The results of the monitoring campaign show that PFAS were hardly removed, or not removed at all, at WWTPs. Influent contained well-known and highly persistent PFAS, such as PFOS and PFOA, in addition to other PFAS groups, including various degradable PFAS – also called precursors. Precursors are not persistent: known and unknown precursors in influent appear to be trans- formed at WWTPs, resulting in higher concentrations of persistent PFAS (and other precur- sors) leaving the WWTPs in the effluent than in the influent.

PFAS in the environment is problematic. PFAS are hazardous, they are poorly biodegradable and they are extremely persistent and found everywhere. Various national studies have been conducted or are underway to better understand PFAS sources. The current study of PFAS in influent, effluent and sewage sludge at WWTPs is one of these. This study answers to the ques- tion of what PFAS are found at WWTPs, and in what concentrations. With the results in hand, the Dutch water boards and Ministry of Infrastructure and Water Management will be better able to determine what remedial actions are necessary.

Eight WWTPs were included in this monitoring campaign. These were a mix of WWTPs, including some known to have high PFAS emissions (hotspots), a former hotspot (where PFAS emissions had previously been reduced at the source) and WWTPs processing differing proportions of industrial wastewater. The largest PFAS contributions by far were found at the hotspots. However, PFAS were found in the influents at all WWTPs. Based on the variation in PFAS found in influent, there appears to be a level of background contamination from domestic wastewater, and in addition, a variety of other sources. What these sources are is not always known. In addition, there is strong evidence of an important role played by PFAS precursors. Precursors can degrade into persistent PFAS. At most WWTPs, greater quantities of persistent PFAS left the WWTP than entered it.

A number of persistent PFAS, including PFOS and PFOA, have been designated as priority hazardous substances and/or Substances of Very High Concern (SVHC). That means their release into the environment must be reduced to zero. Intervention at the source is the preferred option, because once PFAS are in the environment they are difficult if not impos- sible to remove. The Netherlands is collaborating with a number of countries on a proposal for a European restriction on all PFAS. At the national level, the water boards and other government authorities are cooperating with business and industry in the PFAS Action Programme. Via this platform they are pursing interventions to reduce the release of PFAS into the environment and to limit human exposures. Specific attention is being given to the various links in the chain, from the production of PFAS, to its use in industrial processes, to the different emission pathways. The current study offers valuable informa- tion in that respect. However, as this study also shows, unless emissions of PFAS precursors can be reduced, it will be very difficult to achieve a reduction in PFOS and PFOA emissions.

Further research on precursors will therefore be proposed to the national working group on emerging substances.

WWTPs with elevated levels of PFAS and PFAS precursors can be identified by carrying out measurements. Once these WWTPs are identified, water boards, provincial and municipal authorities and environmental services can work in collaboration to better understand the sources. If sources can be identified, dialogues can then be initiated to seek ways to reduce emissions at the source.

This report is the Englisch translation of STOWA-report 2021-46