Dermal Absorption of Chemicals from Liquid Mixtures

摘要

The workplace is one of the most common venues for hazardous chemical contact with skin. Recognition of the dermal exposure hazard is essential for its control. Unfortunately, the present identification of chemicals as skin absorption hazards is inconsistent, poorly documented, and qualitative. Although a new skin notation strategy, announced by NIOSH July 2009, will designate the type(s) of skin hazard potential (e.g., systemic toxicity, direct irritant, corrosive, and sensitizing) for a given chemical and improve documentation for the hazard designation, it will provide no information about the effect of concentration or the solution containing the potentially hazardous chemical. As a result, those charged with protecting human health and safety in the workplace are forced to make judgments about safe or dangerous levels, and the type of personal protection required, with little or no information. The ultimate goal of this research effort is to provide occupational safety and health practitioners with improved guidance regarding potentially dangerous levels of skin exposure to chemicals. While most occupational exposures of skin involve mixtures of chemicals, the interactions between multiple components and skin has received little study. This research was directed toward identifying and understanding the effect of exposures to chemical mixtures and especially non-aqueous solutions. The approach was to develop fundamental understanding of the underlying mechanisms by combining data with mathematical models of skin absorption and phase equilibrium thermodynamics. Specifically, we (i) examined experimentally the extent to which several test solutes (4-cyanophenol, methyl paraben, naphthalene, and 4-chloronitrobenzene) in water and in four non-aqueous solutions (toluene, 1-octanol, cyclohexane and isopropyl myristate) interact with each other or skin to alter the rate and/or amount of chemical absorption, (ii) developed computational procedures for estimating dermal absorption from aqueous and non-aqueous solutions containing two or more organic compounds including the effects of thermodynamic activity in the vehicle, and (iii) developed and used a new method for measuring electrochemical impedance to characterize skin barrier function and the effect of chemical or mechanical insult compared with skin permeation measurements.