Dicyclohexylamine (DCHA) is commonly used in the metal working industry to prevent corrosion of fabricated materials. In the last decade there has been increased use of DCHA as a biocide in metal-working fluids (MWFs); although it is not registered by the U.S. EPA for this purpose. There is no published information describing the dermal absorption of DCHA in spite of the fact that machine workers are most likely to be exposed by the dermal route than any other route and DCHA is a known dermal irritant. The objective of this research was to quantify the dermal absorption of DCHA in vitro using pig skin because pig skin is similar to human skin anatomically and biochemically. DCHA was applied to pig skin in 3 generic MWF formulations commonly used in industry: soluble oil (SO), synthetic (SYN), and semi-synthetic (SS). Dermatomed pig skin (n = 5-6) was loaded in a flowthrough diffusion cell system with the dermal surface perfused for an 8-hr exposure to mimic occupational exposures. Dosing solutions containing MWFs or water were prepared below or near the saturated solutions for DCHA to provide finite or infinite dosing conditions. There was an initial 1.0 hr lag period and peak fluxes occurring at 2.0 to 3.0 hrs for all of the formulations tested. Dermal absorption of DCHA was greatest from SS (12.5%), but significantly less from SO (4.6%) and SYN (5.9%) formulations. Surprisingly, 81% DCHA was absorbed from water mixtures. These preliminary results suggest that DCHA can more readily diffuse across pig skin from aqueous solutions than from complex MWF formulations. This may be due to differential partitioning behavior within the formulations. In conclusion, there are significant differences in absorption of DCHA across the various MWF formulations, thus it is imperative to consider such differences in dermal risk assessments involving this widely used additive in the metal machining industry.
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