Leaching potential of per- and polyfluoroalkyl substances from source zones with historic contamination of aqueous film forming foam - a surfactant mixture problem

Per-and poly fluoroalkyl substances (PFAS) from aqueous film forming foam (AFFF) used at firefighting training facilities (FTF) contaminate waterbodies and pose a threat to human health and the environment worldwide . In this study, leaching of PFAS from historically AFFF contaminated field soil has been investigated under saturated conditions using up-flow columns for four soil samples with varying PFAS concentrations to quantify the long-term release potential of the source zone. PFOS was the most abundant PFAS present in the soils (84–98% of ΣPFAS12), varying from 358 to 1097 µg/kg and the total organic carbon (TOC) content varied from 0.73 to 2.0%. The experiment was run until a liquid to solid (L/S) ratio of 10 was reached (equivalent to 80 pore volumes or approximately 100 years of natural infiltration at the sampled field site). Results show a general trend of decreasing concentrations of short chain PFAS with increasing leaching volume. However, PFOS concentrations initially increased by 45–87% in three samples with relatively low TOC (0.7, 1.0 and 1.4%), before being reduced. In the 2.0% TOC soil PFOS concentrations continued to increase throughout the experiment. The residual PFOS content in the four soil samples showed no correlation with TOC content in the soil. Up to 50% of the initial PFOS content was retained in the soil with the lowest TOC content (0.7%), whereas all PFOS was removed in the soil with a TOC content of 1.4%. It is hypothesized that DOC present in the eluates originates from other non-fluorinated components present in AFFF that can facilitate PFAS leaching.