(157f) Targeted Removal of Bioavailable Metal as a Nanotube Detoxification Strategy

The carbon nanotube community has a window of opportunity to understand and manage nanotube health risks before manufacturing becomes truly widespread. Ultrafine transition metal particles pose documented health risks upon inhalation, but their contribution to nanotube toxicity has been unclear due to their apparent encapsulation by carbon shells. The degree of encapsulation is a key toxicity variable because the major biomolecular pathways of metal toxicity involve soluble ions, which must first be ?mobilized? from metal nanoparticles, or made "bioavailable" by reactive dissolution processes that require fluid access.

Recently we developed quantitative assays for the bioavailability of Ni, Fe, and Y in carbon nanotubes, and applied them to study the effects of nanotube source, physiological fluid properties, and common nanomaterial stresses (sonication, oxidation) on metal bioavailability. We found that from 0.5% to 10% of the total metal is typically bioavailable, and the corresponding release can lead to toxicologically significant metal concentrations in either extracellular or intracellular spaces.

Here we explore the potential for reducing nanotube health risks by selectively removing the small fraction of the total metal that is found to be bioavailable. This talk presents results of nanotube treatment with non-oxidizing acids and chelating agents, and examines the effects of pH, time, wash protocol, and re-deposition of metal on nanotube outer surfaces by ion exchange. By targeting the bioavailable rather than the total metal, it is possible to identify simple purification protocols that may reduce nanotube health risks without causing tube damage.