Sulfamethoxazole, tetracycline and oxytetracycline and related antibiotic resistance genes in a large-scale landfill, China.

Landfills are likely to be important reservoirs of antibiotics and antibiotic resistant genes (ARGs) as they receive unused and unwanted antibiotics and ARGs in municipal solid waste (MSW). The distribution, transportation and dynamics of antibiotics and ARGs in landfills remain largely unknown. In the present study, 3 antibiotics - sulfamethoxazole (SMX), tetracycline (TC), and oxytetracycline (OTC) - and their related ARGs (sulI and tetO) were quantified in 51 refuse samples from different depths at 8 locations within a large-scale landfill in central China. The average concentration of OTC was the highest, up to 100.9±141.81μg/kg (dw, n=48), followed by TC (63.8±37.7μg/kg, n=40), and SMX (47.9±8.1μg/kg, n=30). Both sulI and tetO were detected in all samples. Of the ARGs, sul1 (-3.06±1.18, n=51, log10 ARGs/16SrDNA) was more abundant than tetO (-4.37±0.97) in all refuse samples (p<0.05). Both sulI and tetO negatively correlated to refuse age, suggesting they are attenuated during landfill stabilization. OTC and TC positively correlated to tetO (r=0.41, p<0.01) and sulI (r=0.29, p=0.04), respectively. Chemical conditions (e.g. moisture content and nitrate concentrations) within the refuse correlated to antibiotics and ARGs suggesting environmental factors impact the distribution of antibiotics and ARGs in landfill matrix. This study is the first comprehensive in situ landfill study to connect the concentrations of antibiotic residues to ARGs.