The Comparative Effects of Visible Light and UV-A Radiation on the Combined Toxicity of P25 TiO2 Nanoparticles and Polystyrene Microplastics on Chlorella sp

Abstract

Abstract The ubiquitous presence of TiO2 nanoparticles (nTiO2) and microplastics (MPs) in marine ecosystems has raised serious concerns about their combined impact on marine biota. In the natural environment, marine microalgae can interact with mixtures of nTiO2 and MPs under both visible light and UV-A radiation conditions. However, most of the previous toxicity studies employed visible light conditions, so the influence of UV-A radiation on toxicity remains poorly understood. To address this gap, the current study aimed to compare the effects of visible light and UV-A radiation on the combined toxic effects of nTiO2 and polystyrene microplastics (PSMPs) in the marine microalga Chlorella sp using artificial seawater directly as the test medium. Our results demonstrated that under UV-A radiation the algal growth inhibition was significantly enhanced compared to that in visible light conditions. The mixtures of nTiO2 and PSMPs exhibited significant enhanced toxicity than their pristine forms. Specifically, the mixtures of nTiO2 and NH2-functionalized PSMPs (10mg/L) showed higher toxicity to algae than the mixtures with COOH-functionalized PSMPs (10mg/L). Furthermore, UV-A radiation exacerbated the hetero aggregation between algae and pollutants. The photoactive nTiO2, promoted increased production of reactive oxygen species under UV-A exposure resulting in cellular damage, lipid peroxidation, and impaired photosynthesis. The effects were more pronounced in case of the mixtures where PSMPs added to the oxidative stress. The toxic effects of the binary mixtures of nTiO2 and PSMPs were further confirmed through the Field Emission Electron Microscopy, revealing specific morphological abnormalities. This study provides valuable insights into the potential risks associated with the combination of nTiO2 and MPs in marine environments, considering the influence of environmentally relevant light conditions and the test medium.