In this post, Mirco Bundschuh talks about their recently published paper “Do titanium dioxide nanoparticles induce food depletion for filter feeding organisms? A case study with Daphnia magna”.

In the aquatic environment, nanoparticles can for agglomerates with algal cells. As a consequence of this process, algae may sediment relatively quickly ultimately reducing the availability of food for pelagic filter feeding organisms such as daphnids. Such a reduction in the food availability may affect the life history strategy of daphnids, which should be comparable to food depletion scenarios. To test this hypothesis, we compared the life history strategy of Daphnia magna experiencing different degrees of food limitation as a consequence of variable algal density with daphnids fed with heteroagglomerates composed of algae and titanium dioxide nanoparticles (nTiO₂). In contrast to the hypothesis, daphnids’ body length, weight, and reproduction increased when fed with these heteroagglomerates, while the opposite pattern was observed under food limitation scenarios. Moreover, juvenile body mass, and partly length, was affected negatively irrespective of the scenarios. This suggests that daphnids experienced – besides a limitation in the food availability – additional stress when fed with heteroagglomerates composed of algae and nTiO₂. Potential explanations include modifications in the nutritious quality of algae but also an early exposure of juveniles to nTiO₂.

Flow-through test system used during the present study (photo by F. Seitz)

This study, thus, highlights the substantial gap of knowledge regarding the effects caused by nanoparticles in aquatic systems. Particularly bottom-up directed effects (i.e., via algae on primary consumers) in autotrophic food webs should target a more process-related understanding helping to determine the risks associated with the utilization of such new technologies.

The paper was authored Mirco Bundschuh, Roland Vogt, Frank Seitz, Ricki Rosenfeldt and Ralf Schulz. It is published in Environmental Pollution and can be accessed from the authors’ researchgate pages.

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