 |
|
|
| |
|
Project 1 Abstract
|
|
Redox Transformations, Complexation
and Soil/Sediment Interactions of Inorganic Forms
of As and Se in Aquatic Environments: Effects of Natural Organic Matter
|
| |
| Investigator(s): Donald L. Macalady, Professor of Chemistry and
Geochemistry; Dianne Ahmann, Assistant Professor of Environmental Science
and Engineering; John Westall, Professor of Chemistry, Oregon State University |
| Institution: Colorado School of Mines |
| EPA Project Officer: Mitch Lasat |
| Project Period: 1, 2001 - September 30, 2003 |
| |
| Waters and suspended sediments bearing inorganic forms of arsenic
and selenium occur widely and are especially prevalent in sites impacted
by mining. These systems present significant concerns for human and
ecosystem health and most, if not all, contain natural organic matter
(NOM). The chemical and physical properties of NOM suggest its involvement
in several critical processes that affect the behavior of As and Se,
including oxidation-reduction reactions, competitive interactions
affecting sorption, and formation of metal-organic (bridging) complexes.
NOM is expected to alter the mobility, transformations, bioavailability,
and toxicity of As and Se, and therefore to play an important role
in the design of methods to mitigate contamination problems. |
 |
|
Dr. Donald Macalady presents
at the TMW '02 conference.
|
|
| |
|
| Objectives: We seek to understand and quantify the nature of these
interactions and to delineate the environmental conditions under which they
are expected to occur. Further, the research will assess the extent to which
NOM influences the transport , transformations, bioavailability, and toxicity
of As and Se in aquatic systems as a function of system characteristics.
To meet these objectives, we will test the following general hypotheses:
1. NOM accelerates redox transformations of As and Se, either directly or
by acting as an electron shuttle, to an extent determined by specific properties
of the NOM and the system. 2. NOM increases the mobility of Se and As through
complexation and interference with sorption. 3. NOM alters As and Se bioavailability
and toxicity through its influence on redox reactions, sorption/desorption,
and/or aqueous complexation; the net effects represent a balance among these
mechanisms. 4. Microbial transformations of As and Se are influenced by
the abundance and characteristics of the NOM present, as well as the aqueous
geochemistry of the system. |
| |
| Approach: We will test well-characterized NOM samples from various
environments within and outside EPA Region 8 for their abilities, under
standardized conditions, to affect the processes hypothesized above. Using
techniques already developed in our laboratories, we will evaluate the ability
of each NOM sample to affect As and Se abiotic and microbial redox transformations,
influence surface and aqueous complexation, and to alter bioavailability
and toxicity. These data will be used to develop conceptual models of the
roles of NOM in As and Se biogeochemical processes, and the models will
be used for predictions of As and Se behavior at several field sites. Experiments
using field samples will be used to modify the models and provide recommendations
for the inclusion of the roles of NOM in remediation and abatement plans
for sites contaminated with As and/or Se. |
| |
| Expected Results: The expected result of this project is the formulation
of conceptual models for As/Se/NOM behavior that can be used to inform remediation
design in situations where As and/or Se pose threats to ecosystem and human
health. |
| |
| Supplemental Keywords: groundwater, sediments, environmental chemistry,
mining, geochemistry, toxicology, remediation, metal mobility, subsurface,
microbiology |