Biologically relevant assessment of dermal exposure.

Dermal uptake of hazardous substances is dependent on the concentration of the material on the surface of the skin rather than its mass. It is suggested that it would be appropriate to consider the integral of concentration, over the skin surface and throughout the exposure duration, as an appropriate index of dermal exposure. For a low volatility substance this exposure index would correspond to the product of concentration, area of skin exposed and the duration of exposure. For volatile materials the magnitude of the exposure index would additionally depend on the loss of the substance by evaporation. This dermal exposure index is more likely to reflect the contribution to the overall dose received from the skin than the previously used determinations of mass of hazardous substance on the skin. Suggestions are made for possible methods of making measurements using this index.