Doctoral thesis Ninon SERRE (2022-2025)

Doctoral school: Vegetal, animal, food, sea, environment

Formation d’origine: Environmental and Analytical Chemistry Engineer – Ecole Nationale Supérieure de Chimie de Rennes, 2017-2022

Master's degree in water quality and treatment – Ecole Nationale Supérieure de Chimie de Rennes, 2021-2022.

Thesis supervisor(s): Yann Aminot and Aurore Zalouk-Vergnoux

Funding: Ifremer and Pays de la Loire region

Thesis title: Unravelling the complexity of per- and polyfluoroalkyl substances (PFAS) contamination in marine organisms

Context

Among contaminants of emerging concern, per- and polyfluoroalkyl substances (PFAS) constitute a family of thousands of non-naturally occurring chemicals, reported for their ubiquitous presence in the environment. The combined evidence of their persistent, bioaccumulative, and toxic properties has led to the ban of some compounds (e.g., PFOS and long-chain PFCAs), but a large number of alternative or precursor compounds of unknown environmental fate or effect remain in use. To address the problem of global PFAS contamination, the scientific community is now calling to urgently fill the lack of fundamental knowledge, including on the exposure of biota to PFAS, their subsequent bioaccumulation, and their potential toxic effects. The stability of PFAS in environmental waters and their limited affinity to sediments have made the oceans the largest environmental reservoir of PFAS. High uptake by plankton has been reported, resulting in subsequent exposure of higher trophic levels to PFAS through ingestion. Stable end products such as PFCAs and PFSAs accumulate in marine organisms, directly or indirectly, after being metabolized from precursors. However, beyond the few dozen traditionally studied compounds, a large number of neglected PFAS, particularly PFAA precursors, remain unaccounted for. To better address this still poorly studied fraction, Ifremer developed an innovative approach to non-specifically measure the presence of PFAS precursors in marine biota, namely the total oxidizable precursor (TOP) assay. Applied to the biomonitoring of bivalves from the French coast, the results evidenced that PFAA precursors were by far the main contributors to the total PFAS burden (Veille-POP data). The importance of precursors was the highest in mussels of the Seine estuary, with an increase in PFAS concentrations by 60 times after the application of this protocol. Knowing that bioaccumulative unknown precursors constitute a significant fraction of the total PFAS content along the French coastline, it is now crucial to identify the specific compounds responsible for this contamination using non-targeted screening approaches (NTS). It is also necessary to further our knowledge on their environmental behavior, including their bioaccumulation potential and toxicokinetics (accumulation, depuration and metabolism).

Specific objectives

The aim of this thesis project is to go beyond the traditionally investigated PFAS to obtain a complete view of the contamination of marine organisms by unreported PFAS and to address the urgent need to qualify their bioaccumulation potential. With consistent evidence that PFAA precursors constitute a large majority of the total PFAS burden in mussels of the Seine Estuary (Veille-POP data), our first objective is to provide a definitive identification of these substances using a state-of-the-art non-targeted approach. The information obtained will allow us to investigate the exposure of biota to PFAS, and to address our second objective, namely to determine whether these specific compounds are found in bivalves and other marine organisms from contrasting ecosystems. These will include (but not be limited to) bivalves from the French coast of the ongoing Veille-POP program, organisms from the seabass and sole trophic networks of the EMERTROPH project, and top predators such as dolphins from the DELMOGES project. Finally, our third objective is to characterize the biomagnification capacity of newly identified compounds, from zooplankton to sea bass and sole, from ecosystems of known exposure. Overall, the results of my thesis project will also provide essential data for better effects assessment in the future.