Case Studies - Uptake of Chemical Substances through the Skin

Occupational exposure to airborne hazardous substances is usually discussed in terms of the risk of inhalation. For example, occupational exposure limits are normally developed with a view to controlling this route. However, it is now widely accepted that the uptake of substances which pass through the skin will also contribute to the body burden (although the extent may vary considerably between chemicals).

HSE asked HSL to investigate the extent to which absorption through the skin takes place using vapours from a range of substances with different physicochemical parameters. Tests were conducted on a small group of volunteers in a controlled atmosphere room using four chemicals - toluene, xylene, 1-methoxy-2-propanol and 2-butanone - which represent a range of substances which might pass through the skin.

The uptake of the vapour by the body was assessed by biological monitoring based on an analysis of the parent compound or metabolites. The volunteers wore T-shirts and jeans, and for one experiment the inhalation route was excluded by asking the volunteers to wear air-fed masks. The exposures were for four hours each at the appropriate occupational exposure limit.

The results of the tests showed, as expected from the physicochemical parameters, that 1-methoxy-2-propanol had the greatest penetration while toluene had the least. However, contrary to expectations 2-butanone scored slightly higher than xylene. The tests confirmed that for some substances the uptake of solvent vapour through the skin can contribute significantly to the body burden.

Further work using the solvent 2-butoxyethanol has shown that as temperature and humidity increase the dermal exposure route becomes more significant. Wearing overalls made little difference to uptake of the solvent.

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