Keywords: 
• carboxylated multi-walled carbon nanotubes /
• Chlorella pyrenoidosa /
• cytotoxicity /
• ecological risk

Abstract: Due to the excellent performance of carbon nanomaterials, they are widely produced and applied in many fields. Thus, they will inevitably enter into water environment and cause potential impact on the aquatic ecosystems. As one of functionalized multi-walled carbon nanotubes, carboxylated multi-walled carbon nanotubes (MCNTs-COOH) are also widely applied, and their potential environmental effects attracted more and more attention. In the present study, the biological effects of MWCNTs-COOH on Chlorella pyrenoidosa were investigated by the means of exposure experiment. The results showed that MWCNTs-COOH had weak influence on the growth of Chlorella pyrenoidosa when MWCNTs-COOH concentration was 20 mg·L^-1 or less. Secondly, after 96 h exposure, the produce of soluble protein was promoted by medium and high concentrations (10, 20 mg·L^-1) of MWCNTs-COOH and high concentrations (≥40 mg·L^-1) of MWCNTs-COOH exhibited significant toxic effects on Chlorella pyrenoidosa. Thirdly, with the increasing concentration of MWCNTs-COOH, the total antioxidant capacity (T-AOC) values of Chlorella pyrenoidosa cells decreased, while MDA content in Chlorella pyrenoidosa increased notably and the health state of cells was gradually deteriorated, which indicated that the cells structure was destroyed severely.