Ecotoxicology of Manufactured Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 264

constant challenge to this area of ecotoxicology is the characterisation of the risks
posed by emerging contaminants which may pose new, or hitherto unforseen threats
to our environment. Examples of recent emerging contaminants include endocrine
disrupting chemicals, pharmaceuticals and the breakdown products of fl uorinated
polymers. Clearly, manufactured nanoparticles, which are fi nding increasing appli-
cations in industry and consumer products (Klaine et al. 2008 ), fi t into the category
of emerging contaminants.
As noted in other chapters in this topic, manufactured nanoparticles have dimen-
sions, usually ranging from 1 to 100 nanometres (nm), which compares to the
dimensions of living cells which are typically 1-10 micron in diameter. The nanoscale
confers different properties compared to the bulk material including larger surface
area, enhanced reactivity and changed physical properties (e.g. quantum effects).
For example, as illustrated in Figure 7.1, the percentage of surface molecules
increases exponentially as particle diameter decreases below 100 nm. For a given
mass concentration of a nanomaterial, the actual number of molecules in potential
contact with living cells will therefore be higher than encountered for the same
concentration of micron sized (or greater) particle dimensions of the same material.
This is potentially signifi cant for materials where toxicity is related to surface area
(e.g. catalytic generation of reactive oxygen species, release of toxic species by dis-
solution). Studies examining the toxicity of engineered nanoparticles in cell cultures
and animals have shown that size, surface area, surface chemistry, solubility and
possibly shape all play a role in determining the potential for engineered nanopar-
ticles to cause harm (Maynard et al. , 2006). A key question is whether nanoparticles
have toxicity relating to their size or nanostructure that is different to the bulk
material.

60

40

20

0

1 10 100

Diameter (nm)

1,000 10,000

Figure 7.1 Percent surface molecules as a function of particle size. Note that the percentage
of surface molecules increases exponentially when particle size decreases

100 nm. For
instance, a particle of 30 nm diameter has about 10% surface molecules, whereas a particle
of 3 nm size has 50%. This emphasises the importance of surface area for increased chemical
and potentially biological activity. (Reproduced with permission from Oberdorster, G.,
Oberdorster, E., Oberdorster, J. (2005) Nanotoxicology: An emerging discipline evolving
from studies of ultrafi ne particles, Environmental Health Perspectives , 113 , 2005, 823-39.)

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