PFAS contamination and soil remediation (Signal)

Due to their high persistency and widespread use, PFAS are ubiquitous in humans, animals, food and feed, as well as in other parts of the environment. PFAS are becoming increasingly important in the evaluation of contaminated sites. However, they can be detected in low concentrations in soils virtually everywhere. PFAS can move with percolating water into deeper soil layers and also reach groundwater reserves. This migration can be relatively rapid (as seen, for example, with short chain PFAS such as perfluorobutanoic acid) or may take decades (such as with some long chain PFAS, e.g. perfluorooctanesulfonic acid (PFOS)). Because of this, soils and groundwater can act as either sinks or sources of PFAS. In the EU, 65% of the drinking water is derived from groundwater.

Diffuse PFAS soil pollution can occur via compost, contaminated sewage sludge, deposition from the air, irrigation, soil additives and the use of certain pesticides. Point sources of such contamination include sites of PFAS production and use. Examples include facilities for chemical and electronics manufacturing, electroplating, leather processing, paper milling and textile finishing. Landfills can also be a source as PFAS may evaporate or leach from them. PFAS in soils can enter the food chain via uptake by plants. 

The EU recently established thresholds for some PFAS in drinking waterand food. However, environmental concentrations — including those seen in plants and animals, e.g. fish — often exceed those levels. 

PFAS contamination hotspots  

Europe is seeing an increase in sites identified with high PFAS loads in soil and/or groundwater. The Table above provides a series of examples of hotspots. See the signal Treatment of drinking water to remove PFAS for an overview of the current knowledge in terms of extent and levels of soil and water contamination in Europe based on the work of Dagorn et al. (2023).

High PFAS loads are often related to the use of firefighting foams containing fluorinated substances — i.e. at airports, fire-fighting training facilities and military sites. In fact, PFAS contamination at Duesseldorf Airport, Germany, has impacted both surface- and ground- waters, forcing a nearby lake to close to fishing and other recreational activities. As in many other cases, the remediation process for Duesseldorf Airport is lengthy, expensive and requires significant technical effort. PFAS remediation often forces groundwater wells to close, interfering with private garden irrigation. PFAS hotspots can also be found near fluorochemical manufacturing plants. Here, PFAS can enter the soil and surface water via atmospheric deposition, wastewater and accidental releases. 

Remediation 

Remediating PFAS-contaminated sites tends to be costly and difficult, if at all possible. Remediation approaches used with other pollutants often do not work for PFAS due to their stability and other properties, as noted in Annex B of the PFAS restriction proposal prepared and submitted by four EU Member States (Germany, the Netherlands, Sweden, Denmark) and Norway and published by the European Chemicals Agency.  

Due to the diversity of PFAS, specific remediation approaches do not work in all cases. However, soil and groundwater remediation development projects are ongoing in many European countries — e.g. in Belgium, Germany, the Netherlands, Norway and Sweden — and some focus on small-scale contamination at airports or former fire-fighting sites. Some PFAS stick to the surface of soil particles and for this reason can be removed from groundwater using activated carbon filters. There are already suppliers in Europe who can repeatedly regenerate PFAS-loaded activated carbon.  

Based on current knowledge, 100% removing PFAS from soils is only possible using a high temperature, combustion-based treatment whose effectiveness is tied to the processing time and the turbulence in the combustion chamber. According to EU regulations on persistent organic pollutants, thermal treatment processes are also well-suited to recovering or eliminating PFAS-containing waste.  

Soil washing is another promising technology, but its viability is highly dependent on soil composition. Although PFAS can be removed from granular soils by washing, they cannot be removed from more cohesive soil types (e.g. clays). It should also be noted that soil washing does not degrade PFAS, but instead transfers them into the washing water, which then needs to be treated. Nevertheless, the process can considerably decrease the soil volumes which have to be processed and incinerated, cutting site-specific costs.  

While water can be treated for PFAS contamination, standard wastewater treatment technologies are currently unable to fully remove PFAS from wastewater. 

In order to contain the spread of PFAS within soils and into groundwater, immobilisation or stabilisation methods have potential. However, as of now, providers cannot guarantee that such solutions would be effective over the long-term. In other words: it is uncertain whether these methods irreversibly bind PFAS in the soil and stop future transfer to groundwater.