Bioaccumulation and depuration dynamics of polyester microfibres in Mytilus galloprovincialis

The aim of this study was to assess the bioaccumulation and depuration dynamics of Mytilus galloprovincialis following exposure to varying concentrations of polyester microfibers in a controlled laboratory setting. Specimens sourced from a depuration center in Messina, Italy, were acclimatized for seven days in filtered seawater at a temperature of 15°C. The mussels were then exposed to polyester microfibers (≤200 µm in length and 18 µm in diameter) at concentrations of 100, 10, 1 and 0.1 microfibers per milliliter for 24 hours. Three replicate tanks were prepared for each concentration, each containing ten mussels, totaling thirty individuals per concentration. Controls were included to monitor potential environmental contamination. Following exposure, the mussels were transferred to depuration tanks containing filtered, oxygenated seawater. Microfibers egested in feces and pseudofeces were collected at 24 and 48 hours, filtered onto 0.45 µm cellulose membranes, and counted using stereomicroscopy. After 48 hours, the mussels underwent alkaline digestion with 10% potassium hydroxide to quantify the retained microfibers. The results revealed no significant correlation between the concentration of exposure and the number of microfibers egested or retained. These findings suggest that the bioaccumulation and depuration of microfibers in M. galloprovincialis are influenced by factors other than concentration alone, such as particle size, morphology, and spatial configuration. Using environmentally relevant microfibers at ecologically plausible concentrations rather than virgin plastic fragments at unrealistic doses offers a more accurate representation of microplastic bioaccumulation and depuration mechanisms in mussels. Finally, background microplastics were also detected in control samples. This is significant as it indicates pre-existing contamination of the organisms and further highlights the pervasive presence of microplastics in the environment, as well as the potential for human exposure through the food chain.