What we know about PFAS: the current situation

Poly- and perfluoroalkyl substances (PFAS) are contained in all kinds of products and are present throughout the environment worldwide. Chemicals considered PFAS currently number about 9000. And this number is constantly increasing. PFAS are man-made chemicals and they behave very differently from other substances. So says Arnaut van Loon, a KWR geohydrologist and secretary of the PFAS Steering Group in the drinking water sector’s Joint Research Programme (‘Waterwijs’) , in which PFAS of course receive considerable attention. ‘We conduct lots of research for the water utilities into the subsoil transport of contaminants. The utilities want to know about the challenges that await them. We produced for example an expert document within Waterwijs on the behaviour of PFAS in the soil. In the same context, we carried out a project aimed at elucidating the threats that PFAS represent for Dutch drinking water abstraction. Groundwater of good quality is a theme within Freshwater Resources Management, one of the societal challenges KWR focuses on.

Modelling PFAS

PFAS are already frequently present in surface water, while their concentrations in groundwater are lower or, at this point, non-existent. ‘Groundwater flows very slowly, so that lots of PFAS are moving towards to water abstraction areas,’ says Van Loon. ‘And even if the substances are banned, the lagged effects mean that it will take a very long time to be rid of them. Drinking water utilities therefore need to enhance their water treatment processes. This presents huge challenges. Since we at KWR are developing a greater understanding of the behaviour of PFAS in the soil and underground, we can use models to forecast how these substances spread, and at what moment they penetrate into an abstraction area. We have now done this for an average Dutch groundwater abstraction area. Our models still need to be refined, but we have made a good start in describing and understanding these processes.’

Transport models developed by KWR and that are being further refined can, for example, be used to get an idea of the future developments of PFAS concentrations in groundwater abstraction, in relation to possible exceedances of the future drinking water standard.

Advanced techniques 

KWR has already been working on PFAS-related issues for about 15 years. Ecotoxicologist Stefan Kools speaks of the new knowledge that is required in order to contribute new solutions. ‘We apply advanced techniques aimed at analysing a broad group of PFAS, because the water sector does not yet always look at the total set of substances. The question is therefore: Can we conduct the analyses faster and better, but also more broadly and build a greater understanding of the hazards involved? In this way we can find out whether we are targeting the most relevant PFAS. At KWR we are making significant progress in the further development of the necessary techniques, such as suspect- and non-targetscreening (SNTS).’

Environmental forensics

There is also a great instrument for tracking the sources and emission pathways of contaminants, namely: environmental forensics, adds Kools. ‘This involves applying various analytical and data processing approaches to answer the big question: Where do the PFAS come from? Because only then can you trace the dischargers concerned. Our research for instance reveals the patterns of dissemination, so that you can predict when the peak PFAS concentrations will occur in the river. KWR is also a leading researcher into the dissemination of PFAS in the air, by means of sea spray for example. The more you know about where the substances come from, the better you will be able to take the measures everyone is calling for.’

Measurement instrument for taking high-volume air samples to collect air particles for research into sea-spray aerosols: particles that form on the sea surface and are transported by the wind into the atmosphere, after which they can – often over long distances – fall as precipitation onto the Earth’s surface (photo: Elvio Amato, KWR)

Risk determination

KWR is also working on new knowledge in relation to the forthcoming tightening of the regulatory quality requirements for PFAS. In 2020, the European Food Safety Authority (EFSA) lowered the PFAS safety exposure threshold. On this basis, the National Institute for Public Health and the Environment (RIVM) derived a guidance value of 4.4 nanograms per litre of PFOA equivalents for drinking water. PFOA is a PFAS that is used as a reference in this context. A guidance value is a RIVM-based risk limit that will possibly be included in future regulation and thus become the standard. Kools: ‘Through our research we want to clearly and accurately determine the risks of PFAS, so that people are well informed about how hazardous the substances can be. KWR’s strength is that we have a range of professional disciplines under a single roof. This provides a broad and multi-disciplinary perspective. This powerful combination is absolutely essential in dealing with a substance group that is so widely disseminated. Our clients today often ask us: Can you summarise the current situation with regard to PFAS? And what are our action perspectives? I think it’s great to be able to help deal with questions of this sort.’

Effective treatment techniques

In anticipation of the regulatory quality requirements for PFAS, KWR is already working on the question of how concentrations of these chemicals can be reduced in water treatment. ‘Among the current techniques, activated carbon can apparently be effectively used to this end,’ says is Bas Wols, water-treatment expert at KWR. ‘However, you have to reactivate the carbon five times more than usual, because otherwise the PFAS pass through. Particularly the smaller PFAS compounds can more easily pass through the carbon, and are therefore harder to remove from the water. The reactivation, in which the pollutants that are trapped in the carbon are degraded under high temperature and in the absence of oxygen, is a costly business. Membrane filtration using nanofiltration or reverse osmosis offers an alternative. But while it allows you to remove all PFAS from the water, you’re left with a residual stream to deal with. PFAS degradation is moreover extremely energy intensive. There is therefore a need to thicken the residual stream as much as possible.’

Reality check for drinking water practice

The scientific literature describes the techniques that are suited to this thickening process, continues Wols. ‘We submit these techniques to a reality check for drinking water practice. But the sector requires large-scale applications, not academic tests in a laboratory. Foam fractionation is an interesting candidate for this thickening. In this method, you add soap to produce foam bubbles to which PFAS remain attached. We have done research into this in the context of the TKI programme. The PFAS can then be degraded by means of electro- or photochemical reactions. These techniques are now being tested within the Waterwijs research programme, with very promising results.’

Complex spectrum

Because PFAS are very present in everybody’s mind, the researcher Kools assumes that even more analyses, clarification and solutions will be called for in the near future. ‘KWR can help to determine the societal impact and cost of PFAS discharges into the environment. Studies of this type are most effectively conducted upon a broad knowledge base. You need for instance to consider the effects of PFAS on humans and nature, but also identify the most appropriate measures and how to determine the associated costs. This constitutes a complex spectrum, which is precisely something that KWR is so good at handling. We have the necessary scientific knowledge, and we collaborate with parties that can advise us on the economic aspects. In the years ahead, we need to succeed in clarifying the gravity and extent of the PFAS contamination. Only if you have a clear picture of the right hotspots and the most sensitive parameters, will you know that you are looking at the right thing.’ 

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