Evaluating the safety of nanoscale materials and nanotechnology

Document Sample
Evaluating the safety of nanoscale materials and nanotechnology Powered By Docstoc
					Evaluating the safety of nanoscale materials and nanotechnology-enabled
products

Nigel J. Walker

National Toxicology Program, National Institute of Environmental Health
Sciences, National Institutes of Health, Research Triangle Park, NC 27705, USA
E-mail: walker3@niehs.nih.gov


Abstract
The unique and diverse physico-chemical properties of engineered nanoscale
materials suggest that their toxicological properties may differ from materials of
similar composition but larger size. Studies also suggest that particle size,
surface area and surface chemistry of engineered nanoscale materials can
impact toxicity equally, if not more so, than chemical composition. Ongoing
research is evaluating the toxicological properties of current major nanoscale
materials classes that represent a cross-section of composition, size, surface
coatings, and physico-chemical properties. The studies are designed to
investigate fundamental questions concerning how nanoscale materials are
absorbed and distributed in vivo and whether they can adversely impact
biological systems. Some of these fundamental questions include: What are the
appropriate methods for detection and quantification of nanoscale particles in
tissues? How are nanoscale materials absorbed, distributed in the body and
taken up by cells? Are there novel toxicological interactions? The National
Toxicology Programs 's Nanotechnology Safety Initiative
(http://ntp.niehs.nih.gov/go/nanotech ) is focusing research with respect to
specific types or groups of nanoscale materials to address (1) the fate and
distribution of nanoscale metal oxides and quantum dots in the body following
their dermal application to rodents, with attention given to the role of surface
coating, size, polarity, vehicle, and skin condition on the ability of nanoscale TiO2
to penetrate the skin; (2) whether nanoscale TiO2 applied dermally to mice in
combination with UV-containing light affects cell signaling, and (3) the potential
for TiO2 applied dermally to haired and hairless mice in combination with UV-
containing light to cause skin cancer.

Introduction
Nanotechnology is defined by the National Nanotechnology Initiative (NNI) as
“the understanding and control of matter at dimensions of roughly 1 to 100
nanometers, where unique phenomena enable novel applications.” In theory,
materials that can be manipulated by nanotechnology can be engineered from
nearly any chemical substance. Nanoscale materials (nanomaterials,
nanoparticles), are a broadly defined set of substances that have at least one
critical dimension less than 100 nanometers and possess unique optical,
magnetic, or electrical properties. Ultrafine particulate matter is a well-known
example of nanoscale particles found in the environment. In contrast, fluorescent
semiconductor nanocrystals (quantum dots), organic dendrimers, carbon
fullerenes (“buckyballs”) and carbon nanotubes, and nanoscale metals oxides
such as titanium dioxide are a few of the many examples of what are referred to
as engineered nanoscale materials

While nanomaterials are already appearing in commerce as additives or
modifications to industrial and consumer products and as novel drug delivery
agents, there has been only limited research on the potential toxicity of
engineered nanoscale materials in vivo, mostly upon carbon nanotubes
(Donaldson et al. 2006). As a result concern is growing that the promise of
nanotechnology to address societal needs in energy, manufacturing, therapeutics
and remediation will be impeded by our lagging knowledge about potential
hazards from exposures to the diverse array of nanomaterials available (Maynard
et al. 2006).

The same unusual chemical and physical properties that make nanomaterials so
potentially useful also make their interactions with biological systems difficult to
anticipate and study (Colvin, 2003). The unique and diverse physicochemical
properties of nanoscale materials suggest that toxicological properties may differ
from materials of similar composition but different size. Published studies on the
inhalation of ultrafine particles suggest that particle size can impact toxicity
equally, if not more so, than chemical composition and hints at the complexity of
the topic (Oberdorster et al. 2005). In part this is due to the fact that as particle
size decreases, the surface area per unit mass increases. Surface properties can
be changed by coating nanoscale particles with different materials, but surface
chemistry also is influenced by the size of the particle.

This interaction of surface area and particle composition in eliciting biological
responses adds an extra dimension of complexity in evaluating potential adverse
events that may result from exposure to these materials. If biological and
toxicological effects of a given nanoparticle are due to its surface then because
of the greater surface area, the dose required to elicit a biological or toxicological
response may be less than that of larger sized materials. In addition there are
indications in the literature that engineered nanoscale materials may distribute in
the body in unpredictable ways and that depending upon the surface coatings
certain nanoscale materials have been observed to accumulate preferentially in
particular tissues.

