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Factors Influencing the Partitioning and Toxicity of Nanaotubes in the Aquatic Environment.

Kennedy AJ, Hull MS, Steevens JA, Dontsova KM, Chappell MA, Gunter JC, Weiss CA

Carbon nanotubes (NTs) may be among the most useful engineered nanomaterials for structural applications but could be difficult to study in ecotoxicological evaluations using existing tools relative to lower aspect ratio nanomaterials. While the hydrophobicity and van der Waals interactions of NTs may suggest aggregation and sedimentation in aquatic systems, consideration to how engineered surface modifications influence their environmental fate and toxicology is needed. Surface modifications (e.g., functional groups, coatings) are intended to create conditions to make NTs dispersible in aqueous suspension, as required for some applications. In the present study, column stability and setting experiments indicated that raw multi-walled nanotubes (MWNTs) settled more rapidly than carbon black and activated carbon particles, suggesting sediment as the ultimate repository. However, the presence of functional groups slowed the settling of MWNTs (increasing order of stability: hydroxyl > carboxyl > raw), especially in combination with natural organic matter (NOM). Stabilized MWNTs in high concentrations of NOM provided relevance for water transport and toxicity studies. While aqueous exposures of raw MWNT decreased Ceriodaphnia dubia viability, such effects were not observed in exposure to functionalized MWNT (> 80 mg/L). Sediment exposures of the amphipods Leptocheirus plumulosus and Hyalella azteca to different sizes of sediment-borne carbon particles at high concentration indicated mortality increased as particle size decreased, although raw MWNTs induced lower mortality (concentration inducing 50% lethality (LC50) = 50 to >264 g/kg) than carbon black (LC50) = 18 to 40 g/kg) and activated carbon (LC50 = 12 to 29 g/kg). Our findings stress it may be inappropriate to classify all nanotubes into one category in terms of their environmental regulation.

Published 13 May 2008 in Environ Toxicol Chem.
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