Digging deep—implementation, standardisation and interpretation of a total oxidisable precursor (TOP) assay within the regulatory context of per- and polyfluoroalkyl substances (PFASs) in soil

Over the past decades, thousands of different per- and polyfluoroalkyl substances (PFASs) have been produced and applied in various industrial processes and consumer products. Their structural diversity has reached a level that cannot be covered by classical target screening methods for individual compounds. Large-scale contaminations of soil, however, require the need to adapt new analytical methods that can describe a contamination more comprehensively. While sum parameters such as the total oxidisable precursor (TOP) assay have been developed in the past years, they are not yet applied in the regulatory context of PFASs. In this commentary, we provide an overview on different approaches of the TOP assay as well as its benefits and disadvantages to other sum parameters for PFASs in soil samples. Furthermore, we elaborate its opportunities and its challenges that need to be tackled to implement the TOP assay as a regulatory tool. With several different approaches of the TOP assay being available, a sound and standardised method needs to be agreed upon and more research is necessary to better describe the method. Although the complexity of PFAS contaminations in soil cannot be fully covered by any analytical method alone, the TOP assay can provide valuable data to detect and characterise soil contamination as an inventory for subsequent remediation measures. Therefore, the TOP assay should be implemented as a useful tool both in research and in the regulatory context of PFASs.