When nano may not be nano

Mark Wiesner from Duke University. Photo: Duke University PhotographyAssessing the impacts of Nano on the environment or human health

The same properties of nanoparticles that make them so appealing to manufacturers may also have negative effects on the environment and human health.

However, little is known which particles may be harmful. Part of the problem is determining exactly what a nanoparticle is.

A new analysis by an international team of researchers from the Center for the Environmental Implications of NanoTechnology (CEINT), based at Duke University, argues for a new look at the way nanoparticles are selected when studying the potential impacts on human health and the environment. They have found that while many small particles are considered to be "nano," these materials often do not meet full definition of having special properties that make them different from conventional materials.

Under the prevailing definition, a particle is deemed nano if its diameter is between 1 and 100 nanometers (nm), about 1/10,000 the diameter of a human hair, and if it has properties that significantly differ from its naturally occurring, or bulk, counterpart.

The special properties of nanoparticles come from their high surface-area-to-volume ratio. They also have a considerably higher percentage of atoms on their surface compared to bulk particles, which can make them more reactive. These man-made materials can be found in a vast array of consumer products, including paints and sunscreens, as well as in water treatment plants and drug delivery systems.

For most of this decade, discussions of nanoparticles have tended to focus more on their size than their properties. However, after reviewing the scientific literature, the Duke-led team believes that the old definition is not specific enough. A definition that focuses on properties is critical, they say, to help scientists determine which particular nanoparticles are the most likely to represent a threat to the environment or human health.

Generally speaking, it is the very smallest particles (less than 30 nanometers) that should receive the most attention in studying the environmental and human health impacts of nanomaterials, according to Mark Wiesner, a Duke professor of civil and environmental engineering and director of the federally-funded EINT.

"There are an infinite number of potential new man-made nanoparticles, so we need to find a way to narrow our efforts to those that have the greatest likelihood of having the unique properties with unique effects," Wiesner said.

"A key question to be answered is whether or not a particular nanoparticle has toxic or hazardous properties that are truly different from identical particles in their bulk form," Wiesner continued. "This question has not been answered. To do so, we need to be speaking the same language when assessing any unique properties of these novel materials."

The results of Wiesner's analysis were published online in the journal Nature Nanotechnology. The study was supported by CEINT, which is jointly funded by the National Science Foundation and Environmental Protection Agency.

Specifically, the researchers found that nanoparticles approaching the 100 nm end of the size spectrum tend to have fewer special properties when compared to their bulk counterparts. Furthermore, they found that nanoparticles smaller than 30 nm tend to exhibit the unique properties that should command increased scrutiny, Wiesner said.

"Many nanoparticles smaller than 30 nanometers undergo drastic changes in their crystalline structure that enhance how the atoms on their surface interact with the environment," Wiesner said.

For example, because of the increased surface-area-to-volume ratio, nanoparticles can be highly reactive with other chemicals in the environment and can also disrupt certain activities within cells.

"While there have been reports of nanoparticle toxicity increasing as the size decreases, it is still uncertain whether this increase in reactivity is harmful to the environment or human safety," Wiesner said.

"To settle this issue, toxicological studies should contrast particles that exhibit novel size-dependant properties, particularly concerning their surface reactivity, and those particles that do not exhibit these properties."

Health and environmental effects of carbon nanoparticles

Researchers are reporting that carbon nanoparticles can be transmitted by fruit flies and that certain nanoparticles can be toxic to adult flies. Photo: American Chemical SocietyA new study raises the possibility that flies and other insects that encounter nanomaterial "hot spots," or spills, near manufacturing facilities in the future could pick up and transport nanoparticles on their bodies, transferring the particles to other flies or habitats in the environment.

The study on carbon nanoparticles -barely 1/5,000th the width of a human hair -is scheduled for the Aug. 15 issue of ACS' Environmental Science & Technology, a semi-monthly journal.

David Rand and Robert Hurt and colleagues note that emergence of a nanotechnology industry is raising concerns about the potential adverse health and environmental effects of nanoparticles. These materials show promise for use in a wide range of products, including cosmetics, pharmaceuticals, and electronics.

The study focused on determining how different kinds of exposure to nanoparticles affected larval and adult fruit flies. Scientists use fruit flies as stand-ins for humans and other animals in certain kinds of research. There were no apparent ill effects on fruit fly larvae that ate food containing high concentrations of nanoparticles. However, adult flies died or were incapacitated when their bodies were exposed to large amounts of certain nanoparticles.

During the experiments, the researchers noted that contaminated flies transferred nanoparticles to other flies, and realised that such transfer could also occur between flies and humans in the future. The transfer involved very low levels of nanoparticles, which did not have adverse effects on the fruit flies. Since larvae can tolerate very high doses of nanoparticles in the diet, but adult flies show very different sensitivities, the environmental impact depends on the ecological context of nanoparticle release.

Nano-particle scientist wins environmental award

A computer model of an icosahedral shape, often observed in nanoparticles but not at the macroscale. Photo by: CSIRO

For her work on predicting the stability of nanoparticles in air and water, CSIRO scientist Dr Amanda Barnard has been awarded one of Australia’s most prestigious environmental awards – the 2009 Mercedes-Benz Australian Environmental Research Award.

Presented in Melbourne on Saturday night at the Banksia Awards 2009, the award recognises Dr Barnard’s ground-breaking work on developing computer models designed to predict the stability of nano-particles in different environments.

“Nano-particle research presents exciting opportunities for the development of new technologies, materials and products but, balancing those developments with the need to minimise the environmental impacts, is paramount,” Dr Barnard says.

Using supercomputer simulations, Dr Barnard’s research focuses on enabling scientists to understand how these tiny artificial pieces of matter interact with natural ecosystems.

According to the Awards' judging panel, Dr Barnard has developed an important new approach to modelling the growing array of nano-materials and their interactions with the environment.

“Her approach may provide a way to utilise the advantages of nano-materials in ways that avoid the risks,” the panel said.