Different effecting mechanisms of two sized polystyrene microplastics on microalgal oxidative stress and photosynthetic responses

Abstract

Increasing marine microplastics (MPs) pollution potentially threatens the stability of phytoplankton community structures in marine environments. MPs toxicities to microalgae are largely determined by particle size, while the size-dependent mechanisms are still not fully understood. In this study, two sizes (0.1µm and 1µm) of polystyrene (PS) MPs were used as experimental targets to systemically compare their different effecting mechanisms on the marine model diatom Thalassiosira pseudonana with respect to oxidative stress and photosynthesis. The results indicated the toxicity of 1µm sized MPs was higher than 0.1µm sized MPs regarding to population growth. In condition of similar microalgal population inhibition rates, we found more enhanced cellular oxidative stress and cell death happened in the 1µm MPs treatments, which could be linked to higher zeta potential of 1µm MPs and more severe cell surface damage; microalgal surface light shading and cellular pigments decline were more obvious in the 0.1µm MPs treatment, which could be linked to high aggregation abilities of 0.1µm MPs. Gene expressions supported the morphological and physiological findings on the transcriptional level. Environmental related MPs concentrations (5μgL-1) also aroused gene expression changes of T. pseudonana while more changing genes were found under 0.1µm MPs than 1µm MPs. These results provide novel insights into the size-dependent mechanisms of MPs toxicity on marine microalgae, as well as their potential influence on the marine environment.