Influence of multiwalled carbon nanotubes dispersed in natural organic matter on speciation and bioavailability of copper.

The dispersion of multiwalled carbon nanotubes (MWNTs) by natural organic matter (NOM) may influence the bioavailability of MWNTs and other contaminants. The speciation and bioavailability of copper (Cu) in MWNTs-associated NOM was studied using Daphnia magna. Cu titration data indicated that the binding affinity of Cu for MWNTs-associated NOM was lower than that for NOM alone. The free Cu(2+) ion activity was increased even by the addition of a low nontoxic concentration of 1.0 mg/L MWNTs. The 96 h LC(50) of MWNTs was determined to be 2.48 mg/L. The Fourier transform infrared (FTIR) spectra results showed clearly different features in Cu spiked between NOM and MWNTs-associated NOM, indicating that the interruption of Cu binding was probably due to steric stabilization of the MWNTs dispersed in NOM, which inhibited the complexation by rendering the functional groups in NOM less favorable to Cu. The mortality and biochemical reactive oxygen species (ROS) production in the D. magna bioassay were enhanced in MWNTs-associated NOM compared to NOM alone because of increased free Cu(2+) ion activity as expected from the titration and FTIR results. This study suggests the bioavailability of Cu is enhanced by the presence of MWNTs interacting with NOM.