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Selenium speciation, solubility, and mobility in land-disposed dredged sediments.
Peter T Zawislanski1, Sally M Benson, Robert Terberg
1Lawrence Berkeley National Laboratory, 1 Cyclotron Road, 90-1116, Berkeley, California 94720, USA. peter.zawislanski@lfr.com
Environmental Science & Technology
|July 2, 2003
Summary
Pilot tests show land disposal of selenium-enriched sediments is safe. Selenium remained immobile, with minimal oxidation and solubilization, preventing groundwater contamination.
Area of Science:
- Environmental Science
- Geochemistry
- Soil Science
Background:
- Selenium (Se)-enriched sediments pose environmental risks.
- Land disposal is a potential management strategy for such sediments.
- Understanding Se mobility and transformation in disposal sites is crucial.
Purpose of the Study:
- To evaluate the fate of Se-enriched sediments after land disposal.
- To measure Se oxidation and solubilization rates in a pilot-scale test.
- To assess the potential for Se migration to groundwater.
Main Methods:
- Pilot-scale land disposal tests with instrumented plots.
- Monitoring of soil, soil water, and groundwater over 2-3 years.
- Analysis of Se fractionation using sequential extractions.
- Se speciation analysis using X-ray absorption near-edge structure (XANES).
Main Results:
- Dissolved Se did not migrate below 15 cm depth.
- Low sediment permeability and Se solubility limited groundwater movement.
- In-situ Se oxidation was measurable, increasing soluble Se to ~2.5% within 207 days.
- Sequential extractions and XANES confirmed initial oxidation of organo-Se/elemental Se to selenite.
Conclusions:
- Land disposal of Se-enriched sediments in this pilot study effectively limited Se mobility.
- Selenium is expected to remain largely immobile and in reduced forms.
- Anticipated further solubilization is low (1-2% per year), suggesting a stable long-term outcome.