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Contaminant Speciation in Riparian Soils Demonstration
Primary Issue Addressed: Modeling
Secondary Issues Addressed: In situ Treatment; Lead Stabilization
Project Site: University of Idaho
Collaborating Entities: MSE and University of Idaho
Cost Share: University of Idaho
Project Description
The focus of this project is to evaluate phosphorus-lead soil interactions with respect to mineralogical stability. It is an investigation into the reaction processes that take place when phosphate amendments are added to riparian soils containing lead and other solid-phase materials. Phosphorus (P) has shown excellent potential for the remediation of lead-contaminated soils and reduction of lead bioavailability. However, no existing information correlates the reaction mechanisms of lead in field remediated soils with toxicological studies on waterfowl. This project will serve to fill this gap. In addition, this project will also serve to monitor how the speciation and bioavailability of the other contaminants are affected by phosphorus-based remediation treatments.
Figure 9. Geochemical system.
Status
Soil samples from the Coeur d’Alene River Basin were analyzed for mineralogy and metal contaminant speciation. Both phosphorus-treated soils and untreated soils were examined to determine the effect of P-amendment on metal speciation. Other studies have suggested P-amendments lead to precipitation of poorly soluble lead phosphate minerals. No evidence was found for this behavior in the present study. Instead, P appears to associate with iron-bearing minerals in the soil, whereas lead associates predominantly with manganese-bearing phases.
Based on the results of this research, a conceptual model can be developed
for lead speciation and reactivity in the wetlands. This model can be
used to predict lead bioavailability, transport availability, temporal
fluxes as a function of water table and inundation, and impacts of remediation.
Figure?9 shows a generalized system model.
Information on mineral and contaminant speciation can be input
into this model to predict processes for reactions between the
various phases. This type of predictive model is needed to develop
improved management and remediation strategies and to develop
new experiments that will allow for quantitative analysis of contaminant
availability.
A physiologically-based extraction test model for waterfowl was developed to measure the bioaccessibility of lead to waterfowl (W-PBET) (see Figure 10). The method was used to test lead bioaviability in field remediated soils. The lead concentrations from the W-PBET method were positively correlated to the bird feeding study results and indicate that the extraction test can be used to assess relative changes in bioaccessibility. Therefore, the test will be valuable to help manage and remediate contaminated wetland soils with respect to waterfowl.
The project final report will be completed in fiscal 2006.
Figure 10. Graphed correlations between lead concentrations in W-PBET simulated gizzard and lead concentrations in the blood from in vitro testing on same soils.