Biomedical Engineering Reference
In-Depth Information
harm to aquatic organisms. In contrast, CNTs were found to be suspended
at fairly high concentrations in turbulent stream waters containing natu-
ral organic matter [42]. Whether NMs can induce toxicity in environmental
health is described below.
10.3 Ecotoxicity of Nanomaterials
Most of the toxicological studies of NMs have been carried out using lab-
oratory animals or mammalian cells
in vitro
. Animal studies have shown
that inhaled NPs (e.g., polystyrene beads, airborne ultrafine particles) are
removed less efficiently than larger particles by the macrophage clearance
mechanisms in their lungs, thereby causing lung damage; NPs can translo-
cate through the circulatory, lymphatic, and nervous systems to many tis-
sues and organs, including the brain [2,55]. It can be anticipated that these
effects shown in laboratory animals (rat and mouse) would also be observed
in animals in the wild life upon exposure, with respect to the dose and simi-
lar routes of exposure. On the other hand,
in vitro
results cannot be directly
extrapolated to environmental conditions because additional factors, such as
bioavailability and uptake by biota, are not considered.
In regard to the role of NPs on the ecotoxicity, little or no data can be found
for protists, fungi, birds, reptiles, and amphibians. Most of the studies there-
fore refer to aquatic receptors (microbes, alga, invertebrates, and freshwater
or marine water fish) or to terrestrial receptors (invertebrates and plants). The
information presented here are according to six general classes of NMs: met-
als/metal oxides/semiconductors, carbonaceous compounds, and pharma-
ceutical and industrial organic polymers. The US Environmental Protection
Agency uses a fourth class of NMs called composites. Two examples of com-
posites (Ag-doped TiO
2
and Pt-loaded TiO
2
) were presented under the metal/
metal oxide section because only limited ecotoxicity data are available [56].
Ecotoxicity information for other types of composites such as nanocarbon or
nanocellulose fiber-based materials is not available.
10.3.1 Metal, Metal Oxide, and Semiconductor-Based Nanoparticles
Several metal and especially metal oxide NMs have been in production for
a relatively long time and they are therefore a priority to be studied. Tables
10.1 and 10.2 summarize the available toxicological information. Nominal
(or in some cases estimated) diameters of test particles are reported, when
available. These NMs could be toxic when bioavailability is favored (e.g., in a
low salt medium, absence of organic matter, or solid matrices). According to
the data, bacteria and plants seem to be comparatively resistant (using mass-
based concentrations for exposure) relative to algae and aquatic invertebrates.
