Characterizing Short-Term Hazard from Steady-State Dermal Absorption Data. J. N. McDougal, J. M. Jurgens, and W. H. Weisman, GEO-CENTERS, Inc. and Toxicology Division, Armstrong Laboratory
Absorption of chemicals through the skin causes concern for potential systemic toxicity. There is a delay, or lag time, before most chemicals can make their way across the skin and into the blood. In vitro diffusion cell experiments suggest that this lag time may range from less than half an hour to a couple of hours. Many human dermal exposures to hazardous chemicals last for only minutes, and some deposition in the skin occurs. Laboratory measurements of dermal absorption, however, nearly always require the establishment of pseudo steady-state conditions, where the flux becomes constant. It takes about three to four times the lag time for steady-state to be reached. Application of this steady-state absorption rate to a short exposure does not accurately characterize the dermal uptake and complicates the assessment of systemic hazards of these short-term or splash exposures. Several approaches to relating steady-state data to short-term exposures will be discussed and compared with short term diffusion cell data, including concentration in the skin.