Environmental Engineering Reference
In-Depth Information
known inhalation or systemic toxicity (e.g. asbestos and lead, respectively) for
which specifi c OELs were determined.
Currently, OELs are set using all available data (e.g. human, experimental, in
vivo and in vitro , physico-chemical, mechanistic understanding of pathogenicity,
inter-species differences and cellular responses). However, over time, epidemiologi-
cal research (with improved health surveillance) has shown links between exposure
to ' low toxicity ' dusts and long term illness. For example, crystalline silica is known
to cause silicosis but only recently have its links to increased lung cancer have been
recognised (Nij and Heederik, 2005), suggesting that the ' low toxicity ' determina-
tion may be over optimistic (IEH, 1996; Fairhurst, 2003) and that a chemical' s
species - specifi c long term effects must be considered when setting OELs. Indeed,
the US ACGIH has recently defi ned ' low toxicity ' particles as Particles Not
Otherwise Specifi ed (PNOS; which have no TLV, poor water solubility and low
toxicity). As a result, the ACGIH currently recommends that PNOS have a TLV
(TWA 8 hours) of 10mg/m 3 (inhalable) and 3mg/m 3 (respirable), whereas other
countries (e.g. MAK Commission in Germany) have lower respirable limits based
on extrapolation from large human occupational groups. These limits reinforce the
notion that a simple generic dust standard, based on a premise that the main effect
is that of nuisance, is no longer defensible in view of in vitro and in vivo investiga-
tions demonstrating the importance of particle size, especially surface area, in
determining many factors in lung pathogenicity (Oberdö rster et al. , 1992 ; Penn
et al. , 2005 ).
The establishment of airborne standards for European Union workplaces cur-
rently comes under the Chemical Agents Directive (specifi cally COSHH, which
implements the Chemical Agents Directive within the United Kingdom) and
REACH (WATCH, 2006). As part of COSHH, legal bases have been given to the
occupational exposure standard (OES) and the maximum exposure limit (MEL)
(Figure 10.3). The OEL ensures a minimum level of safety, which can be exceeded
as long as steps are taken to reduce exposure as far as reasonably practical; whereas
MEL is used to maintain safety levels for workers (the MEL must not be exceeded)
(Topping, 2001). REACH (discussed in Appendix 10.A) requires that the manufac-
turer or importer of substances must determine the safe operating conditions and
appropriate risk management for the substance, whereas in COSHH it is the
employer which must assess the risk of a substance and cover all work activities at
that site (e.g. production, application and disposal). REACH (a directly-acting
European Union Regulation) applies, without prejudice, to workplace health and
safety legislation.
The occupational exposure of workers to ultrafi ne particles is a well studied area
(IEH, 1996) and ultrafi ne particles are considered an aerosol particle in the
nanoscale range (e.g. diesel exhaust particulates). However, the occupational risk
assessment of manufactured nanomaterials is less well characterised (Balbus et al. ,
2007a ; Boccuni et al. , 2008). The UK Health and Safety Executive (HSE) considers
there to be three main sources of industrial activities likely to cause exposure to
nanoparticles: nanotechnology research and development (in universities, research
centres and companies), existing ultrafi ne manufacturing processes (carbon black,
titanium dioxide, alumina manufacturing) and powder handling processes (e.g.
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