Long-Term Trends of Per- and Polyfluoroalkyl Substances (PFAS) in Suspended Particular Matter from German Rivers Using the Direct Total Oxidizable Precursor (dTOP) Assay

Suspended particulate
matter (SPM) from 13 riverine sampling sites
of the German Environmental Specimen Bank collected between 2005 and
2019 was retrospectively investigated for per- and polyfluoroalkyl
substances (PFAS). The samples were analyzed both by target analysis
for 41 PFAS and by a modified total oxidizable precursor (dTOP) assay
to capture also unknown precursors. Temporal trends and spatial differences
were investigated by generalized linear modeling (GLM). Time trend
analysis across all rivers showed decreasing trends for ∑PFCA
and ∑PFSA concentrations in SPM. Trends based on target analysis
(∑PFCAtarget: −10.0%, ∑PFSAtarget: −8.2%) were more pronounced than in the dTOP analysis (∑PFCAdTOP: −4.2%; ∑PFSAdTOP: −5.3%),
suggesting that conventional target analysis overestimated actual
decreases as precursors are not considered. ∑PFAS concentrations
determined by dTOP assay were 1.3–145 times higher as compared
to target analysis, indicating substantial amounts of unknown precursors
in the samples. The ∑PFASdTOP/∑PFAStarget ratio increased at all sites between 2005 and 2019. Contamination
was highest in SPM from the Elbe tributary Mulde downstream of a large
industrial park. The results underscore the need to go beyond conventional
target analysis and include precursors when assessing PFAS contamination
in the environment. The dTOP assay is a suitable tool for this purpose.