Microplastic toxicity in marine microalgae: an ecotoxicological synthesis of experimental biological responses

As a pervasive form of marine pollution, microplastics (MPs) are widely distributed across coastal and oceanic systems, raising concerns about their ecological impacts. This review provides an evidence-based synthesis of microplastic-microalgae interactions, integrating physiological responses and associated toxicity pathways. Marine microalgae are particularly relevant in this context because they constitute the foundation of marine food webs and play a central role in primary productivity and global biogeochemical cycling. This study synthesizes experimental ecotoxicological evidence on the effects of microplastics on marine microalgae, with the aim of identifying dominant toxicity endpoints and key knowledge gaps relevant to ecotoxicological evaluation. Publications indexed in Web of Science and Scopus from 1970 to August 2025 were systematically screened, resulting in 59 selected publications, of which 43 experimental studies met the criteria for the comparative ecotoxicological synthesis. The analysis revealed a rapid expansion of research on microplastic-microalgae interactions, with experimental studies predominantly investigating polystyrene and polyethylene, across a broad range of particle sizes. The most frequently investigated biological responses included growth/population parameters, cellular stress and damage indicators, and photosynthetic responses. Despite this progress, several ecologically relevant endpoints and processes remain insufficiently investigated, including aggregate formation, particle sinking dynamics, DNA damage, and long-term exposure under environmentally realistic conditions. Furthermore, most experimental studies rely on short-term laboratory assays using simplified exposure scenarios, which may limit the ecological relevance of current knowledge. Taken together, the available evidence highlights key research priorities and outlines directions for improving experimental ecotoxicological studies.