Environmental Engineering Reference
In-Depth Information
within the skin or alternatively the substance may be absorbed through the skin
and disseminated via the bloodstream, possibly causing systemic effects.
Because of this there have been considerable efforts made to develop quantita-
tive methods for monitoring skin exposure. All of these techniques essentially
measure the mass of material deposited onto the skin, either per body part or per
unit area of skin exposed. Diffi culties in this area are compounded by a multitude
of measuring methods, which are not easily comparable. The development of a
conceptual model of dermal exposure has been benefi cial in clarifying some of
these issues (Schneider et al. , 1999 ).
Systemic effects from dermal exposure are, in particular, unlikely to depend only
on the mass on the skin but are more likely to be related to uptake through the
skin. Uptake is the fl ux through the skin and depends on the concentration of the
substance on the skin, the area exposed and the duration of exposure. Because of
this, some authors have suggested that uptake is a more appropriate metric than
the mass on the skin (Robertson and Cherrie, 1995).
A review of dermal exposure issues carried out by the HSE concluded that
there was no evidence to indicate that specifi c health problems are currently
arising from dermal penetration of ultrafi ne particles (nanoparticles) (HSE,
2000). However, the review conceded that dermal absorption of ultrafi ne
particles has not been well investigated and suggested that ultrafi ne particles
may penetrate into hair follicles, where constituents of the particles could dissolve
in the aqueous conditions and enter the skin. Direct penetration of the skin
has been reported by Tinkle et al. (2003) for particles with a diameter of 1000 nm,
much larger than nanoparticles. It is reasonable to postulate that nanoparticles are
more likely to penetrate through the outer layers of the skin - the stratum corneum
- but this has not yet been demonstrated. Several pharmaceutical companies are
believed to be working on dermal penetration of nanoparticles as a drug delivery
route.
Any metric proposed to assess dermal exposure to nanoparticles should be bio-
logically relevant and should relate to potential health effects. Further work, includ-
ing workplace studies and in vitro assessment of penetration, is required. Based on
the current level of knowledge, measurement approaches should include assess-
ment of mass and particle number concentration, area exposed and duration of
exposure.
8.3.2.3
Ingestion Exposure
In occupational settings very little work has been done up to now on ingestion
exposure. Lead is one of the few materials where the ingestion route has received
some attention. Lead paint removal activity can produce high ingestion exposures
via hand-to-mouth contact and food contamination in certain workplaces. A study
has shown that workers involved in the supply and removal of scaffolding can have
particularly high blood lead levels as a result of hand contamination and subse-
quent ingestion (Sen et al. , 2002). No research work has been undertaken in relation
to ingestion exposure of nanoparticles. Metrics to assess ingestion exposure to
nanoparticles should be biologically relevant and (probably) in the fi rst instance
should be measures of mass uptake.
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