Page 25 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

Nanotechnology and the Environment 11

Ironically, the properties of nanomaterials that may create concern in
terms of environmental impact (such as nanoparticle uptake by cells)
are often precisely the properties desired for beneficial uses, such as in
medical applications. While it may be desirable from the standpoint of
medical therapeutics to have nanoparticles readily taken up by cells, this
same trait may also have negative implications in an environmental con-
text. Early efforts addressing the toxicity of nanomaterials have some-
times yielded results that may be difficult to interpret or even
contradictory, due to evolving methodologies and limited resources.
Studies surrounding the possible health effects of a class of carbon-
based nanomaterials referred to as fullerenes serve as one example.
Medical studies dating as far back as ten years report that the soccer
ball–shaped fullerene molecules known as “buckyballs” are powerful
antioxidants, comparable in strength to vitamin E, while other studies
report that some types of buckyballs can be toxic to tumor cells, cleave
DNA, and inhibit bacterial growth [18–23].
Exposure via inhalation has been an important concern, particularly
in the context of nanomaterials fabrication. Some studies have attempted
to simulate the inhalation of carbon nanotubes, exploring the possibil-
ity that these nanomaterials might damage lungs, as has been observed
with other particles such as silica and asbestos. Although carbon nan-
otubes tend to form large aggregates that may have little opportunity for
transport into the lungs, smaller concentrations of material might be
present in air during fabrication that might not encounter each other
enough to cluster together. Experiments have been conducted wherein
nanotubes were introduced by washing the lungs of laboratory animals
with solutions containing the carbon nanotubes. It is not surprising that
aggregation within the lungs and subsequent suffocation appear to be
the major risks presented in this mode of exposure [7]. Dermal exposure
is also likely to be important for assessing the risks of both nanomater-
ial fabrication and product use. Work on the toxicity of nanomaterials
focused on possible human exposure is reviewed in Chapter 11.
Ecotoxicological studies of nanomaterials are evolving in parallel with
work on toxicity to human cells. Much of the earliest work focused on
fullerene-based nanomaterials. However, studies concluding that bucky-
balls could impair brain functions in fish [8] and were highly toxic to
human tissue cultures [24] are difficult to interpret, in part because
reproducibility in characteristics of the materials used appears to be elu-
sive, and because the nanomaterials used in these studies were con-
taminated with an organic solvent added as part of a process to mobilize
the fullerenes in water. A subsequent study of fullerene toxicity con-
ducted by another group of researchers [25] found no significant toxic-
ity for buckyballs, but did observe a toxic response of cell cultures to a
second group of fullerenes, single-wall nanotubes. Very little is known