Superfund Research Program
Toxicity and Mobilization of Metals and Metal Mixtures in Sediments
Project Leader: Dominic M. Di Toro
Grant Number: R01ES015444
Funding Period: 2006-2009
This research involved the development of models for predicting the toxicity and mobilization of individual metals and metal mixtures in sediments. These predictions are critical in evaluating the risk associated with contaminated sediments at Superfund sites. In past Superfund research projects, project investigators have developed methods of assessing the toxicity of individual metals for sediments with excess acid volatile sulfides (AVS). During this project, researchers at the University of Delaware accomplished the following tasks:
- Iron (II)-catalyzed oxidation of arsenic (III) in a sediment column: The Iron (II)-catalyzed oxidation of Arsenic (III) is examined in a sediment column using both computational and experimental studies. A reactive-transport model was constructed that incorporates the complex kinetics of radical species generation and Iron (II) and Arsenic (III) oxidation. The model was applied to experimental column data and results indicated that transport in sediments plays a vital role in increasing the extent of Arsenic (III) oxidation and efficiency of the Iron (II) catalysis.
- Modeling the solid-solution partitioning of metals in the Trinity River using WHAM VI: WHAM6 (Windermere Humic Aqueous Model) was used to predict the partitioning of specific metals in the Trinity River. The impact of organic matter and Mg/Ca competition were examined in sensitivity analyses.
- A probabilistic model for metal toxicity assessment in rivers: A probabilistic dilution model for metals (PDMM) was described that is well suited to address the need to assess the fate and biological effects of metals in rivers and streams. By coupling this framework to speciation models, the PDMM is capable of describing the distribution of metal between the particulate phase, soluble phase, and the biological receptor site.
- Distribution of proton dissociation constants for model human and fulvic acid molecules: The intrinsic proton binding constants of 10 model humic acid and 6 model fulvic acid molecules are calculated using SPARC (SPARC Performs Automated Reasoning in Chemistry). The accuracy of the SPARC calculations was examined by comparing estimated versus observed microscopic binding constants of various small organic acids. The results suggest that mixture molecular models can be used to investigate and predict the binding of metal cations to humic and fulvic acids.
Polychlorinated biphenyls (PCBs) are persistent and widespread environmental pollutants, and accurate values of their Henry’s law constants (HLCs) are needed to model their global transport and fate. In this work, HLC values for all 209 PCB congeners were predicted at 25°C using two quantum mechanical (QM) continuum solvation models. The two QM models predicted similar values of the HLC, which are consistent with all but one of the available sets of measurements, and have smaller root mean square prediction errors than other models tested. This supports the validity of the QM values.