Effects of polystyrene microplastics on growth, physiological traits of Microcystis aeruginosa and microcystin production and release.

With the increasing pollution from microplastics (MPs) in freshwater ecosystems, the effects of MPs on microalgae warrant further investigation. In our research, we examined how polystyrene microplastics (PS-MPs) with various particle sizes and concentrations affect the growth and physiology of Microcystis aeruginosa at different initial algal densities. The results showed that PS-MPs inhibited M. aeruginosa growth at low initial algal densities, with the highest inhibition rate (62.59%) observed at 0.1 μm, 1 mg/L PS-MPs. Effects on photosynthesis were correlated with changes in initial algal density, and PS-MPs caused notable disturbances to the antioxidant defense system of M. aeruginosa. Compared to medium-sized PS-MPs (1 μm), PS-MPs with smaller (0.1 μm) or larger particle sizes (5 μm) caused greater growth inhibition and more pronounced changes in photosynthesis and oxidative damage. At low initial algal densities, PS-MPs addition led to a substantial rise in the intracellular levels of microcystin-LR (MC-LR), with a 150% increase over the control at 0.1 μm, 1 mg/L PS-MPs. However, at high initial algal densities, apoptosis rates rose, leading to greater MC-LR release. This research offers a foundation for assessing the impact of PS-MPs on algal growth, as well as the production and release of MC-LR, contributing to the evaluation of MPs' risks to aquatic ecosystems.