This study found that human gut bacteria can accumulate high levels of PFAS, even at environmentally relevant concentrations, and this accumulation is increased in the absence of efflux pumps in *E. coli*. Experiments in mice colonized with human gut bacteria showed they excrete more PFAS in their feces than germ-free mice, suggesting that gut bacteria can influence PFAS levels in the host. Further research is needed to determine the long-term consequences of PFAS bioaccumulation on the gut microbiome and its impact on human health, especially under chronic low-dose exposure conditions.

Two authors (A.E.L. and K.R.P.) are listed as inventors on a patent application related to the findings and are co-founders of a related company (Cambiotics ApS). While the remaining authors declare no competing interests, this potential COI should be noted.

This study provides strong evidence of PFAS bioaccumulation in gut bacteria using a combination of in vitro and in vivo experiments, multi-omics, and imaging. While the mouse model and single high dose limit direct applicability to human exposure, the findings raise important questions about the role of the gut microbiome in PFAS toxicokinetics. The potential conflict of interest is noted but does not invalidate the core findings, justifying a rating of 4.