Theme: 7. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7h2. PFAS Fate and Transport in Surface Water

Formatted Title:

Impact of Sea Spray Aerosols as a Diffuse PFAS Load on Soil, Surface Water, and Groundwater

Background/Objectives:

In 2022, PFAS was found in shallow groundwater at a coastal town on the west coast of Jutland in Denmark. At the same time, PFAS was detected in public drinking water wells at levels above the Danish drinking water standards on the west-coast island of Fanø. No potentially contaminated sites could be the source for the PFAS contamination at these locations. This led to the theory that PFAS contamination could spread to coastal areas by PFAS-enriched sea foam and sea spay aerosols (SSA) from breaking waves along the North Sea coastline.

Approach/Activities:

The theory was addressed at two sites. At the Island of Fanø and further north at Husby on the west coast of Jutland. Both sites are nature conservation areas with no actual or former industrial or agro-industrial activities. Sampling transects were set up from the coastline and 4 km inland by sampling of soil, shallow groundwater and surface water (ponds and smaller lakes). Near the impacted drinking water wells on Fanø, the vertical distribution of PFAS was investigated in shallow (less than 2 m bgl) and deeper (up to 18 m bgl) groundwater samples. Samples of soil, surface water and groundwater were analyzed for 22 PFAS including PFOS and PFOA. Furthermore, samples of sea water and sea foam were analyzed for PFAS to document the enrichment of PFAS in foams due to the combination of PFAS surfactant properties and the agitation of breaking waves.

Results/Lessons Learned:

Sea foams are enriched with a content of PFAS of up to 2502,000 ng/L compared to the low levels (<10 ng/L) in sea water. At both sites, PFAS concentrations in surface water and groundwater were significantly higher than known background levels further inland. Concentrations for the sum of 22 PFAS were up to 220 ng/L for shallow groundwater and 260 ng/L for surface water. Along the sampling transect from the coastline and inland, decreasing PFAS-concentrations were observed for surface water and groundwater. PFOS, PFOA and PFHpS were the dominant PFAS in the water samples. The declining trend from the shoreline and inland proves that the PFAS-contamination detected in surface water and shallow groundwater is caused by spreading of PFAS-enriched sea foam and SSA. The highest concentrations in shallow groundwater were detected at Fanø, with lower concentrations at Husby. It is considered that the thickness of the unsaturated zone is a factor that can reduce the impact on shallow groundwater. At Fanø, a decreasing vertical PFAS groundwater content was observed near the drinking water wells, but it was apparent that contaminated shallow groundwater is mixed with uncontaminated deeper groundwater during extraction from drinking water wells. The results document that enrichment and spreading of PFAS in sea foam and SSA have contaminated the drinking water wells. Concentration of PFAS in soil samples was generally below the Danish soil standards (10 µg/kg dw for sum of 4 PFAS). There was no significant change in PFAS levels in the topsoil in relation to distance to the sea, so it is considered that factors like soil type, organic content and water saturation have a major influence on PFAS distribution in soils.

The results of this project show that enrichment of PFAS in sea foam and SSA most likely has a critical impact on surface water and groundwater along the North Sea coastline and in other areas with similar settings.

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Anne Henriksen