ABSTRACT: The widespread use of potassium peroxymonosulfate (PMS) in aquaculture raises concerns about its ecological risks. This study evaluated acute toxicity of PMS to Chlorella pyrenoidosa over 24-96 h to establish a 96 h EC₅₀. Chronic exposure groups (0, 1.70, 3.40, 8.49 mg/L, corresponding to 0, 0.1, 0.2, and 0.5 of the EC₅₀) were cultured for 12 days. Cell growth, oxidative stress, ultrastructure, chlorophyll fluorescence, and transcriptomic genes were measured on days 0, 3, 6, 9, and 12. PMS decomposition products were monitored and correlated with physiological and Biochemical responses. PMS rapid decomposition increased breakdown products, inhibiting algal growth during days 0-3 and causing surface wrinkling, plasmolysis, chloroplast damage, and thylakoid disarray. Oxidative stress rose and growth_x001E_related genes were down_x001E_regulated. After day 6, with the cessation of PMS decomposition and the subsequent reduction in its byproducts, growth recovered, cellular structures were restored, oxidative stress decreased, and ribosome‑related genes were up_x001E_regulated. These findings contribute to the assessment of the potential risks of PMS to C.pyrenoidosa and provide new insights for the application of PMS in aquaculture practices.
