An in vitro comparison of the permeation of chemicals in vapor and liquid phase through pig skin

Percutaneous absorption of thirty-eight organic solvents in vitro using pig skin

Percutaneous absorption is highly variable between chemicals but also within chemicals depending on exposure conditions and experimental set up. We tested a larger number of organic solvents with the same experimental set up, using skin from new-born piglets and static diffusion cells. Thirty-six common organic solvents were studied neat (and 31 of them also in water dilution): acetone, acetonitrile, n-butanol 2-butanone 2-butoxyethanol, 1-butoxy-2-propanol, n-butyl acetate, butyl acrylate, cyclohexane, cyclohexanone, 1,2-dichloroethane, dichloromethane, ethanol, 2-ethoxyethanol, ethyl acetate, ethyl acrylate, ethylbenzene, furfuryl alcohol, n-hexane, 2-hexanone, 2-isopropoxyethanol, methanol, 1-methoxy-2-propanol, methyl acrylate, 3-methyl-1-butanol, methyl tertiary butyl ether, 4-metyl-2-pentanol, methyl methacrylate, 2-propanol, 2-propen-1-ol, 2-propoxyethanol, 1-propoxy-2-propanol, styrene, trichloromethane, toluene and m-xylene. In addition, a mixture of 2-methylbutyl acetate and n-pentyl acetate was tested. For most of the solvents, little or no percutaneous absorption data have been published. Lag times, steady-state fluxes and apparent permeability coefficients were obtained from the time courses of solvent appearance in the receptor medium, as measured by gas chromatography. The use of the same methodology and kind of skin resulted in small variability within experiments, underlining the need for consistent methodology for useful results for developing predictive models. Furthermore, a comparison of the neat and diluted data shows that water dilution affects all these variables and that the direction and magnitude of the effects vary between chemicals. This comparison strongly supports that prediction of percutaneous absorption of neat and water diluted chemicals requires different models.

Predicting the absorption of chemical vapours

The focus of this review is on the systemic absorption of vapours via skin, including experimental data as well as regression and pharmacokinetic models. Dermal contribution ratios (DCR), i.e. amount absorbed through skin relative to total intake (skin and inhalation) at specified conditions, could be identified or calculated from published data for 33 chemical vapours. The ratios vary from ~0.0002 (vinyl chloride) to ~0.8 (2-butoxyethanol), with hydrophilic chemicals having a higher ratio than lipophilic ones. Multiple regression analysis of these data suggests that the DCR is largely explained by the octanol:water partition coefficient, vapour pressure and molecular weight (R(2)=0.69). Several physiologically-based pharmacokinetic models were identified; however, all describe the absorption of single substances. Regarding predictive models, only two models were found. In conclusion, dermal uptake of chemical vapours needs more attention, as such exposures are common, data are scarce and few predictive models exist.

Dermal absorption of benzene in occupational settings: estimating flux and applications for risk assessment

There is growing emphasis in the United States and Europe regarding the quantification of dermal exposures to chemical mixtures and other substances. In this paper, we determine the dermal flux of benzene in neat form, in organic solvents, and in aqueous solutions based on a critical review and analysis of the published literature, and discuss appropriate applications for using benzene dermal absorption data in occupational risk assessment. As part of this effort, we synthesize and analyze data for 77 experimental results taken from 16 studies of benzene skin absorption. We also assess the chemical activity of benzene in simple hydrocarbon solvent mixtures using a thermodynamic modeling software tool. Based on the collective human in vivo, human in vitro, and animal in vitro data sets, we find that the steady-state dermal flux for neat benzene (and benzene-saturated aqueous solutions) ranges from 0.2 to 0.4 mg/(cm²·h). Observed outlier values for some of the animal in vivo data sets are possibly due to the use of test species that have more permeable skin than humans or study conditions that resulted in damage to the skin barrier. Because relatively few dermal absorption studies have been conducted on benzene-containing organic solvents, and available test results may be influenced by study design or vehicle effects, it is not possible to use these data to quantify the dermal flux of benzene for other types of solvent mixtures. However, depending on the application, we describe several potential approaches that can be used to derive a rough approximation of the steady-state benzene dermal flux for these mixtures. Important limitations with respect to quantifying and evaluating the significance of dermal exposures to benzene in occupational settings include a lack of data on (1) factors that affect the dermal uptake of benzene, (2) the dermal flux of benzene for different organic solvent mixtures, (3) meaningful metrics for evaluating the dermal uptake of benzene, (4) steady-state versus non-steady-state dermal flux values for benzene, (5) the effect of skin damage on the dermal flux of benzene, (6) standardized test methods for estimating the dermal flux of benzene, and (7) robust estimates of the evaporation rate of benzene from different liquid vehicles.

Commentary on "Penetration of benzene, toluene and xylenes contained in gasolines through human abdominal skin in vitro"

In this commentary we refer to the new data recently published by Adami et al. [Adami, G., Larese, F., Venier, M., Barbieri, P., Lo Coco, F., Reisenhofer, E., 2006. Penetration of benzene, toluene and xylenes contained in gasolines through human abdominal skin in vitro. Toxicol. In Vitro 20, 1321-1330], which we acknowledge as a reliable basis for the retrospective assessment of percutaneous benzene absorption at the workplace. The data from Adami et al. (2006) are supported by the literature and by a German approach for calculating the contribution of the dermal uptake of benzene to the total body burden. This knowledge is important for the judgment of leukaemia suspected to be an occupational disease.

In-use testing and interpretation of chemical-resistant glove performance

Issuing gloves to workers is the most common approach to protecting against skin contact with hazardous chemicals. Typically, glove materials are selected and duration of wear is estimated based on comparisons of laboratory test data. Those who select the glove materials often fail to verify their selections by testing the glove during actual use. This failure poses a common but potentially serious hazard to workers. Although methods are available for assessing permeation rates during actual use, such testing is unlikely without acceptable exposure guidance criteria for decision making. This document reviews methods for testing glove performance during actual use and suggests an approach for estimating acceptable exposure guidance criteria for evaluation of chemicals that are systemically absorbed. It is the authors' opinion that as of now an approach to estimating exposure criteria for chemical irritants and sensitizers may not be feasible. With available data resources, acceptable glove exposure criteria could be generated for use in assessing the risk of using specific gloves for handling many compounds in occupational settings.

Dermal absorption of cis-1,3-dichloropropene vapour: human experimental exposure

1. The relevance of skin absorption of cis-1,3-dichloropropene (cis-1,3-DCP) vapour as a route of entry compared to inhalatory uptake has been assessed in human volunteers under controlled exposure conditions. 2. Five adults (four males and one female) were dermally exposed on the forearm and hand during 45 min to 86 mg/m3 cis-1,3-DCP. 3. Dermal uptake was assessed by determination of the main cis-1,3-DCP metabolite in urine: the mercapturic acid conjugate of cis-1,3-DCP (cis-1,3-DCP-MA). 4. When whole-body dermal exposure to vapour is compared to inhalatory exposure, the uptake through the skin is estimated to be about 2-5% of the inhalatory absorption.