Biomedical Engineering Reference
In-Depth Information
effect. According to Oberdörster et al.,
106
biological activity and especially
oxidative stress injury
107
appear to be linked to the surface area of the par-
ticle. Particle size plays a key role on the translocation and transfer inside
the body. For the fate and exposure part, it is unclear if nanomaterial behav-
ior depends on surface or on particle mass or number. Properties playing a
key role are solubility, partition properties (hydrophilic/phobic, lipophilic/
phobic), and bioconcentration/bioaccumulation factors that can be linked to
specific surface groups. Some properties can be calculated based on mol-
ecule structure as proposed by Abraham et al.
108
for Buckminster-fullerene
leading to a
K
ow
of 12.6, which is at the highest range of PAH organics.
109
Fate in the environment:
Little is known about the transport mechanisms
and degradation of nanoparticles in the environment and few studies have
been published.
In water, aggregation and dissolution of pristine nanoparticles, which might
affect their bioavailability and mobility,
110
can be influenced by their size dis-
tribution, shape, surface chemistry, and surface charge, but also by the medi-
um's pH, occurrence of organic matter, ionic strength and valence of cations,
and the presence of humic substances, which might stabilize suspensions
of carbon nanotubes or fullerenes.
111-116
Interaction with biotic or abiotic col-
loids present in the water column has been reported by Ju-Nam and Lead.
117
Therefore, besides nanoparticle-specific properties, differences in composi-
tion between water types (e.g., surface water, marine water, groundwater and
wastewater), regarding the properties discussed above, is a critical factor to
consider when determining transport and fate of nanoparticles in water.
In soil, nanoparticles are transported via pore water before deposition to the
soil matrix takes place. While the transport is mainly driven by the nanopar-
ticles' physical properties, such as size or shape, the deposition depends on the
interaction between the particles (van der Waals force, electrostatic force, and
steric repulsion), as well as hydrophobic forces between particles and the soil
matrix surface.
118,119
These hydrophobic forces are therefore a driving capture
mechanism in soil that can be reduced by functionalization, surfactant capping,
or other alterations induced over time in the environment. These properties
will hence also drive the nanoparticles' mobility in soil,
120,121
and may explain
part of the differences observed in their pore water transport efficiency.122
122
The influence of vegetation on fate and transport of nanoparticles is
unknown. Zhu et al.
123
demonstrated the potential for nanoparticles to be
taken up through the roots and be accumulated in the plant tissue of pump-
kins. However, there is not enough evidence yet to conclude about the influ-
ence of vegetation on the fate of nanoparticles.
While thus far studies have focused on engineered or pristine nanoparticles,
aging or weathering is an important but much neglected factor regarding the
behavior of nanoparticles in the environment, as it is likely to alter physical
properties such as size, shape, surface charge, or functionalization of nanopar-
ticles. This will therefore change the behavior of the nanoparticles in the envi-
ronment owing to the observed importance of these properties as discussed in
