Influence of differently functionalized polystyrene microplastics on the toxic effects of P25 TiO₂ NPs towards marine...

Increased utilization of titanium dioxide nanoparticles (TiO₂ NPs) for commercial as well as industrial purposes resulted in the accumulation of nanoparticles in the marine system. Microplastics being an emerging secondary pollutant in the marine ecosystem have an impact on the toxic effects of TiO₂ NPs which has not been evaluated up to date. So it is important to assess the toxic effects of both these pollutants on the marine environment. The present study examines the impact of differently functionalized microplastics on the toxic effects of P25 TiO₂ NPs to marine algae Chlorella sp. The tendency of nanoparticles to undergo aggregation in artificial seawater was observed with increase in time. The median effective concentration for TiO₂ NPs was found to be 81 μM which indicates higher toxic effects of NPs toward algae. In contrast, microplastics irrespective of their difference in functionalization had minimal toxic effect of about 15% at their higher concentration tested, 1000 mg L^-1. Plain and aminated polystyrene microplastics enhanced the TiO₂ NPs toxicity which was further validated with oxidative stress determination studies like reactive oxygen species and lipid peroxidation assays. Negatively charged carboxylated polystyrene microplastics decreased the TiO₂ NPs toxicity with possible hetero-aggregation between TiO₂ NPs and microplastics in the system. The toxicity data obtained for the mixture was further corroborated with Abbott's mathematical model.