Environmental Engineering Reference
In-Depth Information
This makes the size of particles or the scale of its features the most important attribute of
nanoparticles. What is different about a nanoparticle?
There is no strict dividing line between nanoparticles and non-nanoparticles. The size at which
materials display different properties as compared with bulk material is material dependent and can
certainly be claimed for many materials much larger in size than 100 nm.
Most experts in United Kingdom and United States deine nanoparticles as particles smaller than
100 nm. But, for example, in Japan, particles between 50 and 100 nm are classiied as “ultraine”
and only those below 50 nm in one dimension as nanoparticles. Even some agencies in United States
use the term “ultraine” to describe particles under 100 nm (usually in connection with natural or
incidental nanoparticles).
In order to solve such discrepancies, national and international agencies such as International
Organization for Standardization (ISO), International Electronically Commission (IEC), American
National Standard Institute (ANSI), and American Society for Testing Materials (ASTM) are discussing
the standardization of terminology, metrology, characterization, and approaches to safety and health.
Another deinition from Malvern.com is as follows:
A particle having one or more dimensions on the order of 100 nm or less. There is a note associ-
ated with this deinition: “novel properties that differentiate nanoparticles from the bulk material
typically developed at a critical length scale of under 100 nm.”
The “novel properties” mentioned are entirely dependent on the fact that at the nanoscale, the
physics of nanoparticles mean that their properties are different from the properties of bulk material.
It should be noted that these nanoparticle deinitions require special consideration. First,
because in practice nanoparticles represent a complicated structure, it is not easy to measure its
linear size.
We can say also that the second part of the deinition stated that nanoparticles may or may not
exhibit properties completely different from the ine particles or bulk materials, can be call in
question.
In Oberdörsted et al. it was demonstrated that nanoparticles appeared to be more inlammatory
in the lungs than microscale particles. But if the data were plotted against surface area instead of
mass, response was identical for both nano and larger particles (Dufin et al., 2007; Oberdörster
et al., 2005).
In other words, in principle there is no difference between the nanoparticles, ine particles, and
bulk materials. The difference is only that in the case of nanoparticles the ratio of the number of
molecules on the surface to all molecules of particle “surface to volume ratio” (SVR) is much higher
than that of ine particles or bulk materials.
The importance of the surface area as a dosimetric parameter in the study of health effect of
nanoparticles is shown in Dufin et al. (2007).
Of course not only the surface area is responsible for nanoparticles toxicity, but rather surface
area in combination with surface reactivity, and elemental toxicity. Still the surface area is likely the
best dose metric in the case of nanoparticles (Kelly, 2009).
Based on this consideration we propose another deinition for nanoparticles based on the ratio
of molecules on the surface to all molecules of the particle. As an appropriate number for this SVR
boundary portion we propose 3% or 0.03%, which corresponds to spherical particles with a diam-
eter of 100 nm.
Our proposed deinition of the nanoparticles:
Nanoparticles are particles which have the ratio of number of molecules on the surface to all particle
molecules, surface to volume ratio (SVR), of 3% (0.03) or higher.
16.1.3 n
anorisk
First, we have to present the deinitions of all particular parameters associated with the risk, and
consequently the dose as a cause of biological effect in the case of nanoaerosols.
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