Percutaneous chemical absorption

Hostynek JJ (2003) Factors determining percutaneous metal absorption. Food and Chemical Toxicology 41 327-345. 

Chemical absorption pathways can hypothetically involve both intercellular and intracellular passive diffusion across the epidermis and dermis and/or transappendageal routes, via hair follicles and sweat pores. Most available research has concentrated on the stratum corneum as the primary barrier to absorption, although the viable epidermis and dermis can also contribute resistance to the percutaneous penetration of specific chemical classes, for... 

The development of a blophyslcally based model of chemical absorption via human skin Is described. The simulation has been used to analyze the In vivo penetration kinetics of a broad range of molecular species. Four first-order rate constants are Identified with the percutaneous absorption process k -penetrant diffusion through the stratum corneum k2 transport across the viable epidermal tissue to the cutaneous microcirculation k - a retardation parameter which delays the passage of penetrant from stratum corneum to viable tissue k - the elimination rate constant of chemical from blood to urine. 

PERCUTANEOUS ABSORPTION Absoi ption via the skin, e.g. due to local contamination or a splash of chemical. 

The percutaneous absorption picture can be qualitatively clarified by considering Fig. 3, where the schematic skin cross section is placed side by side with a simple model for percutaneous absorption patterned after an electrical circuit. In the case of absorption across a membrane, the current or flux is in terms of matter or molecules rather than electrons, and the driving force is a concentration gradient (technically, a chemical potential gradient) rather than a voltage drop [38]. Each layer of a membrane acts as a diffusional resistor. The resistance of a layer is proportional to its thickness (h), inversely proportional to the diffusive mobility of a substance within it as reflected in a... 

Skin tape stripping can be used to determine the concentration of chemical in the stratum comeum at the end of a short application period (30 min) and by linear extrapolation predict the percutaneous absorption of that chemical for longer application periods. The chemical is applied to skin of animals or humans, and after a 30-minute skin contact application time, the stratum comeum is blotted and then removed by successive tape applications. The tape strippings are assayed for chemical content. There is a linear relationship between this stratum comeum reservoir content and percutaneous absorption. The major advantages of this method are (1) the elimination of urinary and fecal excretion to determine absorption and (2) the applicability to nonradiolabeled determination of percutaneous absorption, because the skin strippings contain adequate chemical concentrations for nonlabeled assay methodology. 

ECETOC. Monograph No. 20, Percutaneous Absorption, ECETOC (European Centre for Ecotoxicology and Toxicology of Chemicals), Brussels, 1993. 

Although dermal absorption of carbon tetrachloride is relatively modest compared to oral or inhalation, it would be helpful to quantify the rate and extent of percutaneous absorption of carbon tetrachloride from water. This information would be useful in determining the contribution of dermal exposure to the total dose received by persons using carbon tetrachloride-contaminated drinking water for bathing or showering, or to those who contact carbon tetrachloride-contaminated water near chemical waste sites. 

Drexler H. Skin protection and percutaneous absorption of chemical hazards. Int Arch Occup Environ Health 2003 76 359-361. 

Absorption. Absorption of foreign compounds from various sites is dependent on the physiological and physical conditions at these sites. These, of course, may be subject to species variations. Absorption of compounds through the skin shows considerable species variation. Table 5.2 gives an example of this and shows the species differences in toxicity of an organophosphorus compound absorbed percutaneously. Human skin is generally less permeable to chemicals than that of rabbits, mice, and rats, although there is variation. For some compounds, rat skin has similar permeability to human skin and seems to be less permeable than that of the rabbit. 

Barber ED, TeetselNM, Kolberg KF, et aL 1992. A comparative study of the rates of in vitro percutaneous absorption of eight chemicals using rat and human skin. Fund Appl Toxicol 19 493-497... 

As part of the safety assessment the assessor must consider the chemical structure and all the available information regarding the toxicological profile of the material. The decision to proceed with human testing should only be made if the information available provides sufficient confidence that the volunteer will not be exposed to undue risk. Key toxicological endpoints of concern for moisturizing products include skin corrosivity, percutaneous absorption, genotoxicity, skin sensitization, skin irritation, systemic toxicity, reproductive toxicity, and phototoxicity. 

This chapter is not an exhaustive list of all chemicals with skin-penetrating abilities. Consequently, any exclusion of a chemical from this list does not necessarily imply an inability for percutaneous absorption. When in doubt, the user should check the chemical label, material safety data sheet, manufacture date, and other details to achieve chemical safety (Table 16-1). 

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