Appraisal of the Position of Water Distribution Systems as a PFAS Exposure Pathway

Regulatory guidelines implementation for per- and polyfluoroalkyl substances (PFAS) is getting attention globally due to the rising concern about its presence in water sources, direct exposure, and toxic properties. The majority of the legal frameworks primarily emphasize perfluorooctanoic acid (PFOA), an anionic organic PFAS. Latest studies found polyfluoroalkyl amides (FA) as a central precursor to PFOA formation in aquatic systems and established the Hofmann-type rearrangement as the dominant PFOA formation pathway during the chlorination of zwitterionic/cationic FA. Intriguingly, higher PFOA concentrations have been identified in water treatment plants after disinfection also. Hence, there is a probability of transforming FA to toxic PFOA during delivery via water distribution systems (WDS). The PFOA formation in the WDS could become an indirect PFAS exposure source and a probable cause for acute and chronic health risks to the communities. We aim to evaluate the involvement of WDS as an exposure pathway for PFOA. We examined the kinetics of PFOA formation during chlorination in aquatic systems. The kinetic relationships were transformed into mathematical equations and were applied to develop an EPANET-MSX-based WDS quality model. Uncertainty analysis was incorporated into the mechanistic modeling using the Monte Carlo method. The data set obtained on model application to a real WDS was applied for human health risk assessment by calculating the daily intake of PFOA contaminated water using USA population parameters. Our study found the one to eight years old age group to be most susceptible to PFASs exposure beyond the tolerable limit of 3 ng/kg/day.