August 10, 2009: Researchers at Brown U. are offering more evidence about the hazards involved with carbon nanotubes, showing how exposure to them might be fatal to fruit flies.

In their work, published online August 10 by the journal Environmental Science & Technology, a team immersed adult Drosophila melanogaster in various carbon nanoparticles (carbon black, C60 “buckyballs,” single-walled carbon nanotubes, and multiwalled carbon nanotubes). The flies in test tube with no nanoparticles ,C60, and MWNTs climbed out “with few or no difficulties” — but the others in carbon black and SWNTs couldn’t, and died “within six to 10 hours.” Postmortem analysis revealed they were smeared with the particles “from wings to legs” (suggesting impaired movement), which clogged breathing holes (possibly causingsuffocation ) and coated their compound eyes (possibly causing blindness, so they couldn’t see the way out). “They just can’t move. It’s like a dinosaur falling into a tar pit,” Rand added.

Microscopy shows a clean foot and leg of a fruit fly (left), and a foot and leg covered with carbon nanostructures (arrows). Adhering nanostructures may have impeded movement, respiration and vision in adult flies but did not appear toxic to fly larvae that ingested it. (Source: Brown U.)

The scientists stop short, though, of saying the particles actually directly caused the flies’ deaths. This is probably partly because it may not simply the nanoparticle itself that is hazardous, but maybe its form is the key, Rand explained. Meanwhile, separate tests on Drosophila melanogaster larvae “showed no physical or reproductive effects” from eating food contaminated by the same nanoparticles. “These same compounds that were not toxic to the (fruit fly) larvae were toxic to the adults in some cases, so there may be analogies to other toxic effects from fine particles,” noted biology prof. David Rand, in a statement. He drew an analogy to the effects of working in a coal mine: “You get sick more from the effects of dust particles than from specific toxins in the dust.” The lack of impact on larvae also suggests that nanoparticles were seen stored in the flies’ tissue The work also suggests that it is not simply the nanoparticle itself that is hazardous, but maybe its form is the key, he added.

The work also shows potential environmental impact of exposure to nanoparticles. The adult flies were shown to transport and deposit carbon nanoparticles during grooming, suggesting contamination can be spread. And though two generations of the fruit fly larvae showed no ill effects from ingesting the nanoparticles, they did store some in their tissue, indicating they can be passed through the food chain.

While fly larvae appear to have ingested carbon nanostructures without harm, the nanostructures remained in their bodies through adulthood, raising questions about accumulation in the food chain. (Source: Brown U.)

Overall, the work indicates that different types of the same material (carbon) can have different effects. Future work will investigate why the flies died after exposure to varieties of carbon nanoparticles (but not others), and also test the flies’ response to nanosilver and other nanomaterials.

The research was funded by the National Science Foundation, the National Institute of Environmental Health Sciences, the Superfund Research Program Grant, and the Research Seed Fund Program of Brown’s Office of Vice President for Research.