Abstract
Microplastic (MP) pollution poses a significant threat to marine ecosystems, with filter-feeding bivalves like Mytilus edulis being particularly vulnerable due to their feeding strategy. This study investigated the bioaccumulation dynamics of polystyrene microplastics (PS-MPs) and their impact on the immune response at a transcriptomic level in M. edulis under controlled estuarine conditions. Mussels were exposed to 100 µg/L PS-MPs (1-5 µm) for 21 days, followed by a 7-day depuration period. Results showed significant bioaccumulation of PS-MPs primarily in the gills and digestive gland, with limited depuration observed within the study timeframe. Transcriptomic analysis of gill tissue revealed 874 differentially expressed genes (DEGs) in MP-exposed mussels, with prominent upregulation of genes associated with immune processes (e.g., Toll-like receptors, C-type lectins, lysozyme), oxidative stress response (e.g., glutathione S-transferases, superoxide dismutase), and inflammation. Conversely, genes related to metabolism and energy production were downregulated. These findings indicate that PS-MP exposure triggers a robust, albeit potentially costly, immune and stress response in M. edulis, suggesting a compromised physiological state. This transcriptomic profiling, coupled with bioaccumulation data, provides critical insights into the sublethal effects of microplastic pollution on sentinel species in estuarine environments, highlighting the need for further research into long-term impacts and ecological consequences.