National Toxicology Program Nanotechnology Safety Initiative
The National Toxicology Program (NTP) is a multiagency program based at the
National Institute of Environmental Health Sciences (NIEHS) that coordinates
toxicology research and testing programs within the federal government and
conducts research to provide information about potentially toxic chemicals to
health, regulatory, and research agencies, scientific and medical communities,
and the public. The NTP is engaged in a broad-based research program to
address potential human health hazards associated with the manufacture and
use of nanoscale materials. This initiative is driven by the intense current and
anticipated future research and development focus on nanotechnology. The goal
of this research program is to evaluate the toxicological properties of major
nanoscale materials classes which represent a cross-section of composition,
size, surface coatings, and physicochemical properties, and use these as model
systems to investigate fundamental questions concerning if and how nanoscale
materials can interact with biological systems.

The NTP, through its research contracts and collaborative interagency activities
is conducting studies that test hypotheses focused on the relationship of key
physicochemical parameters of selected manufactured nanomaterials to their
potential toxicity. Initial parameters of greatest concern are size, shape, surface
chemistry, and composition. This strategy is being accomplished by developing
a suite of analytical approaches to evaluate and characterize the physiochemical
properties of nanoscale materials in their raw form and as formulated when given
to animals or exposed to cells in culture. In addition, NTP is conducting whole
animal-based studies of varying durations with specific nanomaterials using
routes of administration that mimic possible human exposure. These studies
include evaluations of the absorption and handling of the materials by rodents as
well as the assessment of the development of adverse responses in vivo. NTP is
also utilizing in vitro models to evaluate the biological and toxicological effects of
nanoscale materials.

The NTP’s Nanotechnology Safety Initiative
(http://ntp.niehs.nih.gov/go/nanotech) is focusing on 3 areas of research with
respect to specific types or groups of nanoscale materials:
1. Non-medical, commercially relevant/available nanoscale materials to which
humans are intentionally being exposed, e.g., cosmetics, sunscreens and
materials used in nanotechnology enabled consumer products.
2. Nanoscale materials representing specific classes (e.g., fullerenes and metal
oxides) so that information can be extrapolated to other members of those
classes.
3. Subsets of nanomaterials to test specific hypotheses about a key
physiochemical parameter (e.g., size, composition, shape, or surface chemistry)
that might be related to biological activity.

Initial research activities are focusing initially on severla classes of nanoscale
materials: (1) titanium dioxide (2) fluorescent crystalline semiconductors
(quantum dots), (3) fullerenes, and (4) carbon nanotubes. NTP scientists at the
National Center for Toxicological Research (NCTR) NTP Center for Phototoxicity
have been examining the potential dermal toxicity of nanoscale materials
available in non- medical, commercially available products. For example,
nanoscale titanium dioxide (TiO2) is already in use in certain cosmetics and
sunscreens. These studies are addressing (1) the fate and distribution of
nanoscale ceramics and quantum dots in the body following their dermal
application to rodents with attention given to the role of surface coating, size,
polarity, vehicle, and skin condition on the ability of nanoscale TiO2 to penetrate
the skin; (2) whether nanoscale TiO2 applied dermally to mice in combination
with UVA- containing light affects cell signaling, and (3) the potential for TiO2
applied dermally to haired and hairless mice in combination with UVA-containing
light to cause skin cancer. Also in development are systemic studies on
fullerenes (buckyballs) and related compounds because of the current, high
mass production of these compounds, their increasing use in consumer products,
and the use of derivatized fullerenes in drug delivery research.

References
Colvin, V. L. 2003. The potential environmental impact of engineered
nanomaterials. Nature Biotechnol. 21, 1166-70.

Donaldson K, Aitken R, Tran L, Stone V, Duffin R, Forrest G, Alexander A. 2006.
Carbon nanotubes: a review of their properties in relation to pulmonary toxicology
and workplace safety. Toxicol Sci. 92:5-22.

Maynard, A. D., Aitken, R. J., Butz, T., Colvin, V., Donaldson, K., Oberdorster,
G., Philbert, M. A., Ryan, J., Seaton, A., Stone, V., Tinkle, S. S., Tran, L., Walker,
N. J., and Warheit, D. B. 2006. Safe handling of nanotechnology. Nature 444,
267-9.

Oberdorster G, Oberdorster E, Oberdorster J. (2005). Nanotoxicology: an
emerging discipline evolving from studies of ultrafine particles. Environ Health
Perspect,113, 823-39.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:1
posted:7/31/2012
language:English
pages:4
Lingjuan Ma Lingjuan Ma
About