Environmental Engineering Reference
In-Depth Information
determining the extent of uptake and toxicity of many nanomaterials, which have
been shown to be size dependent (Chithrani et al. , 2006 ; Limbach et al. , 2005 ). The
size of nanoparticles may have crucial impact on where nanoparticles end up in the
body in humans and other organisms. In humans, large inhalable nanomaterials
tend to deposit primarily in the nose and throat while smaller particles can fi nd
their way to the upper airways. The smallest particles can penetrate deeper into the
alveolar region and might penetrate to different parts of the respiratory tract.
Because of their small size, nanomaterials can potentially pass through the lungs
into the bloodstream and to be taken up by cells, reaching potentially sensitive sites
such as bone marrow, liver, kidneys, spleen and heart. When ingested, nanomaterials
can end up in the liver, the spleen, the kidneys and elsewhere. Skin penetration is
poorly studied, but nanomaterials smaller than 50 nm may penetrate the skin more
easily, although a number of initial studies suggest that dermal uptake is low in
healthy skin (Borm et al. , 2006a ; Oberdorster et al. , 2005b. Further, the size of
nanomaterials is an important factor in determining their uptake across the gill
membrane or the gastrointestinal tract (GI) of aquatic and terrestrial organisms,
due to passive diffusion to the cell and the ability of nanomaterials to penetrate
the cell membrane. It has been suggested, for instance, that the absolute limit for
passive diffusion through fi sh gills is about 1 nm (Nitta et al. , 2003). For more details,
the reader is referred to the reviews by (Borm et al. , 2006a ; Oberdorster et al. ,
2005b) and to Chapter 9.
The aspect ratio (length/thickness) of nanoparticles along with biological
persistence is likely to be an important factor in their toxicology. Concerns
about the aspect ratio of nanomaterials stem from the previous knowledge of fi bre
toxicology, especially studies on synthetic vitreous fi bres and asbestos, which iden-
tify the important role of length in pulmonary bioresistance (Oberdorster et al. ,
2007). Fibres longer than (
m) cannot be phagocytosed by alveolar macro-
phages, causing reduced clearance and accumulation. Recent work has shown,
dependent on structure, that carbon nanotubes (CNTs) act in a similar manner to
asbestos and may have an even greater biological activity and therefore hazard
(Poland et al. , 2008 ).
Particle composition and surface charge are also important factors determining
the uptake and toxicity of nanomaterials. Mineral particle induced apoptosis was
dependent on particle size, whereas composition and surface reactivity were found
to be most important for the proinfl ammatory potential of the particles (Schwarze
et al. , 2007). Surface charge may alter the blood-brain barrier integrity and perme-
ability in mammals (Lockman et al. , 2004). The effect of the properties of nanoma-
terials on their uptake and toxicity is discussed in detail in Chapters 7 and 9.
2 0
µ
1.13
Environmental Fate and Behaviour of Nanomaterials
The potential environmental fate and behaviour of nanomaterials are not yet
well understood and available studies are scarce. Determining the fate and behav-
iour of nanomaterials in the environment requires understanding of potential
sources of nanomaterials (Section 1.9), their fate in air, soil and water (Chapters 4
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