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

## TL;DR

This study shows that nano-titanium dioxide harms the fertilization process in a marine bivalve by causing oxidative stress and disrupting cellular functions.

## Contribution

The study reveals the specific mechanisms by which nTiO2 impairs fertilization in Tegillarca granosa through oxidative stress and energy metabolism disruption.

## Key findings

- nTiO2 exposure reduced fertilization success and sperm-egg fusion efficiency in Tegillarca granosa.
- nTiO2 triggered oxidative stress and disrupted energy metabolism and Ca2+ homeostasis in oocytes.
- nTiO2 impaired the cortical reaction by inhibiting exocytosis and microfilament migration in oocytes.

## Abstract

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 Tegillarca granosa. 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 T. granosa. 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.