Toxic effect and the mechanisms of colored microplastics containing inorganic pigments on Microcystis aeruginosa

Toxicity of colorless microplastics (MPs) to microalgae has been extensively investigated, but largely not the colored MPs which commonly contain inorganic metal pigments compared to the colorless MPs. Therefore, this study compared the toxicity of the red polyethylene (PE) MPs (containing CdSSe pigments) with the colorless PE MPs towards Microcystis aeruginosa (M. aeruginosa). Red MPs with a particle size of ∼181 μm and pigment mass fraction of 40 % at a dose of 75 mg/L inhibited cell growth by 53.0 % after 8 days, whereas colorless MPs only caused a 23.0 % reduction in cell growth (p < 0.05). Significant inhibition of photosynthesis and activation of the antioxidant stress response was observed as M. aeruginosa exposed to red MPs. These physiological differences were accompanied by visible morphological alterations, including reduced cell size and surface wrinkling. Furthermore, untargeted metabolomics analysis indicates that red MPs disrupted purine metabolism, amino acid metabolism, and phospholipid metabolism, compared with both the control group and colorless MPs. Mechanistically, the release of cadmium ions (Cd²⁺) from the red MPs due to photochemical reactions should be the primary driver to increase toxicity, compared to the colorless MPs. The results improved an understanding of the photochemical behavior of pigments and the potential toxicity risks posed by colored MPs in aquatic environments.