The same properties of nanoparticles that make them so appealing to manufacturers may also have negative effects on the environment and human health, analysis has indicated.
The analysis was done by an international team of researchers from the Center for the Environmental Implications of NanoTechnology (CEINT), based at Duke University, US.
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.
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 CEINT.
"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 said.
"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," he added.
"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.