of exposure,the absolute abundances of all target ARGs were 1.4-6.7 times of those in the control without metallic nanoparticles exposure.The exposure of Fe⁰ NPs resulted in the decreased abundances of target ARGs in leachate.After day 56,the absolute abundances of these target ARGs were reduced by 5.3%-77.5%.Zn O NPs induced the shifted bacterial community and the increased relative abundance of potential hosts for ARGs,which played the dominating role in the propagation of ARGs.At the same time,Zn O NPs exposure increased MGEs abundances and thus the enhanced potential for horizontal transfer of ARGs,promoting the dissemination of ARGs in leachate.In the case of Fe⁰NPs exposure,the decreased abundance of MGEs led to the reduction in the horizontal transfer potential of ARGs,which is the main driving factor of ARGs attenuation.Secondly,the decrease in relative abundance of potential hosts for ARGs induced by Fe⁰ NPs also contributed to the reduction of ARGs.2.The effects of short-term and long-term exposure of nano/microplastics with different size(50-100 nm,200-500 nm,9.0-9.9?m)on the occurrence of ARGs in leachate were explored.The results found that target ARGs were enriched in the nano/microplastics-exposed groups,especially in the 200-500 nm nanoplastics group.The enrichment became more pronounced in long-term exposure samples than short-term ones.After long-term exposure to 200-500 nm nanoplastics,the absolute abundance of all target ARGs in leachate increased significantly to 1.98-2.82 times of those in the control group.Further analysis revealed that the exposure of nano/microplastics caused the changes of bacterial community and the increased abundances of potential hosts for ARGs,which promoted the enrichment of ARGs.Nano/microplastics exposure also led to an increase in the abundances of MGEs,and target MGEs were significantly correlated with target ARGs,especially after long-term exposure,indicating that nano/microplastics exposure-induced enrichment of ARGs may be related to the increasing horizontal transfer mediated by MGEs.In addition,the significant increase in the production of intracellular reactive oxygen species(ROS)and cell membrane permeability were observed in nanoplastics-exposed groups,which increased the potential of ARGs for horizontal transfer,and thus the propagation of ARGs.3.The microplastics biofilm were incubated in leachate with three landfill age(young,middle-aged,old-aged),and the occurrence of ARGs in microplastics and leachate samples were studies.The results showed that ARGs were selectively enriched on microplastics,which were similar on microplastics from three leachate environments.The genes str B and bla _TEM were the most enriched on microplastics,while the enrichment of mef A,erm B,tet M and tet Q were less.The degree of ARGs enrichment increased with time during the 60 days of the experiment.After 60 days,the abundances of str B and bla _TEM on microplastics are 1-2 orders of magnitude higher than those in the surrounding leachate,while the abundances of mef A,erm B,tet M and tet Q were just 1.1-6.2 times higher than those in the surrounding leachate.Compared to the leachate,microplastic biofilm had higher abundances of MGEs and distinctive bacterial community with higher abundance of human pathogens.MGEs and a variety of enriched genera and human pathogens have been identified to be significantly related to ARGs.Therefore,the higher MGEs-mediated horizontal transfer ability and the enrichment of host bacteria for ARGs were important factors driving the propagation of ARGs on microplastics.4.The changes in the abundance of ARGs and ARB in leachate and microplastics samples after different concentrations of chlorination disinfection and Fenton oxidation treatments and in the samples after 48 h of storage at the end of treatment were analyzed.The results showed that chlorination disinfection and Fenton oxidation reduced the absolute abundance of target ARGs in leachate by 54.3-77.6%and>99.9%(4.0-4.5log),respectively,which were higher than the reduction of target ARGs on microplastics(34.0-46.3%and 92.1-97.3%(1.1-1.6 log)).The removal profile of ARB from leachate and microplastics by chlorination disinfection and Fenton oxidation were consistent with that of ARGs.After 48 h of storage at the end of chlorination disinfection(5?10?20?50 mg/L),the more considerable regrowth of target ARGs and ARB on microplastics were observed,compared to target ARGs and ARB in leachate.In contrast,Fenton oxidation achieved a reduced regrowth of target ARGs and ARB.These results indicated that Fenton oxidation had a better ability to reduce ARGs and ARB and restrain their retransmission than chlorination disinfection,and the reduction and control of ARGs and ARB on microplastics were more difficult than that in leachate.In conclusion,this study confirmed the impact of metallic nanoparticles and nano/microplastics on the fate of ARGs in leachate,and revealed the selective enrichment of ARGs on microplastics.Meanwhile,it proved that ARGs on microplastics are more difficult to remove than that in their surrounding leachate.These findings have important implications for in-depth understanding of the environmental risks of metallic nanoparticles and nano/microplastics coexisting with ARGs and the risk prevention and control of antibiotic resistance in landfill systems and other environments.