Long-term trend data for PFAS in soils from German ecosystems, including TOP assay

In this study, soil top layers from the German Environmental Specimen Bank (ESB) covering a period from 2002 to 2018 and 11 sampling sites representing four ecosystem types were analysed for 24 PFAS (11 PFCA, 7 PFSA, and 6 precursors), including the total oxidizable precursor (TOP) assay. Median ΣPFAS levels before and after TOP assay ranged from 0.31 to 19.7 μg/kg dry weight (dw) and 0.32 to 20.4 μg/kg dw, respectively. The most frequently measured PFAS above LOQ were PFOS and PFOA, which were present at concentrations above 0.1 μg/kg dw in each sample. Both accounted, on average, for half to two-thirds of the total identified PFAS load at most sites. The investigated samples from the near-natural and forestry ecosystem types each had significantly higher PFAS levels than those from the urban-industrial ecosystem type, while samples from the agricultural ecosystem type did not differ distinctly from the others. Increases of median ΣPFAS levels after TOP assay ranged up to slightly >20 %, indicating that precursor compounds do not play a major role in the substance spectrum of German ESB soil samples from different ecosystem types. Total organic carbon (TOC) content in analysed samples ranged from about 1 % in sandy soil to >40 % in litter layer and showed a strong positive correlation with PFAS concentrations. It is therefore highly recommended that TOC content is reported along with PFAS levels in soils. PFAS trend analysis for nine sampling sites before and after TOP assay showed that concentration levels at most sites have remained more or less stable for the sampled period of almost two decades. The constant PFAS levels in soil samples indicate that PFOS and PFOA regulations have not yet had a positive effect on the exposure situation in this environmental compartment.