Distribution Of Antibiotic Resistance Genes And Heavy Metals In A Livestock Farms

Antibiotic resistance genes(ARGs)as a new enmerged pollutant,its formation process and the way of transmission and diffusion in the environment are attracting more and more attention in recent years.However,there is growing concern that contaminants such as metals may also co-select for antibiotic resistance,it can also lead to horizontal transfer and even diffusion of ARGs in the environment.In this study,a livestock farm in Dulbert Mongolian Autonomous County,Daqing City,Heilongjiang Province was selected as the research object.Geograghpic Information Systerm(GIS)was used to visualize thie distribution characteristics of heavy metals and ARGs in the livestock farm,reveal the interaction between them,and provide a theoretical basis for the subsequent restoration and management of black soil.The specific research content is as follows:Combined with GIS,surface water(W1 and W2)and cattle drinking water(W3),soil samples(T1-T10,T11-T20)at the depth of 10 cm and 50 cm were collected from the livestock farm.The content of 8 kinds of heavy metals in soil samples and water samples was detected by ICP-MS,AFS and AAS.The pollution level of heavy metals was evaluated by single factor pollution index and Nemerow comprehensive pollution index.ArcMap was used for visual analysis of heavy metals in different soil layers,and preliminary exploration of pollutant sources was conducted.The fluorescence quantitative PCR technology was used to detect the relative aboundance of 28 kinds of ARGs,and the comprehensive score was ranked based on Principal Component Analysis(PCA).Arcscene and ArcMap were used to output cloud map of ARGs in the different soil layers,and the distribution characteristics were analyzed.The correlation between heavy metals and ARGs was discussed by Pearson index method and network analysis,and the similarity between them was also analyzed by cluster analysis.The results showed that In the soil samples,the single factor pollution index of element As in the 10 cm-depth and 50 cm-depth soil all belonged to the heavy polution level(Pi>3),the other 7 elements belonged to the safety level(Pi≤1),and the Nemerow comprehensive pollution index of 10 cm and 50 cm-depth soil all belonged to the heavy pollution level(Pcomprehensive>3).In the water samples,Cu and Hg were not detected.Ni in W1 and W2 was slightly contaminated(Pi>1),and W3 was safe.The distribution of heavy metals in the soil showed that As presented a gradually vertical increasing pollution from top to bottom,while Cu,Zn and Cd were more easily enriched in the surface layer,and the pollution were mainly concentrated in the southeast region.It was analyzed that its source was mainly affected by human activities and soil parent material factors.The pollution characteristics of 28 ARGs were obvious,and the relative abundance of ARGs in different soil layers was significantly different.In the 10 cm soil layer,the relative abundance of tetracycline ARGs was higher,and that of β-lactam ARGs was higher in the 50 cm soil layer.In T13 and T19,blaTEM in the 50 cm was serious,and the relative abundance was approximately 0.65 and 0.59,respectively.In each water sample,the relative abundance of total tetracycline ARGs was higher than that of sulfonamides ARGs and β-lactam ARGs,and the relative abundance of tetG in W2 was the highest,which was approximately 0.011.PCA was carried out to obtain the comprehensive score ranking of ARGs in soil,and the top three were sul2,blctTEM and tetX.The contamination of tetracycline ARGs and sulfonamides ARGs in soil samples was mainly concentrated in the eastern region,while β-lactam ARGs was mainly concentrated in the eastern region and part of the central region.Except for β-lactam ARGs,the pollution degree increased with the increase of soil depth,while the other ARGs tended to decrease.C orrelation analysis showed that there was a correlation between the relative abundance of AR Gs and the heavy metals As,Pb,Cd and Cr(P<0.05).ARGs in the water samples were highly correlated with heavy metals Zn,Ni and As(P<0.05).Cluster analysis showed that the selective pressures of Ni and Cr for ARGs were similar,and that of Cd.Zn Hg,Cn,Pb and As for ARGs were similar.In summary,The content of heavy metals and the relative abundance of ARGs in the soil samples of different soil layers in the livestock farm were much higher than that in the water samples.Soil samples from different soil layers were heavily polluted with As,while W1 and W2 was slightly polluted with Ni,and W3 was safe.The distribution of heavy metals in the soils was mainly concentrated in the southeastern region,while ARGs were mainly concentrated in the eastern region and part of the central region.There was a correlation between the relative abundance of ARGs and the heavy metals in the soil samples and water samples.