The Characteristics And Formation Mechanisms Of Bioaerosols And Airborne Antiobiotic Resistance Genes Released During The Decomposition Of Domestic Waste

The environment transmission,respiratory exposure,and disease infection caused by bio-aerosols have increasingly become hot issues in atmospheric physical chemistry and public health areas.With the intensification of human activities,with the increased production of domestic waste and the widespread of antibiotic-resistant bacteria（ARB）,we are more and more likely to face the contamination of antibiotic-resistant bioaerosols released by waste decomposition.In addition,microbial activities are the core link in the treatment of biodegradable wastes.Airborne horizontal transfer of antibiotic-resistance genes（ARGs）in landfill and the acquisition of antibiotic resistance by co-existed bacteria are posing a huge potential threat to human health and environmental safety.However,little is known about the contribution of waste decomposition to airborne ARGs and bacteria during landfilling of domestic waste currently.Therefore,the main research goal of this thesis is to explore the released characteristics of bioaerosols and the dynamic distribution of antibiotic resistance genes in the process of waste decomposition under simplified environmental conditions in lab scale bioreactors;to research on characteristics and mechanisms of dynamic changes of microbial communities and ARGs,and the corresponding aerosolization laws and related effects from the simultaneous changes of landfill leachate,then finally explore the distribution characteristics and potential risks of bioaerosols and ARGs/Mobile genetic elements（MGEs）under the influence of multiple environmental factors in different functional areas of complex landfill sites.Over all,this thesis Intended to provide a reference for the risk and control of airborne bacteria exposure in landfills.The main research contents of this thesis are as follows:（1）First,we carried out the decomposition of three types of meat（chicken,fish and pork）waste under laboratory conditions for 130 days.There were differences in the bioaerosol concentration,particle size distribution and total microbial activity produced by the three kinds of meat waste decomposition processes.Chiceken bioaerosol was the the highest with a concertration of 449 CFU m^-3for the aerobic or facultative anaerobic bacteria on day1,while fish bioaerosol had the highest microbial activity(287.99 mg L^-1)and the part with a particle size of<4.7μm accounts for 58.29%,which has the highest proportion of inhalable particles and presented a higher risk of bioaerosol exposure.The analysis of microbial diversity found that Firmicutes and Proteobacteria in bioaerosols of the three kinds of meat wastes decomposition process were the shared dominant bacteria phyla at the Phylum level,and at genus level,Bacillus was the shared dominant bacteria genus in bioaerosol of pork,chicken,and fish wastes,respectively.We found that the diversity of bacteria in bioaerosol decreased with the extension of decomposition time.Bacilli,Mycobacterium,Mycoplasma were the main airborne dominant pathogenic bacteria in the decomposition process of pork wastes,while Bacilli,Burkholderia-Paraburkholderia and Mycobacterium were the main airborne pathogenic bacteria in the decomposition process of chicken and fish wastes.The decomposition of meat waste helped to reduce the health risks of bacilli.In addition to exploring the dynamic changes of bacterial communities,we had also conducted research on the pollution characteristics of ARGs,7,7,and 6 subtypes of airborne ARGs/mobile genetic element（MGEs）were detected in the decomposition of pork,chicken and fish wastes respectively.Thresificae types of meat waste share two ARGs（erm B and tet M）and one MGEs（IS1111）,and the total abundance of shared ARGs was reduced from 6.90×10⁵to 2.61×10⁵ copies m^-3 from day1 to day60 of decomposition,which indicated that the the abundance of airborne ARGs could decline during decomposition of meat waste.（2）We further studied the microbial diversity in the leachate produced during the fermentation of the three meats,and analyzed the correlation between bacterial communities and drug resistance genes and physical and chemical factors,and found that Firmicutes and Proteobacteria were the shared dominant bacteria in the leachate of the three types of meat decomposition as well.The leachate of pork wastes had the highest shared bacteria（90）,posing a higher aerosolization potential.We concluded that the ability of bacteria in the leachate to aerosolize does not depend on their abundance and diversity,rather,it depended on the specific bactiera being prone to aerosolization.At the same time,we also studied the ARGs change characteristics in the leachate produced during the fermentation of three kinds of meat,and found that sulfonamides（sul2）,tetracyclines（tet M,tet O,tet T）and MLS（mef A,lnu B）had relatively high abundance and Spearman correlation analysis found that pathogenic bacteria have significant correlations with 7 subtypes of ARGs/MGEs（aminoglycosides,MLS,tetracyclines,sulfonamides,β-lactams,vancomycin and MGEs）and electric conductivity（EC）（p<0.05）,indicating that succession of ARGs in bioaerosols and leachate was likely to be driven by the movement of bacterial hosts.Horizontal transfer and environmental spread of ARGs exxisited in bioaerosols,and ARGs may be transferred horizontally through MGEs,ARGs/MGEs were the main factors affecting the structure of bacterial community.In addition,the meat waste decomposition process can reduce the abundance of airborne ARGs（erm B,sul2,tet M,tet T,int I1 and lnu B）,indicated that the anaerobic decomposition may reduce the resistance in meat waste.（3）In order to study the bioaerosols and ARGs in different functional areas of complex landfill sites under the influence of multiple environmental factors,we further carried out 10sampling sites in a landfill in Guangzhou（office area,operation area,landfill area,leachate treatment plant）,surrounding residential area and campus.We found that relatively high bioaerosol concentrations(1237.25 and 961.52 CFU m^-3)and a high proportion of inhalable particles appeared in operating area and residential area.Among them,the mass concentration of particulate matter in operating area（PM1,PM2.5,PM10）was relatively high,poesd a potential risk of bioaerosol exposure.Redundancy analysis（RDA）showed that Pseudomonas in bioaerosol in the office area was significantly positively correlated with the level of microbial activity.In this area,relatively abundance of multidrug resistance genes had been detected,and ARGs were significantly related to airborne bacteria.MGEs may participate in and mediate the horizontal transfer of ARGs more frequently,and there were Weissella species that are inherently resistant to antibiotics in the dominant bioaerosol genus in the landfill sites.Weissella can cause non-pathogenic infections in humans.The risk of exposure to bioaerosols during waste decomposition and the spread of drug resistance deserve further attention.Above all,our study explored the entire process of waste decomposition in the laboratory and studied the characteristics of bioaerosol and ARGs pollution in landfills.We found that different meat wastes decompose and different functional areas of landfills had differences in the released bioaerosol concentration,particle size distribution,microbial activity level and microbial community change trend,and the pollution characteristics of ARGs.The microbial commuity was important to drive the horizontal transfer of ARGs and the spread of antibiotic resistance,the aerosolization of microorganisms in leachate may accelerate the air suspension of pathogenic bacteria.This study can provide an assessment of the public health hazards of bioaerosols in the decomposition process of domestic waste in landfills,and provide certain basic data for pollution prevention and control.