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when it is relatively inert (Handy et al.
2008
; Dur
´
n et al.
2014
). A recent research
indicates that nanomaterials have different toxicity profiles compared to large
particles, due to their small size and high reactivity (Brayner et al.
2010
). Some
studies suggest that nanomaterials, for their small size, may have a higher perme-
ability through the skin, mucous membranes, and cell membranes, what may
magnify their toxic effect. A classic example is gold, which is virtually an inert
metal, but becomes reactive in the nanoparticle form (Paschoalino et al.
2010
).
However, one may consider that this is a relatively new subject, and then it is still
uncertain whether the environmental impact of materials is inversely proportional
to their size—thus the ecotoxicity profiles cannot be generalized, which makes the
study of the materials on a case-by-case basis necessary.
For humans (and consequently for other organisms), the exposure to these
nanomaterials can occur directly or indirectly (Nel et al.
2006
). Humankind can
be exposed to these materials since their synthesis and production of derived
products (occupational exposure) until their end use (consumer exposure), also
including their removal and subsequent accumulation in the environment (environ-
mental exposure). The main routes of entry of nanomaterials into the human body
are the skin, gastrointestinal and respiratory tracts, either by the use of topical
creams or oral medications or by contact with water, air, and contaminated soil
(Hagens et al.
2007
; Mihranyan et al.
2012
).
The nanoparticles can be found in nature in two main forms. They can be
immobilized in/at a larger size material (composite, functionalized nanoparticles,
part of the surface of a micronized material, etc.) or be free nanoparticles, capable
of mobility in the environment and in the human body (Hansen et al.
2008
). The
latter is the most worrying from a toxicological point of view.
The complexity of nanoparticle effect lies, in part, in their ability to bind and to
interact with biological material, changing its surface characteristics depending on
the environment in which they are into. The latest scientific knowledge on the
interaction mechanisms of cells and nanoparticles has indicated that many cells
readily internalize the nanoparticles through either active or passive mechanisms.
At intracellular level, however, the mechanisms and pathways are more difficult to
understand. Even the same material particles may have completely different behav-
ior due to slight differences in surface coating, drug load, or size. This is one of the
main distinctions between classical toxicology and nanotoxicology. Moreover, the
filing of bioassays involving nanomaterials is still in development and in general
has not yet been internationally validated (Elsaesser and Howard
2012
).
This chapter aims to discuss the toxicological impact of some nanomaterials,
such as ZnO, TiO
2
, and BaTiO
3
nanoparticles. We will emphasize the importance
of nanomaterial characterization before biological tests.
