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Estimation of Dermal Absorption Using the Exponential Saturation Model,☆☆

https://doi.org/10.1006/rtph.1998.1274Get rights and content

Abstract

Estimates of dermal absorption are used in exposure assessment to calculate the internal dose of persons contacting pesticides and are a critical part of risk assessments. An exponential saturation model with lag time was validated against a classic dermal absorption study of 12 pesticides administered to human volunteers. The model gave dermal absorption estimates consistent with reported values in the literature. Moreover, this model gave more realistic estimates of the percentage of dermal absorption for some pesticides, which have special properties. In most submitted dermal absorption studies in animals, especially rats, “bound” skin residues (BSR) at treated skin sites were generally high when animals were sacrificed more than 24 h after the dose was administered. The direct addition of the total BSR as an absorbed dose would likely overestimate actual dermal absorption. From a well-conducted dermal absorption study, this model can be utilized to estimate maximum excretion of the administered dermal dose as a result of further absorption of bioavailable BSR. Resulting dermal absorption estimates are appropriate for regulatory purposes in the risk assessment of pesticides because they take into account the bioavailability of BSR while at the same time the estimates are not overly conservative.

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    Currently, skin residues remaining after washing the treatment site 8–10 h following dose application are assumed to be bioavailable at 24 h when many dermal absorption studies are terminated. An exponential saturation model for estimating dermal absorption was used to compare the calculated rat dermal absorption for five pesticides with and without the direct addition of bound skin residues (Thongsinthusak et al., 1999b). The study indicated that the bound skin residues were frequently not bioavailable.

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    In conclusion, insight in dose accumulation, effects of repeated exposure and assessment of relevant compounds is considered valuable for occupational risk assessment, in particular for the harvesters (re-entry workers). Dermal absorption studies ought to provide information on the systemic available dose, and as such address the fate of the skin residues (Thongsinthusak et al., 1999; De Heer et al., 1999; Ross et al., 2001). Although this is recognised there still remains some debate on how to use these dermal absorption data in risk assessment.

  • Conservatism in pesticide exposure assessment

    2000, Regulatory Toxicology and Pharmacology
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The opinions expressed in this article represent the views of the authors and do not necessarily reflect the views and policies of the State of California. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

☆☆

W. M. Draper

2

To whom correspondence should be addressed at Department of Pesticide Regulation, California Environmental Protection Agency, 830 K Street, Sacramento, CA 95814. Fax: (916) 445-4280. E-mail:[email protected].

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