Geoscience Reference
In-Depth Information
3.6 Nanomaterials
Engineered nanomaterials are usually described as inorganic materials of high
uniformity, with at least one critical dimension below 100 nm. This group of
substances has received considerable attention recently as the basis for the next
''scientific revolution.'' In this framework, nanomaterials are expected to be
incorporated in a wide range of applications, from medicine and cosmetics to new
construction materials and industrial processes, and to many more applications in
all areas of technological development. Based on current estimates, nanotech-
nology is projected to become a trillion-dollar market by 2015. As a consequence,
these materials are expected to be spread around the globe rapidly due to massive
production and use.
Nanomaterials hold promise for elegant solutions to numerous environmental
concerns, from implementation of green chemistry processes for industrial and
agrochemical uses (e.g., Mohanty et al.
2003
; McKenzie and Hutchison
2004
)to
production of novel materials for treatment of various contaminants (e.g., Dror
et al.
2005
; Nurmi et al.
2005
; Nagaveni et al.
2004
; Kuhn et al.
2003
). However,
these possibilities also bring new threats that must be considered and monitored.
Nanomaterials magnify and stimulate properties that, at larger scales, are in many
cases, of minor importance. Below 100 nm—the upper limit of the nanomaterial
range—the surface area to mass ratio and the proportion of total number of atoms
at the surface of a structure are large enough that surface properties become very
significant. This can alter the chemical reactivity, thermal and electrical conduc-
tivity, and tensile strength of known substances (Owen and Depledge
2005
).
Additional physicochemical properties of engineered nanomaterials include spe-
cific chemical composition (e.g., purity, crystallinity, electronic properties), sur-
face structure (e.g., surface reactivity, surface groups, inorganic or organic
coatings), solubility, shape, and aggregation (Nel et al.
2006
). Furthermore, when
the size of a structure is 10-30 nm, it approaches certain physical length scales,
such as the electron mean free path and the electron wavelength, resulting in
quantum-size effects that alter the electronic structure of the particle (Nurmi et al.
2005
; Brus
1986
; Wang and Herron
1991
). These changes modify optical, mag-
netic, and electrical behavior.
The desired size-related properties of nanomaterials also raise major concerns:
the same characteristics that make these substances so appealing may have neg-
ative health and environmental impacts. Recent studies (e.g., Owen and Depledge
2005
; Royal Society and Royal Academy of Engineering
2004
; Balbus et al.
2005
;
Colvin
2003
) state that the data collected to date are inadequate to provide full risk
assessments, but substantial basis for concern exists and should be further inves-
tigated. Only a handful of ecotoxicological studies on nanosized materials have
been published so far. However, the collected data are alarming.
In a recent review, Nel et al. (
2006
) discuss the toxic potential of nanomaterials.
For example, Hote et al. (
2004
) state that nanoparticles entering the liver can
induce oxidative stress locally. It was also found that uptake of polymeric
