Impact of UVA and visible light conditions in modulating the toxicity of binary mixture of polystyrene micro plastics and TiO2 nanoparticles in brine shrimp (Artemia salina)

• Toxicity of TiO 2 NPs, PSMPs and the mixture in Artemia salina under UVA and visible light was compared. • Binary mixtures exhibited more toxicity compared to pristine PSMPs, but less compared to TiO 2 NPs. • Ti uptake by Artemia salina was significantly reduced in presence of PSMPs. • Oxidative stress generation was the major mechanism of toxicity. Due to increased usage and improper management, the marine ecosystem has become one of the primary sinks for titanium dioxide nanoparticles (TiO 2 NPs) and microplastics (MPs). This study aims to understand the impact of ultraviolet-A (UVA) and visible light on the toxicity of TiO 2 NPs, functionalised polystyrene microplastics (PSMPs; NH 2 −MPs and COOH-MPs), and their combination on a marine crustacean. Artemia salina was chosen as an indicator organism due to its ecological relevance and widespread usage in ecotoxicity studies. To evaluate the harmful effects of these contaminants, several toxicity endpoints were assessed, including survival estimation, reactive oxygen species (ROS) generation, malondialdehyde (MDA) content estimation, antioxidant activity, acetylcholinesterase (AChE) activity, uptake of Ti, and bioconcentration factor (BCF). The exposure of TiO 2 NPs to Artemia salina under UVA irradiation resulted in increased oxidative stress, enhanced AChE activity indicating neurotoxicity, and reduced survival compared to those exposed under visible light conditions. Under both light conditions, COOH-MPs exhibited reduced oxidative stress than NH 2 −MPs. The binary mixture of TiO 2 NPs with PSMPs showed more toxicity than the pristine PSMPs toward Artemia salina. Nevertheless, these binary mixtures exhibited a lower toxicity than pristine TiO 2 NPs under both light conditions, indicating an antagonistic effect. This emphasize that the interaction between environmental pollutants may not always enhance toxicity, underscoring the importance of non-additive effects in environmental risk assessments. In addition, titanium uptake by Artemia salina was significantly reduced in the presence of PSMPs, and the BCF also decreased. Abbott’s mathematical model revealed an antagonistic effect between the contaminants. The Pearson correlation and heatmap analysis indicated that heightened oxidative stress impacted the survival . This study provides critical insights into how the toxicity of TiO 2 NPs and MPs changes when they coexist and how the changes in the light conditions (visible light and UVA) could modulate the toxicity.