Effects of potassium ethyl xanthate on Chlorella pyrenoidosa: Physiological, ultrastructural, and transcriptomic insights

Organic xanthate collectors are widely used globally and frequently discharged into tailings ponds. These ecological risks have overlooked, making it a primary focus in international mining pollution research. This study employed Chlorella pyrenoidosa as a model organism to determine the effects of potassium ethyl xanthate (PEX, a representative organic xanthate collector). The toxicity of PEX to algae was evaluated using physiological parameters (i.e., growth, cellular morphology, and antioxidant capacity) and transcriptome analysis. The effects of algae/light on biotic and abiotic PEX degradation were also assessed. Exposure to 30 mg/L PEX significantly reduced the chlorophyll a (35.16 %), chlorophyll b (21.03 %), and carotenoid (43.00 %) contents and inhibited algal growth by 44.19 %. PEX induced oxidative stress, as indicated by the increase in the superoxide dismutase and catalase activities. Ultrastructural changes, such as plasma membrane detachment and cell wall rupture, were also observed. At the molecular level, PEX significantly altered the expression of photosynthesis-related genes. Lower PEX concentrations induced upregulation, whereas higher concentrations caused downregulation of psbB and psbC. Additionally, high PEX exposure suppressed ATP synthase genes (atpA, atpD). PEX degradation was influenced by both the algal inoculation density and light intensity. This study confirms that PEX has significant toxic effects on Chlorella pyrenoidosa and clarifies the regulatory role of algae and light in PEX degradation, providing targeted data support for the ecological risk assessment and pollution control of xanthate reagents in tailings ponds.