Heavy metal uptake and toxicity in the presence of titanium dioxide nanoparticles: a factorial approach using Daphnia magna.

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 Daphnia magna, 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.