Soil background levels of PFAS in Sweden and Finland
The presence of PFAS is ubiquitous in the environment and may come both from point sources and diffuse contamination. Soil is a matrix for which more knowledge has been warranted, not at least for areas without known point sources. These “background” levels are of importance for environmental monitoring and for establishing soil guideline values for contaminated land.
On behalf of the Swedish EPA, SGU (Swedish Geological Survey) has performed a background study of PFAS levels in forest soils, in an area in middle east Sweden without known point sources. In total, 21 soil pits (podzolic moraines) were sampled in five horizons O, E/A, B, BC and C (from surface to ~100 cm depth). In addition, 10 archived C horizon samples from southeast Sweden were analysed. All PFAS (35 substances) and TOC analyses were performed by Eurofins, with extra low quantification of PFOS.
The results showed the presence of PFAS in especially the organic layer (mor/humus; O) with detected levels in all samples. PFAS was also found in the E/A and B horizons very frequently (>86%) while no observations were made for BC and C. Twelve out of 35 PFAS were identified, all perfluorinated PFCA and PFSA C4-C13. PFOS was the most common substance detected (89% across O, E/A, B) followed by PFNA, PFBA and PFOA (33-57%). Median concentration for the sum of PFAS was the highest in O horizon (1.2 µg/kg DM; max 4.2) and decreased in the mineral soil (0.094-0.28 µg/kg DM). Regarding the relative distribution of PFAS there was a shift towards shorter PFAS in the deeper soil. For example, PFDA, PFUdA and PFTrDA were only found in the organic layer while PFBS and PFHxS only in the B horizon.
Regarding soil guidelines, it can be noted that both the 25 percentile and median values for PFAS4 in the O horizon exceed the proposed value for sensitive land use (KM; 0.25 µg/kg DM) in the SGI (Swe Geotech Inst) referral from 2022. SGU points out that investigations of “urban backgrounds” are required as well.
In Finland a similar study has been carried out by GTK (Geological Survey of Finland) in collaboration with SYKE (Finnish EPA). Also in this project, all PFAS analyses were performed by the Eurofins PFAS competence centre in Lidköping. The results were published in a report earlier this year. In total 37 PFAS were determined in 95 archived mineral soils from across the country, plus four new mineral samples (0-25 cm) alongside 5 humus (O) soils. The average concentration for the sum of PFAS in the mineral soils was 0.09 µg/kg DM i.e. comparable to the Swedish levels. PFOA (61%) was the most frequently detected PFAS followed by PFOS (31%). The O layer samples had a mean concentration of 1.2 µg/kg DM, also directly comparable to Swedish conditions. In addition, 48 urban soils (0-10 cm) from three cities were sampled. These soils showed considerably higher concentrations with an average of 10 µg/kg DM for PFAS37 and 7.7 µg/kg DM for PFAS4. Additional analysis of seven samples with high levels revealed detectable amounts of above all diSAmPAP, but also diPAPs in some cases. This was interpreted as potential contributions from construction soils made with sewage sludge.
Contact Eurofins experts!
Questions about PFAS can be answered by our analytical advisory service, which can be reached via the customer support, 010-490 8110 or e-mail: sh-analys.miljo.se@etn.eurofins.com