Toxicity associated with the photo catalytic and photo stable forms of titanium dioxide nanoparticles used in sunscreen

Abstract

The increasing number of applications using titanium dioxide nanoparticles (nano-TiO2) highlights the need to continuously and systematically investigate its toxicity. Particle size, surface area and dose are the classical parameters considered when performing toxicity studies. However, consideration of the size-related properties and altered reactivity can unveil complex and unexpected phenomena arising from the interplay of the different factors. In addition to particle size, altered reactivity can be induced by intentional or unintentional modifications of the nanoparticles by their surrounding matrix. This effect could potentially influence the nanoparticles’ band gap, surface reactivity, agglomeration, mobility and photo catalytic behavior. The remarkable ability to absorb impurities from the surrounding medium could transform nano-TiO2 into a surrogate carrier of trace elements (e.g., heavy metal ions), which heightens their transportation and intracellular accumulation. This review outlines the different characteristics and interactions that may contribute to the underlying mechanisms of health and environmental toxicity of nano-TiO2, and identifies gaps in current understanding.