The teeny, tiny carbon particles known as buckyballs did not harm healthy bacteria living in soil samples in a recent test. The result contrasts with prior studies in which buckyballs killed bacteria in lab dishes, suggesting that components of ordinary soil may counteract the potential dangers of some nanoparticles.
"There was a bit of a fear it was going to have a major negative effect on soil," says environmental microbiologist Ronald Turco of Purdue University in West Lafayette, Ind., who led the study. He says there are still many other nanoparticles to evaluate, however, including flecks of silver and other metals as well as buckyballs' carbon cousins, nanotubes, which are likely to behave in other ways.
Manufacturers have already started adding nano-size chemicals—specks of matter one billionth of a meter in size—to products such as cosmetics. Anticipating a proliferation of nanoproducts, researchers hope to get a leg up on the potential dangers of the tiny particles spreading into the environment, where their minute size might let them enter and damage living tissue.
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Turco says he has seen advertisements for automobile transmission fluid enhanced with buckyballs. "That told me these things are going to hit the environment soon," he says. Prior tests found that high concentrations of the soccer ball–shaped buckyballs can kill pure strains of bacteria growing in the lab. If they did the same in soil, Turco says, they could harm plants and animals higher up the food chain.
To get a more realistic read, he and his co-workers treated soil from a cornfield run by the university with either a solution of buckyballs, yielding a dose of one part per million in the soil, or with dry buckyballs for a concentration of a thousand parts per million. Turco says the group did not know what amounts would best reflect real exposures, because none have happened yet, so they chose a wide range.
They found that after 180 days neither dose led to measurable changes in the soil's mix of DNA and molecules found in bacterial cell walls (which reveals the amount and types of bacteria present), its levels of nutrients or rate of CO2 formation—the latter of which reflects how well the bacteria are utilizing oxygen. "Any way we've cut this and looked at it in soil, we don't see an effect," he says. "We were very happy."
Turco says the negatively charged buckyballs may be clinging to organic matter and salts in the soil, limiting their ability to enter bacterial cells. The result, to appear in an upcoming issue of Environmental Science & Technology, sets a baseline, he says, against which researchers can compare the effects of other nanoparticles.
