Previous studies have shown that engineered nanomaterials can be transferred from prey to predator, but the ecological impacts of this are mostly unknown. In particular, it is not known if these materials can be biomagnified-a process in which higher concentrations of materials accumulate in organisms higher up in the food chain. Here, we show that bare CdSe quantum dots that have accumulated in Pseudomonas aeruginosa bacteria can be transferred to and biomagnified in the Tetrahymena thermophila protozoa that prey on the bacteria. Cadmium concentrations in the protozoa predator were approximately five times higher than their bacterial prey. Quantum-dot-treated bacteria were differentially toxic to the protozoa, in that they inhibited their own digestion in the protozoan food vacuoles. Because the protozoa did not lyse, largely intact quantum dots remain available to higher trophic levels. The observed biomagnification from bacterial prey is significant because bacteria are at the base of environmental food webs. Our findings illustrate the potential for biomagnification as an ecological impact of nanomaterials.
dNanoscale titanium dioxide (TiO 2 ) is increasingly used in consumer goods and is entering waste streams, thereby exposing and potentially affecting environmental microbes. Protozoans could either take up TiO 2 directly from water and sediments or acquire TiO 2 during bactivory (ingestion of bacteria) of TiO 2 -encrusted bacteria. Here, the route of exposure of the ciliated protozoan Tetrahymena thermophila to TiO 2 was varied and the growth of, and uptake and accumulation of TiO 2 by, T. thermophila were measured. While TiO 2 did not affect T. thermophila swimming or cellular morphology, direct TiO 2 exposure in rich growth medium resulted in a lower population yield. When TiO 2 exposure was by bactivory of Pseudomonas aeruginosa, the T. thermophila population yield and growth rate were lower than those that occurred during the bactivory of non-TiO 2 -encrusted bacteria. Regardless of the feeding mode, T. thermophila cells internalized TiO 2 into their food vacuoles. Biomagnification of TiO 2 was not observed; this was attributed to the observation that TiO 2 appeared to be unable to cross the food vacuole membrane and enter the cytoplasm. Nevertheless, our findings imply that TiO 2 could be transferred into higher trophic levels within food webs and that the food web could be affected by the decreased growth rate and yield of organisms near the base of the web.
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