In this post, Ricki Rosenfeldt writes about their recent paper on the modulation of heavy metal toxicity by nanoparticles.

Gammarid feeding on a black alder leaf (photo by F. Seitz & R. Rosenfeldt)

Titanium dioxide nanoparticles are increasingly used in consumer products, including food, toothpaste, and sunscreen. This extensive usage increases the probability of the nanoparticles’ unintentional release into the aquatic environment where they co-occur with, and likely modify the toxicity of, other stressors. Titanium dioxide nanoparticles may, for instance, adsorb dissolved metals to their surface. Thereby, the concentration of freely available metal ions in the water phase is reduced. At the same time, the nanoparticles together with the adsorbed metals agglomerate and settle, ultimately leading to increasing concentrations in the sediment. This scenario may endanger benthic organisms, such as leaf-shredding freshwater shrimps.

To assess for potential risks induced by this pathway, we investigated the individual and combined toxicity of a heavy metal (i.e., copper) and titanium dioxide nanoparticles in a full-factorial experimental design with the freshwater shrimp Gammarus fossarum as test organism. Our results show that titanium dioxide nanoparticles reduced the copper toxicity, both at the lethal and sublethal levels. This pattern may be explained by the adsorption of copper to the titanium dioxide nanoparticles, which reduced the bioavailability of copper (see also our earlier publication on the water flea Daphnia magna). Despite the observed mitigating effect for copper, titanium dioxide nanoparticles affected gammarids’ individual physiological development potentially impacting their population development in the long run. Therefore, it seems sensible to thoroughly investigate for such potential side-effects, before titanium dioxide nanoproducts are judged as environmentally safe or are even suggested for remediation purposes in the field.

Further details can be found in our recent publication in the journal Aquatic Toxicology, which was authored by Ricki R. Rosenfeldt, Frank Seitz, Jochen P. Zubrod, Alexander Feckler, Tobias Merkel, Simon Lüderwald, Rebecca Bundschuh, Ralf Schulz, and Mirco Bundschuh.