Superfund Research Program
Water-Sediment Model and Criteria for Arsenic and Chrome
Project Leader: Dominic M. Di Toro (University of Delaware)
Grant Number: P42ES010344
Funding Period: 2000 - 2006
Progress has been made this year in two areas.
Dr. Di Toro and his research team are continuing work on this mechanism. Additional column studies are being planned and one has been completed. This work is significant because arsenite is more toxic than arsenate, partly because it enters cells more readily. Therefore being able to predict the relative quantities of arsenite and arsenate is very important in performing risk assessments. The experimental work and model development is continuing by adding realism to the experiments and model. The next step in the introduction of sulfide so that the iron(II) is present as dissolved species and as the solid FeS. This is much more realistic. However it complicates the experimental details, particularly the analytical techniques that are required. Additionally more chemical species need to be added to the model. Preliminary experiments have been conducted on the oxidation of metal sulfide species as well. An open and exciting question is whether this iron catalyzed oxidation reaction applies to metal sulfides as well.
Project investigators have also been collaborating with Prof. Young in Project 6 on the microbial oxidation of chrome (III). They have shown that certain microbes can oxidize a chromium (III) NTA complex. This is very important from the point of sediment quality criteria since the usual form of chrome in sediment at Superfund sites is as solid Cr(OH)3. The importance of this work is that it may be that chrome(III) DOC complexes may also be oxidized to Cr(VI), which is the toxic form of concern in aquatic systems. If microbial oxidation of soluble Cr(III) species is ubiquitous in the environment, it would cast a new light on the risk associated with Cr contaminated sediments. This also raises the possibility that the iron catalyzed mechanism may be important for Cr(III) oxidation.
The work on the iron catalyzed mechanism of arsenite oxidation has been continuing and project’s first paper has been published.