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Microplastics in the land-to-sea continuum : what do sediments from the Loire tell us ?
Contribution of an integrated approach of riverine hydro-sedimentary processes

Thèse de doctorat de Camille Croiset, soutenue en juin 2025 à Nantes

Table des matières :
General Introduction
1 State of the art
1.1 Hydrosystems and hydro-sedimentary functioning
1.1.1 Drainage basins
1.1.2 Hydrosystems
1.1.3 Spatial hydro-sedimentary functioning
1.1.4 Temporal hydro-sedimentary functioning
1.2 Microplastics generalities
1.2.1 Definitions
1.2.2 Harmful effects
1.2.3 Emission sources
1.2.4 Environmental release pathways
1.2.5 Transfer to sediment
1.3 Research of microplastics in sediment
1.3.1 Sediment sampling for the research of microplastics
1.3.2 Sediment preparation for analysis of microplastics
1.3.3 Microplastics analysis in sediments
1.3.4 Results review of microplastics in sediment
Context and objectives of this thesis
1.4 Research gaps
1.5 Research questions
1.6 Objectives of this thesis
1.7 Study area
1.7.1 Focus on the Loire river
1.7.2 Sampling map
1.8 Contextualisation of the PhD project
2 Assessment of microplastic contamination in sediment
2.1 Presentation of the protocol
2.1.1 Sample preparation
2.1.2 Micro-Fourier transform infrared spectroscopy
2.1.3 Uncertainties
2.2 Introduction to the recovery rate study
2.3 Material and methods
2.3.1 Standard microplastics
2.3.2 Sediment samples
2.3.4 Standard microplastics spiking and extraction
2.3.5 Extraction rates of standard microplastics
2.3.6 Detection rates of small standard microplastics
2.4 Results and discussion
2.4.1 Detectability of standard microplastics
2.4.2 Extraction rates of standard microplastics
2.4.3 Detection rates of small standard microplastics
2.5 Conclusions and perspectives on the recovery rate study
3 Assessment of the distribution of microplastics in river sediments at several spatial scales
3.1 Study n°1 : Exploration of microplastic contamination at the scale of a river (Loire Sentinelle project)
3.1.1 Introduction and context of study n°1
3.1.2 Article n°1: First assessment of microplastic pressure in the entire Loire River, France. Focus on plastics natures, concentrations and exploration of influence factors of this contamination
3.1.3 Conclusion of study n°1
3.2 Study n°2 : Fine spatial scale study of microplastics in sediments of a river segment
3.2.1 Introduction and context of study n°2
3.2.2 Article n°2: Exploring possible controlling factors of spatial distribution of microplastics in sediments of a river segment (Loire River, France)
3.2.3 Conclusion of study n°2
4 Evaluation of temporal recordings of microplastics in river sediments
4.1 Study n°3: Microplastic records since the 1950s and 2000s in sediments of the Loire River (France)
4.1.1 Introduction and context of study n°3
4.1.2 Article n°3 : Main drivers for microplastic records in river sediments since the 1950s: case study of the Loire river (France)
4.1.3 Conclusion of study n°3
5 General Discussion and Perspectives
5.1 Introduction
5.1.1 Objectives of this general discussion
5.1.2 Samples considered
5.2 Microplastic contamination detected in the Loire river
5.2.1 Concentrations of microplastics
5.2.2 Characteristics of microplastics
5.3 Influence of emission sources on microplastic contamination
5.4 Influence of sediment composition on microplastic archiving
5.4.1 Influence of fine-grained sediment
5.4.2 Influence of organic carbon
5.4.3 Specific sediment composition for microplastic archiving
5.5 Spatial distribution conditioned by depositional environments
5.5.1 Distribution in sediment depositional environments
5.5.2 Influence of depositional environments sediment composition on microplastics archiving
5.5.3 Hydro-sedimentology explaining variability in depositional environments
5.6 Conclusions
5.7 Perspectives
5.7.1 Analytical questions
5.7.2 Depositional environments
5.7.3 Microplastics archiving processes
General Conclusion