Effects of micro-sized polyethylene spheres on the marine microalga Dunaliella salina: Focusing on the algal cell to plastic particle size ratio.

There is increasing concern about how microplastics (MPs) are impacting marine ecosystems. In particular, studies on how MPs impact microalgae are required because of the abundance of MPs and importance of green microalgae as primary producers. This study investigated how MPs that are larger (200 μm) than algal cells impact them, using the marine microalga Dunaliella salina as the test species. The microalga was exposed to polyethylene MPs for 6 days. Of interest, the growth and photosynthetic activity of D. salina was enhanced with exposure to MPs, while cell morphology (size and granularity) was not impacted. This phenomenon might be explained by trace concentrations of additive chemicals (endocrine disruptors, phthalates, stabilizers) that possibly leached from MPs promoting the growth and photosynthetic activity of D. salina. We also confirmed that MP size contributes towards determining how plastics affect microalgae. Specifically, as MP size shrinks compared to algal cell size, MPs have increasingly adverse effects. MPs of very small size (like nanoplastics) induce particularly adverse effects on algae. Further studies are required to establish the relationship between algal cell size and MP size.