Microbial community of a colloidal activated carbon barrier at a perfluoroalkyl substance impacted site and sorption of perfluorooctanesulfonic acid by bacteria

Per- and polyfluorinated alkyl substances (PFAS) including perfluorooctanesulfonic acid (PFOS) are extremely refractory anthropogenic compounds that are widespread in the environment. Their fate and transport are of increasing interest, including the ways that biological activity may affect the efficiency of state-of-the-art mitigation efforts, such as colloidal activated carbon (CAC) injection. The microbial communities of sediments in and around a CAC barrier from 2.7 to 9 m below surface were investigated using 16S ribosomal RNA amplicon sequencing and strains isolated from the samples. The microbial community consisted of taxa commonly associated with the subsurface environment, including a high proportion of Bathyarchaeota in the deeper samples. The presence of PFAS or the CAC barrier used to treat it affected the microbial community. Bacteria in the order Peptococcales had higher relative abundance in the CAC barrier than upstream or downstream of it. The inverse Simpson index decreased with depth, indicating less variety in the microbes that were present, but was higher in the samples downstream of the CAC barrier, which may indicate an impact of the PFAS on the microbial community. The sorption of PFOS was investigated for six newly isolated strains as well as four other strains, and results indicate that sorption of PFOS by different species or genera of bacteria is more variable than previously thought. These results suggest that the microbial community could play a role in the mobility of PFAS within subsurface waters, and emphasizes the need to understand the subsurface microbial community and its interactions with PFAS.