McDougall, J.N., J. L. Jurgens and W.H. Weisman. Effect of Temporal Assumptions on Risk Assessments for Dermal Toxicity. The Toxicologist 48(1S): 85. Abstract #397.

The skin can be an important route of entry for chemicals that may subsequently cause toxicity. After dermal exposures, irritation of the skin may result or if the chemical is absorbed through the skin, systemic toxicity may result. Dermal exposures can occur from contact with contaminated surfaces, spills on the skin or during showering and bathing in contaminated water. Most of these exposures are short duration and the rate of absorption does not approach steady-state. The time before the chemical penetrates through the skin and becomes available for systemic absorption can be minutes to hours and is known as the "lag time". This lag time may impact duration extrapolations used for risk assessments, which assume that flux is constant over time. Using static diffusion cells and rodent skin, we measured time profiles for diffusion of dibromomethane (pure chemical and aqueous solution) into and through rat skin. Chemical concentration in the skin slowly increases and then becomes constant, without any lag time. After a fifteen-minute lag time, the concentration of chemical that comes through the skin slowly increases and then becomes constant. When the total amount of dibromomethane (in both the skin and the receptor solution) is plotted over time, the plot is linear without a lag time. These results suggest that duration extrapolations for chemical in the skin and diffusing through the skin can be inaccurate depending on the length of the lag time compared to the exposure time.