Toxicity of polystyrene microplastics in freshwater algae Scenedesmus obliquus: Effects of particle size and surface charge

Microplastics (MPs) are perpetual contaminants that are mostly generated by human activity and are deposited in aquatic ecosystem. MPs may react differently in aquatic organisms depending on their size, surface charge, and concentration. The current investigation examined the interactions of polystyrene (PS) microplastics (of varied charges and sizes) with Scenedesmus obliquus, a unicellular phytoplankton. It is observed that 1 µm PS-MPs produced increased oxidative stress than 12 µm PS-MPs as indicated by total reactive oxygen species (ROS), superoxide and hydroxyl radical generation, and lipid peroxidation results. Additionally, decreased photosynthetic effectiveness, membrane integrity and esterase activity were also observed for the lower sized MPs. Antioxidant enzyme activities like superoxide dismutase (SOD) activity and catalase (CAT) activity correlated well with the oxidative stress generation in the cells. The effects by both the sizes of MPs were dose dependent in nature. Given the importance of a rapidly developing scientific literature on the effects of MPs in freshwater organisms, understanding the dynamics of interactions with lower-level organisms becomes very relevant.