Carbon nanotubes (CNTs) are often modified for different intended applications which often changes the nanotubes physicochemical properties, such as surface charge. Assessing the extent to which such modifications to carbon nanotubes influence their ecotoxicity, accumulation, and elimination behaviors are thus needed to understand the potential risks of these nanoparticles. We have modified carbon-14 multi-walled nanotubes (MWNTs) with polyethyleneimine (PEI) surface coatings to make the MWNTs more stable in water and to give them positive, negative, or neutral surface charges. Daphnia magna were exposed to these nanotubes and acid-modified MWNTs at concentrations of approximately 40 and 400 μg/L and uptake and elimination behaviors were investigated. Surprisingly, PEI surface coatings did not appear to substantially impact nanotube accumulation or elimination rates. Elimination of the carbon nanotubes was not evident in all samples at both concentrations in the absence of algae, yet near complete removal was observed under most conditions with algae feeding. Even though PEI-modified nanotubes were more stable in solution, they appeared to aggregate in the guts of D. magna similarly to acid-treated nanotubes. These findings also highlight that the presence of a food source will significantly influence the ability of daphnia to eliminate carbon nanotubes. The toxicity of these nanotubes increased with the presence of PEI coatings in a manner that corresponded to the size of the PEI coatings instead of their surface charges.
Citation: Environmental Science & Technology
Pub Type: Journals
Ecotoxicity, fullerenes, nanotoxicology