Panel 1, Presentation 4:Assessing the oral bioavailability of lead in soil in humans. Mark Maddaloni, U.S. EPA
This presentation will focus on stable isotope dilution, previous work on Bunker Hill, ID, soil, and results from ongoing studies of amended soils.
Panel 2, Presentation 1: Assessing model validation and quality management concerns in the review
of predictive models of metals Bioavailability. Larry Zaragoza, U.S. EPA
This talk describes technical and quality assurance considerations
that should be used in the evaluation of metals bioavailability models.
Guidance to be highlighted includes quality assurance, peer review, and
model validation guidance. Moreover, the importance of the recently
released Information Quality Guidelines will also be discussed.
Panel 2, Presentation 2: Estimating the Oral Bioavailability of Arsenic in Soil. Mark Barnett, Auburn University
The generally low bioavailability of arsenic (As) in soils from mining areas has been well documented. However, the applicability of these results to other soils contaminated with potentially more labile As species is unknown. Labile As(V) was added to thirty-six soils from seven major soil orders within the U.S. and As bioaccessibility was measured over time. The Fe oxide content and pH were the most important soil properties governing steady-state As bioaccessibility. A multi-variable linear regression model developed from this data set was able to predict the in vivo As bioavailability in nine soils from a contaminated site within a root mean square error of 10%. Reductions in metal bioavailability as a result of soil properties (as opposed to pre-existing metal speciation, which is difficult to measure and which is subject to change over time) are as stable as the major soil properties themselves. As soils have developed their major properties as a result of interactions with their environment over thousands of years, these properties are unlikely to change over relatively short time frames unless their environment changes dramatically. These results are illustrative of the potential use of predictive models of metal bioavailability.
Day 2: April 16, 2003
Panel 3, Presentation 1: In vitro determinations of arsenic bioavailability: Case study of application at a Midwest site. Teresa Bowers, Gradient Corporation
In vitro determinations of soil arsenic bioaccessibility have not yielded as consistent of results as have been observed for lead. For example, testing of seven samples from two residential yards at a midwest site showed a wide range of results, varying by approximately a factor of 10. Such results have been sometimes cited as demonstrating flaws in the in vitro model for arsenic. However, another possible explanation is that there are multiple sources of arsenic with different intrinsic bioaccessibilities present in soil at any one site. Data from this Midwest site are examined in an attempt to separate soils affected by different sources of arsenic in an effort to understand the bioaccessiblity results.
Panel 3, Presentation 2:Benefits and limitations of EMPA techniques for metal speciation: The current best method. John Drexler, University of Colorado
Analytical and chemical methods for the determination of metal and metaloid speciation abound. Particle size, species form, source, and lability comprise the determination of metal speciation for risk-assessment applications. None of the current methods can provide all four components for all metals of concern; however, EMPA techniques along with some new variations is still likely the best method. This presentation will provide an overview of current speciation techniques, pros/cons, discuss their relevance to bioavailability, and share examples of important risk information gained from previous studies.
Documentation that total soil metal composition can be extremely
variable at a site has occurred. However, documentation of the variable
nature of in vitro or in vivo bioavailability measurements for a site
is lacking. Further, it is unclear if bioavailability is an intrinsic
value of the soil or what intrinsic characteristics of the soil are
responsible for the observed differences in bioavailability. Thus, this
discussion will focus on the issue of measurement of soil
bioavailability and the factors of the soil matrix that appear to be
important to bioavailability. Our ability to quantify and predict these
observed changes in bioavailability can only be overcome when the
mechanisms that affect Pb solubility in the receptors and Pb absorption
by the receptors are understood.
This represents an EPA Science Policy Council initiative to develop a comprehensive framework that could be the basis of future Agency actions. Cross-Agency guidance is needed for a consistent approach to assessing potential risks of metals and metal compounds. The framework will serve as the basis for developing more detailed assessment procedures for metals as needed for specific Agency activities.
Panel 4, Presentation 2:Metals assessment issue paper: Bioavailability and bioaccumulation. R.P. Lanno, Dept. of Entomology, Ohio State University
Bioavailability and bioaccumulation are two concepts that are linked and form an integral part of exposure assessment in environmental risk assessment of metals. The application of these concepts to the development of generic environmental quality guidelines for metals is more obscure. This presentation will focus on the unique aspects of bioavailability as they apply to metals including methods for the measurements of bioavailability, models relating bioavailability and toxicity, and regulatory applications of bioavailability. Bioaccumulation of metals differs from organic compounds and these differences will be highlighted, along with how bioaccumulation can be expressed and how it can be applied in regulatory practice. An integrated approach will provide examples of these concepts using aquatic and terrestrial (humans, plants, soil organisms) organisms.
