Environmental Engineering Reference
In-Depth Information
aerosols showed that such particles induced signiicant pulmonary inlammatory responses as well
as effects in extrapulmonary organs (Oberdörster et al., 2005).
Yet, without direct measurements of the response in humans with accurate dosimetry we cannot
make conclusive estimates of the risks. Examples of the safe use of radioisotopes to label aerosol
particles for human inhalation studies are presented in the literature.
A number of studies on the exposure of ultraine and, especially, nanometer aerosols (Donaldson
et al., 1998; Oberdörster et al., 2005), have indicated that health effects associated with low-solubility
inhaled particles may be more appropriately associated with particle surface area than with mass
concentration. Such data on the correlation between number, surface area, and mass concentration
are needed for exposure investigations.
The use of particle surface area as a dose metric for nanoaerosols is discussed in many reports:
NIOSH (2006), Royal Society (2004), NIOSH (2005), NIOSH (2006a), Aitken et al. (2004), DEFRA
(2007), SCENIHR (2006), and ASCC (2006).
It has been mentioned that particle surface area might provide the most suitable criterion for
assessing inhalation exposure. Currently however, there is a need to develop and expand methods
available by which particle surface area can be assessed in the workplace. The main concern is
with free nanoaerosols that are more available for absorption and distribution within the body.
Investigators found that when lung burdens and clearance rates were expressed as a function of the
surface area, there was a much closer correlation with biological responses, ASCC (2006).
The special importance of the surface area of nanoparticles in the study of the risk assessment is
discussed in Maynard (2007) by comparing the three characteristics: particle number, surface area,
and mass concentration.
Another important issue in the safety of people working with nanomaterials is the eficiency of
respirators, discussed in many reports: NIOSH (2006b), Aitken et al. (2004), Renn and Roco (2006).
It is well known that the determining factor governing the effectiveness of RPE is not absolute
penetration through the ilter, but rather face-seal leakage causing particles to bypass the device
(ASCC, 2006; Brown et al., 2001).
Here we discuss a new approach to the measurement of aerosol surface area concentration based
on the rate of deposition of the unattached activity of radon progeny on aerosol particles. The cor-
relation, results of calculation, and the assessment of the sensitivity of this method will be presented.
16.2.1 a
PProacH
: s
aFety
oF
r
adioactive
M
arkers
in
a
erosol
e
xPosure
s
tudy
We may assume that a radioactive marker is safe in an experiment with human subjects if the radia-
tion exposure is negligible relative to the subjects' background exposures. We already discussed in
this chapter the three scenarios of exposure to radon and its decay products.
A comparison of these three cases shows that radiation exposure in the human experiment was
less than 1/1000th the magnitude of the lifetime background exposure. From a radioactive exposure
point of view, the PSI experiment was safe.
Nonetheless, such human experiments need radiation and environmental health and safety reviews.
Also, the type of radiation, half-life, clearance, and the particle size of the markers should be taken
into account. The chemical characteristics and the size distribution of the nonradioactive aerosol
under study are also important in assessing the safety of human exposure experiments. The experi-
ment at the PSI, mentioned earlier, was conducted after a human subject's internal review board (IRB)
approval by the “Uberregionale ehtische Kommision fur klinische Forschung der Schweizerischen
Akademie der medizinischen Wissenschaften” was granted (Butterweck et al., 2001).
The expected fast particle transport from nasal passages, larynx, and mouth to the GI tract was
not found. The explanation may be that a substantial fraction of deposited activity with diameter of
1 nm is bound to lung tissue. The most important aspect of this study is that from a radiation safety
point of view it is possible to provide similar human experiments in laboratory conditions, after
radiation safety and IRB approval.
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