Carbon nanotubes (CNTs) have been the foci of nanotechnological development because of their special material properties and broad potential applications, but the risks they pose to the environmental and human health are not well understood. To characterize these risks, we have developed a methane chemical vapor deposition method for producing 14C-labeled single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs), a technique that allows for direct quantification of unmodified nanotubes in biological and environmental samples. These nanotubes were purified and extensively characterized with Raman Spectroscopy, Transmission Electron Microscopy, Scanning Electron Microscopy, and Thermal Gravimetric Analysis to ensure minimal amorphous carbon and catalyst impurities. Uptake and depuration behaviors of these carbon-14 labeled nanotubes were then tested using representative organisms, earthworms (Eisenia foetida) and oligochaetes (Lumbriculus variegatus). Organism mortality caused by exposure to nanotubes was not observed under any tested exposure condition, and the CNTs were not significantly accumulated by either organism. The calculated accumulation factors in the organisms did not vary based on the duration of exposure or the composition of the soil or sediment, and the calculated nanotube concentration in the organisms was consistently small. Ongoing research related to the uptake and elimination of nanotubes modified to have different solubilities and surface properties will also be discussed.