[The New York Times 27 April 2012 by Josie Garthwaite] -- Science fiction might have us believe that tiny particles seeping into soil and altering plant DNA will lead to the rise of giant killer tomatoes. But a new study suggests that exposure to certain nanoparticles may in fact have a shriveling effect on some plants. Researchers with the National Institute of Standards and Technology and the National Institute of Standards and Technologyhave documented the first findings that engineered nanoparticles can enter plant cells and damage their DNA. In laboratory experiments, researchers led by Bryant C. Nelson, a NIST biochemist, tested copper oxide nanoparticles ranging in size from one nanometer to 100 nanometers. For comparison, the head of a pin measures about one million nanometers across, and a human hair is generally around 60,000 nanometers in diameter. As controls, the scientists also tested larger copper oxide particles and copper ions. They found that exposure to nano-scale copper oxide particles stunted the shoots and roots of radishes and two species of rye grass. Plants exposed to the highest concentrations of these nanoparticles, which are commonly used as industrial catalysts, were the most severely stunted. And radishes took up significantly more copper from the nanoparticles than from larger copper oxide particles. “What we learned at the bottom line is these nanoparticles do have the ability to enter the environmental stream, to enter specific plant systems,” Dr. Nelson said in a telephone interview. “Once you reach a certain level of excess copper, especially if it can enter the nucleus, then it has the possibility to damage the DNA.” [Photo: H. Wang/Environmental Protection Agency: At left, a radish plant exposed to no copper nanoparticles, and then a range of concentrations, culminating in 1,000 parts per million at right.]
In the lab, plants grew from seeds submerged in petri dishes filled with solutions of the various particles and water. “We really need to stress that our study was limited in scope,” Dr. Nelson said ; he emphasizes that the researchers tested much higher concentrations of nanoparticles (ranging from 10 to 1,000 milligrams per liter) than the levels that might be anticipated in real-world agricultural scenarios.
Radish seedlings exposed to copper oxide nanoparticles developed twice as many lesions, on multiple DNA bases, as radishes that were exposed to larger copper oxide particles. It was the first time that scientists had detected and measured lesions on more than one DNA “base” in plants (bases form the “rungs” of DNA’s double helix structure), Dr. Nelson said. Previous plant studies had found only one lesion, he said.
The finding is striking, Dr. Nelson’s team wrote, “considering that the presence of a single additional mutagenic lesion in a mammalian genome can lead to genomic instability and/or mutagenesis.” The term signifies the formation of genetic mutations.
“If there was an accidental spill of nanoparticles on a farm, then that crop would most likely be lost,” Dr. Nelson said in an interview, adding that such lesions could lead to various crop diseases like rot, mold and other types of plant death.
“If the farmers are affected, if we lose food crops, then who else is affected by it?” he said. “Everyone who eats. It’s not a little concern. It’s something that needs to be investigated.”
Not all plant species are equally susceptible to DNA damage from this ultrafine particle, however. The ryegrass plants formed only about half the lesions found in radish plants exposed to nanoparticles, Dr. Nelson said, and in some cases the larger copper oxide particles actually produced more lesions in ryegrasses than nanoparticles did.
The study comes at a time when engineered nanoparticles are already widespread. According to the paper, these manmade particles are used “in many commercial products and will be intentionally or inadvertently released at increasing concentrations into the natural environment.”
Yet scientific studies on their use in agriculture “are in their infancy, and the extent to which these NP’s may cause long-term toxic effects, such as genotoxicity, to the plants is unknown.”
Future studies should focus on realistic concentrations and growing conditions, Dr. Nelson suggested.
“That is actually much harder to do,” he said. “We don’t know the capacity of these nanoparticles being produced by manufacturers. We can’t control the weather. We don’t know the different types of components in soil that will bind nanoparticles and reduce or enhance their activity.”
For now, Dr. Nelson’s team is turning its attention to rice plants and the potential impact of titanium dioxide nanoparticles, which are commonly used in sunscreens and lotions and can rinse into water when people bathe or swim.
