Risk Assessment of Manufactured Nanomaterials - Environmental and Human Health Impacts of Nanotechnology - page 392

information on: the toxicity of the substances (e.g. from material safety data sheets;
MSDS); the likelihood of exposure of the workers performing the procedure and
of other individuals in the vicinity; and the likely consequence of accidental expo-
sure for the individuals (e.g. minor injury, hospitalisation, severe/permanent injury).
These factors are used to estimate the overall risk, and then consideration is given
to how exposure can be prevented or controlled so as to avoid/minimise the risks.
For airborne exposures, the risk assessment must also include compliance with
exposure limits for individual chemicals. Occupational exposure limits (OELs) are
airborne standards designed to protect workers from the acute or chronic effects
of inhaling hazardous agents. Compliance with OELs is mandatory and OELs are
normally defi ned as an average over a reference period (e.g. eight hours; also
referred to as the time weighted average; TWA). OELs have been used since the
1930s for specifi c substances (e.g. cotton dust) (Topping, 2001). Threshold limit
values (TLVs) are the maximum concentration that a worker can be exposed to
daily in a working lifetime without experiencing adverse health effects. These are
advisory limits set by the American Conference of Governmental Industrial
Hygienists (ACGIH) and are airborne standard guidelines for occupational risk
assessment ( http://www.acgih.org ).
In the case of particulate materials, OELs have not always been scientifi cally
based. Historically, many particles were regarded as ' nuisance ' or ' low toxicity '
dusts, which meant that little attention was given to scientifi cally defi ning the
precise OEL. Few of these dusts produced any systemic toxicity and the control of
exposure was diffi cult (e.g. in construction, mines and welding sectors). As a con-
sequence, a generic approach to standard setting was taken for many particulates,
resulting in a generic inhalable OEL of 10 mg/m 3 and a respirable OEL of 4 mg/m 3
for many substances (Table 10.2). These were not suitable for particles with a

Table 10.2 Particles with generic occupational exposure
limits (OELs) of 10 mg/m 3 (inhalable) and 4 mg/m 3
(respirable).

Particles with generic inhalable and respirable OEL

Aluminium metal Marble

Aluminium oxides Pentaerythritol

Calcium carbonate Plaster of Paris

Calciypum silicate Platinum metal

Cellulose Portland cement

Graphite Rouge

Gypsum Silicon

Limestone Silicon carbide

Magnesite Starch

Magnesium oxide Titanium dioxide

Zinc distearate
Zinc oxide fume