The Behavior Of Antibiotics And Antibiotic Resistance Genes In Circular Agricultural System

Due to the use of antibiotics in livestock feed, residual antibiotics and antibiotic resistance genes (ARGs) could transfer in the circular agriculture system, a new agriculture mode in China. The objective of this study was to determine the abundance and persistence of antibiotics and ARGs in the whole recycling process of the circular agriculture, which starts from swine feed to swine feces, from swine feces to anaerobic fermentation products, then applied in the soil, and the ryegrass grown on the soil become the swine feed.The concentrations of eight antibiotics in all samples were measured using liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS). Ten tet genes (tetA, tetB, tetC, tetG, tetL, tetM, tetO, tetQ, tetW, and tetX), two sul genes (sulⅠand sulⅡ), and one genetic element associated with mobile antibiotic resistance genes [class1integron (intIl)] were quantified by real-time polymerase chain reaction.Results show that OTC and SMX were the most abundant antibiotics in the circular agricultural system and OTC had the highest concentration in manure sample reaching up to138.7mg/kg. The abundance of ARGs fluctuated in this recycling utilization of agricultural waste resources. TetQ had the highest relative abundance which was4.28±6.03×10-2.The anaerobic fermentation, as a new field of application for animal manure generating environmentally friendly energy, could eliminate most antibiotics effectively and the removal rate ranged from11%to86%in our investigation. Compared to the relative abundance in manure, tetC and tetM increased in the biogas residue while three RPP genes (tetO, tetQ, tetW) decreased (P<0.05), with other genes showing no significant change after anaerobic fermentation (P>0.05). In biogas slurry, the relative abundance of tetC, tetG and tetL increased after the pipeline transportation (P<0.05). Most of ARGs in downstream receptacles (soils and fishpond) of the circular agricultural system showed significantly higher relative abundance than the control system (P<0.05), except tetG and sull. Additionally, total ARG copies were also significantly correlated with total nitrogen, total phosphorus, total organic carbon and16S-rRNA gene copies (R2=0.515,0.332,0.451and0.882, respectively; P<0.05). This is the first study to investigate the behavior of antibiotics and ARGs in circular agricultural system in China and provides insight into potential options for prudent use of antibiotics in agricultural activities.