In this study the aim was to establish anthropogenic background values of PFAS in soil and groundwater in Flanders, focusing on areas free from known PFAS sources. Spatial data on known or potential PFAS sources like no-regret zones (i.e. areas with known PFAS impacts), firefighting training grounds, landfills,…  was collected and merged into 1 map to select unsuspected areas. To conduct a comprehensive area-wide study within these unsuspected areas, 147 monitoring wells were studied. At 73 of these monitoring wells, soil samples were also taken. 

Groundwater results showed that PFBA and PFBS were the most prevalent PFAS compounds, with PFOA and PFAS also frequently detected. Based on these background values the P90 values were determined for PFAS compounds with more than 50% of the measurement exceeding the LOQ.  This resulted in target values for PFBA of 21,0 ng/l, for PFBS of 9,4 ng/l, and for PFOA of 8,0 ng/l. 

Of the 73 soil analysis only for PFAS did more than 50% of the measurements exceed the LOQ. Therefore, only for PFOS a P90 value of 1.4 µg/kg dry weight could be derived. This value was confirmed by the in 2021 derived value of 1,0 µg/kg dry weight for PFOS based on a slightly smaller dataset. 

As this study only focused on unsuspected areas like agricultural and nature, it recommends additional research in urban and industrial areas to better understand the diffuse presence of PFAS in areas with multiple potential PFAS sources. The background concentration of PFAS is therefore likely higher in urbanized areas compared to the investigated unsuspected areas. 

The complete report can be found here (report in Dutch with English summary).