Overview of Nanoscience in the Environment - Environmental and Human Health Impacts of Nanotechnology - page 23

different ways, but generally nanomaterials are defi ned as particles smaller than
100 nm in any one dimension. As has been seen, and as is more thoroughly discussed
in the next two chapters, sizes below about 10-20 nm are of particular importance,
as this is the size range in which properties change markedly. To resolve such
confusion national and international standard bodies, such as the International
Organization for Standardization (ISO), International Electrotechnical Commission
(IEC), American National Standards Institute (ANSI), ASTM International, British
Standards Institution (BSI) and others are now discussing the standardization of
terminology, metrology, characterization and approaches to safety and health.

1.16.2 Future Development and Risk

Current risk assessment programs are mainly concerned with the fi rst generation
of nanomaterials or passive nanomaterials, and even here there is fundamental
uncertainty arising from lack of knowledge. Further development of nanomaterials
will involve larger and more complex phenomena and problems and much work
remains to be done.

1.16.3 Dosimetry

Exposure and doses of nanomaterials are generally measured in terms of mass per
unit volume, commonly milligrams per litre. However, there is a consensus that
mass dose alone is insuffi cient to characterize the exposure to nanomaterials. Some
studies have indicated a correlation between toxicity and particle surface area,
suggesting that surface area is a better metric for measuring exposure (Oberdorster
et al. , 2005a, 2005b), while particle number is also an important metric. Although
mass can be correlated to the surface area, large variations can occur in this correla-
tion within different batches or due to differences in shape. Until particle structure
and toxicity are quantitatively related, size, surface area and mass and number
concentrations and other parameters need to be specifi ed and measured
(Oberdorster et al. , 2005b ).

1.16.4 Methods of Detection and Characterization

Determining the concentration and physical and chemical properties of nanoma-
terials in environmental and biological systems is essential. The development and
testing of such methodologies is at an early stage and no published data are avail-
able. Nevertheless, this development is absolutely central to our ability to under-
stand and predict the environmental consequences on nanotechnology.

1.16.5 Environmental Fate of Nanomaterials and their (Eco)Toxicology

Little is known in this area and there is a large range of issues to be addressed.
These issues strongly overlap with the fate and behaviour of natural and incidental
nanoparticles and are (non-exhaustively) summarised below:

• identifying the potential sources of release and concentration of nanomaterials
to the environment,