Tracking down unknown PFAS pollution - The direct TOP assay in spatial monitoring of surface waters in Germany

PFAS contamination of surface waters in central Europe was investigated in a spatial monitoring using suspended particulate matter and sediment samples. The samples were collected in 2021 at 171 sampling sites in Germany and at five sites in Dutch waters. All samples were analyzed for 41 different PFAS by target analysis to establish a baseline for these compounds. In addition, a sum parameter approach (direct Total Oxidizable Precursor (dTOP) assay) was used to investigate the PFAS load in the samples more comprehensively. PFAS pollution varied widely between water bodies. Target analysis detected ∑PFAS concentrations between <0.5 and 53.1 μg kg^-1 dry weight (dw), while levels of <1.0-337 μg kg^-1 dw were determined by dTOP assay. Associations were observed for ∑PFSA_dTOP and the percentage of urban area in the vicinity of the sampling sites and, less strongly, for distances to industrial sites (i.e. galvanic/paper) and airports. PFAS hotspots were identified by setting the 90th percentile of the data sets for ∑PFAS_target or ∑PFAS_dTOP as a threshold. Of the 17 hotspots identified by target analysis or dTOP assay, respectively, there were only six overlaps. Thus, 11 highly contaminated sites could not be identified by classical target analysis. The results demonstrate that target analysis captures only a fraction of the actual PFAS load, while unknown precursors remain undetected. Consequently, if only the results of target analysis are considered in assessments, there is a risk that sites heavily polluted with precursors will not be identified delaying mitigation actions and risking prolonged negative impacts on human health and ecosystems. Moreover, effective PFAS management requires establishing a baseline for PFAS using target and sum parameters such as the dTOP assay, and then monitoring this baseline on a regular basis to support emission control and to inform risk management of its effectiveness.