Biological response of marine microalga Chlorella sorokiniana to single and combined treatments of multi-walled carbon nanotubes and Fe2O3 nanoparticles

Nanoparticles (NPs) are extensively employed due to their distinctive physical attributes and are subsequently released into the natural ecosystems. In scenarios where two distinct NP types coexist within the same environment, the characteristics of one may be affected by the other. This research has investigated the toxicity profiles of individual multi-walled carbon nanotubes (MWCNTs) (5, 10, 20 mg L^-1) and binary mixtures of MWCNTs and α-Fe₂O₃ NPs (50, 100, 200 mg L^-1) on microalga Chlorella sorokiniana, indicating a growth inhibition in cultures treated with 20 mg L^-1 MWCNTs. MWCNT toxicity toward C. sorokiniana can be ascribed to NP homo-aggregation and the shading effect, as validated by an increase in photosynthetic pigments of algal cells. Besides, binary mixtures of NPs imposed greater stress on algal cells, as evidenced by a reduction in microalga growth. The direct interaction between the algal cells and NPs induced a shading effect along with morphological alterations, which were confirmed through scanning electron microscopy analysis. In the case of binary nanoparticle mixtures, the biochemical compounds increased significantly. Oxidative stress was among the key contributors to the toxicity of NPs toward C. sorokiniana, as confirmed by increased lipid peroxidation levels, especially in binary mixtures. Antioxidant defensive mechanism, including enzymatic and non-enzymatic, were considerably activated to deal with oxidative stress. Overall, MWCNTs and α-Fe₂O₃ NPs exhibited mutual interactions that compounded their individual effects, leading to more intricate toxicological impacts on aquatic organisms.