Toxic effects of nanomaterial-adsorbed cadmium on Daphnia magna

Chemical immobilization technologies involving the use of chemical absorbents such as nanomaterials have been recommended for the remediation of Cd-contaminated water and soil. The impact of nanomaterials or nanomaterials coexisting with other contaminants on aquatic organisms has been reported, but information on the toxic effects of nanomaterial-adsorbed cadmium (Nano-Cd) on aquatic organisms is lacking. This study aimed to investigate the acute and sub-acute toxicity of Nano-Cd on Daphnia magna by using a method developed based on the standard Organisation for Economic Co-operation and Development (OECD) 202 guidelines. The toxicity of cadmium chloride (Cd²⁺), nano-manganese dioxide-cadmium (nMnO₂-Cd), 20nm nano-hydroxyapatite-cadmium (nHAP₂₀-Cd), and 40nm nano-hydroxyapatite-cadmium (nHAP₄₀-Cd) to D. magna was in the following order: Cd²⁺> nMnO₂-Cd > nHAP₂₀-Cd > nHAP₄₀-Cd. Further, nMnO₂-Cd, nHAP₂₀-Cd, and nHAP₄₀-Cd showed acute toxicity to D. magna of level II grade according to the Commission of the European Communities and OECD standards. Exposure to low and medium, but not high, Nano-Cd concentrations increased the activities of peroxidase, superoxide dismutase, catalase, and anti-superoxide anion. Thus, Nano-Cd, particularly at high concentrations, could exert oxidative damage in D. magna. An increase in Cd²⁺ and Nano-Cd concentrations gradually increased the malondialdehyde content, indicating cell membrane damage caused by the production of excessive O₂^-. Thus, the use of nanomaterials after adsorption of Cd is associated with a potential risk to aquatic organisms.