Page 430 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 7 ENVIRONMENTAL AND SAFETY ISSUES WITH NANOPARTICLES
stress resulting in increased intracellular calcium and asbestos. A few data are available concerning the
gene activation; (2) transition metals released from biological effects of carbon nanotubes. The biologi-
particles result in oxidative stress, increased intracel- cal effects of carbon nanotubes are being researched.
lular calcium, and gene activation; (3) cell surface Epithelioid granulomas and interstitial inflammation
receptors are activated by transition metals released are induced in mice and rats following exposure to
from particles, resulting in subsequent gene activation; single-walled carbon nanotubes [18–20]. Untreated
or (4) intracellular distribution of insoluble nanoparti- carbon nanotubes contain the nanoparticles of tran-
cles to mitochondria generates oxidative stress. sition metals such as iron and nickel, which are used
In the workplace, the concentration of nanoparti- as catalysts in forming carbon nanotubes. These
cles may be at a high level and most of the nanopar- nickel-containing carbon nanotubes have been
ticles become agglomerates, while nanoparticles reported to be toxic [19].
will form single nanoparticle at low levels in the The concentration of airborne asbestos fibers is
general environment. It is a matter of debate expressed as a number concentration, that is, fibres
whether agglomerates of nanoparticles react as a per cubic centimeter or fiber per liter. When fiber
larger particle or a single nanoparticle in the lung or concentrations are determined by phase contrast
other organs. light microscopy, the fibers with a diameter of less
If insoluble particles are retained in the lung for a than 3 m, a length longer than 5 m, and a length-
longer time without enough clearance mechanisms, to-diameter ratio (aspect ratio) greater than 3 are
they can cause pulmonary inflammation or pneumo- counted [21]. Asbestos fibers having nanosized
coniosis. It is of interest that nanoparticles deposited diameter were often observed in analyses of envi-
in the lung can move into the blood vessel through ronmental samples using electron microscopy.
alveolar epithelium and they can damage vessels or International Agency for Research on Cancer
produce blood clots [14, 15]. In a recent study, (IARC) rated asbestos as a known human carcinogen
nanoparticles deposited in the nose may move directly (group 1) [22] and the concentration of chrysotile
to the brain via the olfactory bulb [16]. asbestos is expressed as a risk level of 0.15
3
fiber/cm [9]. Health effects of vitreous fibers and
(2) Biological effects of fullerene other asbestos substitutes have been assessed to
The biological effects of fullerene have being inves- determine their OELs or their carcinogenicity in
tigated intensively. In rats dosed orally with humans. The health effects of carbon nanotubes are
radioisotope-labeled C 60 fullerenes, most were being intensively investigated now.
excreted in the feces and some were found in the
urine. A small amount of them can be absorbed via (4) Biological effects of carbon black
the gastrointestinal tract. In contrast, in the same The OEL for carbon black respirable dust is 1 mg/m 3
study, 90% of the same labeled fullerenes adminis- and these for activated charcoal and graphite are 0.5
3
tered intravenously were retained after 1 week, with mg/m in each [9]. In the Ref. [23], while rats and
most found in the liver [17]. mice inhaled carbon black with a particle diameter of
3
LD50s (acute toxicity) by intraperitoneal injec- 30 nm at a concentration of 5–13 mg/m did not
tion in mice and rats were 1.2 and 0.6 g/kg, respec- produce any specific changes, particles (agglomerate
tively. The dose of 2.5 g/kg orally in rats did not of small particles) of 450 nm at a concentration of
3
result in death. The reproductive translocation of 2–6 mg/m produced early pulmonary changes.
fullerenes was also observed in mice. Fullerenes
have shown mutagenic activity in Ames tests. (5) Biological effects of metal oxides
Fullerenes have shown no skin irritation or allergic Micronsized titanium dioxide particles are thought to
reactions [18]. have almost no toxicity and often used as a negative
On the other hand, fullerenes are being tested for control substance. The OEL for titanium dioxide is
3
possible medical use. Fullerenes are basically 1 mg/m for respirable fraction [9]. However, the
hydrophobic but water-soluble derivatives have been results of a series of studies by Oberdörster et al.
synthesized to be used as drugs or its carrier. The [3, 11, 24, 25] on submicron- and nanosized titanium
derivative can be anticipated as drugs, for example, dioxide suggested that as size decreases, inflamma-
anti-AIDS drug. It has been stated that the toxicity of tory effects are intensified, and normally nontoxic
fullerenes changes due to slight structural changes substances may assume hazardous characteristics.
including chemical modification [18]. Fig. 7.3.4 shows a part of the results by Oberdörster
et al. in which rats and mice were exposed to anatase
(3) Biological effects of carbon nanotubes titanium dioxide particles [25]. Their results have been
Carbon nanotubes are chemically stable and are sim- frequently cited in the discussion of whether the health
ilar in form and size to asbestos; these characteris- effects of fine particles should be based on its mass
tics have given rise to concern that carbon nanotubes or its surface area. In Fig. 7.3.4, percentages of
may have the potential to cause pulmonary diseases neutrophils in lung lavage of rats are shown as indi-
such as lung cancer and mesothelioma similar to cators of inflammation after intratracheal instillation

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