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Alteration of the migration trajectory of antibiotic resistance genes by microplastics in a leachate activated sludge system
Summary
This study found that microplastics in wastewater treatment systems actively promote the spread of antibiotic resistance genes (ARGs) by acting as a surface for resistant bacteria to colonise and as a vehicle that carries those genes from sludge into the liquid effluent. Adding microplastics to a leachate treatment system increased tetracycline resistance gene abundance and made them harder to eliminate. This matters because wastewater treatment plants are a critical barrier against antibiotic resistance spreading into the environment and ultimately into human communities.
The environmental behavior of emerging contaminants of microplastics (MPs), antibiotics and antibiotic resistance genes (ARGs) in the leachate activated sludge system has been monitored and analyzed comprehensively. The results suggested that MPs could effectively alter the migration trajectory of tetracycline resistance genes (tet genes) in the leachate activated sludge system under intermittent and continuous influent conditions. After adding MPs, the total average abundance of tet genes in leachate increased from 0.74 ± 0.07 to 0.78 ± 0.07 (logtet genes/log 16S rRNA) and that in sludge increased from 0.65 ± 0.08 to 0.70 ± 0.06 (logtet genes/log 16S rRNA). Except for tetA, the abundance of tetB, tetO, tetM and tetQ on MPs increased with increasing TC concentration under both aerobic and anaerobic conditions. MPs not only significantly affect the abundance level and migration trajectory of ARGs in the leachate activated sludge system, but also remarkably improve the level of heavy metals in the ambient environment, indirectly promoting the selective effect of antibiotic-resistant bacteria (ARB) and promoting the development of antibiotic resistance (AR). In addition, MPs changed their physicochemical properties and released hazardous substances with aging to force tet genes to migrate from the leachate activated sludge system to the MPs, making AR more difficult to eliminate and persisted in wastewater treatment plants. Meanwhile, microorganisms played a driving role, making MPs serve as a niche for ARGs and ARB colonization. The co-occurrence network analysis indicated the specific distribution pattern of tet genes and microorganisms in different media, and the potential host was speculated. This study improves the understanding of the environmental behavior of emerging contaminants in leachate activated sludge system and lays a theoretical for protecting the ecological environment.