A carbon nanomaterial with multiple industrial applications could pose an environmental risk if released in lakes or rivers, researchers in the United States say.

Laboratory experiments at Georgia Institute of Technology showed carbon nanotubes can remain suspended with water containing organic materials for more than a month, raising questions about their impact if accidentally released into the environment.

These beakers contain various samples of carbon nanotubes or the nanomaterial C60, also known as buckyballs, mixed in water stabilized either by surfactants or natural organic matter.
(Georgia Institute of Technology/Gary W. Meek Photography, Inc.)

Carbon nanotubes are cylindrical carbon molecules, thousands of times narrower than the width of a human hair. They can be several millimetres in length. Some have a single layer of atoms around the outside of the cylinder — called single-walled nanotubes. If they have two or more layers, the nanotubes are referred to as multi-walled. 

Their conductivity and strength have made them the subject of research for potential industrial applications, including use in electronics, computer chips, optics and pharmaceuticals.

The researchers at Georgia Tech discovered carbon nanotubes settle quickly when added to organic-free water.

But when the nanotubes were added to water containing a sample from the Suwannee River, the mixture went dark and cloudy and took four days to settle. Some multi-walled cylinders remained suspended in the water for more than a month.

The results raise new questions about the potential dangers of a release of carbon nanotubes into lake or river systems.

Jaehong Kim, an assistant professor in the Georgia Tech School of Civil and Environmental Engineering, told the Georgia Tech Research News on Monday new emphasis must be placed on how these materials are stored.

"Natural organic matter [NOM] is heterogeneous," he said. "It's a complex mixture made from plants and micro-organisms, and it's largely undefined and variable depending on the source."

"So we have to continue to study nanomaterial transport in the lab using various NOM sources to try to better understand their potential interaction in the natural environment."

The scientists have expanded their research into other carbon nanomaterials, including "buckyball" molecules, a carbon nanostructure in which carbon atoms form a sphere.