Heavy Metal Uptake and Toxicity in the Presence of Titanium Dioxide Nanoparticles: A Factorial Approach Using <i>Daphnia magna</i>.

Unintentionally released titanium dioxide nanoparticles (nTiO₂) may co-occur in aquatic environments together with other stressors, such as, metal ions. The effects of P25-nTiO₂ on the toxicity and uptake of the elements silver (Ag), arsenic (As) and copper (Cu) were assessed by applying a factorial test design. The test design consisted of two developmental stages of <i>Daphnia magna</i>, two levels of nTiO₂ (0 versus 2 mg/L) as well as seven nominal test concentrations of the respective element. The presence of nTiO₂ increased Ag toxicity for juveniles as indicated by a 40% lower 72-h EC₅₀, while the toxicities of As and Cu were reduced by up to 80%. This reduction was even more pronounced for Cu in the presence of dissolved organic carbon (i.e., seaweed extract) and nTiO₂. This outcome coincides with the body burden of the elements, which was elevated 2-fold for Ag and decreased 14-fold for Cu in the presence of nTiO₂. Although the underlying mechanisms could not be uncovered, the data suggest that the carrier function of nTiO₂ plays a central role. However, to understand the processes and mechanisms occurring in the field due to the presence of nTiO₂ further systematic investigations considering environmental variables and nanoparticle characteristics are required