Nanowaste: Predicting the environmental fate of buckyballs

As companies gear up to make industrial quantities of nanomaterials, worries mount about the safety of these products should they end up contaminating the environment. A new study indicates that buckyballs, one of the most well-studied nanomaterials, undergo considerable changes in different aquatic environments. So, their effects probably will vary from place to place.

A buckyball is made up of 60 carbon atoms arranged into the shape of a miniature soccer ball. How buckyballs react in natural aquatic ecosystems is a matter of special concern because laboratory studies have shown that this nanomaterial can damage brain cells of fish (SN: 4/3/04, p. 211: Tiny Trouble: Nanoscale materials damage fish brains).

Buckyballs could soon find their way into pharmaceuticals, solar cells, batteries, and many other products. By 2007, Frontier Carbon Corporation based in Tokyo, expects to produce about 10 tons of buckyballs annually.

Recalling all-too-sobering experiences with chemicals such as DDT and PCBs, Joe Hughes is working to determine potential hazards of nanomaterials and to alert manufacturers before they ramp up production. “PCBs were fabulous for what they were designed to do, but when they got into the environment, they had bad effects,” says Hughes, an environmental chemist at the Georgia Institute of Technology in Atlanta. “We want to avoid those kinds of legacy issues.”

Reporting in an upcoming Environmental Science & Technology, Hughes and his colleagues at Rice University in Houston analyzed the chemical and physical behavior of buckyballs in water. Because buckyballs repel water, the researchers thought that the materials would not dissolve and would therefore be unlikely to affect fish and other organisms.

When the researchers mixed buckyballs with water, however, the carbon molecules aggregated into crystal structures. Dubbed nano-C60, the aggregates contained up to several hundred thousand buckyballs. The crystal’s surface is negatively charged, and the researchers suspect that the charge permits nano-C60 to remain suspended in water.

“It was such a surprise,” says Hughes. “Just by looking at the chemical properties of buckyballs, one would never expect to find them in any appreciable amount in water,” he says. The researchers also discovered that low concentrations of nano-C60 halted the growth of bacteria.

The water’s chemistry strongly influenced how much nano-C60 remained suspended. For instance, when Hughes’ team increased the salt concentration to approximate that of seawater, the buckyball aggregates sank to the bottom. The salt’s positively charged sodium ions surrounded the negatively charged nano-C60, neutralizing the crystals, explains coauthor John Fortner.

Although seawater and fresh water have more-complicated chemical compositions than do the solutions that Hughes’ group formulated in the laboratory, the scientists’ findings suggest that in brackish or salty environments, buckyballs are likely to accumulate in sediments instead of dissolving in water.

Ronald Turco of Purdue University in West Lafayette, Ind., says that the new research “is going to change our perception of how these materials could enter and behave in the environment.”

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