Jun 6, 2005
Buckyballs could restrict growth of soil bacteria
Researchers at Rice University and Georgia Institute of Technology in the US have found that the nano-C60 aggregates that may form when C60 molecules are exposed to water can have a detrimental effect on soil bacteria. Under certain conditions, the aggregates restricted the bacteria’s growth and respiration rates.
“We have found that these C60 aggregates are pretty good antibacterial materials,” said Joseph Hughes of Georgia Tech. “It may be possible to harness that for tremendously good applications, but it could also have impacts on ecosystem health.”
C60 molecules have a solubility of less than 10-9 mg/L in polar solvents such as water. But the molecules can also form colloidal nano-C60 aggregates with diameters of 5-500 nm that have solubilities in water of up to 100 mg/L.
“We haven’t really thought of water as a vector for the movement of these types of materials,” said Hughes.
The team tested the response to nano-C60 of two types of bacteria that are commonly found in soil - the Gram-negative Escherichia coli DH5α and Gram-positive Bacillus subtilis CB315.
The aggregates prevented growth of both types of bacteria in a minimal media at relatively low concentrations of nano-C60 (>= 0.4 mg/L). In a rich growth media, however, bacterial growth did not stop until nano-C60 concentrations of more than 2.5 mg/L were reached. The scientists believe this may be because the media salted the fullerenes out of solution or coated them with excess protein.
Similar C60 concentrations also reduced bacterial respiration rates, whereas hydroxylated fullerenes (C60(OH)22-24) did not significantly affect respiration.
Hughes and colleagues also found that the aggregates contained underivatized C60, had an ordered crystal structure, and that their size and stability depended on the conditions under which they formed, such as the rate of water addition and the pH of the solution.
The aggregates were not stable in solutions simulating seawater or brackish waters. But in solutions with ionic strengths of or below 0.05 I, as in most freshwater environments, an “appreciable percentage if not all” of the aggregates remained stable for 15 weeks.
Current guidelines in the US for the handling and disposal of buckyballs are based on the properties of bulk carbon black. But Hughes says that buckyballs have different properties from this bulk material and should be treated differently.
“As information becomes available, we have to be ready to modify these regulations and best practices for safety,” said Hughes. “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.”
The researchers reported their work in Environmental Science & Technology
About the author
Liz Kalaugher is editor of nanotechweb.org.