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Assessing the ecotoxicology of MWCNTs
02/11/2009
A study published this month in Environmental Science & Technology (ES&T) assesses the influence of multi-walled carbon nanotubes (MWCNTs) dispersed in natural organic matter on the speciation and bioavailability of copper.
Both single- and multi-walled carbon nanotubes have attracted widespread interest for commercial and industrial applications due to their novel properties, such as high tensile strength, low weight, high electrical and thermal conductivity. Despite rapid growth in the manufacturing and use of CNTs, however, concerns have been raised about their potential adverse effects on both human health and the environment.
Natural organic matter (NOM), broken down organic matter from plants and animals whish is ubiquitously present in the environment at concentrations ranging from 1-100 mg/l, plays an important role on the fate and behaviour of xenobiotic compounds in aquatic ecosystems. The consideration of potential interactions between MWCNTs and NOM is therefore an important component in assessing their behaviour in the environment.
Within this study, Kim et al. have studied the speciation and bioavailability of copper (Cu), a toxic heavy metal prevalent in the environment, in MWCNTs-associated NOM using Daphnia magna (a type of planktonic crustacean). The researchers firstly investigated the binding affinity of Cu for both MWCNT-associated NOM and NOM alone using titration methods, revealing that Cu had a lower binding affinity for MWCNTs-associated NOM. Thus, the free Cu2+ concentration was higher in the presence of MWCNTs, increasing proportionally with increased MWCNT concentrations. The free Cu2+ ion activity was found to increase even by the addition of a low non-toxic concentration of 1.0 mg/l of MWCNTs.
The fractionation of NOM was then measured using Fourier Transform Infrared Spectroscopy (FTIR), in order to investigate the influence of Cu and MWCNT additions on the NOM’s functional groups. The resulting spectra showed clear differences in features for Cu spiked with NOM and MWCNTs-associated NOM. Based on analysis of the FTIR spectra, the authors suggest that the interruption of Cu binding was probably due to steric stabilisation of the MWNTs dispersed in NOM, resulting in inhibition of complexation by making the NOM functional groups less favourable 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 Cu2+ 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.
Using a Daphnia magna bioassay, Kim et al. investigated mortality and reactive oxygen species (ROS) production for both MWCNT-associated NOM and NOM alone. The mortality and biochemical (ROS production were enhanced in MWNTs-associated NOM compared to NOM alone, which the authors attribute to the increased free Cu2+ ion activity as indicated from the titration and FTIR results. Investigations of the Cu bioavailabilty in the presence of NOM and MWCNTs was also evaluated, and shown to increase in the precense of MWCNT-associated NOM.
The authors conclude that "…the interaction between stabilised MW[C]NTs in NOM and other coexisting toxic compounds should be seriously considered when the environmental risks of carbon nanomaterials are evaluated."
Source: ES&T
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