Species-specific deformation of microalgae in the presence of microplastics

Ocean pollution by microplastics represents a threat to phytoplankton health, yet there is few knowledge on physical interactions between microplastics and microalgal cell surfaces. We studied the contact between environmentally aged microplastics and four microalgal species by atomic force microscopy. After seven days, microalgae showed malformations at specific sites, and these malformations varied with species. Depending on whether the cell had a porous or a smooth surface, microplastics adsorbed to the cell surface via embedding or denting, leading to minor defects or noticeable wrinkles in cell walls. Results also showed that microplastics penetrate into microalgae. Such cellular engulfment of microplastics was less present in typical diatoms because diatoms bear a porous frustule capable of trapping tiny particles. Moreover, we observed a novel type of deformation, bowl-shaped depressions, only in non-porous microalgae. The geometric features of malformations are correlated with the shape and size of microplastics. Our findings reveal for the first time the species-specific deformation in microalgae due to microplastic exposure.