Nanomaterials: Properties, Preparation and Applications - Environmental and Human Health Impacts of Nanotechnology - page 65

widespread use. In the Graeco-Roman period mixtures of calcium hydroxide and
lead oxide were used to dye hair, and it has been shown recently that this results
in the formation of small (about 5 nm) nanoparticles of lead sulfi de in the hair itself
(Walter et al. , 2006). Similarly, nanoparticles were applied in the glaze layers of
pottery in the ancient world and there are examples from the eleventh century of
shards of pottery painted with typical Islamic patterns which contain nanoparticles
of silver and copper (Darque-Ceretti et al. , 2005). Michael Faraday is one of the
fi rst people to take a scientifi c interest in gold sols or nanoparticles. He produced
gold nanoparticles by the in situ reduction of gold chloride using white phospho-
rous and citrate as a capping agent. Carbon black has been produced on a
commercial scale for more than 150 years and, similarly, asbestos has seen a rise
and fall in use over the past 70 years. More recently, widespread commercial use
of carbon black and asbestos probably represents the largest market for
nanomaterials.

2.6.1.1 Asbestos

Asbestos is a generic term for a range of naturally occurring minerals based on
fi brous silicates. Asbestos is probably one of the best known nanomaterials in the
general public and its detailed history provides an excellent background to the
issues relating to very small particles and especially fi bres. There are several reviews
and topics which deal in detail with the subject (Vallarino, 2001; Williams et al. ,
2007) and many more research papers and reports detailing its hazards. It is worth
noting that as a material it is fairly ill defi ned, having a range of possible chemistries
and an exceptionally broad range of sizes, which often fall at the upper scale of
nanotechnology. The mineral crystallises in a fi bre-like form which combined with
its chemical composition results in its excellent insulation properties. The material
itself is ill defi ned by current standards of engineered nanoparticles, consisting of
a wide range of diameters (25- 300 nm) and lengths (0.5 - m) (Langer, 1974 ).

The hazards of asbestos are well documented and are related to a combination of
the chemistry of the material and its nanoscale, fi brous form.
The initial applications of asbestos were in the ship building industry during the
second world war where it was employed as a insulation material. By the 1960s the
main user of asbestos became the building industry, accounting for more than 74%
of the total mined material in the United States (NIOSH, 1972). By the 1980s there
were about 3000 industrial or commercial products which had asbestos as one of
the components (Anderson et al. , 1982). Regulation in the 1970s (OSHA, 1986,
1994; US Environmental Protection Agency, 1988) resulted in a rapid decline in the
market and use. The use of asbestos was on a scale of thousands of tonnes per
annum and fi gures for 1979 show that, even after regulation, 130 000 tonnes per
annum were being used in fl oor tiling alone (OSHA, 1986, 1994; US Environmental
Protection Agency, 1988). It was even considered as a component of feminine
hygiene products (OSHA, 1986, 1994; US Environmental Protection Agency, 1988),
although there is no evidence that the concept was ever put into production. By
1997 the total asbestos market in the United States was still as high as 21 000 tonnes
per annum distributed mainly in the building industry (Figure 2.20). The huge

> 20 µ