The impact of nTiO2 and GO (graphene oxide), and their combinations, on freshwater Chlorella sp.: a comparative study in lake water and BG-11 media†

Abstract

Titanium dioxide nanoparticles (nTiO₂) and graphene oxide (GO) are extensively used nanomaterials in various products and applications. Freshwater ecosystems are a crucial sink for these pollutants, posing severe threats to aquatic organisms. Although multiple studies have investigated the pristine toxicity of nTiO₂ and GO in freshwater organisms, the combined toxicity of these materials remains unexplored. Interaction media is a crucial factor in evaluating toxicity nanomaterial toxicity towards algae. In this study, we have investigated the comparative effect of sterilized and filtered freshwater and BG-11 medium on the pristine and combined toxicity of nTiO₂ and GO on freshwater algae Chlorella sp. Results indicated that the combination of nTiO₂ and GO showed more toxicity when compared to their respective pristine forms. This could be due to the additive effect exhibited by nTiO₂ and GO on Chlorella sp. The enhanced growth inhibition for the combined toxicity was in the order of 1 mg L⁻¹ nTiO₂ + 1 mg L⁻¹ GO > 1 mg L⁻¹ nTiO₂ + 0.1 mg L⁻¹ GO > 0.1 mg L⁻¹ nTiO₂ + 1 mg L⁻¹ GO > 0.1 mg L⁻¹ nTiO₂ + 0.1 mg L⁻¹ GO. All test groups that interacted in BG-11 media exhibited less toxicity when compared to corresponding groups in the lake water medium. This could be attributed to the cushioning effect of BG-11 medium, providing supplementary nutrition to the algal cells. This signifies that the environmentally relevant conditions could be more detrimental than the laboratory conditions. This study elucidates valuable insights into the potential detrimental effects associated with the combination of nTiO₂ and GO on freshwater algae. Furthermore, we have evaluated the growth inhibition, oxidative stress, and photosynthetic activity of Chlorella sp. in both environmentally relevant interaction medium and well-defined culture medium.