Effects of trace PFOA on microbial community and metabolisms: Microbial selectivity, regulations and risks

•PFOA promoted biofilm formation in porous media by stimulating EPS production.•Glutathione-based antioxidant system defended against oxidative damage of PFOA.•Microbes achieved cell membrane repair by regulating metabolic and biosynthetic pathways.•Enrichment and generation of efflux ARGs enhanced microbial tolerance to PFOA.•An increase in human bacterial pathogens exacerbated the vertical transmission risk of ARGs. Perfluorooctanoic acid (PFOA), a "forever chemical", is continuously discharged and mitigated in the environment despite its production and use being severely restricted globally. Due to the transformation, attachment, and adsorption of PFOA in aquatic environments, PFOA accumulates in the porous media of sediments, soils, and vadose regions. However, the impact of trace PFOA in the porous media on interstitial water and water safety is not clear. In this work, we simulated a porous media layer using a sand column and explored the effects of µg-level PFOA migration on microbial community alternation, microbial function regulation, and the generation and spread of microbial risks. After 60 days of PFOA stimulation, Proteobacteria became the dominant phylum with an abundance of 91.8%, since it carried 71% of the antibiotic resistance genes (ARGs). Meanwhile, the halogen-related Dechloromonas abundance increased from 0.4% to 10.6%. In addition, PFOA significantly stimulated protein (more than 1288%) and polysaccharides (more than 4417%) production by up-regulating amino acid metabolism (p