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Nanoparticles May Pose Environmental Threat

Tests show one type of nanoparticle can mutate plant DNA.

Increasing exposure to nanoparticles by radish plants also increases the impact on growth, nanoparticle exposure concentrations increasing from left to right.
Credit: H. Wang, U.S. Environmental Protection Agency
No longer the stuff of science fiction, nanoparticles are becoming more and more common. The extremely tiny objects can do just about everything, from filtering pollution to delivering medicine in the body. However, no one is sure of the effects if they get loose in the environment.

A team of scientists from the National Institute of Standards and Technology and the University of Massachusetts at Amherst thinks there may be something to worry about.

They have not proven the particles are dangerous, but have shown that some nanoparticles can be absorbed into plants and mutate the plant's DNA, and that, they say, is worth a further look.

Nanoparticles are so small that they act as a bridge between the size of atoms and something of tangible substance. The thickness of a human hair is measured in millionths of a meter; nanoparticles, in billionths of a meter.

And now, they are everywhere. Manufacturers put them in clothing such as socks to kill bacteria. They are in a type of house paint that cleans itself in sunlight and in the coating on eyeglasses. Clear sunscreen lotion now on the market contains zinc or titanium nanoparticles. Cars will soon have paint that heals itself from scratches.

Nanoparticles have become so common it is assumed inevitably they will end up in the environment.

To see what would happen to plants exposed to nanoparticles, the researchers took particles of copper oxide and exposed three kinds of plants to them: radishes and two types of rye, the researchers reported in Environmental Science & Technology.

They chose nanoparticles of copper because they are widely used for coloring glass, in ceramics, as a polish and in the manufacturing of rayon. They also are used in the electronics industry to manufacture semiconductors, said Bryant Nelson of the National Institute of Standards and Technology.

The research team also used particles of copper oxide larger than nano-size as a comparison as well as regular copper ions.

Copper oxide is an oxidizing agent, and some oxidizing agents from metals can cause cancer in humans, a reason for the concern.

"We were testing to see whether or not the particles had the ability to enter plants and cause damage to the plant DNA," Nelson said.

 According to their results, they did.

"The damage was visible to the eye," Nelson said.

Results, Nelson said, varied.  The radishes showed considerable damage, forming lesions in the DNA base of the plants, which looked stunted. There were twice as many lesions with the nanoparticles than with the larger particles, and the plants took in more copper with the smaller particles. There were fewer lesions in the two types of rye, but the results were not the same for each. All the three kinds of plants had absorbed particles.

Nelson emphasized they used far more nanoparticles than the plants are likely ever to encounter in the environment. The study was merely to see whether absorption and damage was possible. Further experiments, using a more natural exposure level, is planned, and with fewer particles.

Kathleen Eggleson at the Center for Nano Science and Technology at the University of Notre Dame said that the study demonstrates the complexity of nanotechnology research. In testing rye, the researchers had two plants of the same genus reacting differently to the nanoparticles, Eggleson said.

Also, it is not clear how different environments would affect the uptake, or whether the nanoparticles would meet the plants through water or from the soil, she said.

But the technology already is ubiquitous.

"Nanotechnology is developing more and more complex structures," Eggleson said. "It is more of an evolutionary phenomenon than revolutionary. It will not be one big splashy new invention."

"To look at all the nanoparticles and all the permutations, coatings, and all of the different organisms and concentrations, is absolutely overwhelming," Eggleson said.

Joel Shurkin, Inside Science News Service

Joel Shurkin is a freelance writer based in Baltimore. He is the author of nine books on science and the history of science, and has taught science journalism at Stanford University, UC Santa Cruz and the University of Alaska Fairbanks


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