Nanopartículas de dióxido de titânio e avaliação da sua toxicidade no mexilhão dourado (Limnoperna fortunei)

Abstract

Nanotechnology is one of the fastest-growing areas of the actuality. Nanoparticles of titanium dioxide (TiO2-NP) have been widely used in many products and processes in recent years. As consequence, these nanoparticles are release into effluent and wastewater, reaching water compartments. Thus, the evaluation of the biological impact of TiO2-NP becomes of great importance for ecotoxicity. The golden mussel (Limnoperna fortunei) is a freshwater bivalve mollusk often used in biomonitoring, considered target organism for TiO2-NP toxicity in the aquatic environment. In this work, L. fortunei were exposed to TiO2-NP (1, 5, 10 and 50 μg mL-1), which were previously physic-chemically characterized. The toxicological evaluation was performed using the comet assay, micronucleus test, evaluation of oxidative damage to lipids and proteins, assessment of antioxidant defences through the activity of the enzymes superoxide dismutase (Sod) and catalase (Cat) and the protein sulfhydryl content. The TiO2-NP interaction with the haemocytes of golden mussel was evaluated by transmission electron microscopy (TEM). The results showed that TiO2-NP presented average size about 20nm, composed of the anatase and rutile crystalline structures, with surface area of 46.26 m2 g-1. The TiO2-NP solutions of 1, 5, 10 and 50 μg mL-1 used showed low stability with a tendency to form aggregates. The genotoxicity of TiO2-NP was evidenced by DNA damage of L. fortunei after 2 h of exposure and increased after 4 h for all concentrations tested. TiO2-NP was not able to induce micronucleus in haemocytes of golden mussels. The mussels showed an increase in lipid peroxidation levels and carbonylated proteins content after 2 h of exposure to the concentrations of TiO2-NP used. After 4 h of exposure, these values showed no difference compared to control. Sod enzyme activity was decreased after 2 h of exposure for all tested concentrations of TiO2-NP. Cat enzyme activity decreased after 2 h of exposure of the mussels to concentrations of 10 and 50 μg mL-1 TiO2-NP. The non-enzymatic antioxidant defences decreased after 2 h of mussels exposure of all TiO2-NP concentrations used. The mussels showed increased levels of lipid peroxidation and carbonyl proteins after 2 h of exposure to TiO2-NP, showing no similar effects after 4 h of exposure. The enzymatic and non-enzymatic antioxidants defences were depleted after 2 h of TiO2-NP exposure to the mussels. After 4 h of exposure, both enzymatic antioxidant and non-enzymatic defences were restored. As shown by the TEM image analysis, TiO2-NP was internalized by haemocytes of the golden mussel, causing changes in plasmatic membrane structure. The TiO2-NP cause toxicological effects on the golden mussel, which are able to cause genotoxicity and changes in redox metabolism of cells. These results reinforce the care that must be applied to the release of TiO2-NP in the environment due to problems caused by nanoparticles exposure. Furthermore, the data presented demonstrate the potential L. fortunei as biomonitor organism for exposure to nanoparticles.