PFAS uptake and xylem storage in trees along an aqueous film-forming foam contaminated groundwater flow path

Cores extracted from several species of deciduous and coniferous trees (n = 11) located immediately downgradient from an aqueous film forming foam (AFFF) contaminated source area were used to determine PFAS concentrations and compositions within these trees and evaluate the use of tree cores to forensically reconstruct past trends of PFAS concentrations in shallow, root-accessible porewater over time. The tree cores were divided into mostly decadal increments (n = 95), subjected to a solid-phase PFAS extraction process, and analyzed for 40 PFAS. PFBA, PFHxS, PFOA, and PFOS were the most detected PFAS. Variability in the tree core concentrations appear to be influenced by PFAS concentrations in root-accessible porewater, tree species, and growth rates. PFOS served as the most useful compound for reconstructing past trends of contamination due to relatively high detection rates and concentrations, and less radial translocation than PFBA, PFHxS, and PFOA, which were commonly found in decadal increments formed before the first purported usage of AFFF. Reconstructions from four trees (cedar, poplar, and white pine) were used to identify peak PFOS concentrations of 7, 15, 17, and 18 years after the first reported AFFF application in 1970 that systematically occur in sequence with increasing distance from the source. This time range appears feasible, particularly for the tight range of 15-18 years for the white pines and cedars which are located 450, 497, and 588 m along their respective groundwater flow paths.