PFAS: an ongoing focus in the water sector

PFAS stands for Per- and PolyFluoroAlkyl Substances. This is a group of thousands of substances, several dozen of which are produced in large quantities, with a wide range of applications. PFAS were first produced in 1938 and they have been used in more and more products since the 1950s. In the Netherlands, PFAS were mainly produced in Dordrecht and processed in Helmond. The drinking water industry is not entirely unacquainted with the dangers associated with PFAS. For more than a decade, KWR has been working actively on research into PFAS in the drinking water chain. For example, results from research conducted by KWR and the University of Amsterdam as early as 2010 showed that these substances are present in sources of drinking water and are difficult to eliminate. Recently, the focus on this group of substances has intensified rapidly, particularly since new insights suggest that they could have effects on humans, even at low concentrations. It is also now clear that PFAS are very widespread, and their presence in the Western Scheldt has now been covered extensively in the Flemish and Dutch media. In the light of the knowledge about water quality that has become available recently, the important knowledge questions relating to PFAS will be presented here.

KWR research in a nutshell

The research at KWR into PFAS initially focused primarily on developing sensitive and wide-ranging analysis methods. For example, high resolution mass spectrometry (LC-HRMS) is available at KWR’s chemistry laboratory. It allows researchers to measure a wide range of PFAS. This recent research therefore provides us with a clear picture of the presence of PFAS in the environment (such as major rivers), identifying specific sources such as industrial effluents and deposition from the sea (‘sea spray’). Using its hydrological and chemical knowledge, KWR has modelled the leaching of PFAS to the subsurface. KWR has acquired knowledge about how toxicity is determined by the properties of substances and how the combined risk of mixtures of PFAS can be estimated even better. KWR technologists are looking at which water treatment techniques can remove PFAS from water and how residual flows containing PFAS can be processed.

Safe threshold

A group of scientists at the EFSA (European Food Safety Authority) derived a safe threshold for humans in 2020. The value was determined for four specific PFAS (PFOS, PFOA, PFNA and PFHxS). These were the substances that have been best studied and that have frequently been found in human blood. After considerable national and international debate about this EFSA threshold, this approach is currently accepted in the Netherlands as the state of knowledge with respect to the risks of PFAS in food and drinking water. RIVM added a method in 2021 to consider concentrations including more than these four EFSA-PFAS on the basis of their toxic potency. This method was also used to calculate a safe value in drinking water, the ‘indicative guideline value’ for PFAS in drinking water. This value is much lower than the prevailing standards for PFAS in food and water. The World Health Organization (WHO) is currently working on the development of guideline values for PFAS in drinking water for application worldwide.

EFSA threshold

The different thresholds also play a key role in the recent RIVM study (2022) based on data supplied by Dutch drinking water companies. The study compared the concentrations in drinking water not only with the European standards but also with the lower EFSA threshold (safe intake through all pathways) and the even lower indicative guidance value for drinking water based on that threshold. Exposure via drinking water was lower on average than the total exposure threshold at all sites studied (the monitoring locations for PFAS concentrations in drinking water in the current dataset). According to the RIVM report, Dutch drinking water does comply with the European Drinking Water Directive, the implementation of which is also required in the Netherlands by 2023. However, not all the drinking water samples in the study complied with the indicative guideline value for drinking water. The RIVM nevertheless concluded that it is responsible to drink tap water.

Because exposure to PFAS via all the combined exposure pathways is higher than desirable, policies are being developed to effectively reduce that exposure. Further research will focus on identifying the principal route for the ingestion of PFAS by humans.

New knowledge required

• Although drinking water complies with European standards and drinking water is not the principal exposure pathway for the four PFAS studied by EFSA, it is essential to know which type of exposure makes the largest contribution, and which contributes least. That is because people ingest PFAS in many ways: through food, drinking water, consumer products and air, for example. These different pathways need to be mapped out further through measurements, and also to be calculated on the basis of the substance properties of the different types of PFAS. This will allow for an even better estimate of the ultimate total exposure to PFAS, and of how, for example, people’s diets and residential locations, as well as any mitigation measures, affect PFAS exposure.
• The EFSA threshold is based on four PFAS but there are many more types of PFAS and it is not always known to what extent they could contribute to a greater or lesser degree to the risks. It is therefore essential to study the presence and toxicity of PFAS other than these four PFAS in order to determine exposure levels and the effects, and therefore to estimate the possible health risk.
• The persistent properties of PFAS mean that the effects of tackling PFAS at source will only become observable in the medium term. Treatment may therefore also be needed to reduce exposure to PFAS in the shorter term. For example, even more knowledge is needed about the elimination of PFAS by a range of water treatment technologies in order to prevent emissions to the aquatic environment through wastewater flows. These technologies can also be used for the production of drinking water. A simple method is lacking at present.
• In the context of the increasing focus on PFAS (in the media and elsewhere), it is reasonable to assume that consumer concern could increase. In addition, consumers are increasingly able to monitor their own health with ‘smart wearables’ such as phones and watches. It is therefore becoming increasingly important to acquire knowledge about the relative contributions that different pathways, including the water pathway, make to exposure. Exposure studies and Citizen Science projects could provide more understanding, while enhancing confidence among consumers.
• The development of this knowledge opens up the opportunity to predict even better how historical, current and future PFAS emissions will impact the water system.

Understanding PFAS better

The ongoing research into PFAS means that the water sector will not be surprised by the presence of these substances in the water chain and that it will have an overview of which steps can be taken, and by whom. An important secondary goal is to understand better where PFAS come from and which measures outside the realm of the water sector will be effective, for example to reduce human exposure to PFAS. Equipped with this knowledge, we can identify the most effective strategies for contributing to a healthy society.