Effects of nTiO2 on Oocytes of the Marine Bivalve Tegillarca granosa: Implications for Fertilization Success

The increasing environmental release of nano-titanium dioxide (nTiO₂) due to its widespread industrial application raises concerns about its potential effects on aquatic ecosystems, particularly marine organisms. Fertilization, a critical reproductive process for broadcast-spawning bivalves, is highly sensitive to environmental pollutants. In the present investigation, we explored the effects of nTiO₂ at environmentally relevant concentrations on oocyte quality and the fertilization process in the economically important marine bivalve <i>Tegillarca granosa</i>. nTiO₂ exposure significantly reduced fertilization success and sperm-egg fusion efficiency, while markedly increasing polyspermy incidence. Mechanistically, nTiO₂ triggered oxidative stress in oocytes, elevating ROS and MDA levels and causing structural damage to the oocyte membrane. Moreover, nTiO₂ exposure disrupted cellular energy metabolism by inhibiting PK and PFK activities, depleting ATP content, and reducing MMP. Additionally, nTiO₂ exposure impaired Ca²⁺ homeostasis by suppressing Ca²⁺-ATPase activity, which reduced intracellular Ca²⁺ levels. These cellular disruptions collectively compromised the cortical reaction by inhibiting cortical granule exocytosis and microfilament migration. Our findings suggest that nTiO₂-induced oxidative stress, coupled with an imbalance in energy and Ca²⁺ homeostasis, impairs the cortical reaction and fertilization capacity in <i>T. granosa</i>. This study provides valuable insights into the mechanistic pathway underlying the reproductive toxicity of nTiO₂ in marine invertebrates, offering a basis for evaluating the ecological risks associated with the presence of nanomaterials in marine environments.