PFAS Monitoring in groundwater: Current status and challenges in France

In France, two-thirds of the water withdrawn for drinking water supply comes from groundwater (OFB, 2017), hence monitoring PFAS is essential to document spatial distribution, dynamics and anticipate potential impacts on water quality.A good monitoring resolution in term of spatial extend, frequency, analytic performance is crucial to better understand sources, pathways and potential impacts. We propose a focus on the regulatory groundwater monitoring for France, where an increasing number of PFAS compounds have been regulated for monitoring, going from 6 in 2015 to 20 in 2022, in compliance with the European Drinking Water Directive (Directive 2020/2184). However, as PFAS represent a family of more than 10,000 compounds, it is necessary to assess the total PFAS contamination, beyond the list of regulated parameters.The concept of the “total PFAS” is not yet clearly defined and is open to question. Measurement by combustion ion chromatography (CIC) provides access to adsorbable organic fluorine (AOF), i.e. the total measurement of fluorinated organic compounds, without the need to identify each individual compound. It is a fast, inexpensive method that gives an indication of the overall level of contamination. However, it can also include substances other than PFAS (e.g. fluorinated pharmaceuticals). Methodological and analytical developments under the framework of the H2020 PROMISCES project (GA No 101036449) will contribute to the deployment of this approach in water monitoring.At the French level, we analysed the available data on PFAS concentrations in groundwater (from the ADES[1] database) from different perspectives.In terms of spatial contamination, PFAS occurrences were mapped in relation to different hydrogeological contexts and pressures (emission sources, aquifer types, density of use,…). These groundwater occurrence maps are of interest for the implementation of health monitoring of water intended for drinking water supply, both from the point of view of geographical sectors and water ressources, but also for the analysis of the contexts to be targeted. This will support decision making for drinking water supply where health risk is of primary interest.In terms of time, the first PFAS analyses are reported for the period 2009-2011. In the whole dataset, the more densely monitored parameters (> 30,000 analyses) are PFOA, PFOS, PFHpA, PFHxA, PFDS, and PFHxS.Quantification rates vary considerably between the different molecules analysed. PFOS is the compound with the highest quantification frequency (17.8%). It is also the most frequently researched compound (about 38,000 analyses). Other compounds researched with the same intensity (about 35,000 analyses) have lower quantification frequencies: PFHxA (12.3%), PFOA (11.2%), PFHxS (10.5%), PFBS (7.8%), PFHpA (7.1%), PFBA (5.4%). For the dataset considered, 12 of the 20 compounds were found, on average, less than 3 times out of 100.Our work highlights that PFAS are widely observed in French groundwaters. Quantification rates are among the highest reported for micropollutants at the national level. Given the potential time-delay effect, due to stock effect, in the soil and unsaturated zone is suspected, and the documented adverse effects on human health, careful monitoring of these compounds is essential in the near future to support decision-making.