Understanding the Relationships Among Low Level Metal Influx, Remediated Sediments, and Biological Receptors

Dr. Anna Knox | Savannah River National Laboratory



Capping technology can restore aquatic environments by eliminating or reducing sources of contaminants into aquatic food chains, but cap effectiveness may be compromised by the influx of new contaminants. The objectives of this project are to: (1) evaluate the effectiveness of in situ remediation technologies (including single amendment active caps, multiple amendment active caps, and passive caps) subjected to continued low level metal influx as a result of recontamination from uncontrolled sources; and (2) improve understanding of the relationships among surface sediment recontamination, remediated contaminated sediments, and biological receptors.

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Technical Approach

Previous research has shown that the sequestering agents in active caps can create a zone of influence (ZOI) in sediment beneath the caps in which altered metal speciation results in reduced metal mobility and potential bioavailability. This project hypothesizes that a ZOI will also form in contaminated sediment deposited over active caps, thus resulting in chemical changes to the contaminants and a reduction in their environmental impact. The research consists of three tasks:

  • Task 1 – Researchers will study the linkages between contaminant loading and recontamination of remediated sediments in flow through microcosms. This work will help improve understanding of the mechanisms of recontamination and generate key parameters (e.g., partitioning coefficients) that influence model-simulated flux rates.
  • Task 2 – Mesocosms will be used to investigate the effects of particulate contaminant loading on remediated sediments.
    • In Experiment 1A, contaminated sediment will be gradually deposited over several types of active and passive caps (as well as uncapped controls), thus simulating the recontamination of remediated sediment by the influx of particle-bound contaminants from uncontrolled sources. The effectiveness of the caps will be assessed by evaluating the spatial extent and chemical characteristics of the ZOI that develops in the sediment that accumulates over the caps.
    • Experiment 1B will be similar to Experiment 1A except that it will include bioturbating organisms. Bioturbation may be important in ZOI development by mixing accumulating sediments with cap materials. The mesocosms will contain caged organisms that represent different taxonomic groups, feeding strategies, and metal sensitivities. Biouptake by these organisms will be compared with the results from diffusive equilibration in thin-films (DET), diffusive gradients in thin films (DGT) probes, which have the unique ability to detect fine vertical gradients in metal availability and speciation – a necessary capability when assessing the chemical changes that occur in vertically accreting layers of contaminated sediment.
    • Experiment 2 will focus on evaluating sediments that have been deposited over active caps at existing demonstration sites (Steel Creek, South Carolina, and the Anacostia River, Washington, D.C.), thereby providing an opportunity to compare the mesocosm results with conditions existing in the field.
  • Task 3 – Researchers will study the long–term effectiveness of remedial methods through modeling that synthesizes the results from Tasks 1and 2. The team will develop numerical models and identify model inputs needed for the prediction of long-term relationships among the low level of influx of metals, biological receptors, and remediated sediments. The results will provide a rigorous approach for the selection of remediation and risk management strategies that are resilient in the face of ongoing contaminant influxes and exhibit long-term effectiveness.

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This project will explore a range of scenarios involving the low level influx of metals on sediments remediated by different methods and exposed to different environmental conditions, thereby providing a comprehensive understanding of the relationships between recontamination and remediation as well as modeling tools for evaluating the effects of recontamination on different remedial methods. The results will provide a rigorous approach for the selection of remediation and risk management strategies that are resilient in the face of ongoing contamination and exhibit long-term effectiveness. The expected outcome is a better understanding of the relationships among low level metal influx, remediated sediments, and biological receptors, which will result in setting more defensible cleanup goals and more realistic cleanup priorities, while ensuring the protection of human health and the environment. This enhanced understanding will increase the confidence of site managers to incorporate in situ remediation methods into site management decisions. (Anticipated Project Completion - 2020)

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Knox, A.S. and M.H. Paller. 2020. Effect of Bioturbation on Contaminated Sediment Deposited over Remediated Sediment. Science of the Total Environment, 713:136537.

Knox, A.S., M.H. Paller, and J.C. Seaman. 2019. Removal of Low levels of Cu from Ongoing Sources in the Presence of Other Elements – Implications for Remediated Contaminated Sediments. Science of the Total Environment, 668:645-657.

Knox, A.S., M.H. Paller, C.E. Milliken, T.M. Redder, J.R. Wolfe, and J. Seaman. 2016. Environmental Impact of Ongoing Sources of Metal Contamination on Remediated Sediments. Science of the Total Environment, 563-564:108-117.

Knox, A.S., M.H. Paller, and K.L. Dixon. 2014. Evaluation of Active Cap Materials for Metal Retention in Sediments. Remediation, 24(3):49-69.

Paller, M.H., S.M. Harmon, A.S. Knox, W.W. Kuhne, and N.V. Halverson. 2019. Assessing Effects of Dissolved Organic Carbon and Water Hardness on Metal Toxicity to Ceriodaphnia dubia using Diffusive Gradients in Thin Films (DGT). Science of the Total Environment, 697:134107.

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Points of Contact

Principal Investigator

Dr. Anna Knox

Savannah River National Laboratory

Phone: 803-725-7021

Fax: 803-725-7673

Program Manager

Environmental Restoration