Effects of Biodegradable and Non-Biodegradable Microplastics on the Microbiota of Eurytemora affinis

Estuaries and the marine environment are particularly impacted by microplastic (MP) pollution. The aim of this thesis was to investigate the ingestion and impact of MPs on the calanoid copepod Eurytemora affinis. Indeed, this model has proven to be a metric of choice in ecotoxicology due to its sensitivity to a wide range of environmental contaminants at non-lethal concentrations. Initially, a new method was developed to identify and characterize MPs ingested by this organism in the laboratory and is also transposable to samples from the natural environment. Indeed, numerous studies have determined the effects of MPs on this model using fluorescent MPs. However, this method remains limited when it comes to studying the effects of MPs corresponding to those sampled in the natural environment, due to their diversity in shape, nature, and color. Our methodological work has therefore demonstrated the ingestion capability of MPs in this copepod. It has also proved to be generalizable to copepods contaminated with MPs sampled from the environment and has proven to be more sensitive than existing methods. Furthermore, it has confirmed a higher than previously estimated ingestion of MPs <10µm by copepods in the natural environment. Subsequently, an aging experiment of compostable (PBAT) and non-compostable (LDPE) polymers in the size range of MPs, and exposure over several generations of E. affinis was conducted. TGA, FTIR, and DSC analyses showed almost no chemical modification of the two types of plastics during aging, and a bacterial adhesion dynamic more linked to the duration of aging than to the nature of the plastic. During the multi-generational exposure experiment, our results demonstrated a true dynamic of the copepod microbiota from generation to generation. This microbiota was characteristic of the copepod compared to the water of the experiment and the algae used for feeding. At an environmental concentration, exposure to MPs caused an effect on the composition of the E. affinis microbiota for LDPE and PBAT. Interestingly, the type of MPs had no significant effect on the E. affinis microbiota. In conclusion, these results suggest that the compostable nature of a polymer like PBAT does not reduce the effects on the microbiota of E. affinis compared to another non-compostable polymer like LDPE.