Leachate treatment reduces but does not eliminate antibiotic resistance gene contamination: Associations between Pseudomonadota and resistome persistence in treated leachate.

Landfill leachate is a hotspot for pharmaceuticals and personal care products (PPCPs) and antibiotic resistance genes (ARGs), but systematic research on their removal and ecological risks remains limited. This study investigated 30 leachate treatment plants using four techniques: biological + advanced oxidation (AOP), membrane bioreactor + nanofiltration/reverse osmosis (MBR+NF/RO), pretreatment + two-stage disc tube reverse osmosis (DTRO), and pretreatment + mechanical vapor recompression (MVR). Overall, 86.67% of target PPCPs achieved 90100% removal, though diethyltoluamide, caffeine, ibuprofen (IP), ofloxacin, and carbamazepine showed inconsistent results. Pretreatment + DTRO exhibited the most stable removal (coefficient of variation 0.013.21%). Despite the limited sample size (n = 2), pretreatment + MVR achieved high PPCP removal efficiencies (95.8100%), except for IP. IP presented high risk in effluents from biological + AOP and MBR + NF/RO. Treatment reduced 252 ARG subtypes and plasmid abundance, but chromosomally encoded multidrug and aminoglycoside resistance genes increased by 24.6100% in effluent, likely driven by selective enrichment of intrinsic resistance in persistent bacterial hosts. Pretreatment + DTRO (n = 6) and MVR (n = 2) showed relatively higher ARGs removal performance than the other techniques. Treatment weakened bacterial-ARGs associations and reduced selection pressures from PPCPs, heavy metals, and nutrients. However, horizontal gene transfer potential remained, associated with residual Pseudomonadota and five mobile genetic elements. Importantly, high-risk Rank I human pathogen-associated genes (bacA, mdtB, ompR, sul1) persisted in effluent. This first systematic study of four full-scale leachate treatment techniques provides a scientific basis for risk management under the One Health framework.