Mucus Production as a Strategy of Oysters Against Synthetic Textile Microfibers

Synthetic textile fibers are a key source of microplastics in marine environments, mainly released during clothing use and laundry. These contaminants can be taken up by filter-feeding bivalves like oysters, which hold significant ecological and economic importance. Once ingested, microfibers can accumulate in different organs, including the mantle—an essential tissue for protection and shell formation, and can therefore compromise the health of the oysters, with potential environmental, economic, and human health consequences. Polyester fibers were sourced from machine-washed fabrics and characterized using FTIR. Oysters (Crassostrea brasiliana) were purchased from producers in the Mandira extractive reserve near Cananéia, São Paulo, and acclimated for 11 days. The study lasted 28 days, with two groups: Control (filtered seawater) and Polyester (filtered seawater + 531 mf/L). The oyster mantle was fixed in 10% formalin, preserved in 70% alcohol, and processed for histology. Semi-serial 5-μm sections were prepared, stained with Alcian Blue, and analyzed using three photomicrographs under a 400X light microscope. Mucus cells were quantified by area (mm²) using Image Pro-Plus 3.0.1 software. Microfibers averaged 905 μm in length and 23 μm in diameter, confirmed by their characteristic polyester spectrum. Exposure to polyester fibers significantly increased mucus-secreting cells in the mantle (P=0.047), indicating a defensive response against microfibers and a potential inflammation-related pathology. Textile microfiber exposure led to a marked rise in mucus cells within the oyster's mantle, suggesting a defense mechanism where mucus acts as a barrier to foreign particles, pathogens, and pollutants. Increased mucus production may thus be a strategy to mitigate the toxic effects and prevent microfibers from penetrating deeper tissues.