The prevalence of microplastics in marine environments is recognized for its ecotoxicological risks as vectors for hydrophobic organic contaminants (HOCs). This study explored the role of microalgae as vectors in the transfer of Phenanthrene (Phe) from contaminated microplastics to marine filter feeders. Employing a spatial exposure system, the sorption of Phe onto polyethylene (PE) particles, its desorption mediated by microalgae into microalgal suspensions, and subsequent accumulation in the tissues of filter feeders were investigated. In the spatial exposure system for clams, after 28 days of exposure, Phe concentrations in clams' tissues were 67.71 ng/g and 84.21 ng/g for the medium with and without microalgae, respectively
however, no statistically significant difference was observed between them (p >
0.05). In the spatial exposure system for mussels, the highest Phe concentrations in mussels' tissues were 277.71 ± 25.98 μg/g in the digestive glands after 3 days of exposure and 185.32 ± 35.76 μg/g in the mantle after 6 days of exposure, both in the Tetraselmis helgolandica suspension. Significant differences were observed between the control group and the T. helgolandica suspension group from 3 to 10 days of exposure (p <
0.05). Although microalgae were confirmed to enhance the desorption of Phe from PE particles, their role in significantly increasing the bioaccumulation of Phe in filter feeders was less than anticipated, showing no significant long-term differences between experimental groups with and without microalgae. The potential biodegradation of Phe by marine organisms was also observed, which may have contributed to the overall transfer and bioaccumulation processes, introducing an additional layer of complexity to the interpretation of the results. These findings suggest that microalgae can act as intermediate carriers facilitating the transfer of Phe, albeit with the impact of various influencing factors not aligning with initial hypotheses. The study highlights the need for further investigation into how different microalgal species and environmental conditions affect the fate of HOCs absorbed by microplastics, contributing to an enriched understanding of microplastic impacts in marine ecosystems. This establishes that microalgae mediate the transfer of Phe from microplastics into benthic filter feeders, affirming their role as significant vectors in contaminant dynamics.