Comparative impacts of fragmented versus spherical microplastics on the marine rotifer Brachionus koreanus:...

This study investigated the toxic effects of microplastics (MPs) of different sizes and shapes on the marine rotifer, Brachionus koreanus, at both the individual and molecular levels. A multigenerational chronic toxicity test showed that only small fragmented MPs (fragment-S) significantly reduced the fecundity and lifespan of rotifers, which was enhanced in subsequent generations. Transcriptomic modulation of rotifers was most significant in the group exposed to fragment-S, followed by those exposed to large fragments (fragment-L), small beads (bead-S), and large beads (bead-L). However, significant metabolomic perturbation was detected only in the group exposed to fragmented MPs (fragment-S > fragment-L), suggesting that shape is a more critical factor than size in determining the toxicity of MPs. Pathways related to energy metabolism were commonly affected by MP exposure, whereas different genes related to transcription, the nervous system, and translation were primarily affected by specific MP types, indicating size- and shape-dependent toxic mechanisms of MPs. Overall, our findings suggest that the molecular toxicity mechanisms of MPs depend on their size and shape, highlighting that physical properties are a major factor in determining the toxicity of MPs.