PFOA Increases Microbial Risk by Promoting Iron Release and Weakening Biofilm Adhesion in Unlined Iron Drinking Water Pipes

Perfluorooctanoic acid (PFOA) entering drinking water distribution system (DWDS) could induce complex processes affecting the water quality at consumer taps. Here, we first found that PFOA could greatly increase microbial risk by triggering high iron release or reducing the biofilm adhesive ability depending on the concentration levels of PFOA in unlined iron pipes. The heterotrophic plate counts (HPC) of three scenarios TP (without PFOA, control), TP100 (PFOA 100 ng/L, moderate concentration), and TP1000 (PFOA 1000 ng/L, high concentration) were 180, 692, and 192 CFU/mL, and the corresponding total iron concentrations were 0.67, 1.84, and 0.26 mg/L, respectively. Obviously, PFOA enhanced iron release in TP100 but inhibited iron release in TP1000, and the highest HPC in TP100 was in accordance with its highest iron release. Notably, TP1000 had the lowest iron release, but its HPC was the second highest. The extracellular polymeric substance (EPS) composition analysis revealed that PFOA stimulated EPS production but decreased the ratios of polysaccharides/proteins and carbohydrates/proteins, indicating that the biofilm adhesion ability was reduced due to PFOA, which was accountable for the relatively higher HPC in TP1000. This study provided new insights into the water quality risks associated with PFOA in DWDS.