ALGAL RESPONSES TO MICRO- AND NANOPLASTICS EXPOSURE: UNDERSTANDING THE ROLE OF EXTRACELLULAR POLYMERIC SUBSTANCES
While the potential threat of micro- and nanoplastics (MNPs) to marine ecosystems is gain- ing attention, research often utilizes unrealistically high exposure levels. This study bridges that gap by investigating the effects of environmentally relevant MNP concentrations on the saltwater microalgae Rhodomonas salina. It further explores the role of Extracellular Poly- meric Substances (EPS) in mitigating these effects. Microalgae were exposed to a range of PET and aged-PET concentrations (10, 100, 1000, and 10000 particles/mL) to account for potential changes in polymer properties and additive release due to aging. Kaolin served as a control for non-plastic particle effects. Although the study’s findings on algal growth didn’t show a clear trend, they did reveal some intriguing patterns in EPS quantity and com- position. Notably, at the low MNP concentrations used, there were no significant changes in total EPS amount. However, the Protein-to-Carbohydrate (P/C) ratio within the EPS dis- played distinct responses depending on the exposure type. While the P/C-ratio remained stable for PET exposures, it significantly increased for aged-PET and kaolin at higher con- centrations. Interestingly, kaolin exposure resulted in more and larger aggregates, whereas higher concentrations of PET and aged-PET led to fewer and smaller ones. Furthermore, at the highest exposure (10000 particles/mL), all treatments displayed a shift in aggregate composition, with a higher proportion of algal cells relative to EPS. These findings signifi- cantly improve risk assessment of MNPs under current marine pollution conditions. They also highlight the critical role of algal EPS in the aggregation of both microalgae and MNPs, ultimately influencing their environmental fate.
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