Coupling Between Pore Water Fluxes, Structural Heterogeneity, and Biogeochemical Processes Controls Contaminant Mobility, Bioavailability, and Toxicity in Sediments
ER-1745
Objective
The Department of Defense (DoD) is responsible for managing a large number of sites with substantial metals-contaminated sediments. Sediments, with their resident organisms, represent a highly complex system, and the behavior and effects of metals are highly dependent on an interrelated suite of sedimentary processes, including pore fluid flow, bioturbation, bioirrigation, and numerous biogeochemical processes that lead to the precipitation and dissolution of solid phases. The uncertainties resulting from the limited knowledge of metals behavior in sediments, notably feedbacks associated with biological activity and the development of sediment structure, preclude reliable linkage of contaminant distributions to organism exposure, biological uptake, and ecological effects. This hampers the management of contaminated sites, increasing costs and making it difficult to set and achieve desired end points.
The objective of this project is to improve understanding of how the interplay of physical, chemical, and biological processes controls the transformation, mobility, bioavailability, and toxicity of metals in sediments. Researchers will focus on the following key controls on the behavior of metals in sediments: (1) the effects of biological activity and overlying flows on pore water transport, sediment structure, chemical speciation, and contaminant fluxes; (2) the role that sediment structure (heterogeneity) plays in the exposure of organisms to contaminants; (3) the role of sediment diagenesis in modifying contaminant speciation, mobility, and bioavailability; and (4) the net effects of these processes on overall contaminant efflux and the bioavailability and toxicity of metals to benthic organisms.
Technical Approach
A series of laboratory experiments will be performed in systems that provide the ability to house typical benthic organisms under realistic hydrodynamic transport conditions, including both pore water advection and pore water mixing induced by turbulence in the overlying water column. This will enable researchers to observe how the interplay of overlying flows, pore water flows, and benthic biological activity affects contaminant mobility, bioavailability, and toxicity. These experiments will focus specifically on evaluating the effects of pore water flow and biologically induced mixing on redox zonation in the sediments; redistributing metals between sediments, pore water, and overlying water; and altering metals toxicity both by changing speciation and by inducing precipitation/dissolution of binding phases. Three different sediments having a range of hydrogeologic properties and compositions will be used, including metals-contaminated sediments from DoD sites and reference sediments spiked with copper (Cu), zinc (Zn), lead (Pb), and arsenic (As). Experiments will be repeated with and without typical benthic organisms, providing biological modification of sediment structure and a direct measure of toxicity. A variety of sophisticated analytical methods will be used to evaluate sediment structure (XMT), oxygen distributions (microelectrodes, optodes), contaminant distributions (XRF, DGTs, XDMT, microelectrodes), contaminant speciation and binding phases (EXAFS, XANES, STEM-EDS, HPLC-ICP-MS), as well as the bioavailability and toxicity of contaminants to benthic organisms.
Benefits
This project will provide basic information that is critically needed to support management of contaminated sediments by DoD, the metals industry, and regulators. Important outcomes will include improved scientific knowledge of solute transport and redox processes in sediments that control the formation of oxidized and reduced metal-binding phases; improved understanding of how hydrodynamic transport and biological activity structure sediments and thereby control the long-term fate and effects of metal cations (Cu, Zn, Pb) and oxyanions (As); and improved methods for evaluating site-specific physical, chemical, and biological factors that mediate contaminant efflux, biological uptake, and ecological effects. (Anticipated Project Completion - 2013)
Points of Contact
Principal Investigator
Dr. Aaron Packman
Northwestern University
Phone: 847-491-9902
Fax: 847-491-4011
Document Types
- Fact Sheet - Brief project summary with links to related documents and points of contact.
- Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
- Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
- Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
- Guidance - Instructional information on technical topics such as protocols and user’s guides.
- Workshop Report - Summary of workshop discussion and findings.
- Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
- Model/Software - Computer programs and applications available for download.
- Database - Digitally organized collection of data available to search and access.