The rising use of contaminants such as nanoparticles and microplastics has taken a heavy toll on the marine environment. However, their combined toxic effects on the species across various trophic levels remain quite unexplored. The aim of this study was to explore the effects of three surface-functionalized (carboxylated, plain, and aminated) polystyrene microplastics on nano-TiO2 toxicity across two trophic levels containing Chlorella sp. as the prey and Artemia salina as the predator. The experiments carried out on Chlorella sp. include the toxicity assessment, oxidative stress determination, and uptake of nano-TiO2 (both in the presence and absence of microplastics). Results revealed that the aminated and plain polystyrene microplastics enhanced nano-TiO2 toxicity, while carboxylated microplastics decreased the toxic effects in Chlorella sp. On the other hand, toxicity assessment in Artemia salina was carried out using two different modes of exposure: aqueous and dietary routes. The aqueous route involving the direct exposure of nano-TiO2 and microplastics indicated greater toxicity, uptake, and accumulation in Artemia salina than the dietary route of exposure. Since dietary exposure decreased the toxicity, uptake, and accumulation of nano-TiO2, no change (p > 0.05) in the biomagnification factors of nano-TiO2 was noted for all the test concentrations of nano-TiO2 combined with and without microplastics. The computed values were less than 1, indicating negligible transfer of nano-TiO2 from Chlorella sp. to Artemia salina. Overall, the study highlights the two-level trophic toxicity and the transfer potential of nano-TiO2 under the influence of different microplastics. © 2021 Elsevier B.V.