Human Toxicology and Effects of Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 353

In the last fi ve years much of the attention of particle toxicologists has turned to
nanoparticles, previously termed ultrafi ne particles (see below). As outlined in
Chapter 8, the British Standards Institution (BSI) has recently defi ned nano - objects
as 'discrete pieces of material with one or more external dimensions in the nanoscale'
and nanoparticles as a 'nano-object with all three external dimensions in the
nanoscale' (BSI, PAS 136: 2007). Engineered nanoparticles are diverse in their
chemistry, shape and applications. Many are engineered due to changes in their
properties that occur at the nanoscale, and that impart useful properties such as
catalytic activity, electrical conductivity and relative strength.
The interest of particle toxicologists in nanoparticles is driven by a number of
factors. Firstly, exposure of humans and the environment to combustion derived
nanoparticles via air pollution already occurs and is suggested to be linked to a
number of health effects (see below, Chapter 5 and Chapter 8). In addition, expo-
sure to manufactured nanoparticles already exists through the use of a wide variety
of consumer products ranging from cosmetics, suntan lotions, food additives and
clothing, to medicines and diagnostics (http://www.nanotechproject.org/44, observed
04/01/07). With the rapid expansion of nanotechnology and the ever increasing
applications for which nanoparticles are developed, such exposure is likely to
increase further (Aitken et al. , 2006). At present the consequences of such exposure
are poorly understood. While many nanoparticles may prove to be relatively harm-
less, it is important to understand the risks associated with such new materials,
especially when exposures are likely to be from multiple sources and to a variety
of nanoparticle types. In addition, the physico-chemical properties that make
nanoparticles so exciting for the development of new products could also be the
same properties that drive interactions with biological systems.

9.1.3 Risk Assessment

Toxicology is part of the risk assessment procedure:

Risk

= Hazard toxicity

( ) ×

Exposure dose

( )

An understanding of toxicity and dose therefore allows companies, regulators
and individuals to assess the risk associated with the use of a particular substance
(Figure 9.1). At this time something is known about the hazard of a small number
of manufactured nanoparticles (summarised below) but very little about exposure,
or even how to measure exposure (Maynard and Aitken, 2007). In the current
climate it is therefore diffi cult to generate clear evidence-based advice to compa-
nies and consumers regarding the safe use of nanoparticles.
To bridge this current knowledge gap, particle toxicologists are now working
to assess the physico-chemical factors that determine the fate and behaviour of
different types of nanoparticles in the body of humans (Figure 9.2) and in
the environment. An understanding of the relationship between particle properties
and toxicity will allow improved approaches to testing and risk management, as
well as improved safety design of nanoparticles for future use and applications
(Figure 9.3 ).