There’s more cautionary news about buckyballs. At concentrations as low as 0.4 ppm, water-soluble nanocrystalline aggregates of C₆₀ inhibit the growth of two types of common soil bacteria, according to a report from a team at Georgia Institute of Technology and Rice University (Environ. Sci. & Technol., published online April 28, dx.doi.org/10.1021/es048099n). The researchers discovered that at higher concentrations, the aggregates inhibit respiration in the bacteria.

NANO-C60 In the presence of water, buckyballs form the nanocrystalline aggregates seen in this transition electron micrograph.

COURTESY OF JOSEPH B. HUGHES

The study adds to the growing body of evidence for fullerenes’ potentially harmful effects. Earlier reports demonstrated that the C₆₀ aggregates can damage human skin and liver cells (C&EN, Sept. 27, 2004, page 22) and the brains of largemouth bass (C&EN, April 5, 2004, page 14).

Because C₆₀ is made entirely of carbon, many scientists assumed that it would not be soluble in water. Researchers have found, however, that upon contact with water, these molecules aggregate into nanocrystals—dubbed “nano-C₆₀”—having a weakly negative-charged surface that makes them hydrophilic.

Hughes and coworkers also found that nano-C₆₀ forms under a variety of conditions, indicating that the aggregates could have an impact on the environment. Current guidelines for handling and disposing of buckyballs are based on the properties of bulk carbon black. In light of the current research, Hughes suggests that these guidelines may need to be revisited, particularly as the materials reach industrial-scale production.

“As information becomes available, we have to be ready to modify these regulations and best practices for safety,” Hughes says. “If we’re doing complementary studies that help to support this line of new materials and integrate those into human safety regulations, then the industry is going to be better off, and the environment is going to be better off.”