Thèse sur les Trace de l'Invisible les Effets des Pfas sur les Vers de Terre et leurs Fonctions dans les Agroécosystèmes H/F - 84

Établissement : Avignon Université
École doctorale : Agrosciences et Sciences
Laboratoire de recherche : EMMAH - Environnement Méditerranéen et Modélisation des AgroHydrosystèmes
Direction de la thèse : Céline PELOSI ORCID 0000000271005760
Début de la thèse : 2026-10-01
Date limite de candidature : 2026-05-05T23:59:59

Les substances per- et polyfluoroalkylées (PFAS) constituent une vaste classe de xénobiotiques persistants et bioaccumulables dans l'environnement. Certaines de ces molécules sont connues pour nuire à la santé des organismes vivants. Les PFAS pénètrent dans les champs agricoles par l'utilisation de produits phytosanitaires, de déchets organiques, d'eau d'irrigation contaminée et de dépôts atmosphériques. Les conséquences des PFAS sur la faune du sol, et en particulier sur les vers de terre (organismes clés impliqués dans plusieurs fonctions du sol) et leur activité dans les sols, font l'objet d'une attention chroniquement insuffisante. Ce projet de doctorat vise à évaluer la toxicité chronique sublétale des PFAS et ses conséquences pour les vers de terre à l'échelle sub-individuelle, individuelle, populationnel et des écosystèmes. Il combinera des expériences sur le terrain et en conditions contrôlées de laboratoire afin de paramétrer un modèle de dynamique des populations dans les sols et de mettre en lumière les processus cellulaires affectés par les PFAS, une première étape vers la détermination des voies d'effets délétères à des niveaux supérieurs.

Healthy soils produce food, biomass and store carbon. They protect groundwater by filtering and storing nutrients and contaminants, and provide habitat for the soil biota. Over 30% of European soils are considered as degraded (Panagos et al., 2022, Vidal et al. 2025). In agricultural soils, some of these degradations can be mitigated by recycling organic waste products (OWP) from various sources. These nutrient-rich materials increase the soil organic matter (OM) content, which improves or restores several soil properties while contributing to achieving circular economy objectives. However, OWP also contain various contaminants including per- and polyfluoroalkyl substances (PFAS).

PFAS are a broad class of xenobiotic substances containing at least one perfluorinated methyl (-CF3) or methylene (-CF2-) group. PFAS have been increasingly used for over 80 years. To date, the structure of nearly 15000 PFAS molecules has been documented (Comptox, 2022). Most of these are, or can decompose into, molecules that are persistent in the environment and bioaccumulative. Some of them are known to impair the health of living organisms, including humans (Lyu et al. 2022, Delor et al. 2023). OWP are not the only source of PFAS in agricultural soils. Recent evidence suggests that PFAS can reach the soil through (i) irrigation with contaminated water, (ii) wet and dry atmospheric deposition, (iii) the use of pesticides belonging to the PFAS class (Cousins et al. 2022, Korsiarski et al. 2024, Joerss et al. 2024).

Among soil organisms, earthworms fulfil various services in agrosystems: they increase the availability of nutriments, enhance the stability of the soil structure, participate in organic matter cycles, and are preys for numerous other living organisms (Blouin et al., 2013; Vidal et al. 2023). They can also be used as bioindicators of soil quality, land use and management, and soil contamination (Vidal et al., 2025).

The consequences of PFAS on earthworm health and activities suffer from a chronic limited attention. An ongoing meta-analysis realized in the framework of the ADEME funded IPANEMA project highlighted that PFAS bioaccumulation values in earthworms were reported in only 21 research articles. Surprisingly, all but two of these articles focused on the earthworm Eisenia fetida, a compost worm that is known to be less sensitive to pesticides than other earthworm species (Pelosi et al. 2013) and that does not dwell in natural soils.

Only a few research considered endpoints other than bioaccumulation, such as effects on mortality and growth. In most cases, these studies considered PFAS concentrations well above those found in agricultural fields. And none of them studied the impact of sublethal concentrations of PFAS on earthworm activities: creation of burrows and vertical transport of soil particles. Interestingly, preliminary experiments in our team highlighted lower burrowing rates in PFAS-contaminated soils. The impacts of bioturbation activities on PFAS fate in the soil have not been considered either: wide and vertical macropores like those created by certain earthworm species act as preferential flow pathways for water and thus PFAS (Jarvis 2007), facilitating the rapid transfer of these xenobiotics towards groundwaters as suggested by recent knowledge gained during the IPANEMA project. Conversely, the upward transfer of soil constituents by earthworms may contribute to maintain high concentrations of PFAS in the root zone as observed for other persistent and strongly sorbing contaminants: radionuclides and PCBs (Jarvis et al. 2010, Cousins et al. 1999).

Overall, there is a critical need for research studies to characterize the effects of PFAS on earthworms, which are key organisms in maintaining and restoring ecosystem services related to soil, as well as the role of earthworms on PFAS mobility in soils, and to predict with adequate models these complex biological phenomena. For that, we need to understand and model the cascade of consequences of earthworm exposure to low doses of PFAS from the sub-individual level (damage to DNA or protein productions) to ecosystem functioning (mobility of PFAS in soils). This doctoral project will therefore address these issues at different levels of biological organization.

The main assumption that will be evaluated in this work is that sublethal concentrations of per- and polyfluoroalkyl substances (PFAS) present in agricultural soils will have consequences at different biological levels: sub-individual (DNA, primary metabolites), individual (growth, survival), population (reproduction), and ecosystem functioning (burrowing and bioturbation, i.e., the transport of soil particles carried out by the soil fauna, essentially invertebrates, including earthworms).

An assumption related to the previous one is that biomarkers at the sub-individual level may be used as early-warnings of effects observed at higher levels (i.e., population level or higher, e.g., behavior and effects on the system functioning).

Another assumption is that it is possible to define a contamination level deemed safe for earthworm communities and the functions they fulfill in agroecosystems. This would help setting guidelines in terms of fluxes of PFAS in agrosystems. To do so, this study will emphasize on the consequences of soil PFAS exposure on two distinct earthworm species:
-Lumbricus terrestris, an anecic (i.e. earthworms that form continuous vertical macroporosity in soils) species;
-Aporrectodea caliginosa, an endogeic (i.e earthworms that form complex horizontal macroporosity in deeper soil horizons) species.
The inclusion of these two species, commonly found in temperate agricultural soils, will provide a realistic view of the bioporosity resulting from earthworm bioturbation.
The two studied earthworm species, according to their ecological category (endogeic and anecic) will have different exposure (A. caliginosa eat more soil than L. terrestris which targets fresher OM) and thus will be differently affected by PFAS.