Biomedical Engineering Reference
In-Depth Information
and interact with their specific biota. Once deposited in the soil, they can cause contamination or
seep into the groundwater. NMs in solid wastes, effluents, waste water, or accidental spillages can
be transported to aquatic systems by wind or rainwater.
NMs can play an important role in ecotoxicity by serving as carriers of various substances, some
of which may be harmful. As the presence of environmental NMs could potentially have an effect
on the bioavailability of living organisms, the persistence of NPs is being recognized as one of the
key factors in environmental effects assessments. Several assays for the ecotoxicological testing
of NMs have been developed, but the challenge in analyzing environmental concentrations is still
dependent on reliable methods and analytical tools (Tuominen and Schultz 2010).
The toxicity of metallic NPs on bacteria has been described through various mechanisms that
govern toxicity as well as the usefulness of bacterial systems to study the toxicity of manufactured
NPs (Niazi and Gu 2009) (Figure 1.10). C
60
fullerene suspensions have been found to be toxic to bac-
teria (Lyon et al. 2005, 2006), fathead minnows (Zhu et al. 2006), and zebra fish embryos (Usenko
et al. 2007, Zhu et al. 2007). SWCNT-based NMs have been shown to be toxic to estuarine copepods,
Daphnia
, and rainbow trout (Roberts et al. 2007, Smith et al. 2007). The ZnO NPs were found to be
more toxic to
Bacillus subtilis
as compared to aqueous TiO
2
and SiO
2
NP suspensions (Adams et al.
2006). The ecotoxicity of ZnO NPs was found to be significantly higher than that of TiO
2
or Al
2
O
3
NPs on embryonic zebra fish experimental models (Zhu et al. 2008). A dose-dependent increase in
acute toxicity was demonstrated (Zhu et al., 2006) to
Daphnia magna
in a 48-h study with water
suspensions of six manufactured NMs (i.e., ZnO, TiO
2
, Al
2
O
3
, C
60
, SWCNTs, and multiwall carbon
nanotubes (MWCNTs)), using immobilization and mortality as toxicological endpoints.
Zebra fish embryos are a useful model system for judging NM toxicity because of the similari-
ties between the zebra fish and human genomes, early life development, and disease processes. The
reduced toxicity of ZnO NMs was evaluated on fish embryos upon Fe doping in ZnO (Xia et al. 2011).
The release of NPs to the environment from its limited use and from disposable products is of
particular concern. Released NMs can readily undergo transformations via biotic and abiotic pro-
cesses. Understanding the fate of engineered NMs under environmental transformations will be
useful in evaluating the design and development of environmentally benign NMs, as well as their
use as environmental tracers in environmental sensing and contaminant remediation. This was
demonstrated in a biomimetic, hydroquinone-based Fenton reaction, which provided a new method
by which to characterize the expected transformations of nanoscale materials that occur under oxi-
dative, environmental conditions (Metz et al. 2009). Current computational techniques are being
used to study the interactions of NPs with biological systems (Makarucha et al. 2011). Such studies
could also be used to complement experimental data on toxicity.
Cd
2+
+
Release hazardous constituents,
e.g., metals, ions
Ag
+
-
Interrupt electron
transport/respiration
Disruption of
membrane/
membrane potential
DNA
Damage DNA
e
-
CYP
Protein
e
-
ROS
Protein
Produce reactive
oxygen species (ROS)
Oxidize/damage
proteins
FIGURE 1.10
Biointeractions of nanomaterials. (Reprinted with permission from Klaine, S. J. et al. 2009.
Environmental Toxicology and Chemistry
27(9):1825 -1851.)
