Effect of co-exposure of multi-wall carbon nanotubes and cadmium on microalga Dunaliella salina

Great efforts have been made so far to evaluate the influence of nanomaterials (NMs) on aquatic organisms, however, co-exposure of NMs and other pollutants on microalgae has remained largely unstudied. In this regard, the present study first investigated the biological responses of Dunaliella salina to different concentrations of multi-wall carbon nanotubes (MWNTs) and cadmium, separately. Furthermore, the influence of Gum Arabic (GA)-modified MWNTs was also explored on the microalgae. Following this, D. salina was co-exposed to low concentrations (5 mg L−1) of uncoated and GA-coated MWNTs with 300 µM Cd to evaluate the effects and underlying mechanism of MWNTs on metal toxicity. Results showed a growth inhibition in culture media containing uncoated MWNTs. The observed toxicity disappears when MWNTs coated with GA. The toxicity of uncoated MWNTs to D. salina can be ascribed to higher algal cells-nanoparticles (NPs) hetero-aggregation, higher lipid peroxidation, and lower content of the non-enzymatic antioxidants. In addition, shading effect was one of the main reasons for the rise in the chlorophyll content of microalgae exposed to uncoated MWNTs. It was found that both uncoated MWNTs and Cd2+ could inhibit growth of D. salina. However, the introduction of GA-coated MWNTs mitigated the adverse effects of Cd on microalgae, as indicated by algal growth, lipid peroxidation, and non-enzymatic antioxidant component. Adsorption of Cd on GA-coated MWNTs was responsible to attenuate the cadmium toxicity by adding MWNTs. Altogether, these findings bring out the possibility of GA reducing the toxicity of MWNTs and cadmium, making it an ideal capping agent.