Ingesting, digesting, and egesting oh my: nanoparticles and water fleas

Years ago when I first met my husband, I am ashamed to say, I may have belittled the importance of his research project. He was studying larval fish, and observing what they ate, how much they pooped and how quickly they grew. Who cared I wondered? I was a toxicologist I’d thought at least my work was somewhat applicable to….to something! That was almost twenty years ago and now he’s out saving wild fish populations, and I’m here typing at my desk! But recently I came across an article entitled “In Vivo Biomodification of Lipid Coated Carbon Nanotubes by Daphnia Magnia” by Aaron Roberts, et al., published in Environmental Science and Technology, which highlights the importance of ingesting and egesting (or eating and pooping) in an environmental context that even a toxicologist can appreciate.

Turns out that what little critters eat, digest and poop may have some important implications for nanomaterials. Roberts et al. reports on the fate (and to some extent toxicity) of single-walled carbon nanotubes or, SWNTs, in aquatic creatures known as Daphnia magnia, or better known as water fleas.

Alone, SWNTs are not water soluble, which apparently limits their utility. In this case, the authors first combined SWNTs with an amphiphilic coating, (that means it goes both way water loving and fat loving,) to render them soluble in water. Rendering SWNTs more water soluble, according to the authors will:

“..not only enable biological studies of cellular responses but also empower the development of next generation single-molucule chemical and biosensors and self-assembled nanodevices,.”

But, they noted, this new and improved water soluble nanomaterial comes with a caveat,

“Because of the large number of applications there may be great potential for discharge of coated, solubilized nanomaterials into the environment.”

Enter, the fleas.

Since solubilized nanomaterials might end up in watery environments, the authors exposed Daphnia to concentrations of coated SWNTs. They reported that up to a point, the Daphnia not only tolerated but (under conditions of starvation) may have even benefited from the coated materials. Daphia ingested the materials, stripped the coatings, and apparently used them as a food source (those in SWNT water survived to a greater extent than those without), and egested (pooped out) uncoated and now insoluble SWNTs. But we all know what happens when we over indulge. When exposed to higher concentrations, the Daphnia didn’t fare so well, and survival was reduced. Additionally the authors noted that coated SWNTs also accumulated on the outer surfaces of Daphnia (also not good.) I would also suggest that all food sources are not created equal. For example what keeps one generation going, might not be sufficient for producing the next, so that further studies of such materials might include life-cycle tests and more intensive investigation into the quality of "food" provided by similarly coated nanomaterials.

In conclusion, the authors note that:

“Our data show that biomodification of lysophospholipid-coated carbon nanotubes in vivo can occur and have dramatic effects on the physical properties of the nanomaterial. These modifications may result in unanticipated effects both on the materials properties as well as the organisms exposed to the nanomaterial. Biomodification is an important phenomenon that should be considered in studies on the biological applications, environmental fate, and toxicity of convalently and noncovalently functionalized nanomaterials.”

You can find the full article, by Aaron P. Roberts, et al., In Vivo Biomodification of Lipid Coated Carbon Nanotubes by Daphnia Magnia in Environmental Science and Technology, ASAP Articles, March 7, 2007.