Globally Distributed Shale Gas Extraction Flowback and Produced Water Serves as a New Hotspot for Antibiotic Resistance Genes

Wastewaters with antibiotic residues are recognized as potential "hotspots" for antibiotic resistance genes (ARGs) due to their release of ARGs into the environment. Meanwhile, nonantibiotic wastewater may also serve as ARG hotspots, driven by other selective pressures fostering ARG development. Flowback and produced water (FPW), a byproduct of global shale gas extraction, harbors diverse ARG selective pressures and rich microbial communities, making it an ideal environment for ARG screening. This study characterized ARG profiles in FPW using metagenomic sequencing, comparing them with established ARG hotspots to assess FPW's potential as an ARG hotspot. The findings revealed that (1) FPW exhibited a substantial abundance of ARGs, approximately 1.8 times higher than that in natural environments, such as soil, natural water, and natural sediment; (2) clinically relevant ARGs were prevalent in FPW; (3) ARGs in FPW exhibited high mobility; and (4) diverse hosts of ARGs identified in FW included human pathogens. In summary, the ARG profile in FPW fulfills all the criteria defining an ARG hotspot. Consequently, we posit for the first time that FPW could be a novel ARG hotspot, emphasizing the need to underscore health risks associated with ARGs in future shale gas extraction activities.