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Size-Dependent Effects of Polystyrene Nanoplastics on Freshwater Microalgae After Long-Term Exposure
Summary
Researchers exposed a common freshwater algae species to polystyrene nanoplastics of three different sizes over an extended period. They found that the smallest particles caused the most damage to algae cells, while the largest particles had relatively mild effects, revealing a clear size-dependent toxicity pattern. The study suggests that the tiniest nanoplastic particles in freshwater environments may pose the greatest risk to the base of aquatic food webs.
Nanoplastics (NPs), an emerging pollutant distributed in different sizes in the aquatic environment, adversely affect aquatic ecosystems. However, knowledge of the effects of NPs of various sizes on phytoplankton, especially freshwater microalgae, is still limited. In this study, we explore the effects of three polystyrene NPs (PS-NPs) with different particle sizes (20, 50, and 80 nm) on the chronic toxicity of a widely distributed freshwater microalga, Chlorella pyrenoidosa. The results showed that PS-NPs-20, PS-NPs-50, and PS-NPs-80 promoted the growth of C. pyrenoidosa at the early stage of exposure, with the highest promotion rates of 46.1%, 56%, and 86.2%, respectively. PS-NPs-20 and PS-NPs-50 inhibited the photosynthesis and growth of C. pyrenoidosa during the mid- and late-exposure periods and also induced an increase in the secretion of reactive oxygen species and extracellular polymers. The highest inhibition rates were 33.2% and 13.6%, respectively. By contrast, the growth-promoting effect of PS-NPs-80 continued until the middle stage, and it was only at the late stage of exposure that some growth-inhibitory effects occurred, with the highest inhibition rate of only 7.8%. The results of transmission electron microscopy showed that PS-NPs-20 damaged algal cells more severely than PS-NPs-50 and PS-NPs-80 on day 21. Notably, a size-dependent effect of PS-NPs was observed on the toxicity of C. pyrenoidosa, but no dose-dependent effect was found. These results will improve our understanding of the toxicity of PS-NPs to microalgae and may provide a basis for evaluating the ecological risk of PS-NPs in freshwater environments.