PFOS and PFOA in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality

29 November 2023

In view of the public health concerns of per- and polyfluoroalkyl substances (PFAS), the World Health Organization (WHO) initiated the development of a background document for the Guidelines for drinking-water quality (GDWQ) on PFAS in drinking-water with a focus on perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA).

As part of this process, the draft background document was offered for public consultation from 29 September to 11 November 2022, during which 25 sets of comments were received from different stakeholders. (WHO responses to the most common comments can be found here).

The WHO review and assessment of the PFAS group of substances is an ongoing process, and has now been expanded to consider sources of exposure beyond focusing principally on drinking-water. The review will also include further examination of the occurrence and health effects of additional substances (beyond PFOS and PFOA) of health concern, and a further examination of whether international health-based guideline values could be established.

What are PFAS, PFOS and PFOA?

Per- and polyfluoroalkyl substances (PFAS) is the collective name for a large group of fluorinated compounds, which are used in a wide range of applications, such as aerosol propellants; solvents; pesticides; antifoaming agents; surface treatments for textiles, leather, masonry and paper and board; leveling agents in paints, coatings and waxes; plastics; lubricants and greases; and fire-fighting foams.

The most widely studied of these PFAS are perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA).  Although the stability of PFOS and PFOA as well as their surfactant properties make them useful in consumer and industrial applications, there are concerns with their persistence and impacts on the environment and human health, as a result of exposure through the widespread uses of these chemicals. Drinking-water is one of several environmental sources of human exposure to PFAS, along with exposure via food, use in consumer products and occupational exposures.

What is the status of the process in developing the background document?

WHO’s GDWQ chemical working group guided the preparation of the draft background document for the GDWQ on PFAS in drinking-water with a focus on PFOS and PFOA.

The process was initiated in 2017. Preliminary drafts were discussed at numerous consultations with the authors and the chemical working group, including in July 2018, April 2019, March 2021 and October 2021. The document also went through a peer review process in 2021, with the feedback provided considered by the chemical working group. 

“PFOS and PFOA in drinking-water: Background document for development of WHO Guidelines for drinking-water quality” was offered for public review from 29 September to 11 November 2022.  During this period, WHO received 25 sets of comments from different stakeholders. WHO responses to the most common comments can be found here. In light of comments received and to ensure that the latest evidence is taken into account since the background document was drafted, WHO will continue its review of PFAS. The updated assessment will consider, inter alia, the International Agency for Research on Cancer's (IARC’s) carcinogenicity assessment on PFOS and PFOA. It will also include further examination of the occurrence and health effects of related substances (beyond PFOS and PFOA) of health concern. Furthermore, the review will be expanded to consider sources of exposure beyond focusing principally on drinking-water. The review will also further examine whether international health-based guideline values can be established. If it can, WHO will eventually determine tolerable daily intake or equivalent values that can be a starting point to establish drinking-water guideline values. It is noted that the FAO/WHO Codex Committee on Contaminants in Food has included PFAS on its list of substances for evaluation by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) at its 16^th session. The updated WHO review of PFAS described above will play a critical role in the planning of a future JECFA safety assessment of PFAS, which is scheduled to be undertaken in the coming years.

The draft background document mentions chemical guideline values.  What are those?

A guideline value normally represents the concentration of a constituent that does not result in any significant risk to health over a lifetime of consumption.  The health effects information in the chemical background documents, including guideline values, are usually based on international chemical risk assessments (e.g. from WHO’s chemical safety team).  In the absence of a suitable WHO assessment, guideline values may be based on one or more recent high quality, peer reviewed national or regional assessments.

In certain cases, WHO recommends a provisional guideline value that is higher than the health-based value (i.e. based on a chemical risk assessment).  The provisional guideline value takes into account practical issues, including those associated with the feasibility of monitoring or treating the contaminant. [1]  WHO has established a number of provisional guideline values at concentrations that are reasonably achievable through practical treatment approaches or that are detectable by standard analytical methods. 

