Dermal uptake of solvents from the vapour phase: an experimental study in humans

The control of exposure to hazardous substances in the workplace has traditionally focused on uptake via the inhalation route. Control of skin uptake has generally been considered for solids and liquids but the potential for uptake from vapours and gases has received relatively little attention. The current work was undertaken to establish a methodology to study the dermal uptake from vapours and to provide new and comparative information on a range of substance vapours. Groups of human volunteers were exposed to a small range of substances either 'whole body' or via the skin only. Substances (xylene, toluene, tetrahydrofuran [THF], methyl ethyl ketone [MEK] and 1-methoxypropan-2-ol [M2P]) were selected on the basis of their predicted dermal uptake from the vapour phase; their industrial use and potential for occupational exposure; the existence of a health-based occupational exposure limit; the availability of an analytical technique(s) for the substance and/or metabolite(s); and as representatives of chemical classes. Exposures were for four hours generally at the level of the UK Occupational Exposure Standard. Uptake was assessed by monitoring of parent or metabolite in blood, single breath or urine following exposure. Uptake of xylene, toluene and THF vapours via the skin under the conditions of this study was estimated to contribute around 1-2% of the body burden received following whole body (including inhalation) exposure. MEK showed more uptake via the skin, contributing around 3-3.5% of the body burden. Most dermal uptake was seen for the glycol ether M2P for which estimates of between 5-10% of whole body exposure body burden were obtained. The results of this and other studies indicate that uptake of vapours across the skin can occur but that for some substances (e.g., xylene, toluene, THF) this is likely to contribute little to the body burden. For other substances, such as the glycol ethers, skin uptake from vapours may be an important contributor to total uptake, particularly in situations where respiratory protective equipment is used to control inhalation exposure.