Relationships between antibiotics and antibiotic resistance gene levels in municipal solid waste leachates in Shanghai, China

Many studies have quantified antibiotics and antibiotic resistance gene (ARG) levels in soils, surface waters, and waste treatment plants (WTPs). However, similar work on municipal solid waste (MSW) landfill leachates is limited, which is concerning because antibiotics disposal is often in the MSW stream. Here we quantified 20 sulfonamide (SA), quinolone (FQ), tetracycline (TC), macrolide (ML), and chloramphenicol (CP) antibiotics, and six ARGs (sul1, sul2, tetQ, tetM, ermB, and mefA) in MSW leachates from two Shanghai transfer stations (TS; sites Hulin (HL) and Xupu (XP)) and one landfill reservoir (LR) in April and July 2014. Antibiotic levels were higher in TS than LR leachates (985 ± 1965 ng/L vs 345 ± 932 ng/L, n = 40), which was because of very high levels in the HL leachates (averaging at 1676 ± 5175 ng/L, n = 40). The mean MLs (3561 ± 8377 ng/L, n = 12), FQs (975 ± 1608 ng/L, n = 24), and SAs (402 ± 704 ng/L, n = 42) classes of antibiotics were highest across all samples. ARGs were detected in all leachate samples with normalized sul2 and ermB levels being especially elevated (-1.37 ± 1.2 and -1.76 ± 1.6 log (copies/16S-rDNA), respectively). However, ARG abundances did not correlate with detected antibiotic levels, except for tetW and tetQ with TC levels (r = 0.88 and 0.81, respectively). In contrast, most measured ARGs did significantly correlate with heavy metal levels (p < 0.05), especially with Cd and Cr. This study shows high levels of ARGs and antibiotics can prevail in MSW leachates and landfills may be an underappreciated as a source of antibiotics and ARGs to the environment.