Production of perfluoroalkyl acids (PFAAs) from precursors in contaminated agricultural soils: Batch and leaching experiments.

Contamination of soils with per- and polyfluoroalkyl substances (PFAS) (e.g., aqueous film forming foams (AFFFs) or PFAS containing biosolids applied to agricultural soils) can lead to large scale groundwater pollution. For site management, knowledge about the extent and time scales of PFAS contamination is crucial. At such sites, often persistent perfluoroalkyl acids (PFAAs) and so-called precursors, which can be transformed into PFAAs, co-occur. In this study, the release of PFAAs from 14 soil samples from an agricultural site in southwest Germany contaminated via compost/paper sludge was investigated. Rapid leaching of C4-C8 perfluoroalkyl carboxylic acids (PFCA) was observed in saturated column tests, while slowing down with increasing chain-length (≥ C9 PFCAs). Two selected samples were further incubated in batch-tests after removal of existing C4-C8 PFCAs in extensive column leaching tests until a liquid-solid ratio of 10 l/kg. During 60 days of incubation, aqueous concentrations of C4-C8 PFCAs increased linearly by a factor of 29-222, indicating continuous production by transformation of precursors. The potential PFAA-precursor reservoir was estimated by the direct total oxidizable precursor (dTOP) assay. PFCA concentrations after the dTOP increased up to two orders of magnitude. Production rates determined in batch-tests combined with the results of dTOP assay were used to estimate time scales for the duration of C4-C8 PFCAs emission from the contaminated agricultural soils which likely will last for several decades.

PFAS-Contaminated Soil Site in Germany: Nontarget Screening before and after Direct TOP Assay by Kendrick Mass Defect and FindPFΔS.

Soil contaminations with per- and polyfluoroalkyl substances (PFAS) are of great concern due to their persistence, leading to continuous, long-term groundwater contamination. A composite sample from contaminated agricultural soil from northwestern Germany (Brilon-Scharfenberg, North Rhine-Westphalia) was investigated in depth with nontarget screening (NTS) (Kendrick mass defect and MS2 fragment mass differences with FindPFΔS). Several years ago, selected PFCAs and PFSAs were identified on this site by detection in nearby surface and drinking water. We identified 10 further PFAS classes and 7 C8-based PFAS (73 single PFAS) previously unknown in this soil including some novel PFAS. All PFAS classes except for one class comprised sulfonic acid groups and were semi-quantified with PFSA standards from which ∼97% were perfluorinated and are not expected to be degradable. New identifications made up >75% of the prior known PFAS concentration, which was estimated to >30 µg/g. Pentafluorosulfanyl (-SF5) PFSAs are the dominant class (∼40%). Finally, the soil was oxidized with the direct TOP (dTOP) assay, revealing PFAA precursors that were covered to a large extent by identified H-containing PFAS and additional TPs (perfluoroalkyl diacids) were detected after dTOP. In this soil, however, dTOP + target analysis covers <23% of the occurring PFAS, highlighting the importance of NTS to characterize PFAS contaminations more comprehensively.

Long-term behavior of PFAS in contaminated agricultural soils in Germany.

PFAS contaminated compost materials have been applied over the last few decades to agricultural fields in Germany, resulting in large-scale diffuse PFAS plumes. The leaching behavior of PFAS from the first two identified contaminated agricultural sites in Germany were investigated, one at Brilon-Scharfenberg, North Rhine-Westphalia Site (BS-NRW), and the other at Rastatt/Mannheim, Baden-Württemberg. The specific objectives of this study were to assess the longevity of the PFAS agricultural sources and compare standardized column percolation tests to long-term leaching of PFAS from contaminated sites. The advection-dispersion model (ADM) was used to compare the leaching behavior of PFOA and PFOS from standardized column percolation tests and long-term field leaching data from the BS-NRW site. Column leaching tests conducted with PFOS and PFOA contaminated soil simulated the initial rapid decline but did not predict the long-term behavior (tailing) observed at the field site over 12 years. Trend analyses of the PFAS field data from the BS-NRW showed that concentrations had stabilized and that individual PFAS exhibited distinct seasonal fluctuations; the latter is likely due to the ongoing transformation of precursors and a seasonal influence on production rates of mobile PFAS. Mass balances conducted at both sites indicate that complete removal of these compounds will likely take years to decades to occur, which is expected from the results of the column leaching tests.