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AN EQUILIBRIUM-APPROACH MODEL FOR SIMULATING CONTAMINANT TRANSFER BETWEEN SURFACES AND SKIN IN SUPPORT OF FQPA
Citation:
Furtaw Jr., E J., C C. Dary, M. Dellarco, AND C G. Saint. AN EQUILIBRIUM-APPROACH MODEL FOR SIMULATING CONTAMINANT TRANSFER BETWEEN SURFACES AND SKIN IN SUPPORT OF FQPA. Presented at Society for Risk Analysis, 1999 Annual Meeting, Atlanta, GA, December 5-8, 1999.
Description:
The Food Quality Protection Act (FQPA) demands that exposure of infants and children to pesticide residues from non-dietary sources be included in EPA's aggregate risk assessment. Ideally, the informed assessment would aggregate exposures from all reasonable sources, primarily food and drinking water and from dermal contact with surface residues that may result in dermal absorption or nondietary ingestion. To avoid severe overprediction of aggregate exposure, models should conform with the physical and chemical nature of the mechanism of exposure. This is particular important for the process of dermal exposure of infants and children to surface residues. In this regard we have observed that most existing models for simulating contaminant transfer between surfaces and skin are based on the implicit assumption that contaminant transfer is unidirectional, from the surface to the skin. These models do not account for return of residues on the skin back to the surface. The effect of this unrealistic assumption is that during modeled episodes of repeated contact with contaminated surfaces, the dermal loading can continue to increase to unrealistically high levels. To improve the conceptual basis of dermal transfer models, an alternative modeling approach is proposed that accounts for the equilibrium ratio of loadings (mass/area) on surface and skin. Each contact is assumed to provide a given mass fractional approach to equilibrium. Values for model parameters representing the equilibrium loading ratio (RL) and the fractional approach factor (F) can be estimated from available data. It is assumed that appropriate values for RL and F will vary as a function of multiple factors such as the contaminant species and its vehicle, the surface type, contact pressure and duration, and moisture level.
This work has been funded wholly or in part by the United States Environmental Protection Agency. It has been subjected to Agency review and approved for publication.