Cytotoxic effects of molybdenum oxide nanoparticles and {Mo36} polyoxomolybdate nanoclusters to the green microalga Chlorella vulgaris

Abstract In recent years, molybdenum-based nanomaterials have been widely used in different industrial sectors because of their multifunctional properties. Despite their extensive industrialization, there is a lack of needed information concerning their adverse influences on ecosystems and living organisms. In this study, molybdenum oxide nanoparticles (MoO3 NPs) and {Mo36} polyoxomolybdate nanoclusters ({Mo36} NCs) were synthesized using hydrothermal methods and characterized using FT-IR, XRD, and SEM techniques. Subsequently, their toxic effects on the green microalgae Chlorella vulgaris were measured. Both nanomaterials (NMs) induced cytotoxicity by reducing the cell number and biomass of algae in a dose- and time-dependent manner. Scanning electron microscopy revealed shape modification and plasmolysis of the microalgal cells after exposure to nanomaterials. Flow cytometric analyses confirmed the reduction in cell viability in the samples exposed to 100 mg L− 1 of MoO3 NPs and {Mo36} NCs for 4 days. According to the results, MoO3 NPs had more drastic effects on the viability of C. vulgaris cells compared to {Mo36} NCs. In addition, after exposure of algal cells to the high concentrations of nanomaterials, the content of photosynthetic pigments has decreased. Enhanced activities of antioxidative enzymes including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) concurrent with alteration of phenol and flavonoid contents as non-enzymatic antioxidants indicated the activation of cell defense systems in response to the oxidative stress induced by nanomaterials. Our findings conclusively established that MoO3 NPs and {Mo36} NCs cause life-threatening cytotoxicity in algal cells and induce oxidative stress.