The comparative effects of visible light and UV-A radiation on the combined toxicity of P25 TiO 2 nanoparticles and polystyrene microplastics on Chlorella sp.

The ubiquitous presence of TiO 2 nanoparticles (nTiO 2 ) and microplastics (MPs) in marine ecosystems has raised serious concerns about their combined impact on marine biota. This study investigated the combined toxic effect of nTiO 2 (1 mg/L) and NH 2 and COOH surface functionalized polystyrene MPs (PSMPs) (2.5 and 10 mg/L) on Chlorella sp. All the experiments were carried out under both visible light and UV-A radiation conditions to elucidate the impact of light on the combined toxicity of these pollutants. Growth inhibition results indicated that pristine nTiO 2 exhibited a more toxic effect (38%) under UV-A radiation when compared to visible light conditions (27%). However, no significant change in the growth inhibitory effects of pristine PSMPs was observed between visible light and UVA radiation conditions. The combined pollutants (nTiO 2 + 10 mg/L PSMPs) under UV-A radiation exhibited more growth inhibition (nTiO 2 + NH 2 PSMPs 66%; nTiO 2 + COOH PSMPs 50%) than under visible light conditions (nTiO 2 + NH 2 PSMPs 55%; TiO 2 + COOH PSMPs 44%). Independent action modeling indicated that the mixture of nTiO 2 with PSMPs (10 mg/L) exhibited an additive effect on the algal growth inhibition under both the light conditions. The photoactive nTiO 2 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 nTiO 2 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 nTiO 2 and MPs in marine environments, considering the influence of environmentally relevant light conditions and the test medium.