Estimating Human Health Risk from Dermal Exposure to Contaminated SoilsEPA Grant Number: R826684
Title: Estimating Human Health Risk from Dermal Exposure to Contaminated Soils
Investigators: Bunge, Annette , Macalady, Donald L. , Navidi, William C.
Institution: Colorado School of Mines
EPA Project Officer: Hahn, Intaek
Project Period: October 15, 1998 through October 14, 2001
Project Amount: $371,959
RFA: Exploratory Research - Human Health (1998) RFA Text | Recipients Lists
Research Category: Health Effects , Health
The potential health risk from dermal exposure to soils contaminated with toxic chemicals depends on the amount absorbed and the toxicological potency. The parameters which influence the rate and extent of absorption from soils remain poorly quantified, and existing methods for estimating the amount absorbed are based on little or no experimental evidence. The overall goal of this research is to produce an experimentally validated procedure for computing reasonable estimates of dermal absorption of chemicals from contaminated soils. Developed around fundamental physicochemical mechanisms, this procedure would require only known, or easily determined, input parameters, such as the conditions of the exposure (e.g., contact time, mass of soil adhering to skin, and chemical concentration on the soil), characteristics of the soil (e.g., organic carbon and water contents), and properties of the absorbing chemical (e.g., lipophilicity, molecular size, and vapor pressure).
Previous research by the investigators and others suggests that dermal absorption is limited by chemical transfer from soil to skin, perhaps through the vapor phase, even for chemicals which are not considered volatile. Thus, the primary objective is to determine the mechanism(s) of chemical transfer from soil to skin (e.g., through the vapor or by other means) for a group of relevant environmental pollutants with varied properties, especially vapor pressure. This information will be essential to the second and third objectives, which are to develop equations relating the rate and extent of chemical release from soil to known or estimatable parameters such as vapor pressure, Henry's constants, melting point, water solubility, and lipophilicity. The final objective is to experimentally test if information about soil-to-skin transfer combined mathematically with information on chemical transfer across skin can produce reasonable estimates of dermal absorption.
The approach will utilize experimental study and mathematically modeling of a group of judiciously selected chemicals on two different soils that have been well-characterized in our laboratories. Measurements of equilibrium vapor pressure and kinetics of chemical transfer to air (from contaminated soils, the pure solid chemical, and from saturated aqueous solutions) will be compared. If the vapor pressure and kinetic observations do not correlate, then kinetic limitations or non-equilibrium chemical distribution would be indicated. The mechanisms of soil-to-skin transfer will be explored by comparing vapor phase transfer with the rate and extent of chemical absorption into polymeric solids (simulating skin), and skin. Methods for estimating the physicochemical parameters defining the soil-to-skin transfer process will be developed from previous literature studies of chemical interactions of soil with water and air, and of water with air and human skin. Finally, mechanistic mathematical models of soil release kinetics and the dermal absorption process (suitable for use in PBPK models) will be compared to experimental measurements.
This project will greatly improve risk assessment estimates from dermal exposure to contaminated soils by providing a validated procedure for estimating the resulting body burden based only upon structure-activity information of the absorbing chemical and the basic properties of the soil. Coincidentally, standardized protocols will be developed for experimental measurements of dermal absorption from soils. An additional outcome from this project is the ability to identify those chemicals of greatest concern for dermal exposure to contaminated soils (i.e., chemicals warranting more detailed experimental evaluation).