Trophic Transfer of Nanoparticles in a Simplified Invertebrate Food Web

We demonstrated that carboxylated and biotinylated quantum dots (QDs) can be transferred to higher trophic organisms (rotifers) through dietary uptake of ciliated protozoans. QD accumulation from the surrounding environment (bioconcentration) was limited in the ciliates and no QD enrichment (biomagnification) was observed in the rotifers. Our findings indicate that dietary uptake of nanomaterials should be considered for higher trophic aquatic organisms. However, limited bioconcentration and lack of biomagnification may impede the detection of nanomaterials in invertebrate species.

The potential environmental risks, including their impact on aquatic organisms, have been a central argument for regulating the growth of the nanotechnology sector. One area of significant concern for the risk assessment community is the potential for engineered nanomaterials to trophically transfer and accumulate (a process called biomagnification) along a particular food chain. Such behavior has been demonstrated for toxic contaminants such as DDT and mercury and necessitates human consumption limits of certain finfish, for example. The main objective of this project was to determine whether engineered nanoparticles (surface modified quantum dots, QDs) were trophically transferred in a simplified invertebrate food web. A stable invertebrate community, consisting of the microbial loop and metazoan food web, are recognized as important components of productive aquatic ecosystems. Demonstration of such transfer would first require QD uptake from the liquid phase by the prey species (single celled organisms called ciliates) followed by ingestion of the ciliates, with subsequent assimilation of the QDs, by a predatory rotifer species. To that end, we utilized carboxylated and biotinylated QDs and a representative ciliate (Tetrahymena pyriformis) and rotifer species (Brachionus calyciflorus) to investigate the trophodynamics of a model engineered nanomaterial in a simplified freshwater invertebrate food web. QDs were used in these experiments due to their straightforward detection with both optical and transmission electron microscopy, their unique elemental composition that allows nanomaterial quantification (we used Cd²⁺ as a QD surrogate), and their variety of available surface functionalities.

• Quantified trophic transfer rates of quantum dots in simple invertebrate food web
• Quantified assimilation and depuration (loss) rates of quantum dots by lower trophic level aquatic organisms
• Provided detailed images of internalized quantum dots using complimentary microscopy techniques