Bioaccumulation of radio-labeled carbon nanotubes by Eisenia foetida. 
Carbon nanotubes comprise a class of nanomaterials having demonstrated promise for broad ranges of potential applications.  Because of difficulties associated with quantifying these materials in environmental media, however, their behaviors therein and associated potential risks are yet largely unknown.  To address this problem, a modified chemical vapor deposition process employing carbon-14 labeled methane was used to synthesize single- and multi-walled carbon nanotubes.  The labeled nanotubes and a representative polynuclear hydrocarbon, pyrene, were then individually spiked to identical soil samples.  The uptake and depuration behaviors of the spiked materials by the earthworm Eisenia foetida, a potential entry point to terrestrial food chains, were then assessed.  Bioaccumulation factors determined for the nanotubes were almost 2 orders of magnitude smaller than those measured for pyrene, indicating that purified carbon nanotubes, unlike pyrene, are neither readily absorbed into organism tissues nor manifest equilibrium partitioning thereto.