The elevated toxicity of toxic metals in the presence of nanoparticles (NPs) has raised significant concerns on the NP environmental safety. This research focuses on the impact of environmental conditions, specifically algae, on this type of toxicity. An indicator aquatic organism, Ceriodaphnia dubia (C. dubia), was used to examine the combined toxicity and toxicity mitigation from algae by monitoring its 24-h mortality. Four papers are included in this research, which focus on four aspects of the combined toxicity and the corresponding algae (Raphidocelis) impact. The first paper examines the algae impact on the combined toxicity of lead (Pb) and nano-TiO2. The effect of algae was determined through Pb accumulation by, depuration from, and distribution within the C. dubia. The second paper develops a two-compartment kinetic model to quantify the iron (Fe) and Pb accumulation in C. dubia in the presence of nano-TiO2. The model was used to investigate the major uptake, depuration, and distribution pathways of Fe and Pb in C. dubia. The third paper presents a toxicokinetic-toxicodynamic (TK-TD) model that was used to develop fundamental understanding of the combined toxicity of Pb and nano-TiO2, more specifically, the role of nano-TiO2 in the combined toxicity. The fourth paper focuses on the algae impact on the combined toxicity of Pb and an emerging containment, microplastic (MP). The combined toxicity mechanisms and the effect of algae were investigated through Pb and MP interaction, Pb accumulation, and MP accumulation. This research provides a fundamental understanding on the role of algae, a natural food source for aquatic organisms, on the toxicity of NPs in the presence of other background toxins --Abstract, page iv
