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Toxicity of microwave-synthesized silver-reduced graphene oxide nanocomposites to the microalga Chlorella vulgaris: Comparison with the hydrothermal method synthesized counterparts

Abstract The increased applications of nanomaterials in industry and biomedicine have resulted in a rising concern about their possible toxic impacts on living organisms. It has been claimed that the phytosynthesized nanomaterials have lower toxicity in comparison to their chemically synthesized counterparts. Therefore, it is important to evaluate their toxic effects on the environment. In the present study, we investigated the toxic effects of microwave-synthesized silver-reduced graphene oxide nanocomposites (MS-Ag-rGO) on Chlorella vulgaris. Algal cells were treated by 1, 2, 4 and 6 mg L−1 MS-Ag-rGO for 24 h. The obtained data with three replicates were examined using analysis of variance. Analysis of different growth parameters revealed that MS-Ag-rGO possessed significant dose-dependent toxic effect on C. vulgaris. Scanning electron microscope and fluorescence microscope images of the treated cells established morphological shrinkages and alteration in position of nucleoli. Moreover, reduction in the phenol and flavonoid contents, enhancement of H2O2 content, changes in the antioxidant enzymes activity and decreases in the growth parameters as well as photosynthetic pigments quantities confirmed the toxicity of MS-Ag-rGO to the C. vulgaris cells. Our findings revealed that MS-Ag-rGO possessed higher toxicity on C. vulgaris than Ag-rGO synthesized by hydrothermal technique.