Fluoroquinolones and Β-lactam antibiotics and antibiotic resistance genes in autumn leachates of seven major municipal solid waste landfills in China

Landfills are reservoirs of antibiotics, heavy metals, disinfectants and other emerging contaminants, and they are closely associated with the increasing prevalence of antibiotic-resistance genes (ARGs). In this study, two classes of clinical use antibiotics, i.e., fluoroquinolones (FQs) and β-lactams (BLs), twelve subtypes of their parallel ARGs, and five mobile genetic elements (MGEs), were measured in municipal solid waste (MSW) landfill leachates from seven mega-cities in China. The highest concentration of FQs was detected in Shanghai (48,326.67 ng/L), and the highest concentration of BLs was detected in Hangzhou (1304 ng/L). In landfill leachates in Suzhou, the total contents of targeted ARGs subtypes ((1.44 ± 4.64) × 10⁻⁴ (ARGs/16S)) and MGEs (7.88 × 10⁻² ± 1.18 × 10⁻¹ (ARGs/16S)) were the highest. The relative abundance of ARGs and MGEs was significantly correlated with the contents of As and Cr, and the presence of MGEs was highly correlated with the content of Cd (r = −0.438, p = 0.475). Linear regression analysis showed that MGEs are closely associated with the abundance of genes resistant to FQs and BLs. These results suggest that the occurrences of FQs and BLs ARGs in the landfills of China are substantially influenced by heavy metals and MGEs. Regional differences concerning the antibiotics and ARGs contents in leachates were observed across seven mega-cities, and FQs were significantly correlated with the local population level (p < 0.01). Further, the nitrogen input to the landfills contributes significantly to the elevated levels of target ARGs.