Estimates of lung burden risk associated with long-term exposure to TiO₂ nanoparticles as a UV-filter in sprays

Titanium dioxide (TiO₂) nanoparticles (NPs) are employed as an ultraviolet filter in sunscreen products because of their high ultraviolet absorptivity. However, sunscreen sprays may pose health risks due to the toxicity of inhaled TiO₂ NPs. Therefore, we estimated the potential human health risk posed by inhaled TiO₂ NPs emitted from sunscreen sprays. The physiology-based lung model was employed to predict the lung TiO₂ NPs burden caused by long-term exposure. A Hill-based dose-response model described the relationship between lung inflammation and TiO₂ NP accumulation. The Weibull threshold model was used to estimate the threshold amount of accumulation inducing 0.5% of the maximum increase in neutrophils. The potential health risk was assessed using a hazard quotient-based probabilistic risk model. All data obtained to date indicate that application of sunscreen sprays poses no significant health risk. However, using data simulations based on the threshold criterion, we discovered that in terms of practical strategies for preventing the risks posed by inhaled TiO₂ NPs emitted from spray products, the suggested daily use amount and pressing number are 40 g (95% confidence interval: 11-146 g) and 66 (18-245), respectively. In this study, we successfully translated the potential health risk of long-term exposure to NP-containing sunscreen sprays and recommendations for daily application into mechanistic insights.