Page 413 - Book Hosokawa Nanoparticle Technology Handbook

CHAPTER 7 ENVIRONMENTAL AND SAFETY ISSUES WITH NANOPARTICLES

7.1 Introduction from the land. On the other hand, the latter particles
are brought about by human activities. Although
occupying only 16% of the total emitted particles,
Since nanoparticles have superior surface activity their size is mostly of submicron order and because
and can be applied to the production of particles they contain hazardous chemical components such as
with various functions, they are extremely impor- nitrates, sulfates, hydrocarbons, heavy metals, etc. in
tant for the future development of sophisticated high concentration, their effects on the ecosystem are
material technologies. On the other hand, this supe- serious.
rior activity of nanoparticles is a cause of trouble Fig. 7.2.1 shows an overview of the size and con-
from the perspective of safety, and does not always centration ranges of various aerosol particles. As it
have a positive influence on the environment. can be seen, the number concentration of atmos-
Attention must also be paid to impact on health. pheric aerosol which we inhale every day ranges
Nevertheless, all technologies have negative from several thousand particles per cm in clean area
3
aspects, and overcoming these kinds of problems, to several hundred thousands in dusty areas, and the
we will be able to utilize the superior characteristics size range lies between 10 nm and several tens of
of nanoparticles for practical purposes. To achieve micrometer.
this goal, it is necessary to fully understand the Fig. 7.2.2 shows mass-based size distribution of
influence of nanoparticles on the environment and atmospheric aerosol particles. Since the size distri-
the relevant safety issues. bution in the nanosize range appears only when the
This chapter evaluates the relationship between
nanoparticles and the environment, and also describes sources of particle generation exist, the size distri-
bution is usually bimodal with peaks in the size
the trouble caused by nanoparticles as well as the range of a few to 10 micron and submicron. The for-
safety issues. mer peak consists of naturally generated coarse par-
The relationship between nanoparticles and the
environment will be clarified from the viewpoint of ticles such as soil dust, sea salt spray, and so on. On
the contrary, the latter contains plenty of artificially
what kind of influence nanoparticles generated either generated particles, some of which grow from mole-
artificially or naturally have on the environment. The cules (in most cases vapor state) exhausted by
influence on the indoor environment, where nanopar- human activities through chemical reaction, conden-
ticles are produced, will also be clarified. sation, and coagulation. Particle growth rarely leads
The safety of nanoparticles will be clearly described
from the perspective of the trouble caused by the supe- to particles larger than 1 m unless high concentra-
tion of vapors or particulate matters which cause the
rior surface activity of nanoparticles; the effect of the above-mentioned growth mechanisms exist in the
compositional characteristics of nanoparticles, and atmosphere.
also the influence on health. A method for assessing As it can be seen from the differences in the parti-
the influence of nanoparticles using quantum dots is cle generation process, fine particles generated from
also explained. In the final section, methods for molecules or nanoparticles are much more compli-
removing nanoparticles from gas and liquid are cated in their chemical component than the coarse
described as technology to control the influence of particles, and sometimes have serious adverse health
nanoparticles on the environment.
effects. Such fine particles are called PM2.5, which is
defined for particles less than 2.5 m including nano-
sized particles. Recent epidemiologic investigation
7.2 Nanoparticles and environment
reports that the concentration of PM2.5 showed a pos-
itive correlation to the mortality due to pulmonary
7.2.1 Nanoparticles in atmospheric environment diseases [1].
Various research techniques are used in order to
In our atmospheric environment, particles ranging understand the process of particle growth and to
from several nanometers to several tenth micron orders trace back to the source of pollution. An example is
are suspended. They are emitted into the atmosphere at shown in Fig. 7.2.3 where a characteristic function
the rate of 2.5 billion tons every year. Emission sources of sulfur dioxide is shown taking into account all
are classified as either natural or artificial. possible factors related to particle growth. Where f is
Natural particles occupy 60% of total particles, the characteristic function that expresses particle
consisting mainly of salt particles ( 1 billion ton) size, particle concentration, particle composition,
from the sea and soil particles ( 0.5 billion ton) and so on [2, 3].

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