A fruit fly walked into a test tube, got coated in carbon black, and lost its ability to climb. Sound like the set up for some bad science-based joke? Nope, it's the premise of a preliminary safety test for carbon nanoparticles.

Nanotechnology—whether multiwalled carbon nanotubes, buckyballs or nanosize particles of silver—has barely begun to make its way into everyday products. But, in an effort to stave off the kind of after-the-fact bad news that has plagued introduced materials ranging from asbestos to bisphenol A (BPA), scientists are preemptively testing the potentially ill effects of the tiny molecules and even atoms engineered at the scale of one billionth of a meter or smaller.

So biologist David Rand of Brown University and his colleague set out to see what impact four types of carbon nanoparticles—buckyballs (fullerene C60), carbon black as well as single-walled and multiwalled carbon nanotubes—had on larval and adult fruit flies (Drosophila melanogaster).

By mixing the different carbon nanoparticles into fruit fly food—small enough to be ingested by larval mouths as tiny as 50 micrometers wide—the scientists delivered a dose of as much as 1,000 micrograms per gram of food without any ill effect on the young insects. Some of the carbon nanoparticles ended up discoloring portions of the subsequent adult flies (see picture), proving it was ingested in quantity but without ill effect, and those adults were able to breed normally in turn.

But carbon black and single-walled nanotubes were not so kind to adult fruit flies exposed in test tubes to layers of the fine nanoparticles in powder form. These quickly engulfed the flies and could not be cleaned off by normal grooming behavior, killing them within six hours. These extrafine nanoparticles also made it impossible for the flies to climb the walls of test tubes—a requisite ability for the average fruit fly—perhaps by blocking or interfering with the foot pads or fluids that enable this feat, the scientists speculate.

Further, flies exposed to lower doses that did not kill them spread the tiny particles to an uncontaminated adjacent test tube, and even to other flies. "Such transport and redeposition may bring nanoparticles into contact with human or environmental receptors that might not otherwise be exposed," the researchers wrote in the upcoming August 15 Environmental Science & Technology. "In these scenarios, we expect nanoparticle–insect adhesion and transport similar to microbial transport by flies [that] act as disease vectors."

It remains unclear what the impact of such human exposure might be, although some studies have suggested breathing some nanoparticles might have health impacts similar to asbestos, which is a carcinogen. If that's the case, beware of flies bearing nanotubes.