The impact of titanium dioxide nanoparticles (nano-TiO₂) on the bioavailability of metals in aquatic filter-feeding organisms has rarely been investigated, especially in the presence of algae as a food source. In this study, we quantified the accumulation and subcellular distribution of arsenate (As^V) in Daphnia magna in the presence of nano-TiO₂ and a green alga (Scenedesmus obliquus) food source. Results showed that S. obliquus significantly increased the accumulation of total arsenic (As) and titanium (Ti) in D. magna. The presence of this food source increased As in metal-sensitive fractions (MSF) and as biologically detoxified metals (BDM), while it decreased Ti levels in MSF but increased levels as BDM. The difference in the subcellular distribution of As and Ti demonstrates the dissociation of As from nano-TiO₂ during digestion at subcellular partitioning irrespective of food availability. In turn, the presence of algae was shown to increase metal-based toxicity in D. magna due to the transfer of As from BMD to MSF. Furthermore, S. obliquus significantly increased the concentration of As and Ti in soluble fractions, indicating that As and nano-TiO₂ ingested by D. magna could be transferred more readily to their predators in the presence of S. obliquus. Our study shows the potential of algae to increase the toxicity and biomagnification of As^V. Furthermore, it highlights food as an important factor in the toxicity assessment of nanomaterials and co-existing pollutants.