Assessment of Oxidative Responses in Halophilic Green Microalga Dunaliella salina Exposed to Functionalized Carbon Nanotubes: Effects of Functional Group and Particle Type

The large-scale production and extensive utilization of carbon nanotubes (CNT) in numerous industries have raised significant concerns among environmentalists. The objective of this study was to assess the toxicity and environmental impact of functionalized carbon nanotubes (fCNTs) on the halophilic green alga Dunaliella salina.

The present work evaluated the effects of single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) functionalized with carboxyl and amine groups (as representatives of NTs with negative and positive surface charges, respectively) on photosynthetic pigment (chlorophyll), cell proliferation, and some oxidative stress indicators, including lipid peroxide, protein carbonyl, and hydrogen peroxide content, in a strain of halophilic green algae native to Iran.

The findings indicated that the presence of NTs did not have a notable impact on the levels of chlorophylls a and b, as well as the intracellular hydrogen peroxide levels in algae. However, when examining cell density, it was observed that CNTs exhibited varying degrees of toxicity, particularly at high concentrations and during the logarithmic growth phase of the algae. The results confirmed that the inhibition of alga growth is influenced by the type of functional group. When carboxyl-functionalized SWCNT was used, there was no alteration in the lipid peroxidation (LPX) level at any examined NT concentration. However, when carboxyl-functionalized MWCNT was employed, the level of LPX was consistently lower than the control. On the other hand, amine-functionalized CNTs demonstrated a significantly increasing impact on LPX at high concentrations. Although both functionalized forms of SWCNT can increase the levels of protein carbonyl in algal cells, MWCNTs have no significant effects on cell protein carbonylation.

The results suggest that at concentrations less than 10 mg/L, the anti-stress properties of carboxyl-functionalized CNTs outweigh their cytotoxic properties. Furthermore, SWCNTs have a higher potential for inducing protein carbonylation compared to MWCNTs, regardless of the type of functional group.