The Presence of Selenium Nanoparticles May Enhance the Toxicity of Cadmium to Chlamydomonas reinhardtii – Evidence from Wild-Type and Cell-Deficient Chlamydomonas reinhardtii Cells

Selenium nanoparticles (SeNPs) can mitigate cadmium (Cd2+) toxicity in crop cultivation and aquaculture. This study investigates the impact of SeNPs on Cd-induced toxicity in Chlamydomonas reinhardtii, a model organism, aiming to mitigate Cd damage in crops. SeNPs were synthesized using sodium carboxymethyl cellulose (CMC) as a dispersant and vitamin C to reduce H2SeO3. Characterization by transmission electron microscopy (TEM) and nanoparticle granulator revealed uniform, stable spherical SeNPs. Cd2+ and SeNPs of varying concentrations were introduced into culture media of wild type (CC125mt+) and cell wall defect type (CC400mt+) Chlamydomonas reinhardtii. Growth curves, photosynthetic pigment content, enzyme activities (T-SOD and CAT), MDA content, and ROS levels were assessed. Fluorescence induction kinetics, QA oxidation kinetics, and Cd2+ content in cells were measured to evaluate SeNPs' effect on Cd toxicity. Results showed SeNPs exacerbated Cd2+ toxicity in CC125mt+ by inhibiting growth and increasing catalase activity, indicating enhanced oxidative damage. SeNPs intensified PSII damage by Cd2+ and increased intracellular Cd2+ content, possibly exacerbating toxicity. SeNPs had no effect on Cd2+ toxicity in CC400mt+. Overall, SeNPs exacerbated Cd2+ toxicity in wild type CC125mt+ but not in cell wall defective CC400mt+. These findings caution against indiscriminate use of nano-selenium to mitigate Cd damage, stressing the importance of careful target selection, dosage, and range considerations.