Realistic Environmental Exposure of Microplastics in European Flat Oyster, Ostrea edulis: Evaluation of Accumulation and Depuration Under Controlled Conditions and Molecular Assessment of a Set of Reference Genes

Marine plastic waste represents, in recent decades, a major threat to the environment, as plastics degrade into microplastics (MPs) that a wide range of organisms ingest. Filter-feeding taxa, including bivalves, serve as indicators of environmental contamination due to their ingestion of MPs. This study investigated (a) the bioaccumulation and depuration capacities of Ostrea edulis exposed to MPs and (b) the identification of reference genes for assessing stress responses in bivalves under MP exposure. The experimental protocol comprised a 28-day exposure to MPs followed by a 7-day depuration period. The mean concentration of accumulated MPs was 5.31 ± 0.86 particles/g, comprising filaments (79%), beads (19%), and fragments (2%). Depuration reduced MP concentrations by 69% after 24 h and by an additional 23% after 120 h. In conclusion, a two-day depuration period significantly reduced MPs in oysters intended for human consumption. Additionally, the molecular analysis identified EF-1α, GAPDH, and L5 as stable reference markers for MPs exposure experiments, supporting the development of a monitoring toolkit for MPs in marine environments.