High Aspect Ratio Nanomaterials - Aerosols: Measurement, Dosimetry, and Health Effects - page 244

although several studies have reported CNTs persisting within tissues for extended periods (Elgrabli
et al., 2008; Pauluhn, 2010a). In the study by Osmond-McLeod et al. (2011), the durability of several
CNT samples consisting of both MWCNT and SWCNT was evaluated using artiicial system based
on the use of a ringer's solution (Gambles) developed to mimic the low pH environment of being
digested by a cell. The authors found that to the most part, the CNTs were indeed durable over a
period of 6 months in solution with little loss of pathogenic activity when tested. They did note that
one sample did lose a signiicant portion of its mass, which was relected in a signiicant reduction in
its pathogenicity, which aids the contention that the FPP is relevant and applicable to HARN where
they meet its criteria.
10.4 CONCLUSIONS
In summary, the responsible technological development and application of HARN needs to be
accompanied with adequate and relevant characterization and safety assessment.
The complete chemical characterization of nanoparticles often requires the concurrent applica-
tion of several techniques. In addition to those highlighted, others, including inductively coupled
plasma (ICP) mass spectrometry, nuclear magnetic resonance (NMR), UV-vis, and luorescence
spectroscopy, are widely used to characterize the composition of nanoparticles (Powers et al.,
2007).
Techniques such as Raman and IR spectroscopy have been popular choices for the charac-
terization of HARN to determine impurities, surface functionalization/chemistry, and catalytic
properties. Raman spectroscopy, in particular, has been widely used for the characterization of
CNTs to obtain a variety of information to include structural, chirality, surface modiication/
functionalization, and in the determination of their vibration and electronic energies.
When considering the potential toxicity of HARN, it is crucially important to consider what
form the dose is taking. It should be stressed that the adequate physicochemical characterization of
a sample is of paramount importance. Failure to do this can result in inappropriate comparison and
potentially an under- or overestimation of the relative risks. Likewise, it is nonsensical to say that all
forms of CNT exhibit iber pathogenicity akin to asbestos, as not all CNTs are ibers and even those
which are would be subject to the same criteria which dictate asbestos toxicity. Other important
considerations are the similarities and differences in the behavior of particles in the real environ-
ment compared to those in a test system during hazard assessment (Oller and Oberdörster, 2010).
HARN are available in many different forms based on a wide range of attributes, including
chemical composition, diameter, length, number of walls (for CNT), surface area, level of contami-
nants, without even approaching the various forms of surface functionalizations that are possible.
As such, it is impossible currently to fully assess each form of HARN (or even that of a subset such
as CNT) for adverse health effects using in vivo models. To identify the forms that may pose a haz-
ard and focus attention on these, it is important to identify valid structure-activity relationships and
in vitro techniques, which may help predict toxicity. The FPP is one such structure-activity relation-
ship, which, if used correctly to access truly ibrous material with appropriate controls, could help
identify those HARN that may pose a health risk.
REFERENCES
Adamson, I.Y. and Bowden, D.H. 1987a. Response of mouse lung to crocidolite asbestos. 1. Minimal ibrotic
reaction to short ibres. J. Pathol ., 152(2), 99-107.
Adamson, I.Y. and Bowden, D.H. 1987b. Response of mouse lung to crocidolite asbestos. 2. Pulmonary ibrosis
after long ibres. J. Pathol ., 152(2), 109-117.
Allen, T. 2004a. Particle Size Measurement, Vol 1: Powder Sampling and Particle Size Measurement , 5th edn.
London, U.K.: Chapman and Hall.
Allen, T. 2004b. Particle Size Measurement, Vol 2: Surface Area and Pore Size Determination , 5th edn. London,
U.K.: Chapman and Hall.