Chemical guideline values should be adapted in national standards and regulations, including establishing stricter values in national standards compared to the provisional guideline values, when resources are available.

What is WHO advising its Member States in relation to PFOS and PFOA in drinking-water?

Although the process of developing the guideline values is still ongoing, WHO’s advice to its Member States in relation to PFOS and PFOA in drinking-water is guided by key principles laid down in the draft background document for the GDWQ on PFAS in drinking-water, namely:

• Member States should strive to achieve concentrations in drinking-water that are as low as reasonably practical.
• Contamination of water sources should be minimized, including preventing new sources of contamination.
• Non-essential uses of PFAS should be stopped.
• Risks from PFAS need to be balanced with other risks in the water supply including not having adequate supplies of drinking-water.

Who are the experts who have participated in developing the latest update to the GDWQ? 

The contributors included the experts from the Guideline Development Group and working groups for the Guidelines for drinking-water quality: Fourth edition incorporating the first and second addenda, who formulate the recommendations  related to  chemical, microbial or protection and control aspects based on the evidence.  Their names can be found in the Acknowledgement section of the Guidelines.

Additional contributors provide expertise and comments for all WHO assessments of drinking-water contaminants, including for PFOS and PFOA.  For the PFOS and PFOA document, their names will be included in the final background document. As of 29 September 2022, contributors include:

• Dr Ruth Bevan, independent consultant, United Kingdom; Mr Brad Lampe, WHO Collaborating Centre NSF International; Professor Peter Jarvis, Cranfield University, United Kingdom; and Professor John Fawell, Cranfield University, United Kingdom prepared the initial drafts of the background document, under the coordination of WHO and its experts from the chemical working group.
• Experts from the chemical working group of WHO’s Guidelines for Drinking-water Quality guided the development of this document: Dr Mari Asami, National Institute of Public Health, Japan; Mr Richard Carrier, Health Canada, Canada; Dr Joseph Cotruvo, Joseph Cotruvo & Associates, United States of America; Dr David Cunliffe, South Australian Department of Health, Australia; Dr Alexander Eckhardt, Umweltbundesamt (Federal Environment Agency), Germany; Dr Akihiko Hirose, National Institute of Health Sciences of Japan, Japan; Dr Peter Marsden, formerly Drinking Water Inspectorate, United Kingdom; Dr Ed Ohanian, Environmental Protection Agency, United States of America; Professor Choon Nam Ong, National University of Singapore, Singapore; Dr Betsy Behl, Environmental Protection Agency, United States of America; and Dr Emanuela Testai, National Institute of Health, Italy.
• Peer reviewers included Antonia Calafat, CDC, United States of America; Milou Dingemans, KWR Water Research Institute, the Netherlands; Dr Michael Dourson, Toxicology Excellence for Risk Assessment, United States of America; Nick Fletcher, Food Standards Australia New Zealand, Australia; Tony Fletcher, London School of Hygiene and Tropical Medicine, United Kingdom; Philippe Grandjean, University of Southern Denmark and Harvard T.H. Chan, School of Public Health, Denmark and United States of America; Roberta Hoffman-Caris, KWR Water Research Institute, the Netherlands; Philip McCleaf, Uppsala Vatten Och Avfall AB, Sweden; Katie Pelch, University of North Texas Health Science Center, United States of America; Marc-Andre Verner, University of Montreal, Canada; Graham White, formerly Health Canada, Canada; and additional experts from the Environmental Protection Agency, United States of America.
• WHO Unit on Water, Sanitation, Hygiene and Health provided coordination, strategic direction and liaison with the WHO Unit on Chemical Safety and Health. 

Did the experts and contributors declare their conflicts of interest?

All authors, chemical working group members and peer reviewers  have disclosed circumstances that could give rise to actual or ostensible conflicts of interest and have signed a Declaration of Interest form.  No authors, working group members or reviewers declared any interests that were considered by the WHO Secretariat to preclude their involvement in development of the draft background document. 

See also

Chemical hazards in drinking water