Toxicology of Industrial Compounds

F.A.DE WOLFF ET AL. 7
is usually no longer than a few minutes. The exposed area is usually in the
order of 20 cm 2 .
In the case of dermal exposure to vapour, the volunteer places the lower
arm into a piece of drainage pipe through which the vapour is led with
controlled flow and concentration in air. Uptake of liquid or vapour is
measured in both cases by determination of the solvent in expired air, by
the sampling method described earlier.
Figure 1.2 shows the dermal uptake and elimination of two different
liquids in one volunteer. A surface of 27 cm 2 was exposed during 3 min to
pure 1,1.1-trichloroethane and to tetrachloroethene. It is clear that 1,1,1trichloroethane
is absorbed through the skin much faster and to a much
greater extent than tetrachloroethene, at least in exposure to the liquids.
However, when the skin is exposed to the same solvents in the vapour
phase the picture becomes totally different. Here the lower arm, which has
a surface of about 500 cm 2 , was exposed during 15 min to solvent
concentrations of approximately 500 µmol 1 −1 air (Figure 1.3).
In the case of vapour exposure no difference in absorption kinetics is
observed, and only a small difference in expired air concentration is seen.
The reason for the discrepancy between vapour exposure is that 1,1,1trichloro-ethane
causes skin irritation as the liquid, but not in the vapour
phase. Irritation leads to hyperaemia and, hence, increased absorption.
As it is known that dermal exposure to vapour may lead to detectable
absorption, the contribution of vapour uptake of the skin in comparison to
inhalatory absorption should be evaluated. This was done with
trichloroethene as an example (Figure 1.4). Both curves were obtained in
the same volunteer. The dermal exposure was performed first, followed by
the inhalatory test after a wash out period of 2 weeks. The exposure period
was 15 min, and the inhalatory concentration was 4.1 µmol l −1 . Dermal
exposure of the lower arm took place at 1.4 mmol l −1 .
It appears that uptake from the lungs occurs much faster than via the
skin. This is conceivable because the stratum corneum is a stronger barrier
than the alveolar epithelium, and causes a shift to the right of the t max. It
can also be seen that inhalatory exposure leads to a much higher expired
air concentration than dermal exposure. But in this respect we should
realize that only a small part of the skin was exposed, namely about 500
cm 2 . In fact the result should be extrapolated to the total surface of the
human skin, which is about 2 m 2 . These results indicate that dermal
exposure to solvent vapour should not be neglected when the safety of the
industrial environment is evaluated. This is of special importance when
ambient air concentrations are high, and workers are protected with
protective masks but not with gloves. Another example in which skin
absorption may be high in comparison with inhalation are those solvents
which are readily absorbed by the skin, such as 2-butoxyethanol (Johanson
and Boman, 1991).