MASS-BASED EVALUATION OF PFAA STORAGE AND TRANSPORT IN A WASTEWATER REUSE SYSTEM

Perfluoroalkyl acids (PFAAs) are regularly found in effluent discharged from wastewater treatment facilities. Effluent is often discharged directly to surface water bodies, but increasingly, it is reused for agricultural irrigation. When effluent is reused in this way, the long-term environmental fate of discharged PFAAs depends on both soil PFAA retention properties and effluent PFAA loading history. Unfortunately, the relative importance of retention properties remains uncertain, and the historical record of effluent PFAA concentrations is limited. At the Penn State Living Filter, a site irrigated with treated wastewater effluent for nearly 60 years, we evaluated PFAA mass balances using PFAA measurements from samples of irrigated soils, groundwater, and effluent. Total accumulated perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) masses measured in soils cores collected in 2014 were orders of magnitude greater than the mass applied during the 2020 effluent irrigation. Soil column mass balance models reproduced the observed PFOS and PFOA profiles, providing an estimate of historical effluent PFOS and PFOA concentrations: 70–170 ng L⁻¹ and 1,000–1,300 ng L⁻¹, respectively. These estimated concentrations are comparable to wastewater effluent PFAA concentrations measured at other treatment facilities in the 1990s and 2000s, indicating that wastewater-irrigated soils can serve as integrated records of historical PFAA loading to the environment. Mass balance calculations indicated that PFOS first reaches groundwater 50 years after the start of wastewater irrigation, whereas simulated PFOA reaches groundwater after only 10 years of irrigation. While wastewater irrigation of soils reduces near-term PFAA loading to surface waters from effluent, the resulting PFAA storage in soils potentially creates long-term sources of PFAAs to groundwater.