Environmental Engineering Reference
In-Depth Information
14.1
Introduction and Overview
Nanoparticles have received considerable interest in the past two decades. Their
toxicity for human health is relatively high because they can readily enter the
human body through inhalation and have a large specific surface area. The presence
in the environment of nanoparticle with size ranging from 50 to 200 nm has a
profound impact on human health. Once inhaled, due to their tendency to remain
trapped in the inner respiratory ways, the nanoparticles infiltrate into the blood and
cannot be eliminated, because the macrophage cells cannot identify them. Inhaled
nanoparticles may generate free radicals, affect the DNA, and alter the genes, being
responsible for mutagens and carcinogenic effects or causing a variety of lung-
disease typologies [
1
,
2
].
Filtration of submicron particles suspended in flue gas is an important techno-
logical challenge, as they are produced in large numbers from material synthesis
and combustion emission; in urban environment, the burning processes including
incinerators of waste or diesel emissions are responsible for the emission of a
significant amount of nanoparticles [
2
,
3
]. Along with carbon, dioxide and water,
the gaseous products resulted from combustion processes contain at least traces of
finely divided carbon (VOC), carbon monoxide, oxides of nitrogen, phosphorus and
sulfur, halogen acids, metal oxides and heavy metal vapors. By the de novo
synthesis, VOCs and carbon monoxide in the presence of halogenated acids pass
into the halogen derivatives of dioxins and furans, which are included as such in the
form of nanoparticles or adsorbed on finely divided carbon evacuated through the
flue gas stream, along with the other mentioned components. All chemical com-
pounds contained in flue gas have adverse effect on the atmosphere, biodiversity,
and human body. Spreading both as nanoparticles or adsorbed on finely divided
carbon, they maintain long as very fine suspension in the atmosphere. These are the
most direct ways for pulmonary and blood assimilation, and cells establishment of
these emissions [
1
,
4
,
5
].
From a public health standpoint, the size of a particle is as important as its
composition, recent research showing that although raw materials may not be
dangerous, they can become toxic under the form of nanoparticles [
2
,
3
]. Although
the nanoparticles have smaller masses than microparticles, their number is at least
four orders of magnitude higher than the number of all other particles found in the
flue gas. The pollutant emitting sources are generally equipped with various filters
for particles, but they work only on micrometric particles, while the nanometric
particles almost entirely escape in the environment [
1
,
3
].
In many scientific and technical areas, a considerable interest is shown to the
separation of nanoparticles in accordance with their physical or chemical charac-
teristics, and several methods of nanoparticle manipulation were explored. Due to
the quantum confinement effect, the nanoparticles show distinct physical and
chemical properties depending on the sizes and shapes, particularly when the
sizes are close to or smaller than the dimensions of exciton of the corresponding
bulk materials. However, their wide distributions of sizes always give rise to the
