Biomedical Engineering Reference
In-Depth Information
Finally, a word of caution should be said about the use of nanoscale zero-
valent iron for the remediation of contaminated groundwater, a most widely
studied environmental application of nanotechnology [19,42,54,63]. The eco-
logical evaluation of nanoiron is not available; however, the possible neuro-
toxicity of nanoscale zero-valent iron has been studied in rodent cells [63].
Complete or partial oxidation of nanoscale zero-valent iron was found to
be effective in decreasing the toxicity, as well as agglomeration, sedimen-
tation rate, and “redox” activity [63]. These results suggest that weathering
or aging of the nanoiron will decrease the environmental burden at treated
sites, although ecotoxicological data are still essential.
10.3.2 Carbon-Based Nanomaterials
Localization of redox-active carbon-based NMs into cell membranes
prompted additional research on their toxicity for aquatic receptors [112].
Because underivatized fullerenes (C
60
) and single-walled or multiwalled
CNTs are almost insoluble in water, it is difficult to measure their toxicity
in aqueous medium [4,112]. The earlier study on tetrahydrofuran (THF)
as a cosolvent and carrier of C
60
(and nanotubes) has shown high toxic-
ity, whereas recent toxicological data suggest that water-stirred fuller-
ene has a low toxicity for a number of ecological receptors. The toxicity
observed for THF-C
60
was later shown to be due to the presence of C
60
-
bound degradation products of THF, notably gamma-butyrolactone [13].
Further investigations on the bioavailability of environmental contami-
nants bound to C
60
or CNT may be warranted as these NMs can transport
toxicants across cell membranes [113]. From the data summarized in Table
10.3, fish appear particularly sensitive to the effect of carbon-based NPs,
and bacteria are quite resistant. As discussed for other NPs, exposure to
C
60
in complex medium (soil, humic matter) strongly reduced the toxicity
[14,114,115].
10.3.3 Organic Nanomaterials, Nanopesticides,
Polymers, and Dendrimers
In addition to pesticides, organic NMs in the general class of nanopharma-
ceuticals may also become environmental contaminants, similar to hor-
monally active drugs (known as an endocrine disruptors), when released
into the environment through wastewaters. It is not apparent whether the
nano-based drugs emerging from biomedical nanotechnology will have
to be tested for ecotoxicity. While preliminary toxicological information
is available for polymers and dendrimers (polycationic organic NP), little
information is known for the nanopesticides, including their fate. Despite
the constant NM development, the prior knowledge existing on these gen-
eral classes of compounds suggests that they may have an impact on the
environment.
