Pure buckyballs toxic at 20 parts per billion
In the study, the researchers exposed two types of human cells to various solutions containing different concentrations of buckyballs. Four types of solutions were tested. One contained tiny clusters of smooth-surfaced buckyballs [ie, pure C60]. In the other three, researcher s modified the buckyballs by attaching other molecules to their sides. Researchers measured how many cells died within 48 hours of exposure to each solution, and they repeated the tests until they found the exposure level for each that resulted in a 50 percent mortality rate.
In general, the greater the degree of surface modification, the lower the toxicity. For example, the undecorated buckyballs [ie, C60] showed the highest toxicity — about 20 parts per billion— while the least toxic proved to be buckyballs decorated with the largest number of hydroxyl side-groups . To achieve the equivalent level of toxicity as that of bare buckyballs, the researchers had to increase the concentration of these modified buckyballs by 10 million times to more than 5 million parts per billion.