Exposure to Oxidized Multi-Walled CNTs Can Lead to Oxidative Stress in the Asian Freshwater Clam Corbicula fluminea (Müller, 1774)

Abstract

The increasing attention that carbon-based nanomaterials have attracted due to their distinctive properties makes them one of the most widely used nanomaterials for industrial purposes. However, their toxicity and environmental effects must be carefully studied, particularly regarding aquatic biota. The implications of these carbon-based nanomaterials on aquatic ecosystems, due to their potential entry or accidental release during manufacturing and treatment processes, need to be studied because their impacts upon living organisms are not fully understood. In this research work, the toxicity of oxidized multi-walled carbon nanotubes (Ox-MWCNTs) was measured using the freshwater bivalve (Corbicula fluminea) after exposure to different concentrations (0, 0.1, 0.2, and 0.5 mg·L^-1 Ox-MWCNTs) for 14 days. The oxidized multi-walled carbon nanotubes were analyzed (pH, Raman microscopy, high-resolution electron microscopy, and dynamic light scattering), showing their properties and behavior (size, aggregation state, and structure) in water media. The antioxidant defenses in the organism's digestive gland and gills were evaluated through measuring oxidative stress enzymes (glutathione-S-transferase, catalase, and superoxide dismutase), lipid peroxidation, and total ubiquitin. The results showed a concentration-dependent response of antioxidant enzymes (CAT and GST) in both tissues (gills and digestive glands) for all exposure periods in bivalves exposed to the different concentrations of oxidized multi-walled carbon nanotubes. Lipid peroxidation (MDA content) showed a variable response with the increase in oxidized multi-walled carbon nanotubes in the gills after 7 and 14 exposure days. Overall, after 14 days, there was an increase in total Ub compared to controls. Overall, the oxidative stress observed after the exposure of Corbicula fluminea to oxidized multi-walled carbon nanotubes indicates that the discharge of these nanomaterials into aquatic ecosystems can affect the biota as well as potentially accumulate in the trophic chain, and may even put human health at risk if they ingest contaminated animals.

Keywords: Corbicula fluminea; biomarkers; oxidative stress enzymes; oxidized multi-walled carbon nanotubes.

Figure 1

Representative Raman microscopy spectrum.

Figure 2

Representative TEM and HRTEM micrographs of the Ox-MWCNTs suspensions (scale bars: 0.2 μm, 200, 100 nm).

Figure 3

(a) Catalase activities measured in gills and (b) in digestive glands of C. fluminea exposed to different concentrations of Ox-MWCNTs. Legend: significant differences from controls (*) and between exposure periods (**).

Figure 4

(a) GST activities measured in gills and (b) in digestive glands of C. fluminea exposed to different concentrations of Ox-MWCNTs. Legend: significant differences from controls (*) and between exposure periods (**).

Figure 5

(a) MDA contents measured in gills and (b) in digestive glands of C. fluminea exposed to different concentrations of Ox-MWCNTs. Legend: significant differences from controls (*) and between exposure periods (**).

Figure 6

(a) SOD activities measured in gills and (b) in digestive glands of C. fluminea exposed to different concentrations of Ox-MWCNTs. Legend: significant differences from controls (*) and between exposure periods (**).

Figure 7

(a) Total ubiquitin measured in gills and (b) in digestive glands of C. fluminea exposed to different concentrations of Ox-MWCNTs. Legend: significant differences from controls (*) and between exposure periods (**).

Figure 8

(a) Correlation matrix for G and (b) DG (values: Pearson r correlation coefficient).