Moving up the food chain

The notion of nanotechnology escaping into the environment is not only a staple of science fiction, but also a concern raised by the general public. However, reality is far less terrifying than that portrayed in film and literature, as rather than nano-robots wreaking havoc the worst we currently have to contend with are nanoparticles.

 

Of course there are many types of nanoparticle, some of which can be harmful. Until recently it was known that nanoparticles could be passed up the food chain, from prey to predator; however, it was unclear as to whether these materials could be biomagnified. That is, could the concentration of the particles be increased on moving up the food chain. Researchers at the University of California, Santa Barbara, have recently demonstrated that such biomagnification can occur within a simple food chain [Werlin et al., Nature Nanotechnol (2010) 6, 65].

 

The team cultivated Pseudomonas aeruginosa bacteria in an environment of CdSe quantum dots (QDs), along with a separate control batch and bacteria in a cadmium acetate solution. After allowing the bacteria to internalize the surrounding contaminates, they were then washed and placed with the predatory Tetrahymena thermophilia protozoa. While the initial behavior of the three batches of protozoa was similar, differences soon became apparent. The growth rate of the protozoa feeding on the cadmium acetate fed bacteria dropped to zero after the first doubling, and even after being transferred to a healthy environment they were unable to resume growth. This was apparently due to the toxic effect of the cadmium. The protozoa feeding on the QD fed bacteria fared slightly better, with protozoa remaining mobile for longer, and maintaining some growth once placed in a healthy medium.

 

Examination of the protozoa revealed that those that had fed on the quantum dots possessed large (approximately 5 micron) food vacuoles that contained undigested bacteria. Thus the QD fed bacteria inhibited their own digestion. As digestion is needed to free the QDs into the vacuole, this inhibition actually helps the protozoa survive longer than the cadmium acetate fed protozoa, as they do not succumb to the toxic effects of cadmium so quickly. This delayed death means that as the protozoa continue to survive, and feed, the QDs are biomagnifed.

 

Prof. Holden explained that their research into this area continues. “We are interested in the possibility for further trophic transfer, but also are very interested in understanding more about the QD effects observed in this trophic transfer study”. “We are trying to do research to understand better how nanoparticles, including QDs, change in cells over time.”