Objective

Metals in soils (1) pose a human-health risk via soil ingestion (2) and an ecological risk via plant and animal uptake (3). The goal of this research was to develop a model to predict in vitro-measured (4) bioavailability based on soil properties (5) using XAS (6) to provide a fundamental understanding of the link between molecular-level speciation and bioavailability.

Considerable research and other evaluative efforts have been ongoing in recent years to identify environmentally acceptable endpoints (EAE) in soil, develop protocols that can be used to determine EAEs, and make site-specific decisions using EAE data. When applied effectively, these efforts have provided useful descriptions of risk. EAEs for soil most commonly are defined as concentrations of chemicals or other measures of contamination (e.g., biological response or leachability) that are judged acceptable by a regulatory agency or an appropriate entity and are derived either from standard guidelines or following an analysis of site- or chemical-specific information and/or testing. There is a need to supplement the current lack of information regarding metals-contaminated soils, which are of particular relevance to the Department of Defense (DoD).

The overall objective of this project was to investigate the relative bioavailability of toxic metals in soils, primarily in relation to the human health risk posed by soil ingestion, which often controls the degree of cleanup required at metal-contaminated sites. Specific objectives included: (1) measure changes in relative bioavailability over time in a wide range of soil types that may be encountered at DoD sites within the United States, (2) develop a predictive capability to quantify toxic metal bioavailability on the basis of soil properties, and (3) investigate the fundamental relationship between molecular-level speciation and bioavailability to enhance the understanding and predictive capability of the fate of toxic metals in soil.