Perfluoroalkyl and Polyfluoroalkyl compounds (PFAS) in in situ soils and excavated materials (soils and sediments) : identification, quantification and reference values

Synthesis

Disclaimer: The content of this publication is based on the state of knowledge and the regulatory framework in force at the time of publication of the documents.

The issue of per- and polyfluoroalkyl substances (PFAS) represents a particularly evolving and complex thematic to study due to several factors:

• The multitude of compounds (more than 10,000),
• Their highly varied physicochemical characteristics,
• The difficulty in analyzing them,
• The lack of reliable data on some aspects,
• The absence of scientific consensus on other field of study.

Characterization studies of potential environmental contamination are also challenging to conduct. Indeed, the use of common analytical methods such as LC MS MS mass spectrometry is not always the most informative. Since PFAS are ubiquitous in all environmental matrices, it is difficult to distinguish between background noise, cross-contamination, and confirmed contaminations. Additionally, due to particularly low environmental thresholds, analyses with very low limits of quantification are necessary. For all these reasons, it is necessary to implement a reliable sampling and analysis strategy to properly study real contamination.

Therefore, this report pursued several objectives. First, it aimed to provide an overview of current knowledge on various topics such as the physicochemical characteristics of PFAS, international regulations, toxicological and ecotoxicological data, and existing analysis methods.

After outlining the many uses of these compounds, this report lists the various physico-chemical parameters available in the scientific literature, and then attempts to sketch a picture of the usual behaviour of these compounds in the environment.  Given their physico-chemical characteristics, particularly their high water-solubility, PFASs run off into surface water and/or leach rapidly into groundwater. Once in the hydrosphere, these compounds become particularly mobile. Because of their high persistence and bioaccumulation potential, these compounds fall into the category of ‘vPvM substances’ (very Persistent and very Mobile substances) as well as ‘vPvB substances’ (very Persistent and very Bioaccumulative substances). In view of these characteristics and their toxicity, PFASs are particularly closely regulated.

These regulations vary considerably from one geographical area to another, and have also changed considerably in recent years. This report has therefore listed the various legislative texts in force at the time it was written, and has attempted to explain the points of interest and modes of action of the various administrative authorities. In its conclusions, the report set out to list the matrices for which the regulatory aspects are not yet mature and which should evolve as a result of the creation of toxicological or ecotoxicological values or dedicated analytical methods. The report also lists the main toxic and ecotoxic effects observed and the toxicological reference values in existence at the time of writing. 

Finally, the report sought to clarify the metrological challenges of these compounds and to propose a coherent and structured methodology for defining contamination accurately.

This methodology first involves implementing a rigorous conceptual sampling scheme identifying all potential secondary sources and, importantly, assessing background noise using samples taken outside the influence zone of different sources. The implementation of a conceptual scheme is well described in existing guidelines, so the report detailed the specificities of PFAS by identifying different primary and secondary sources while specifying transfer pathways.

Next, sampling should be conducted with particular attention to managing cross-contamination during sampling and analysis. This involves:

• Prohibiting many products and equipment,
• Thoroughly cleaning equipment between two samplings,
• Implementing a quality assurance and control strategy,
• Employing a monitoring strategy using blank samples (field, laboratory, equipment...), replicates, and performance evaluation samples.

The report specified the different existing methodologies while leveraging the experience of the authors and RECORD members who participated in the steering committee to evaluate their effectiveness.

The crucial element in conducting a good environmental diagnosis is the choice of relevant analysis method(s). Indeed, each technology (LC MS MS, CIC, FTICR...) and each analysis method (targeted, total organic fluorine, TopAssay...) does not provide the same information. Therefore, it is necessary to use these methods in the appropriate context, in line with the objectives pursued, and in some cases, to combine several analytical methods to have a comprehensive view. To do this, several scenarios were defined, and typical analytical schemes were designed. These analytical schemes were designed to cover issues found in polluted sites and soils while offering different levels of precision with primary and complementary analyses. These schemes are presented in the following table:

Table: Summary of the characteristics of the different analytical methods (RECORD 2024)