Characteristics Of Antibiotics Contents In Municipal Solid Waste Landfills And Correlation With Antibiotic Resistance Genes

Currently,the abuse of antibiotic is an important environment problem that is faced by many countries and regions.Potential ecological risks can stem from antibiotics discharged into environment,which could result in the selection and spread of antibiotic resistance bacteria?ARB?and antibiotic resistance genes?ARGs?.They are considered to have huge risks to the public health.In China,the production and usage of antibiotics is unnecessarily high.Considerable amount of expired drugs were believed discarded into municipal solid waste?MSW?landfills along with household refuse given the poor wastes treatment systems.However,there were few studies investigating the antibiotics residuals in MSW landfills.Considering their high consumption and discharging rates,investigations focusing on antibiotics contents and their correlations with ARGs in landfill systems are significant for anitiboitic residuals'transformation and antimicrobial resistances risk assessment in MSW management.In this study,samples of solid and leachate were collected from Laogang and Liming landfill in Shanghai,China.In total,fifteen tpypes of antibiotics were quantified by ultra performance liquid chromatograph-tandem mass spectrometry?UPLC-3Q-MS?.Seven types of ARGs were detected by quantitative polymerase chain reaction?Q-PCR?;and then their relationships were analyzed.In landfill leachates,all antibiotics from five classes?TCs,FQs,SAs,MLs and BLs?were detected.Among them,detection frenqunecy of five antibiotics including SMZ,NOR,OFL,RTM,ETM-H₂O were 100%.The highest concentration of ETM-H₂O was 20200.0 ug/L and mean concentration was 5695.7 ng/L,which werefollowed by OFL and NOR,whosethe maximum concentration was 6950.0 ng/L?mean concentration 1870.9 ng/L?,3225.0 ng/L?mean concentration 1101.2 ng/L?respectively.The concentration of AMOX was lowest?mean concentration 8.6 ng/L?and was only detected with a frequency of 22.0%.Antibiotic concentrations in mature leachates?3075.8±4004.0 ng/L?were lower than the fresh?15063.6±2475.9 ng/L?and Liming?13628.5±8792.5 ng/L?leachate?p<0.01?.However,there was no significant difference between fresh and Liming leachate?p=0.107?.In contrast to dry season,antibiotic concentrations in mature leachate decreased from 5737.9±4229.4 ng/L to 413.6±38.0 ng/L?93%?in rainy leachate.And their concentrations of samples from Liming and fresh leachate reduced by 78%?22398.6±887.1 ng/L vs 4858.4±24.4 ng/L?and 28%?17135.0±1931.4 ng/L vs 13003.4±322.6 ng/L?,respectively.In landfill refuse,three classes?TCs?QNs?MLs?of antibiotics can be 100%detected,while the SAs,BLs' detection frequency ranged from 23.4%to 93.6%.The highest concentration of NOR and OFL were 1497.5 ?g/kg and 1250.0 ?g/kg,and their mean concentration were 260.1 ?g/kg and 215.8 ?g/kg,respectively.The concentration of AMOX is low in all refuse samples and total means concentration was below 0.1 ?gg/kg.Compare with the detected refuse from Liming landfill,the concentration of TCs,QNs and MLs in Laogang landfill were significantly lower?p<0.05?.However,there were no significances between Liming and Laogang landfill regarding the concentrations of SAs and BLs.In the surface of Laogang landfill?0.5-1.5 m?,the characteristics of antibiotics varied with depth.Generally,antibiotic concentrations?expecially of TCs?QNs?SAs?MLs?in 1.5 m were higher than 0.5 m?p<0.05?.However,there was no significant variation characteristic in the surface of Liming landfill.Seven antibiotic resistance genes?tetQ?tetW?mefA?ermB?sul1?sul2 and mexF?and Class I integron?int1?were detected in this study.In the landfill leachates,the quantification results showed that the concentrations of seven ARGs ranged from 2.91×10²?4.88×10⁶ copies/ngDNA,the int1 was from 4.55 ×10⁴ to 8.31 × 10⁷ copies/ngDNA.In contrast,of the contents of tetQ,tetM and mefA in the refuse were lower than the standard curves.and the detection concentrations of ermB,sull,sul2 and mexF were from 1.85 × 102 to 5.07 × 106 copies/ngDNA,and the integron int1 was 6.90 × 105?1.86 × 108 copies/ngDNA.Further analysis showed that there was a significant correlation between tetracycline antibiotics and antibiotic resistance genes tetQ in landfill leachate,and ETM-H₂O,MLs and mefA.Besides,sulfamethoxazole?SMX?and SAs were significantly correlated with sull and sul2 in a negative way;but there was no correlation between the multiple resistance gene mexF and the detected antibiotics.In the surface refuse of Laogang landfill,only RTM showed a significantly positive correlation with ermB and a negative correlation with multiple resistance gene mexF.In the surface refuse of Liming landfill,only sul2 and SAs exhibited a significant negative correlation.The weak correlations between target ARGs and antibiotics may be the results from complex the envirionmental conditions in landfill?temperature,light,pH,etc.?and the interference of other pollutants?heavy metals,toxic substances,etc.?.They are commonly believed to affectthe generationand spread of ARGs in landfills diffusion as well.In the Laogang landfill sampleds,significantly positive correlations between int1 and sull,sul2 and mexF were detected however,they were not significantly correated in the Liming landfill.This may indicate that the spread of the sull and sul2 by the horizontal gene transfer in refuse is more frequent in the mature stage of landfill.In summary,the fifteen commonly used antibiotics in the MSW landfill refuse and leachates were detected with high contents at different landfill stages.The ARGs and some kinds of residual antibiotics were significantly related,but the complex physical and chemical properties of landfill environmental media and high concentrations of pollutants could affect the generation,attenuation and spread of the ARGs in the landfill.